The Subjective Is Objective

Taking sentience seriously
Par David Olivier Whittier

This text is the English translation of "Le subjectif est objectif", initially published in issue #23 (2003) of the journal Les Cahiers antispécistes. The original French text can be found on this site or on the site of the Cahiers antispécistes.


This translation is currently undergoing review (text in a lighter colour).

Sentience, the central object of all ethics and of all action, is a reality of the world. It is a reality in itself; an objective reality, one that does not exist merely from some private point of view. In the same sense as a table or a stone are made of matter, our brains too are made of matter; thus, sentience is a potential property of matter in general. It is in the domain of physics, and it is the task of physics to give us an account of how sentience is linked to the other aspects of reality, and to show us how to determine when, where and with which qualities (suffering, pleasure and other qualia1) it occurs.

Despite this, present-day physics is incapable of making place for sentience in its description of the world. The problem would not be solved by discovering some new phenomenon or some new law. We need a complete overhaul of our ideas of reality and of physics. I do not have the keys to such an overhaul; I will be content here with showing why I believe it necessary, and suggest a few conditions that it will have to satisfy.

My reflections are in large part inspired by the views of the English mathematician Roger Penrose as expressed two works of his2 in which he argues that our current physics is unable to explain mental processes. He considers specifically our capacity to understand mathematical reasoning, a capacity he says cannot be simulated by the execution of an algorithm; this limitation following, he argues, from the well known Gödel incompleteness theorem (1931). I believe this line of reasoning very important, but not quite conclusive. Between the lines in the works of Penrose I see the basis of my own central argument: the unescapability of the internal, subjective point of view, and the fact that this point of view makes it impossible to build a theory of the world without attributing to the subjective to sentience, and also to the truth value of prescriptive assertions and to the reality of freedom of choice – the status of facts. It's on this basis, I believe, that can be confirmed Penrose's conclusions, and particularly his assertion that the evolution of the world cannot be entirely subject to a calculable determinism. If the world is deterministic, it must be so at least partly in a non-calculable manner, that is, in a manner that is not algorithmically reproducible.

Penrose reasons on the basis of one of the most abstract, and specifically human, forms of thinking, specifically mathematical reasoning. What his works suggest, however, is that all authentic forms of comprehension – including very practical reasoning, of the kind certainly many non human animals are capable of – necessarily comprise a non algorithmic process. Authentic comprehension implies the perception of the truth of certain facts, whether these be the approach of a predator or some mathematical fact; it cannot be reduced to the necessarily unsentient execution of an algorithm. I will argue that sentience, intelligence (the faculty of understanding), freedom and ethics (the non algorithmic search for the right answer to the question “What is to be done?”) are closely connected, and that consequently intelligence, freedom and ethics are properties of every sentient being.

Gwenva the cat playing with the water running from a tap.
Figure 1: Gwenva the physicist

This will give us means to discern, or rather to better found, a number of criteria that we feel natural to resort to in order to determine if a given being is or isn't sentient; such as the non “automatic” nature of its behaviour or the presence of tissues of a certain kind, such as nervous tissues. It will give us indications concerning the place of sentience in evolution. It will allow us to found, as true, our moral obligations towards all sentient beings. Lastly, it will imply the necessity of reconstructing our conceptions of physical reality, and will allow us to sketch some constraints that these new conceptions will have to satisfy.

1. Conflicting Certainties

My assertion that our current physics is unable to account for sentience may come as a surprise to some. Indeed, my position is at odds with that of quite a few philosophers, and particularly of several antispeciesist philosophers. Peter Singer, for example, spends eight pages in Animal Liberation3 countering the Cartesian position according to which animals are entirely unsentient and feel nothing at all. Singer advances several arguments, all of a scientific nature, without ever mentioning any problem about the scientific status of sentience itself. His arguments concern the behaviour of animals, the presence of nervous tissue and the evolutionary relevance of pain. It's on the same basis that he argues against sentience in plants4. One also often finds mentioned the presence in some animal of certain chemical substances, such as endorphins mentioned by Joan Dunayer in her article “Fish: Sensitivity Beyond the Captor's Grasp”5. Following my experience, antispeciesist activists quite generally tend to believe that the scientific status of pain and sentience is unproblematic and that our inability, for example, to determine whether or not an ant can suffer is only the result of a lack of attention on the part of scientists to the issue.

This attitude sharply contrasts with a view very frequently shared precisely by persons with a scientific background and who claim to speak for a certain rationalism. Their tendency is instead to declare the question whether or not a given animal is sentient as meaningless. Erwin Schrödinger, one of the founders of quantum mechanics, expressed this idea – that he didn't share – very clearly, in the answer he imagines a “rationalist” would give to the question “what kind of material process is directly linked to consciousness”6:

A rationalist may be inclined to deal curtly with this question, roughly as follows. From our own experience, and as regards the higher animals from analogy, consciousness is linked up with certain kinds of events in organized, living matter, namely, with certain nervous functions. How far back or “down” in the animal kingdom there is still some sort of consciousness, and what it may be like in its early stages, are gratuitous speculations, questions that cannot be answered and which ought to be left to idle dreamers. It is still more gratuitous to indulge in thoughts about whether perhaps other events as well, events in inorganic matter, let alone all material events, are in some way or other associated with consciousness. All this is pure fantasy, as irrefutable as it is unprovable, and thus of no value for knowledge.

Mind and Matter, ch. 1

This position, which claims to be “rationalist”7 discards as meaningless the issue of animal sentience (consciousness). It does accept, however, without qualifications that “we” are sentient – “we” being human beings. It treats our own sentience as an empirical fact, one that is part of the reality of the world; one that is furthermore linked some way to “nervous functions”, in other words to ordinary observable physical events. But outside of the human species – and of a few “higher” animals – the status of sentience changes radically. For “lower” animals and inanimate objects, the claim is not that they lack sentience; rather, it is that in their case the issue of sentience is meaningless. It is no longer, in their case, in the realm of facts.

These two parties have in common that they see the issue of the scientific status of animal sentience as a unproblematic: the pro-animal philosophers because they believe that it has essentially been solved; the “rationalists” because they regard it instead as meaningless. I wish to call in question these two calm certainties; and in particular, that of “my side”, of those who struggle for the respect of the interests of animals. Indeed, the opposing position, that dominates among scientists, is not without reasons; and to dialogue with these scientists, and with our society as a whole which trusts these scientists, and to answer their arguments with sincere and convincing counter-arguments, we must recognize these reasons. More broadly, reality belongs to us as much as to anyone; we must not allow that in the name of science, that is in the name of reality, the existence or relevance of animal sentience be denied. We must thus understand the real difficulties there are for making place for sentience in the scientific point of view, and start looking for ways to solve them.

This question has direct practical consequences regarding the interests of non human animals. Florence Burgat has described8 the tendency among researchers of the INRA (French national institute for agricultural research) in charge of the issue of animal well-being to view the object of their study as a non-issue, as a mere reflection of “social pressure”, that is of a fantasy of the ill-informed public opinion (ill-informed because out of lack of scientific vision laypeople take seriously the idea that animals may have an authentic well-being). Their studies will consequently aim at contenting this social pressure as cheaply as possible. The well-being of animals will be measured by their health, a criterion seen instead as “objective” and itself measured in terms such as rates of weigh gain and other such data very much in harmony with the interests of the tradesmen, these interests being for their part viewed as very real. When scientists have the mission of studying what is, and they believe that animal suffering is not, or – equivalently, as they see it – that the question of animal suffering is meaningless, any serious social consideration of animal interests is impossible.

2. Humans and stones

The central thesis of this article is twofold, both supporting and opposing each of these two certainties. It posits both:

— the unescapability of the subjective point of view, the impossibility of not believing that ethical assertions, i.e. prescriptions, possess a truth value, and in the objective reality of sentience and of free will;

— the impossibility of integrating sentience and the above other facts into the framework of physical reality that still dominates our minds today.

These two impossibilities lead to a contradiction, if one takes this conception of physical reality for granted. I will return to each at length, but I also believe that there is a hazy but widespread and persistent awareness of them in our culture. The two assertions are rarely articulated, and the contradiction to which they lead rarely brought to light. Instead, we divide the world mentally into two radically dissimilar compartments: we treat it as made of humans on one side and of stones on the other. The two contradictory assertions will each be viewed as true, but separately: one as true in the world of humans, the other in that of stones.

Let us take up the “rationalist” position depicted above by Schrödinger. It starts by admitting sentience as a fact in humans: “According to our own experience, (...) consciousness is connected...”. Consciousness, therefore, is a reality in human beings. Since they are part of the physical world, one could imagine that the same concept of sentience would be applicable everywhere in this world; not that sentience is necessarily present everywhere, but that where it is not present, it is at least absent. But this is not what this “rationalist” position goes on to say; it tells us that beyond the limits of the human world9 the very question of sentience is a matter of “gratuitous speculation”; to such questions “no answers can be given”. Outside the human world, sentience is a concept without meaning.

Schrödinger's “rationalist” does not, however, completely deny that the laws governing the non-human world also apply to the human world; sentience, he says, is connected to certain kinds of events in matter. But he does not specify in any detail this “connection”; and if there is a connection, it is not clear why its presence or absence should not remain discernible outside the human species, including anywhere “down” the ladder of animal species. So he does not seem to be really convinced of the possibility of establishing the said connection. Others, who are less attached to their reputation as “rationalists”, will explicitly make of “man” a domain ruled by different laws than those that govern mere matter; they insist that we are both body and spirit. This was the position of Descartes, who is often regarded as one of the main founders of rationalist thinking. Today, such attitudes are often less openly proclaimed, and what is displayed is a kind of schizophrenia elevated to the status of an article of faith; on the one hand, one claims to accept the laws of modern physics in their entirety, and on the other, one maintains that the human being is of another order. This is typically the religious-secular attitude; it is the one promoted by the Catholic Church, and which it still blames Galileo for not having displayed, or not having displayed enough.

The general rule is to admit in principle that the human being, including the nervous system, must surely be subject to the same laws of physics as the rest of the universe; but this statement remains vacuous, devoid of any operative power. The complexity of the nervous system serves as both a good reason and an alibi for this; a good reason because this complexity is real and would make it impossible to analyze in detail, particle by particle, all the events that take place in a brain; but an alibi because, beyond the petition of principle, one feels, confusedly or clearly, that complexity does not really change anything, and that sentience simply cannot arise from this kind of physics which, basically, describes the world as a set of billiard balls evolving “mechanically”, that is, according to laws of calculable determinism.

This division of the world between humans and stones extends to virtually all our concepts. At the heart of our law is the distinction between persons and things; everything that is not human is a thing, including all non-human animals. At the heart of our philosophy is the opposition between culture and nature; only humans have to do with culture, everything else belongs to nature. Our universities are systematically divided into literary disciplines on the one hand, which study the mind and the “humanities”, and the scientific disciplines on the other hand, also known as hard science (hard like stones), which study rocks together with trees and mice. Sociology and anthropology belong to the former, ethology to the latter, just as does chemistry. A gulf exists, it is said, between humans and other animals; the former think and decide freely, the latter are driven by instinct like a stone by gravity.

Animals: the grains of sand among the stones

The radical Cartesian exclusion of all non-human animals from the realm of sentience is intimately linked to the division of the world into humans and rocks; and this in turn is linked to the double impossibility mentioned above. The animal question is thus directly involved in the solving of this double impossibility.

If the world were really made up of two easily identifiable categories of objects, a sharp conceptual partition could be defensible. We could consider that some concepts apply to one category of objects but not to the other. This would be the case, in particular, for those that underpin our ethics, in their various forms. Even without a precise definition of the notions of sentience, autonomy, dignity, free will and so on, we could see that all the signs that spontaneously lead us to believe that a given human possesses one of these characteristics are satisfied by all humans and by no stones. Therefore, given any object of the world, we would need no other criterion than that of its belonging or not to the category of humans to allow us to decide whether it should be viewed as a moral patient, i.e. whether we should take it into consideration for its own sake in our deliberations.

This is the world as humanism would have it, as our culture in general would have. Yet this is not how the real world is, as we know very well. Already within the human species, not everyone has, at least in a clear way, the signs that I have mentioned; there are embryos and fetuses, the comatose, the profoundly mentally handicapped. It is above all the moral status of embryos and fetuses that is debated, because of the issue's practical importance, and also because of the obvious continuity in the development from the fertilized egg to the newborn and beyond. If there is a chasm between things and people, it is quietly and effortlessly that the embryo seems to cross it, at some moment we are not even able to determine.

However, this gap is awkwardly contained by invoking the fact that the beings concerned, even if they do not possess the features of a typical adult human, are at least destined to acquire them (in the case of embryos), or used to possess them (in the case of the comatose); or possess them by essence, though by “accident” they do not (in the case of the profoundly mentally disabled). The partition of the world into persons and things is thus saved.

It is the non-human animals that make this view untenable. Apart from human beings, there are not mere stones. The world is not made up of two categories of objects that are sufficiently distinct for the problem of ethical criteria not to arise. It is not obvious that a chimpanzee is not sentient, has no dignity or no free will. And if there is doubt concerning chimpanzees, there doubt too in the case of cats; and in that of fish, and that of octopuses, ants and jellyfish, and perhaps even for plants. The coral is an animal, related to jellyfish, but does a coral not resemble a stone? Is there any doubt about stones themselves? Probably not, but we would like to know why.

The animal question, by simply pointing at the existence of animals, and thus to a prima facie continuity between the world of humans and that of stones, forces us to acknowledge the need for a criterion of moral patience that can be applied to any object in the world. All objects of physics are thus, at least potentially, objects of ethics; the question of their possession of this or that ethically relevant feature – and first among these, of sentience – can, for each of them, be answered positively or negatively, but is never without meaning.

Therefore, the solution that our society adopts to “solve” the double impossibility, by sealing off the two conflicting theses from each other, each in its own domain, breaks down. These theses instead meet and collide in a common domain, that of the non-human. We cannot believe that “asking how far down the ladder of animal species there is still some form of consciousness” is a question without meaning; we will need to answer it in order to determine whether or not we have moral obligations to these non-human objects. This will be true even if we adopt the ethics most hostile to the consideration of non-human animals; if our criterion is not sentience but the possession of rationality, for example, we will need to be able to apply it to any object in the world, even if our plan is to show that in fact only humans are rational.

From this point on, there is no point either in trying to preserve the domain of the human from the indignities of physics; we must accept that there is only one world, and that we are fully of that world; and that sentience, or any other characteristic that we deem relevant to ethics, is of that world, and as such belongs to physics. We must recognize that ethics and physics have the same field of study, the same world. Ethics cares about the humblest pebble, at least in the sense that its criteria must be able to tell us whether and why we should care about it or not.

The criteria of ethics must apply to all objects of the physical world, and it is only by physical means that we can determine whether or not these objects satisfy these criteria. If our criterion is sentience, we can only determine whether an object is sentient by observing it. And we know that everything we observe – the movements, sounds and so on it may make – are physical occurrences, and are related, through the laws of physics, to processes taking place in the object. If we believe that these observed occurrences are indications of the object's sentience, while they are caused by physical processes taking place in the object, sentience itself must be a physical phenomenon. The same reasoning applies to any other ethical criterion one might wish to adopt.

The ongoing crisis of physics

It follows that we have no way out of the double impossibility without altering our conceptions of physics. In the following sections, after examining in more detail the first impossibility, namely the inescapability of the subjective point of view and the impossibility of not believing certain things, I will turn to the reasons for the second impossibility, that of incorporating sentience and other subjective features into the dominant view of physics. One might answer: very well, but modern physics appears almost unassailable, and cannot be subverted just because of the ethical problem of the moral status of animals. I recognise the strength of modern physics. However, I also know that it is in deep crisis and that it has lost its foundations. The solidity that is generally attributed to it is largely due to its practical accomplishments, to the impressive power that it gives us to master matter; but also to its alleged capacity to provide a consistent and comprehensible view of the world. However, it has in fact lost this capacity since the advent of quantum mechanics in the 1920s. The previous picture, now obsolete, of the way physics explained reality has nevertheless remained by default dominant, a picture of ideal physics, both in the minds of the general public and in those of a vast majority of scientists, even those who are familiar with quantum mechanics. It has remained so precisely because quantum mechanics has given us no credible alternative vision.

I believe, however, that this classical ideal of a calculable, billiard-ball determinism is itself inconsistent and ultimately indefensible; this is because it is incompatible with sentience, but also because, if its logic is carried to its conclusion, it self-dissolves into a pure mathematical abstraction devoid of substance. Therefore, we should not hope to solve the crisis of modern, quantum physics by returning to the previous paradigm, as physicists such as Einstein dreamed of doing in the early days of quantum mechanics. Rather, I believe we must draw on the “quirks” of quantum mechanics, and on the constraints that follow from the reality of sentience, to try to imagine what an alternative worldview might be.

I will explicit later (section 5) the elements of the structure of this pre-quantum physics that serve my argument. I will not attempt to paint a picture of quantum mechanics, however, and will only refer where useful to some of its features. There are good introductory books on quantum mechanics on the market that give an idea of the strange structure of this theory, the most orthodox interpretation of which denies the existence of an objective reality10.

The cry of the carrot

If taking the animal question and the issue of sentience seriously has profound implications for our physical conceptions, I believe that conversely a reflection on physics, and at least an awareness of the inadequacy and inconsistence of our traditional conceptions of physical reality, can allow us to move beyond empty debates and start providing valid responses to some of the objections that we, as animal activists, receive. One example is the infamous objection of the “cry of the carrot”. Beyond the obvious bad faith that motivates it, this objection expresses almost explicitely the unease that derives from the impossibility of integrating sentience into our vision of the physical world. We do not get the answer “what about the cry of the carrot?” if we argue in favour of oppressed Chechens; these are humans, and so the question of what physical criterion justifies ethical consideration for them is not asked. But if we are care for non-humans, even for some as close to us as are pigs or cows, we implicitly show that we do not believe in this partition; our criteria must then necessarily be physical. We are thus referred to a physical phenomenon – the crunching sound of a carrot being grated – and are asked how we can distinguish it from a cry, from a real expression of suffering, since we do not limit this notion of suffering to the human world alone, but view it as part of the physical world, that of stones.

Today, we can answer, of course, that carrots have no nervous systems and so on. But we have to admit that we don't know why these criteria are not arbitrary. What is it about nerve tissue that makes it the unique site of potential suffering? What we lack is a theory of suffering, and a global vision of the physical world that makes this theory possible. From then on, we will be able to tell from the outside whether or not this or that phenomenon that we observe – a certain sound, for example – corresponds to suffering, without needing to be “in the shoes” of the carrot any more than we need to be in the shoes of an electron to determine its state.

3. Argumentation by the impossibility of nonbelief*

One may distinguish between three kinds of “reasons to believe” the truth of an assertion:

A. Demonstrative reasons (data and reasoning that make the assertion probable, such as believing that tomorrow it will rain because the weatherperson says so and is rarely wrong).

B. Ethical reasons (in particular, for the utilitarian, it is right to believe something if doing so will increase the total happiness in the world).

C. Causal reasons (any cause of which the belief is an effect; such as the fact that most people believe in a certain religious creed because their parents and relatives believed in it).

It may seem odd to view a purpose as a reason for believing something (reasons of type B). However, for acts in general, a purpose is usually viewed as a valid reason.

One may believe that the ideal reasoning in favour of a thesis must be of type A, the model of which is perhaps mathematical reasoning. In such cases one does not appeal to the advantages for the reader of believing in the truth of an assertion (which would make it an ethical argumentation, type B) and one does not try for example to hypnotise the reader into believing in this truth (an “argument” of type C). Whether the reader likes it or not that in a right triangle the square of the hypotenuse is equal to the sum of the squares of the other two sides, that is what he or she is shown.

Only type A reasons for belief can be a valid answer to a question “Why do you believe...?” An answer of the type B, that is, “I believe it because it is better for me (or for others)”, cannot replace a reason of type A11. Nor can I answer that I believe the assertion because of my upbringing, or because my neurons are configured in such and such a way (answer of type C). Such answers may well actually be true, but are not answers to the question as asked.

My wish is to show that ethical (i.e. prescriptive) assertions correspond to an objective truth, and thereby to show in particular the objective reality of sentience and of free will. I would be happy if I could base these developments solely on type A reasons. But I cannot.

Shall I then turn to a type B argument, and simply make you desire to believe what I myself enjoy believing? Or find a way to persuade you by rhetorical tricks that my ideas are correct? That is not my intention. I believe that I am justified in using yet another form of “argumentation” in this case. It does not consist in giving a reason to believe, but in highlighting the fact that we already actually do believe, and can but believe12. Henceforth, acknowledging this fact is only a matter of consistency.

One may find such an argument weak, since it does not constitute a demonstration. My response is partly ad hominem, but not, I think, without force. It consists in noting that it is this same form of argumentation that ultimately underpins everything we believe, starting with our conviction that there is a real world.

This last fact is actually universally recognised; I will get back to this in a moment. What is remarkable is that while being recognised it is generally ignored, the impossibility of basing our belief in a real world on pure reasoning being perceived as a sort of philosophical curiosity that detracts nothing from the good standing of this conviction; whereas the corresponding impossibility in the ethical domain – the impossibility of basing the truth of ethical propositions on pure reasoning – passes for irrefutable proof of the relative or conventional character of these, or, in the views of religious people, of the need to base them on faith in a god.

On the contrary, I think that the truth of ethical (prescriptive) assertions is as well-founded as that of those assertions that are classically called “descriptive” such as those that describe material realities13. Both are based on the same impossibility of not believing certain assertions despite the impossibility of proving them. If my argument is to be considered weak, it cannot be more so than our belief in the existence of the world; which should suffice.

Before we discard this argument as weak, we should grasp its full meaning. The impossibility of not believing that grounds it is not a mere difficulty; it does not refer, for example, to the psychological suffering that nonbelief would cause. It refers instead to an impossibility that is inherent to our way of being in the world. Let us consider that, because of our very presence in the world, because of our situation as sentient beings, it may be impossible for us not to believe something. It is then futile to pretend not to believe it. Any theory we build that contradicts this belief would be impossible to take as true without believing both one thing and its opposite; that is, it would be impossible to take seriously as true, once we become aware of its implications for our inescapable belief. This does not, of course, preclude us from speculating, imagining false what we cannot believe to be false; we may possibly draw interesting conclusions from such speculations, but cannot believe the world thus contrived to be real.

I now come to the substance of my argument; my first step will be to highlight the impossibility of our nonbelief in the reality of the truth value of (prescriptive) ethical assertions.

4. Ethics

The impossibility of universal nonbelief

We often know clearly whether or not we believe something. I believe that we are now on Saturday, and I know that I believe it. But sometimes things are not so simple. A good example is the question of faith in Christianity, which is central to that religion since the necessary and sufficient condition for being “saved” is belief in Jesus (in his existence, in his divinity, in his resurrection, etc.). Hence the nagging concern for every Christian: “Do I really believe?” The simple statement – the “profession of faith” – is obviously not enough. The story of Jesus walking on water and of Peter sinking because his belief that he could do the same was not strong enough is a good illustration of the fact that we do not always know ourselves whether we believe something or not, or to what extent we believe it; for Peter rises up, believing that he believes, but not believing enough; he sinks, and Jesus, somewhat perversely, asks him: “O thou of little faith, wherefore didst thou doubt?”14.

In this story, sinking or not sinking represents a supernatural test of belief. A more mundane test is this: if we believe something, it will be reflected in our decisions.

Do we believe in the existence of a physical world? I don't mean whether we believe in the precise validity of some specific physical theory; I mean, in a minimal sense. For example, do I believe in the existence of the keyboard in front of me? The answer must be yes; the fact that I am typing on the keys, in order to write this text, is explained by my belief that this action will change something in the world. I may not actually know very well what the world is, what matter is, and what it means for it to be changed. But I do know one thing: that it will change something for sentient beings. If I type on the keyboard, tomorrow I will be able to read what I will have written; and perhaps others will read it. I believe in the existence of the world at least as a basis for a causal chain such that depending on how I act, sentient beings – myself, at least – will be affected.

The fact that I type on these keys thus testifies to my belief in the existence of the world, at least in this minimal sense of “existing”.

This, one may say, is trivial. But it means that we are many to believe in the existence of the world! All sentient beings, in fact, do so, as I see it; but for the moment we will accept that this belief seems plausible at least for all typical adult human beings – for the non-comatose, for example. They eat, hence believe in the existence of what they see on their plates, or at least in the fact that in some way the movements they perform will cause or remove some sensation of pleasure or of hunger.

An unimpressive result, perhaps, but one that contradicts a tradition that goes back at least as far as the Greek skeptic Pyrrho (4th-3rd century BC), who claimed to doubt the very existence of this world. According to Diogenes Laërtius, Pyrrho believed so little in the testimony of his senses that he only avoided falling off cliffs thanks to the actions of his friends** This is a very rare case; yet, if this account may testify to Pyrrho's nonbelief in the existence of those cliffs (leaving aside doubts about what he would have done in the absence of his friends), it does not imply his nonbelief in the world in general. Quite the opposite: for why then did he put one foot ahead of the other, if not to move forward, or at least to relieve the urge to move – which by itself implies a belief in some effect, never quite immediate, of his actions?

In fact, Descartes, taking up this same question of the ultimate foundation of our beliefs in the existence of the world, began by “doubting” everything; but this doubt was only provisional, heuristic, and did not imply any practical consequences15:

(...) so that I might not remain irresolute in my actions, while my reason compelled me to suspend my judgement, and that I might not be prevented from living thenceforward in the greatest possible felicity, I formed a provisory code of morals, composed of three or four maxims (...).

These “three or four maxims” are practical and imbued with solid common sense. They aim, as Descartes says, at felicity (happiness), i.e. at a sensation. Descartes derives action from belief (“judgement”), since he fears that in the absence of any belief he will remain “irresolute in [his] actions, while [his] reason compelled [him] to suspend [his] judgement”; yet he claims to be able to compensate for this lack of belief by a “provisory” (provisional) morality. It seems clear, however, that this morality itself necessarily presupposes a belief. The first maxim, for example, “was to obey the laws and customs of my country”; he therefore believed in the existence of that country. Descartes thus never really ceased to believe in the reality of the world; he was never irresolute in his judgements on this point. His doubt, which was provisional, was only about their foundations.

By these examples I want to suggest that the existence of skepticism, philosophical or otherwise, concerning the existence of the world does not imply the existence of any real doubt on this subject. This is not to say that these people are faking it. Descartes himself did not really claim to have doubted of the existence of the world. Others may have sincerely believed they had such a doubt, but that doesn't imply that they actually had it16.

But my point is not simply to note that particular persons did not really doubt everything, or even to assert that no one ever really entertained such a doubt; it is to show that such a doubt is impossible, because of our situation – because of the situation of every deliberative being, and therefore, I believe, of every sentient being.

Our situation is that we must, at every moment, decide. It is not that it is our interest to decide; it is that it is impossible for us not to decide.

Let us imagine that we do not believe anything. Then we do not believe that our action will have any particular effect. Why then should we bother to act? We could just as well do nothing. But why do nothing? To avoid getting tired? If we do not believe anything, we do not believe that acting will tire us, nor that doing nothing will tire us less.

Nor can we decide without reasons. When we are irresolute, we look for a reason to decide one way or the other; only with such a reason can we decide. Yet, as long as we remain irresolute, we have at least decided one thing – namely, to decide nothing else. We could run around, or take some other decision; if we don't, it is because we have a reason not to, if only, for example, not to tire ourselves unnecessarily. Descartes, in order not to “remain irresolute”, adopts a moral system, i.e. a system of reasons for deciding one way or the other; but he does not choose just any moral system. When he states his “three or four maxims” he also justifies them. He does so on the basis of practical, “reasonable” reasons, which he obviously believes in, despite the “doubt” imposed on him by reason.

Descartes therefore believes in reasons for deciding, in the “factual” sense; that is, he believes in the existence of a certain country, namely, the one in which he lives, in the existence of its laws and customs and so on. But he also believes in these reasons in the prescriptive sense: he believes that these are reasons to decide to act in a certain way. He believes in the existence of prescriptive reasons.

In short:

— it is at every moment impossible for us not to take decisions;

— we cannot take decisions without believing in reasons for doing so (prescriptive reasons);

— it is therefore impossible for us not to believe in reasons for taking decisions (prescriptive reasons).

Inside and outside viewpoints

It is worth emphasising here the position from which this conclusion is reached. This is what I call the “inside viewpoint”. One could imagine describing the same events – a person deliberating, then deciding and acting – from an outer point of view, as a physical system going through a sequence of states according to certain laws. Perhaps we will then identify some of these states as certain beliefs; and find that the system always happens to be in a state of belief in one thing or another, and that this state determines the system's subsequent evolution, and in particular determines its future actions. No doubt will we also try to explain this state of belief by the laws of motion of atoms, or, at another level, by Darwinian mechanisms of evolution. This outside point of view is valid in its principle, since we are part of the world, and are therefore are physical systems; such descriptions and explanations are necessarily possible. Nonetheless, however legitimate it may be, this outside viewpoint cannot abolish the inside viewpoint. The outside viewpoint observes and explains our belief; but the observation and explanation of our belief are not our belief, and do not, by their mere existence, abolish our belief.

However, it may happen that the way in which we observe and explain one of our beliefs constitutes a reason to cease believing it; for example, when we explain an optical illusion. We may then abandon the belief. But it may also be that this is not the case, and that we do not abandon the belief, perhaps because we have not been convinced by the explanation, or because it does not really seem to contradict the belief, or for any other reason; whatever the reason, it is vain to attempt to persuade ourselves that we do not believe, as long as in fact we do believe. And this will always be the situation with regard to certain beliefs, if, as I hold, it is impossible for us not to have them because of our condition as deliberative beings.

A criticism often levelled at scientific descriptions and explanations of subjective phenomena is that of “reductionism”. I view this criticism as, in its substance, correct; not that we should refrain from describing these phenomena in scientific terms, nor that we should attempt to add, as is so often done, some holistic layer of “emergent phenomena” based on the questionable principle that the whole is more than the parts. Rather, I believe that these descriptions and explanations are themselves made in the terms of a physics that is actually incompatible with subjective phenomena, and that to accept them would be to accept that this outside point of view could abolish the inside one. But this abolition, as I have said, is not possible. A physics that has implications we cannot believe is itself a physics we cannot believe.

The reality of the truth value of prescriptive assertions

Foremost among those things that we cannot nonbelieve is the existence of reasons for making decisions, that is, the existence of the right (correct) answer to the question “What to do?”. The answers (right or wrong) to this question are not descriptive assertions, in the classical sense, but instead prescriptive. They are of the form “Do this!”. They are not to be confused with simple predictions, such as “I will do this.”.

One may find this new category of assertions mysterious. What is their truth value? In what sense can the proposition “Do this!” be true? First of all, such a proposition does have a negative: “Do not do this!”. Secondly, belief does not in itself constitute the truth of such propositions; it is possible for us to be wrong. After having thought “Do this!”, we may change our mind: “No, instead, do this other thing!”. We may also reconsider afterwards: “I should not have done that.”. If belief in the assertion was its truth, we could not change our minds, that is, feel that we were wrong. The act of deliberation itself would be meaningless – any conclusion we reached would be right, by the mere fact that we reached it. It would be like looking in a meadow for the blade of grass that we will have found in it.

If the truth value of prescriptive assertions does not consist in our belief in their truth, then it exists independently of this belief. To search for the right answer to “What to do?” necessarily assumes that a certain answer is the right one, whether we find it or not. It would make no sense to search for it if we did not believe that; but it is impossible for us not to search for it, and it is therefore impossible for us not to believe that a certain answer is right, regardless of our perception of its being right. It is in this sense that we cannot nonbelieve in the reality of the truth value of prescriptive assertions.

Ends and means

It would be a mistake to view deliberation as a purely factual search, such as “Given that I have a certain end, what is the best way to achieve it?” If this were the case, what I call a “prescriptive assertion” would be no more than a descriptive assertion, in the usual sense: “Given that I have a certain end, this is the best way to achieve it”. But we also choose our ends. Even a completely “selfish” person has made the choice to consider only her own interests, excluding those of others. This implies at least her belief in the factuality of the possible future satisfaction of her interests, that is, if she conceives her interests in terms of obtaining pleasure and avoiding suffering, that she believes in the reality of her future pleasure and suffering17. She cannot believe that things that do not exist in reality are an end for her. But she will also have to believe that this future pleasure and suffering can be the result of her own actions; she will therefore have to believe in the existence of a physical world, at least in this minimal sense. Finally, the satisfaction of her own interests will represent in many cases not one, but several at least partially conflicting ends; she will have to choose between qualitatively different pleasures, between pleasures in the near future and others more remote, to decide whether a certain pleasure is worth the suffering needed to obtain it...

It is also possible to imagine that an individual may view his “interests” in terms other than pleasure and suffering. One example is the idea (stemming from a misinterpretation of Darwinism) that our “real” interests are the propagation of our genes. Another results from a certain romantic individualism, for which our interests consist in something like “self-realisation”18. If some people really do take such ends seriously, this only confirms the plurality of our possible ends, and thus the fact that these, like our means, are the result of a choice.

I believe that in reality this distinction between the choice of ends and that of means is artificial. In our real deliberations both are intertwined. No doubt the temptation to posit such a distinction and to seek to eliminate the choice of ends by making constants of them comes from our difficulty in conceiving on what basis this choice could be made, if we view it as free. I will return to the problem of free will. For the moment, let us just remark that the choice of means, once the ends are determined, is not necessarily less problematic in its mechanism. The solutions that a sentient being finds to achieve a given end are often “innovative”, and the hypotheses put forward by Penrose suggest that our brains allow for modes of problem solving that could not be simulated by an algorithm, and are therefore not deterministic in the sense of calculable determinism.

A meaning “for me”?

We cannot refrain from deciding, and cannot decide without asking ourselves “What to do?”; and we can only ask this question, like any question, if we believe it has meaning.

We cannot say, “Yes, I give this question a meaning, but that is because I cannot do otherwise; but I do not believe that it really has a meaning”. If we don't believe it really has a meaning, we don't believe it has a meaning at all.

Nor can we say, “Yes, it has a meaning, but only for me”. This process of relativisation is often used also in relation to “descriptive” statements in the classical sense. I think it is worth examining what sense it can have.

“For me” may mean “this is what I believe”; then “x has a meaning for me” signifies “I believe that x has a meaning (but others, perhaps, do not)”. The assertion that x has a meaning is then not itself relative, but instead absolute. I can say, “for me the earth is flat”; the flatness of the earth remains an absolute question, because it is true or false that the Earth is flat, independently of me. To assert that prescriptive assertions make sense to a certain individual is then to assert that this individual believes that they make absolute sense. This then grants my point: that we all believe that prescriptive assertions have a meaning.

In other cases, the expression “for me” denotes a different kind of relationship between the statement and an individual. An apple may taste sweet to Anne, and sour to Valerie; its “objective taste” does not exist. This does not mean, however, that the taste it has objectively for Anne does not exist, as does the taste it has for Valerie! In this case, we could say that the having-a-meaning of x is an objective truth, but in relation to me. This relation could be the simple fact that it is indeed I who believe that x has a meaning; we are then back to the first interpretation of “for me”. The relation could also be the fact that the prescriptive assertion x is itself related to the entity “me”, if we admit the existence of such a “personal identity”19: it prescribes what I should do. It is a truth about me, in that sense; but a truth I believe in, just as I believe (or not) in the flatness of the Earth.

It is remarkable that this relativisation – this “true for me” – works as if “me” were an entity somehow beyond the world, and could as such somehow bring the very truth in question with it into its retreat. Given that we are part of the world, our very view of the world is part of the world. If we believe that prescriptive assertions have a meaning “for us”, we believe that they have a meaning, period.

Ethics as a theory of the correct answer to “What to do?”

I have so far discussed prescriptive assertions; I think we can also call them ethical assertions. More precisely, I believe that a prescriptive assertion – the assertion “Do this!” – is true if what it commands us to do is what ethics commands us to do; and that therefore deliberation – the pondering of the question “What to do?” – is the search for the ethically right action.

I do not say this in a normative sense; that is, that all deliberation should be the search for ethically right action. I am saying that in fact it is such. I propose to define ethics as the theory of the right (true, correct) answer to the question “What to do?”

I will be told that I am free to define words as I wish, but that my “ethics” is plainly not ethics in the ordinary sense of the word. I do not believe that this objection is justified. More specifically, I believe that my definition of ethics follows from the common usage of the term if only one ceases to make an arbitrary exception for decisions that concern only oneself, and accepts the absolute truth of prescriptive assertions.

Selfish and ethical behaviour are usually contrasted. The point of ethics, in this view, is to lead us to consider others and to respect their rights and interests, instead of paying attention only to ourselves. This restriction is explicit in some ethical conceptions. Contract theories, for example, essentially require us to respect the terms of our “contract” with others, but otherwise leave us “free” to do “as we please”20. At least one ethical theory, however, governs in principle all our choices, placing on an equal footing those that concern ourselves and those that concern others: for hedonistic utilitarianism we must act to maximise net happiness in the world; therefore, an act that increases our own happiness without affecting that of others is ethically obligatory, just as is an act that increases the happiness of others.

This fact is rarely perceived, perhaps simply because there is little need to order people to pursue their own happiness. Yet such a command is still ethical in nature, even though we usually adhere to it without the aid of an elaborate ethical theory. The same is true of many propositions in physics; we do not need to study fluid mechanics before drinking a glass of water. Physics would nonetheless be artificially mutilated if we removed from its domain what happens when we drink a glass of water; just as it is an artificial mutilation of ethics to remove from its domain the “trivial” prescriptions such as those commanding us to consider our own interests.

Among the commonly mentioned ethical theories, there is at least one other that gives us obligations in choices that concern only ourselves21. This is the so-called “egoistic ethic”, whose single command is: maximise your own happiness. The fact that it is frequently mentioned as an ethic, even only as a “textbook case”, shows that common use does not exclude, at least in theory, decisions that concern only ourselves from the scope of ethics. This egoistic ethic, like hedonistic utilitarianism, governs in principle all our choices.

However, the basic reason why I say that ethics should be defined as the general theory of the true answer to “What to do?” is that all deliberation is fundamentally altruistic. Even if I am thinking only of “myself”, I am necessarily thinking of a future “myself”. My actions cannot determine the pleasure or suffering I experience at the time I choose them; they will necessarily determine my future pleasure or suffering. We are used to taking for granted our concern for ourselves. The fundamental problem of justifying ethics seems to us to be “Why should I rationally care about others?”, and this is a question that many feel has no answer. Rarely do we ask ourselves “Why should I rationally care about the feelings I will experience in five minutes?” We can just as easily say that these future feelings are completely indifferent to us! We are rarely totally indifferent to how we will feel in five minutes, just as we are rarely completely indifferent to the fate of people close to us; on the other hand, we are often rather indifferent to how we will feel in thirty years. If this were not the case, tobacco sales would be much lower.

The idea that there is a radical difference between concern for one's own – necessarily future – interests and concern for those of others therefore appears to me as a dogmatic and artificial construct, with little justification in either theory or practice. It is in this sense that I believe that all deliberation is altruistic; the interests it takes into account are always those of an “other”, whether that other is another individual or our future self.

“I find this hard to believe”

There remains an objection to this conception of ethics: our decisions are not, in fact, always ethical, even by the ethical standard that we ourselves recognise. It is perfectly possible to say “I see what I should do, but I cannot bring myself to do it”22.

I believe, however, that this objection can be answered if we regard prescriptive assertions as possessing a truth value, independently from our knowledge of them. It is not our verbal adherence to a prescription that makes it true; nor is it the fact that we believe we are adhering to it.

It may be useful to draw a parallel with assertions that are descriptive in the classical sense. When a would-be parachutist finds himself unable to jump from an airplane, is it not because he is cannot entirely convince himself that to do so is safe? He may well insist that he knows it is safe, and go over mentally a hundred times the facts that prove it is safe. But somewhere inside he continues to believe there is danger. It seems to me that this implies, at the very least, that we are not quite “individuals”, in the sense of being indivisible. Consciousness is not an illusion (in whose eyes would it be one?), but its unity may well be illusory, at least in part. Hence the fact that one part of our consciousness is convinced of a fact does not prevent other parts from believing the opposite.

We often know without knowing. “I can't believe it” is often said of the death of a loved one. It can happen that we act as if he were still there; that we set the table for him, “out of distraction” – or rather, because a part of us still does not believe in his death.

To return to prescriptive assertions: we may well know that what we are about to do is not what we should do; because, for example, it will cause others more suffering than it will bring us pleasure. But we know this without fully knowing it; just as we know, for example, that the pleasure of smoking a cigarette may cause us much suffering in the future, while finding it hard to believe it. In this light, it is because part of us does not really believe what we think we believe that we act in contradiction with our stated beliefs; and this is true whether the issue is descriptive (in the classical sense) or prescriptive in nature.

A few months ago I climbed to the top of one of the towers of the Basilica of Fourvière in Lyon. This tower, which is open to visitors, has been climbed by hundreds of people every day for ages; I knew that it was not going to collapse just because I put one foot wrong! Everything told me that I was safe. Yet I felt dizzy as I climbed the steps; I was filled with dread that the building might collapse. I climbed slowly, for fear of causing any shock. I reached the top with clenched teeth. My fear was undoubtedly irrational, but it was nonetheless real; it reflected a real belief in me that I was in danger.

I see no difficulty in viewing the problem of our non-compliance to our own ethical beliefs in the same way. We simply believe them only in part.

Description and prescription

My thesis is that we believe in prescriptions as we believe in descriptions; we believe that their content is true (or that it is false). I also speak of their “objective truth” and their “reality”. A famous assertion – the origin of which I cannot find, and which I quote from memory – was in substance that nowhere in the universe is there anything that would resemble a prescription; and that prescriptions, therefore, do not exist as such. Moral duties, right and wrong, would only reflect our personal, “subjective”, preferences, cultural or otherwise. There would be no such thing as real ethics.

I admit that neither I can clearly define in what sense ethical prescriptions are real objects. However, I believe that the generally accepted idea that “material” objects exist is quite as problematic. The verb “to exist” seems transparent, but transparency is like opacity in that it shows no content. In fact, in modern, quantum physics, the issue of the very existence of an objective reality has become highly opaque; the “standard” (so-called “Copenhagen”) interpretation is that this issue is itself meaningless. Physics is a mere set of “recipes” for predicting future observations from past ones. Everything else is no more than “gratuitous speculation”23. Paradoxically, according to this interpretation, utility (for humans), that is, a subjective, indeed, prescriptive entity, is all that is left – physical reality has disappeared, including that of non-human animals.

Classical, pre-quantum mechanics, which I term “Laplacian”, appears to impart a greater consistency to physical reality. This vision remains today, as I said, a kind of ideal model of physics, including for many scientific minds who are eager for a belief in a cold and hard reality. Therefore few perceive to what extent the very logic of Laplacian physics itself leads to a dissolution of the notion of reality. I will devote the next section to a brief description of this Laplacian worldview and will highlight some of its weaknesses.

In any case, I would like us to suspend somewhat our habitual certainties according to which, in order to be “real”, a “thing” must be made of matter and be located “somewhere in the universe”. We are not sure what it really means for a stone to be real. Nor are we sure in what sense mathematical truths exist. Nor can I say precisely in what sense prescriptive assertions exist. I only know that neither stones, nor mathematical truths, nor ethical truths can be entirely taken out of existence. I believe that these things exist in the world, and therefore exist there objectively, are real. I will not make sharp distinctions between these notions, because I do not believe in those that are commonly made.

In particular, I think that if a prescriptive assertion, of the form “Do this!”, is true, then it describes a reality. The descriptive and the prescriptive are classically opposed; I believe instead that every assertion is descriptive. This is why I also speak of descriptive assertions “in the classical sense” for those that are usually considered as such (the mass of a stone, for example).

Animals as moral agents

Anti-speciesist moral theories commonly distinguish between the twin notions of a moral agent and a moral patient. Humans are typically both moral agents, which means that they can (and should) act ethically, and moral patients, meaning that they should be taken into consideration when ethical decisions that concern them are made (their interests should count, and/or their rights or dignity should be respected...). Non-human animals, on the other hand, are generally only viewed as moral patients: we are to care about them, equally as for humans, but they have no duties, because they are incapable of ethical reasoning, just like young human children, for example.

If instead one accepts, as I propose, that all deliberation is by definition an ethical activity, and that there is no difference in nature between the deliberating individual's consideration for his own (future) interests and for the interests of other beings, then it appears that every animal who deliberates is a moral agent, in the same sense the term can be applied to a human.

This does not mean that there are no distinctions to be made concerning the level of complexity and abstraction that an individual can reach in her ethical reasoning. The same applies to ethics as to physics. Deliberating animals are also necessarily physicists; they foresee consequences of their actions. Only a few among them, namely some humans, can build complex and abstract physical and/or ethical theories; much more often, the ethical and physical horizon is more limited; it comprises what is perceived, the near future, proximate interests and the interests of one's family or group. This limited ethics and physics is nonetheless an ethics and physics.

When we scream in fear and pain, we are saying: “This is bad!”. The scream of a pig being slaughtered says the same thing: that what is happening is bad. The anti-speciesist says the same thing: that the slaughtering of the pig is bad, and says it for the same reason that the pig says it. This same assertion, from whomever it comes, has the same meaning and the same nature: it is an ethical assertion.

If we are to believe the words that the vegetarian writer J.M. Coetzee puts into the mouth of one of his characters24, it was in part the ethics of a hen that led to the abolition of the death penalty in France:

As for animals being too dumb and stupid to speak for themselves, consider the following sequence of events. When Albert Camus was a young boy in Algeria, his grandmother told him to bring her one of the hens from the cage in their backyard. He obeyed, then watched her cut off its head with a kitchen knife, catching its blood in a bowl so that the floor would not be dirtied.

The death-cry of that hen imprinted itself on the boy’s memory so hauntingly that in 1958 he wrote an impassioned attack on the guillotine. As a result, in part, of that polemic, capital punishment was abolished in France. Who is to say, then, that the hen did not speak?

5. The Laplacian model of reality

What I call the classical, or Laplacian, model of reality emerged in the 17th century with Galileo and Newton, replacing Aristotle's physics which was dominated by finalist, animistic ideas about the nature and desires of bodies. The Laplacian model formed the basis of scientific rationalism and dominated the scientific worldview until the early 20th century. Einstein's theory of relativity (1905, 1915) still fits into this framework, which was only subverted in the 1920s by quantum mechanics, which made it untenable, without however providing any alternative view of physical reality.

I hope it will be clear from the short analysis I will propose of the Laplacian model that it is the one that we “spontaneously” tend to view as the model of scientific description. When we insist, for example, on rejecting the notion of free will because our choices must be determined by something, this requirement is evident neither in the Aristotelian framework nor in that of quantum mechanics, which implies that certain events do indeed occur without reason. I do not believe however that the model, or rather non-model, that quantum mechanics proposes gives us a satisfactory account of free will; my purpose here is to shake up some of our certainties concerning the validity of the Laplacian model. I will also show that this model does not itself live up to its own requirement that everything should happen for a reason.

I name this model “Laplacian” in reference to the striking formulation that the physicist Pierre Simon de Laplace (1749-1827) gave of the notion of determinism25:

An intelligence which, for a given moment, would know all the forces with which nature is animated and the respective situations of the beings that compose it, if moreover it were vast enough to submit these data to analysis, would embrace in the same formula the movements of the largest bodies in the universe and those of the lightest atom: nothing would be uncertain for it, and the future, like the past, would be present to its eyes.

In this view, reality – all that exists – consists of a finite or infinite collection of objects – the “beings” mentioned above by Laplace – each of which can be characterised by a number of properties that may vary over time; knowledge at a given moment of the list of these objects and their properties constitutes a complete description of reality at that moment.

A simplified view that I will often use is that of billiard balls. In an ideal billiard game, the balls move at all times according to a perfectly defined and calculable law. As long as they do not meet a wall or another ball, they move in a straight line at a constant speed; when they collide, they bounce back elastically, following a simple law that brings into play their intrinsic characteristics (mass, radius), their motion and their position. The evolution of the whole can be complex, if a large number of balls are involved, but always remains entirely predictable, at least in theory, by an “intelligence”, as Laplace calls it, informed of the laws of motion as well as of the mass and the situation (position, speed) of each ball. The “billiard ball” image of the world assumes that the whole world is a vast collection of such balls moving in three-dimensional space.

Of course, classical physics has never seriously proposed such a simplistic model of reality. The “billiard balls” picture remains relevant, however, because it captures the basic logic of classical physics, with a few subtleties. In classical physics, we don't have balls, but instead we have “material points” – dimensionless “atoms” or “particles” that possess, for example, mass and charge – and attractive and repulsive forces of a more complex form than the simple contact repulsion that make balls bounce. To these material points were later added fields, such as the electric field, that are distributed throughout space, mediating the forces between particles but also evolving according to their own laws. It followed that the complete knowledge of which Laplace spoke also includes that of the fields, and therefore an infinity of variables, since it is necessary to know the intensity of the fields at each point of space26. Despite this, the “billiard ball” model has all the features that I will discuss of the Laplacian model. If subjectivity cannot find its place in a “billiard ball” model, it cannot find its place in Laplacian physics27. I will often speak as if Laplacian physics were really only about billiard balls, because this is a simple image that allows us to highlight its workings and limitations.

It should be noted that classical physics never really succeeded in proposing a consistent and plausible theory of reality; there were always details that went wrong in the corners28. The Laplacian image nevertheless remains as a paradigm for any physics that claims to be objective and allows for an observer-independent reality, since quantum mechanics proves incapable of providing such a model.

The completeness of the Laplacian model

Completeness means that all that can be said about the world is deemed to be contained in the “respective situations of the beings that compose it”; that is, to use our billiard balls image, in the position and speed of each of them.

In particular, the movements of our hands, our thoughts, our feelings, all of this would be the “mechanical” colliding of these balls according to the laws of motion. To say that I perceive the world is only to say that some of these balls, those of the world outside my body, collide in a certain way with the balls of my body, creating movements that will, passing from one set of balls to another, end up provoking certain movements and dispositions of balls in my brain or elsewhere, movements and dispositions which will of necessity, in some way, constitute my perception. My feelings and emotions will in the same way be dispositions and movements of balls somewhere in me. When I act on my perceptions and feelings, for instance when I write down my thoughts on a sheet of paper, it will be because these dispositions and movements will have in turn, still following the same “mechanical” laws of motion, provoked certain movements in yet other sets of balls, which I call my hands, which will produce the writing on the paper.

Because of this completeness, the balls themselves have no “interiority”. The expression “billiard balls” is misleading in this respect. The physics of real billiard balls moving on a table describes some of their characteristics, such as their position and speed, but these parameters are relative to objects that exist independently of them and have many other characteristics that give them existence: colour, roughness, chemical composition, solidity... On the other hand, in the Laplacian “billiard ball” model, the balls have no colour or roughness; they are not made of “something”. All that can be said about them is a small collection of numbers, namely their mass, radius, position and speed. The “radius” itself is not the boundary between a full interior and an empty exterior, but a simple parameter determining if and when a “collision” with another ball will occur. This “collision” will be a change in the movement of the “centre”; but what is this center the centre of? The answer can only be: of nothing. It is but a moving point in space. Its only existence is through its determining “collisions”, that is, events affecting other “balls”, which are themselves no more than points of the same kind. Yet all of space is points; what is special about these particular ones? There can be nothing, outside of the fact that their positions are those described by this particular collection of numbers...

If there were ever anything else to be said of this reality, if the “balls” possessed a reality beyond these few numbers, this additional reality would be absolutely unknowable to us; for our knowing it would be the same thing as particular positions and movements of certain balls in our brains, and, by virtue of the deterministic laws of movement, these positions and movements are entirely determined by those of all the other balls, and therefore cannot depend in any way on this additional reality.

As previously mentioned, the real picture proposed by Laplacian physics, based on particles and fields, is much more complex than the “billiard ball” model. The absence of interiority remains, however; the world has no “substance” and remains totally describable by a collection of numbers, which appear to describe no more than themselves. It is therefore difficult to see how the world could actually be anything other than a collection of numbers. It is paradoxical that the Laplacian paradigm, often perceived as the epitome of “materialism”, actually dissolves the world into an abstraction without substance.

A reversible determinism

The Laplacian model is deterministic, in a sense defined by the above quotation: the world is governed by a set of laws such that if I know its state at a given moment (the set of numbers that describes it), I can in principle deduce (calculate) its state at any future moment. The word “determinism”, however, refers to something more, that includes the notion of a cause-and-effect relationship: that the state of the future world is entirely caused by its present state. This common interpretation is suggested by the origin of the word: the future is determined, that is caused, by the present, since a given present state can produce only one possible future state. It thus seems natural to equate physical, Laplacian determinism with a principle of total causality (“everything that happens is determined by what previously happened”); but paradoxically, as I shall show, the very notion of causality is an empty word in Laplacian determinism.

It is significant that Laplace's quotation gives the same role to the past and the future: “and the future, like the past, would be present to its eyes”. Indeed, all classical models of physics are reversible with respect to time. This means, in graphic terms, that if I film any event, and then play the sequence backwards, the reversed sequence I see still satisfies the same laws of evolution. This property is verified in the “billiard ball” model: both the uniform rectilinear motion and the changes in motion during collisions are reversible.

This is a property shared by all current physical theories, including, with some qualifications, by quantum theories29.

Schematic representation of the movements and collisions of a group of billiard balls, and the same movements with time reversed.
Figure 2: Reversibility of the evolution of billiard balls. The film played backwards shows us an evolution that satisfies the same laws.

Laplacian determinism implies that if I know the state of the world at the present time, only one single state can follow at a given future time; but because of its symmetry between the past and the future, it also implies that the present state can stem from only one single possible state at a given past time. Does this mean that the present causes the past? The present “determines” the past as much as it does the future, if by determination we mean that for a given present, there can be only one past, just as there can be only one future. And Laplacian determinism says no more than this. The notion of causality, which is always dissymmetrical – the past causes the future, but not the reverse – cannot therefore be founded on this basis alone.

This paradox illustrates the contrast between Laplacian reversibility and common sense: we do not feel that the past and the future are symmetrical at all. We view time as having a well-defined “arrow”, as being able to “move” only in one direction; and causes as being all on one side – which we call past – and effects on the other – which we call future. But it seems impossible to derive such an arrow from completely symmetrical evolutionary equations; the problem of the “arrow of time” has been one of the major difficulties of physics since the 19th century.

I will later return to the notion of causality because it is linked to that of laws – itself problematic in the Laplacian framework – and to that of free will, which I view as an unavoidable ingredient of the subjective.

The epiphenomenalist hypothesis

Epiphenomenalism is the idea that sentience (subjectivity, consciousness) is only an epiphenomenon of the physical world; that is, in short, that it may “look but not touch”. This is less a thesis that anyone really defends than the unpleasant conclusion to which many attempts to account for sentience within a Laplacian framework seem to lead.

I said above that by virtue of the completeness of the Laplacian paradigm, our sensations, feelings and emotions are necessarily identical to certain “dispositions and movements of balls”, or, in the terms of a more realistic model, to the dispositions and movements of particles and the states of the fields inside our brains.

Intuitively, many people, including myself, find it difficult to believe that sentience can be “just” that. At the very least, it is not clear how particle movements and other “mechanical” processes can be sensation; subjective sensations and phenomena seem to involve something more. I will return to more reasoned justifications for this feeling. Here I only want to note that if we try to make sentience into “something more”, while remaining within the framework of the Laplacian model, we necessarily end up with an epiphenomenalist position.

Formally, the idea that sentience is something more than the movement of billiard balls directly contradicts the completeness hypothesis of the Laplacian model, which implies precisely that there is nothing more in the world than what this model contains. We can, however, imagine a “Laplacian+” model, consisting of what we may call the “physical” world, the one of the billiard balls, which would behave in a strictly Laplacian way, plus that “additional thing”, namely sentience, the seat of feelings. When fire burns my hand, for example, this would set in motion a succession of movements in the balls forming my hand, in turn influencing the balls in my brain, and lastly causing the balls forming my mouth to emit a scream; at the same time, the state of the balls in my brain would not itself constitute pain, but would cause pain to passively appear in that “additional thing” where my sentience lies.

Such a conception, which appears capable of resolving our difficulty in conceiving sentience within the Laplacian framework, while maintaining this framework as a theory of the “physical world” (to which a mental world would nevertheless be added), necessarily implies epiphenomenalism. For it is assumed that sentience is affected by what happens in the Laplacian world; it is informed of pain, or, rather, of the dispositions of the billiard balls that correspond to pain. It does not seem impossible to give it such a passive position; but it is impossible to make it play an active role without violating, precisely, the determinism of the Laplacian world. The billiard balls evolve according to their state and that of the other billiard balls; it would be a departure from these laws to allow consciousness, our volition, to act on their evolution. And such a derogation cannot be admitted without bringing consciousness straight into the physical world, which would no longer be either Laplacian nor “Laplacian+”30.

This is what leads us to consider the epiphenomenalist position, according to which consciousness is affected by the physical world while being in return unable to act upon it. Moreover, it appears to me that a certain number of positions that are current among philosophers who reflect on these issues imply epiphenomenalism. I have in mind in particular position B in Penrose's classification, which I will discuss in section 8, and which is the position of the philosopher John Searle. It is rare, however, that the defenders of these positions explicitly embrace epiphenomenalism, because it is difficult to embrace consciously.

Epiphenomenalism implies that nothing in our behaviour is the result of our being conscious. This means that when we scream in pain, for example, we are not really screaming in pain; the pain, the desire for it to stop, and all other perceptions are felt by the spectatorial subjectivity, but play no causal role in our screams, which result only from the non-sentient mechanics of “billiard balls”. Even the memories we believe we have of our own emotions are not memories of emotions, but the subjective effect of a present “purely physical” state “remembering” a certain past “purely physical” state, which, additionally, was (perhaps – how would we know?) producing a certain subjective state at the time.

If epiphenomenalism were true, we could not know it; or rather, we could not express it, or would only express it “by chance”. Epiphenomenalism is an attempt to explain consciousness, i.e. the fact that we feel things; but it precisely denies that our actions, and thus in particular our talk about epiphenomenalism, can in any way result from these feelings! Epiphenomenalism parks subjectivity on a one-way street.

More generally, if epiphenomenalism were true, we could know nothing of subjectivity; except perhaps of our own instantaneous subjectivity. We could not predict the consequences of our actions on our future subjectivity, since we cannot rely on any authentic experience of their past consequences. There would be no point in deliberating, doubly so: because we could not base our choices on anything, and because our choices could not affect anything.

If one accepts my thesis that we are deliberative beings, and cannot believe that deliberation is meaningless, one will accept that we cannot believe in the epiphenomenalist position.

It should be noted, however, that the definition I have given of epiphenomenalism depends on the notion of causality, which is itself problematic in the Laplacian framework. I do not want to develop this point here, but only to highlight the fact that epiphenomenalism, a tempting solution, is a false solution.

The Turing test

The name of the British mathematician Alan Turing is not well known to the general public, yet he is a major contributor to one of the central themes of science fiction and to the almost messianic expectations we have had concerning “Year 2000”: the myth of the thinking, even desiring, indeed pathetic, robot such as Hal in 2001: A Space Odyssey. This theme presents the computer as an artificial equivalent of the human brain, and suggests – more often than it asserts – that these beings, once they show themselves capable of behaving (more or less) like humans, are perhaps really sentient and thinking.

I call this a myth, because at least for the moment it remains a myth. We do have machines today that we call “robots”, but they have little resemblance with Hal or R2-D2. They are certainly far from giving the impression that they really think, let alone that they have emotions.

It was in an article written in 1950 that Turing asked the question: “Can machines think?”31 He wondered about the definition of the terms “machine” and “thinking” and immediately replaced the initial question with another one, which he deemed “closely related”. Namely: “Is it possible for a machine to succeed in the ‘imitation game’?” This test, which Turing described at the time, has become known as the “Turing test”.

It involves having the machine “converse” remotely with a human, called the “interrogator”, who does not know whether he is dealing with a machine or a human being. The “conversation” takes place via teletype, the 1950s equivalent of our keyboards and computer displays. The machine can think, Turing says in essence, if it is able to deceive the interrogator in a conversation lasting several minutes and pass for a human.

Turing proposes to define thought as the ability to pass this test – at least this is what is suggested by the way in which he introduces the test, as well by as several other considerations in the article. Other passages, however, as well as common sense, suggest the opposite; I will return to this issue. There is on the other hand no ambiguity in the way he defines a “machine”, as a computer, that is, as a device the behaviour of which is entirely determined by a program, or algorithm.

His view was that “in about fifty years' time it will be possible to programme computers (...) to make them play the imitation game so well that an average interrogator will not have more than 70 per cent chance of making the right identification after five minutes of questioning.”32 Year 2000 is behind us and this prediction has been proven wrong. Despite the technical power of computers, which far exceeds that predicted by Turing, and despite more than fifty years of effort by a large number of “artificial intelligence” research teams worldwide, no programme on any computer is today capable of passing for a human being for even 30 seconds.

One may distinguish the three following claims in Turing's thesis:

(a) That one may validly define the fact that a system thinks by its passing such a test, that is, by its being able to exhibit the same behaviour as a human33.

(b) That the fact that a system thinks can be deduced from its behaviour.

(c) That a computer can indeed think, that is, can exhibit the same behaviour as a human being.

Statement (b) is an immediate consequence of (a): if thinking is defined by behaviour, it can certainly be deduced from behaviour. The converse is not true, however. Realism – the belief in the existence of a real world – implies that things exist by themselves, in one way or another, whether or not we have the means to ascertain this existence. This remains true even if we do, in fact, always have these means. Even if it were always possible to know whether it is daylight by looking out the window, the fact that it is daylight is not defined by the operation of looking out the window.

There is a view, called “operationalism”, which consists in asserting, on the contrary, that scientific notions must be defined by operations performed on the world. For example, the temperature of a body would be defined by the position of the mercury in a thermometer constructed in a certain way, brought into contact with the body in a certain way and for a certain time.

Operationalism is implicitly based on the separation of the world into humans and stones. For who is this “we” that is deemed to bring the world into existence, if not the set of all humans? Operationalism, however, is a particular version of this separation, in which the stones do not actually exist by themselves; it is therefore incompatible with realism, and thus, in particular, with the Laplacian worldview, which presumes that the world exists. Yet the operationalist creed is part of the standard baggage of the modern scientific mind, cohabiting without too many clashes with the Laplacian paradigm. Here again, in fact, we have a sharing of fields of application; operationalism rears its head especially in those fields of science that seem to escape the Laplacian paradigm, such as thermodynamics34, quantum mechanics and – precisely what interests us here – psychology.

It is according to the operationalist criterion that Schrödinger's “rationalist” declares that the sentience (or non-sentience) of an animal is meaningless: that is, we have no criterion for demonstrating it. Turing, on the other hand, states that in humans and computers, sentience has meaning, but that it is reduced to the success of his test. Later, he responds to the objection that thought, emotion and other sensations are real things by saying, in essence, that this negation of (a) implies the negation of (b) and must therefore be rejected35 as leading to solipsism.

Other passages, however, seem to indicate that he does not really take his test seriously as a definition of thought. For example, he wonders whether, on the other hand, “machines do not perform certain operations that should be described as a very different form of thinking from that performed by man”36 , a form of thinking that would not be taken into account by his test. If, however, he really considered his test as a definition of thought, one could not assume that anything else should be considered as thought. Finally, his definition would lead to many humans being considered incapable of thinking; a young child, a paralytic, a person who spoke no common language with the interrogator, etc., placed in the situation of the “machine” in the test, would not pass it any better than a rock would; yet Turing does not seem to want to exclude such people. It seems, then, that he has in mind that his test is just that, a test, not a definition; a test implies the a priori existence of the thing under test, and at the same time its accessibility (at least in principle) to experience.

I believe that Turing's hesitations reflect the impossibility of taking the operationalist view really seriously, especially in the field of psychology; for if we accept (a) and define sentience by an operation conducted by an observer, who, in order to observe, must himself perceive, i.e. be sentient, we obtain a circular definition. But if we reject (b), says Turing, we have no way of knowing whether a being is sentient; sentience can then only be ascertained by the person himself. This is why he speaks of solipsism.

I think that we must indeed accept, in essence, (b), but reject (a); that is, we must admit that sentience exists in itself, and that at the same time its existence cannot always be inaccessible to externally conducted experience. It seems to me that we can arrive at this conclusion from the reasoning set out in section 4: if it were in principle impossible to determine “from the outside” that a being is or is not sentient, ethics would be impossible, just as physics would be impossible if it were in any case impossible to determine “from the outside” the state of a physical system. We would find ourselves in the situation postulated by epiphenomenalism: a real sentience but without action on the world.

However, I have not yet analysed the link between ethics and sensibility. I will come back to this in section 8, to establish these conclusions in a more rigorous way.

Note that accepting (b) in this sense does not mean that in every case it is actually possible to observe this sensibility. It was impossible for Galileo to map the far side of the moon; we may not be able to determine today whether flies are sentient or not. The dark side of the moon and the sentience or non-sentience of flies are nonetheless realities, which are not defined by the possibility that “we” might have of becoming aware of them. This double aspect of potential accessibility and inaccessibility seems to me essential.

Why does Turing seem to believe that accepting (b) implies accepting (a)? I believe it is because he accepts (c), that is, in essence, that it is possible to simulate by a computer – and thus by the execution of an algorithm – any behaviour of sentient beings. It is therefore impossible to distinguish such a computer from a sentient being from the outside. If we accept (b), then we must conclude that this computer is, indeed, sentient. But on the other hand, there is nothing in the computer's guts that seems to correspond to anything like sentience; we find only transistors and wires, and, at another level of analysis, algorithms determining behaviour. Above all, no theory exists that allows us to recognise sentience when we happen to encounter it; worse, within the implicitly accepted Laplacian framework, we cannot see what such a theory might look like – indeed, I think that within this framework such a theory is impossible.

If we are unable to find sentience in the computer, but must admit that it is sentient (if it cannot be distinguished by its behaviour from a sentient being), we are left with the task of considering it as sentient, and this by virtue of its behaviour alone; and thus, for want of a better word, of defining sentience operatively, by this behaviour.

If this is indeed Turing's underlying reasoning, it is made necessary by:

— his acceptance of (c);

— the impossibility of founding a realistic theory of sentience in the Laplacian framework.

The acceptance of (c), in particular, is a direct consequence of the computable character of Laplacian determinism. It is this very point that underpins Penrose's theses, which conclude that the real physics of the world cannot be computable, i.e. that we must reject (c). I agree with Penrose on this point; I think we should reject (c), and therefore accept (b) as a test of sentience, seeing it as real, rather than defined by it as postulated in (a).

We have seen that (c) has not been validated within the time frame envisaged by Turing; but this does not in itself imply the falsity of this proposition. It is for other reasons, which I will develop in Section 7, that I believe that it is not possible to simulate the behaviour of a sentient being by an algorithm, and that therefore the world cannot be computable. Before doing so, it will be useful to specify this notion of computability, and to distinguish it, following Penrose37 , from simple determinism.


Determinism implies that if the state of the world is fixed at a given moment, its state at a future moment is determined. Calculable determinism further implies that this future state can be calculated. One might think that they are the same thing, but they are not.

In the Laplacian model, the world can be described at each moment by a collection of numbers. The laws of evolution allow us to calculate, from these numbers at time t, their new value at an immediately subsequent time t + dt. This calculation can be broken down into elementary arithmetic operations (addition, multiplication...), which can be done by applying simple “recipes”, i.e. automatically; in short, by an algorithm. In fact, for several reasons it is rarely possible to perform this calculation with perfect precision; for example, it would have to be done with an infinite number of “decimal places”. However, it is always possible to do it with as much precision as one wants, at least in theory38.

The notion of algorithm was formalised in a rigorous manner by the same Alan Turing, as being any operation of which what is now called a “Turing machine” is capable. I will note the main points39. The Turing machine has a program, which represents the particular algorithm it is to execute; this is a finite (but as large as you like) list of instructions. It is provided with a set of starting data; in this case, the description (as precise as we like) of the world at a certain time t1. By running its programme, it transforms this data step by step. After a certain amount of time (as long as necessary) it reaches a “stop instruction”. The data it then leaves behind is the result of its execution, which will represent, in the case we are interested in, the state of the world at another time t2 (with as much precision as we want).

Note that the algorithm is unique, independent of the data. With this unique algorithm, we can obtain, from any possible state of the world at t1, its state at t2.

There are two facts that we can distinguish here:

— Necessity. If the world at time t1 is in a certain instantaneous state I1, then at time t2 it is necessarily in another state I2.

— Computability. If I know I1, I can calculate the state I2 using an algorithm known in advance (independent of I1).

It turns out that these two notions are not identical; more precisely, the first does not necessarily entail the second. In the case of Laplacian physics, both are verified. There are, however, classes of mathematical problems in which every particular problem in the class has a precise, “necessary” answer; but where no algorithm exists, or can exist, that allows this answer to be obtained “mechanically” for all problems in the class.

Penrose gives as an example of such a class of problems that of the tessellating the plane with geometrical “blocks”, such as the three in Figure 340. For these, the problem will be: is it possible, with these three blocks alone, reproduced indefinitely, turned and/or turned over at will, to completely pave the (infinite) plane, without overlaps or holes? It turns out that for this set of blocks, the answer is yes: it is possible to do so. Figure 3 shows the beginning of such a tiling. However, there is no such thing as a periodic tessellation with these three blocks, so the proof of this positive answer is not simple, but it does exist.

For other such sets of blocks, the answer will be negative. What is important to note is that for each set of blocks (i.e. for each problem in the class of problems) the answer is perfectly definite; paving is possible, or it is not. Here we find the notion of necessity; we can say that the specification of a set of blocks makes necessary, or determines, the yes answer, or the no answer.

Example of a tessellation of the plane.
Figure 3: Example of a tessellation of the plane. The three figures on the left allow the plane to be completely tiled. On the right, the beginning of the tessellation.

It has been shown, however, that this answer is not computable; that is, there is no algorithm, no recipe that can be applied mechanically, that can tell, for any set of blocks, whether it can or cannot tessellate the plane. Certainly, for any given set of blocks, there is an algorithm for that set that gives the right answer; indeed, that answer is either yes or no, and therefore one of the two elementary algorithms “answer yes” and “answer no” will suffice! What does not exist is a single algorithm, common to all sets of blocks (to all problems in the problem class), capable of giving, for each of these sets, the right answer.

For a given set of blocks, how can we know, therefore, whether it paves the plane? The only possible answer is: look for a demonstration (of the positive or negative answer). In short: “Think!” This “recipe” is not guaranteed! We cannot know in advance, in the general case, either that we will succeed or that we will fail. No mechanical recipe can tell. And if we find a demonstration, for the next game we will have to start again; each demonstration will be an innovation.

We see in this example of paving the distinction between necessity (determinism) and calculability. Penrose, on the basis of this, shows how we can imagine a (not plausible, but it doesn't matter) “universe” subject to a deterministic but non-computable law of evolution. The state of the universe is simply represented at each moment, not by a collection of numbers as in the Laplacian model, but by a set of blocks. The evolution law is such that the state of the universe at time t + 1 depends on whether the set of blocks corresponding to time t paves the plane or not. Such a law is deterministic, in the sense that at each instant the set of blocks that describes the state of the universe does or does not pave the plane, which makes the next state necessary. It is not, however, calculable, since no algorithm can “mechanically” pass from the state at time t to that at t + 1. A computer, for example, would be unable to predict the evolution of such a world, however determined.

The Laplacian model of the world is deterministic, and computable. Penrose's thesis is that the evolution of the physical world cannot be computable. On the other hand, he seems to presuppose that it must be deterministic, as in the fictitious world of the paving stone games I have just described; this will of course be a much more complex world, which we can assume would incorporate the whole of current physical knowledge as an approximation. Penrose looks for such non-computability in a relationship between gravitation and the “wave packet reduction” problem in quantum mechanics; and notes the existence in some nerve cells of very particular structures suggesting the possibility of such phenomena within them41.

The constructive part of Penrose's thinking is very interesting, but by no means a finished theory. Nor does it in any way provide a characterisation of sentience as such, i.e. that we feel things, rather than that they merely “happen” in a non-sentient way. In section 6, I will seek to detail some questions about the very structure of the physical world that still seem to me to result from certain facts that we cannot nonbelieve. In this context, the non-computable determinism of the physical world does not seem to me to be self-evident.

In any case, the very possibility of non-calculability, which in fact exists in the mathematical field, seems to me to be very suggestive, already by the parallel with the deliberative situation I mentioned in section 4. We believe in the existence of a right answer to the question “What to do?”; this answer is determined, “exists”, in the same sense perhaps as exists, for a given set of paving stones, the right answer to the question “Do they pave the plane?” How do we arrive at this correct answer? In the case of paving stones, there is no recipe; we have to think. I suggest that the same is true for the deliberative situation. To answer the question “What to do?”, we have to think. In either case, we know that the right answer exists, but we usually have no recipe for getting there, no guarantee that we will get there, and no certainty that we will not.

This distance between knowledge and its object is perhaps essential to the existence of both. What is striking about models of calculable determinism is that the result can be obtained by an algorithm, i.e. by a process in which this relationship, known as “intentionality”, between knowledge and its object is unnecessary and, in fact, absent. The data manipulated by the algorithm need not have any meaning for the calculation to proceed, and to lead to the correct result for sure. The algorithm represents a kind of “thinking without substance”. We are often presented with non-human animals as driven only by “drives”. The impulse directly determines behaviour; there is no need for the animal to understand anything, to decide anything, and therefore to desire anything: the impulse could be directly connected to the muscles! Of course, there may be a conflict of impulses; the vision of a watering hole accompanied by the smell of a predator. To flee or to drink? According to this view, the stronger impulse wins. Here again, there is no need to think, a three-neuron brain weighing machine is enough. There is no need to understand that there is a predator, to anticipate a danger, to feel a fear of the predator, a desire for water, to evaluate the existence of alternative water sources; there is no need for an intentional relationship, a feeling, a substance...

I am aware of the vagueness of these words; what is this “substance” I am talking about? However, this “lack of substance” seems to me to be central to the difficulties our science has in accounting for sentience. Our sensations are things that exist as such; but science seems to want to admit only empty things, which exist only in relation to other things that are themselves empty.

The “substance” I am talking about is perhaps simply existence. But how do we define the fact of existence? What seems certain to me is that if we take the Laplacian model seriously, this word seems quite hollow. To see this, a little formalisation of its conceptual framework will be useful.

The conceptual framework of the Laplacian model: real world, possible worlds, imaginable worlds

The Laplacian model assumes that the world as a whole can be described by a mathematical object. In the example of the billiard balls, this will be the enumeration of the three position and velocity coordinates of each of the balls at a given moment, i.e. if n balls exist in the universe, a sequence of 6n real numbers. The world is therefore entirely described by this sequence, i.e. by an element of the set noted R6n of all sequences of 6n real numbers. Everything that can be said about the world at this moment is contained in this object; and the knowledge of the world at this moment allows its knowledge at all past and future moments, i.e. that of the whole world in all its history.

Generally speaking, I will therefore distinguish the instantaneous world – the whole world at a given moment – from the historical world, which is the whole universe in the totality of its past and future history. This notion of the historical world may seem fictitious to us; we are tempted to ask, “When does it exist?” Yet we might also ask about the instantaneous world, “Where does it exist?”, and the lack of a possible answer in this case does not make the notion of the instantaneous world fictitious. Must an object exist in a time, but not necessarily in a place? Here is an illuminating remark by Penrose42:

Consciousness, after all, is the only phenomenon we know of that implies that time must somehow “flow”! The status of time in modern physics is not essentially different from that of space, and in fact the “time” of physical descriptions does not “flow” in any way; we simply have a static-looking “space-time” in which the events of our universe are arranged! Yet our perceptions tell us that time does flow (...).

What Penrose says about modern physics already applies to the Laplacian model43. In this framework, if the world is a reality, then the historical world is the totality of reality, even if this notion is contrary to our intuitions. If these, as I believe, ultimately prove to be correct, then it is the Laplacian model itself that we must reject; meanwhile, since we are examining this model here, we must accept the historical world as real.

Since we can describe the instantaneous world by a mathematical object belonging to a certain set I – in the case of billiard balls, I is the set R6n – we can also describe the historical world by a mathematical object, belonging to the set of applications M which at any date t make a certain instantaneous world I = M(t) correspond.

We thus have two sets: the set I of all imaginable instantaneous worlds, of which the real instantaneous world is a part at any moment; and the set M of imaginable historical worlds, of which the single real historical world MR is a part – the subscript “R” serving to indicate that it is the real historical world.

A graphical representation of this can be given if we imagine the set of imaginable instantaneous worlds as being able to be plotted on a straight line; this is an extreme simplification, since in reality, even in the simple case of a world of billiard balls, not one but a large number (6n) of dimensions would be needed to represent this set; but it allows us to draw a two-dimensional graph, with the instantaneous worlds on the ordinate, and time on the abscissa (fig. 4).

The real historical world, among all imaginable historical worlds.
Figure 4: The real historical world, among all imaginable historical worlds.

The real historical world MR is then represented by a curve, formed by the succession of instantaneous worlds that it traverses in the course of time. In Figure 4, this is the thick solid curve. The dotted line represents some of the innumerable conceivable historical worlds; any arbitrary succession of instantaneous worlds is a conceivable historical world, only one of these successions corresponds to the real historical world.

What is the status of the laws of physics in this framework? They allow us to deduce the real state of the world at any moment in the past or future, as long as we know this state at the present moment. If we know that at time t1 the world is in state I1 we can deduce the instantaneous state I2 of the world at any other time t2. Knowing I1, we can therefore deduce the real historical world in its totality; we are in the position of the “intelligence” of which Laplace speaks, for whom “the future, like the past, would be present to his eyes”.

The real historical world and two possible historical worlds.
Figure 5: The real historical world and two possible historical worlds.

However, these laws tell us more than that. The law of gravitation, for example, tells us not only how the planets will behave in the real world orbiting the real sun, but also how they would behave if they were placed differently than they actually are, or if the sun were twice as massive, and so on. The laws of physics thus allow us not only to deduce the real state I2 of the world at time t2 from its real state I1 at time t1, but also to deduce the instantaneous state I'2 that the world would have at time t2 if it were in any other instantaneous state I'1 at time t1 (fig. 5). In short, they allow us to trace not only the trajectory corresponding to the real historical world, but also a whole family of trajectories of historical worlds that are not real, but that conform to these laws in their evolution and that I will therefore qualify as “possible”. I have represented two of these possible (but not real) historical worlds in Figure 5, by thin solid curves. These curves do not cross each other, which reflects the determinism of the laws (only one possible historical world passes through a given point).


The laws of physics thus appear as rules specifying a set of “possible” historical worlds among a larger set of imaginable historical worlds. I can imagine that the world evolves in any way; that I jump out of the window, for example, and fly like Superman. Any succession of states of the world is imaginable. It is the laws of physics that tell me that if I jump out of the window, I will fall rather than fly; and so the world where I jump and fly is imaginable, but not possible. The world in which I jump and fall is possible, but not real (because I will not jump).

A flawed determinism

The idea that things could happen without reason seemed scandalous when quantum mechanics was formulated in the 1920s; and this sense of scandal persists and explains part of the nostalgia for the old framework that we still feel today. All of a sudden, it appeared that there were unanswered questions, things that happened “by chance”, just like that. “God doesn't play dice”, Einstein would have protested. In the Laplacian framework, indeed, everything seemed to have a cause. The state of the world today was entirely caused by the state of the world yesterday, and so on, ad infinitum. One could always find a “because” for every “why?”.

Yet in the Laplacian model there is a “why?” – and not the least – that does not find a “because”. This is worth noting, if only to introduce doubt into our attachment to absolute determinism and open our minds to other perspectives.

In the Laplacian framework, our “why”s' are always answered as long as they relate only to instantaneous states of the world or part of the world. The laws of evolution infallibly determine the instantaneous states of the real world in relation to each other. But if we consider this succession of instantaneous worlds as a whole and thus fix our attention on the real historical world MR, there is nothing in Laplacian determinism that tells us why the real world must be this one, rather than any other possible historical world. It explains the results of the lottery to us by the initial position and velocity of each ball, but it does not explain why we are in this world, with these initial positions and velocities and results, rather than in another, with other initial positions and velocities and results.

To people who claim that God exists because the world must have a cause, rationalist atheists often reply that the cause of the world today is the world of yesterday, and so on. The explanation by God is clearly a non-explanation; but we see that the same is true of the explanation of today by yesterday. Laplacian determinism does not provide us with an answer to these questions any more than belief in God does.

6. Causality, freedom and laws

On the basis of this same principle of the impossibility of not believing certain things, I come to two consequences that have a direct bearing on physics, in that they directly contradict the Laplacian worldview.

The first of these consequences – the reality of the causal relation – is usually taken for granted, and compatible with the Laplacian worldview; it would even be almost synonymous with the notion of determinism that underlies that view. The second – the reality of our freedom, or free will44 – is also taken for granted in everyday life, and in the practice of the courts45 , but is paradoxically seen as incompatible with the Laplacian view, which would imply that we have the illusion of it.

I believe that the causal relationship is real, but that, contrary to the common view, it is incompatible with Laplacian determinism. I also believe that freedom is real, and that it too is incompatible with the Laplacian view.

Finally, these two notions are linked to that of physical law. The latter is the same as causality: it is, contrary to what is commonly believed, incompatible with Laplacian determinism. Yet it cannot be abandoned.

We must build a physics that admits the reality of causal relationships, of our freedom and of physical laws. It cannot therefore be consistent with Laplacian determinism.

Causality and determinism

Causality implies a certain relationship, called “cause and effect”, between two events. This is not a simple juxtaposition. Elodie threw a stone through the window (event A) while saying the word “pumpkin” (event B). The stone fell on the road (event C). We will say that A was the cause of C; but we will not say that B was the cause of C.

Why not? The simple answer – and a good one, I think – is that if Elodie had not thrown the pebble, it would not have fallen on the road. We will not say the same thing about B: that if Elodie had not said “pumpkin”, the stone would not have fallen on the road46.

But what can these statements mean? They are counterfactual assertions, i.e. they speak of events contrary to the facts. In the world that exists – the one and only, the one we noted MR in section 5 – Elodie threw the stone, and said “pumpkin”. To talk about what would have happened if Elodie had not done these things is to talk about a world that does not exist. What can we say about a world that does not exist?

One can, of course, imagine it. The statement “if Elodie had not thrown the stone, it would not have fallen on the road” refers to a world we can imagine where Elodie does not throw the stone and it does not fall on the road. We find it logical to imagine such a world; indeed, we give it, as it were, a status of partial reality, by considering the counterfactual assertion “if... then...” to be true.

Can we do the same for the other counterfactual assertion, the one we reject: “if Elodie had not said “pumpkin”, the stone would not have fallen on the road”? Of course, we must imply “all other things being equal”, i.e., Elodie throws the stone (as in reality) but refrains from saying “pumpkin”.

We can indeed imagine such a world, where the pebble, rather than falling on the road, floats in the air, for example, and returns by itself to land on the table. This world is perfectly imaginable (you have just imagined it); is this enough to conclude that if Elodie had not said “pumpkin”, the pebble would not have fallen on the road? Of course not.

It is therefore not enough that we can imagine an alternative world where an assertion is true for us to consider it true as a counterfactual assertion. It is still necessary that this alternative world is possible, in the sense that I used this term in my description of the Laplacian model. The imaginary world corresponding to the first counterfactual assertion is consistent with the laws of physics, and in particular, with the law of gravitation. On the other hand, the second counterfactual assertion corresponds to a world in which the pebble remains suspended in the air; this world contradicts the laws of physics, and is only imaginable, but not possible.

Is this enough? I do not think so. To do so, one would have to be able to give the notion of physical law itself a higher status of reality than that of the real world itself. If the MR world is all that exists, physical laws cannot have such a status.

So what are physical laws? In the Laplacian perspective, only the MR world exists. However, it is not just any world: it conforms to certain physical laws. These laws appear to us as a collection of “regularities”. We have seen in the past that every pebble, once dropped, falls. Without this regularity, we would have to list the behaviour of the pebble on each occasion to describe MR. Thanks to this regularity, a single sentence is sufficient.

Generally speaking, the laws appear in the Laplacian framework as the expression of the somewhat “miraculous” fact that this historical real world – this succession of an infinite number of instantaneous worlds – can be “summarised” by the knowledge of any one of these instantaneous worlds, plus a few relatively simple laws of evolution.

This conception of laws – the only one possible, it seems to me, within the Laplacian framework – runs up against three difficulties, the first two of which have long been recognised:

— How is it that such a summary is possible?

— How can we, from the observation of these regularities in the past, deduce that it will still be verified in the future (problem of induction)?

— If the laws are just that – the observation of a regularity within MR – they do not in any way constitute a discourse in relation to other worlds.

I believe that these three difficulties are linked, but I leave aside the first two; the third is sufficient for my purpose. If the law notes a regularity, and predicts the repetition of the regularity in the future, it can tell us that when the rock has been dropped by Elodie, in the real world where she says “pumpkin” at the same time, it will fall. She still doesn't tell us anything about another world, which doesn't exist!

We might want to consider that these laws can tell us about these other worlds in some way by extension. A bit like saying “since half of any number divisible by four is even, if ten were divisible by four, five would be even”. However, it turns out that the same reality – that of the real MR world – can be described with a large number of different sets of laws. We can also state that “any number divisible by four minus five is odd”; hence if ten were divisible by four, five would be odd! The same applies to physical laws.

For example, we can state the following law:

Every time a stone is dropped, it falls, unless the words “556841278025 pumpkins” are spoken at the same time, in which case the stone floats.

As it happens, in MR, these exact words are never uttered when a stone is dropped; or if they are (you can, now that I have stated this law, make it false!), an infinite number of other such sentences are not. Let us suppose, then, for the sake of argument, that this is the case with this one. This law is then true. Moreover, it satisfies all the desired criteria of regularity. It has as much validity as a law describing MR as the usual law, which says that the stone will fall in all cases.

Yet the usual law, and this modified law, disagree about what would have happened if Elodie had uttered “556841278025 pumpkins” when dropping the stone: the usual law predicts that the stone will fall, the modified law specifies that it will float. So we cannot say, on the basis of the laws, what would have happened in this case. Therefore, we cannot determine whether Elodie's failure to say this sentence is, or is not, the cause of the stone falling.

It may be objected that this modified law is more complicated than the other; that the simpler law “prevails” (Ockham's razor criterion). I agree; but in what sense does it “prevail”? This criterion is undoubtedly correct as a heuristic principle; it does not change the fact that neither the usual law nor the modified law can be “tested” in relation to a world that does not exist, the world in which the sentence would be uttered; and only that world is likely to decide between them.

So what is left? We can say that it does not matter what would have happened if the world had been different. Laws govern what happens in the real world; what would happen in another world is a matter of convention. So is the cause of an event; if A, B and C happened, it doesn't matter to us whether A or B caused C; what matters to us is that they happened!

Can we accept such a conclusion? I think not. Causality is a fundamental concept in our daily lives, as is the notion of law. For the courts, for example, it is not irrelevant whether it was the action of one person or the word spoken by another that caused, say, a stone to fall on the policeman's skull! This attribution of responsibility by the courts is simply the translation of the fact that each of us – of us, I would say, sentient, deliberative beings – decides on our actions according to their consequences. To do this, we must believe in future causality at the moment of deliberation.

We have already noted another difficulty with the notion of causality in the Laplacian model, which is its asymmetry with respect to time. The cause necessarily precedes the effect; this seems to be an absolute, even definitional, rule of the notion of cause. However, we have seen that in the Laplacian model, time does not have an “arrow”, i.e. the same laws remain verified if the direction of time is reversed. In particular, if an “intelligence”, as Laplace said, knew the present entirely, then “the future, like the past, would be present to it”. This seems to suggest that the before and after have no objective existence. Laplacian determinism is such that if the world is, at time t1, in an instantaneous state I1, at time t2 it must be in some determinate state I2; in this sense, one can say that the state at time t1 determines that at time t2. The reverse is also true, however: the state at time t2 determines the state at time t1; I have not specified the temporal order of t1 and t2.

It is not in such a poor sense that we generally understand the concept of determinism. By this we mean first of all that the future is determined – entirely determined – by the past. That it is caused by the past. The verb “to determine” is, in everyday language, almost synonymous with “to cause”; and determinism is often presented as a theory of absolute causality. We have seen that we cannot attribute such a meaning to Laplacian determinism; in the Laplacian worldview, the world simply is; nothing is the cause of anything. It is ironic that it is precisely in this framework, perceived as deterministic par excellence, that the notion of causality loses its status as reality.

This makes sense, however, if one perceives that in the notion of determinism, or causality, there is a double aspect: that of necessity, and that of freedom. “Determining that...” is also “choosing that...”. Elodie determines that the stone will fall on the road by her gesture of throwing it out the window; she could have refrained from doing this gesture. The aspect of necessity in the notion of determination is that which follows this gesture, and which inexorably leads the stone to fall. Without this necessity, there would be no freedom of choice. When we say that the present determines the future, and are reluctant to consider that it could also be the opposite, it is because we think we can act, at least a little, on the present, and thereby modify the future. We cannot directly influence the future, and thereby modify the present. Elodie cannot directly cause the stone to fall in ten seconds on the pavement, and thereby cause her hand now to throw the stone.

The reason why Laplacian determinism dissolves causality, and thus represents only determinism in an impoverished sense, is precisely because of the absolute character of its triumph. If everything is determined, nothing can determine anymore.

In particular, in Laplacian determinism, we are determined. Determinism is often seen as contradictory to what is traditionally called “free will”; if “everything is written”, nothing can be chosen. To this, the rationalist tradition often replies: everything may be written (determined), but since we do not know what is written, we cannot escape the necessity of choosing, even if the result of this choice could be known in advance by a Laplacian “intelligence”. For a long time I myself believed such an answer to be valid; today this is no longer the case. On the contrary, I think that there is indeed an incompatibility between the notion of freedom and Laplacian determinism. Again, this stems from taking the internal point of view seriously, and the principle of foundation by the impossibility of not believing.

Dessert or tofu?

Let us look again at the deliberative situation. Let us take the case where we have to choose between these two possibilities: dessert or tofu. Let us assume that Laplacian determinism is true. The choice we make is then determined by the initial conditions, by the arrangement of atoms in our brain. Let's say it is dessert. Then we can't have tofu. Better still, the word “can” is meaningless; in the real world, the only world that exists, we will take dessert.

Yet, as we deliberate, we are fully convinced that we can have tofu, and that we can have dessert. This is the very basis of our deliberation. It is not just that we do not know what we will have. Suppose we are told that whatever we decide to ask for anyway, the cook will do as he pleases; he will give us the dessert or the tofu, depending on what he has most in stock. Again we don't know what we're going to get, but this time deliberation seems unnecessary. So it is not the uncertainty alone that underlies the deliberation, but the feeling of being able to make one of the choices, or the other.

Now suppose we are told that the cook has already determined what he will prepare for us, but this time it is a more helpful cook. When we entered the restaurant, he scanned our entire body, and he also knows, with all the necessary precision, the environment that is the restaurant. By the laws of Laplacian determinism, and using his state-of-the-art personal computer, he calculated that we would choose dessert. This is all possible, in principle, within the framework of Laplacian determinism.

Now suppose we know all this; we are even told that the choice we are going to make is written inside a small folded piece of paper on the table. The future really is written. What logic would there be in deliberating then? We don't know what is written on the piece of paper, but we know that we are not going to change it anyway! We can rest our minds, and wait to be served!

This is, one may say, in contradiction with our premises: for the cook has foreseen that we will deliberate, and choose dessert. On the contrary, his Laplacian calculations should have told him that his client, informed of the presence and meaning of the little paper on the table, would refrain from deliberating. The cook would then not have known which choice to write on the piece of paper!

The problem is that he can come to the same conclusion about each of us, as long as we believe in Laplacian determinism; and this, whether the future is physically written on a piece of paper or not! If we believe in Laplacian determinism, we have no motivation to deliberate. Yet we do deliberate. I think this means that we do not believe in Laplacian determinism.

I also believe that this means that we cannot believe in Laplacian determinism. For we can only deliberate; even the choice to “rest our minds” involves initial deliberation.

The attempt I have mentioned to reconcile Laplacian determinism with the logic of the deliberating individual only works because it refuses to take the latter's viewpoint seriously. The description of the individual in terms of billiard balls has its internal consistency. But there is nothing in this description that corresponds to being able to make a choice. Billiard balls can't do anything; they just do. At most we could find, if sentience, beliefs, etc. were “emergent properties” of a Laplacian system, something within the nervous tissue that is the belief in our possibility of choice; but finding the belief in a thing is not finding the thing. The Laplacian view may agree that we believe; it does not agree with what we believe. It cannot be ours; we cannot believe it to be true.

Newcomb's paradox

This is a well-known paradox, formulated by the physicist William Newcomb in 196047. I will give a slightly modified version, which, starting from the assumption of Laplacian determinism, leads to a contradiction.

This time, we will once again assume that there is a Laplacian “intelligence” which, armed with its calculator, is capable of predicting our actions. This time it will not be a cook, but a Zlork, who has come from the Galaxy of Andromeda and who proposes a test to an Earth woman, let's call her Noumène.

It is a test where Noumène can only win, but the amount of her winnings will depend on her choice.

Noumène is taken to a room where there are two closed boxes. The rules of the game are explained to her. Each box contains a certain amount of money. Noumène can choose to take both boxes or just one; she will only open them after she has made her choice. The amount of money in each box was determined the night before by the Zlork as follows:

if the Zlork anticipated that Noumène would take both boxes, he placed ten zlotys in each;

if the Zlork predicted that Noumeni would take only one box, he placed one thousand zlotys in each.

The Zlork made this prediction the day before on the basis of the information acquired by scanning Noumène, as well as the entire environment with which she would come into contact in the meantime; including the environment to which she would be exposed in the room where the test takes place. He could not, of course, take into account in these calculations the amount of money that the boxes would contain, since this depends precisely on the outcome of the calculations; but since this amount is not communicated to Noumène before she leaves the room, her behaviour cannot be affected. The Zlork therefore has all the information that could determine Noumène's behaviour, and can therefore, if Laplacian determinism is true and his calculator is sufficiently powerful, predict, with certainty, that behaviour.

If Laplacian determinism is true, then all this is, at least in principle, possible.

Noumene, being the average earthling that she is, wants to win as many zlotys as possible. She knows the rules of the game. What should she choose?

Answer (1): she had better take both boxes. If she takes both boxes, she is bound to get twice as much as if she takes only one.

Answer (2): It is better to take only one box. The box will contain one thousand zloty, since the Zlork will have foreseen her behaviour and will have put this amount in it; on the other hand, if she takes both boxes, each will contain only ten zloty, for the same reason; she will therefore only earn twenty zloty, which is much less.

I believe that both of these arguments are irrefutable. The first is the one that Noumenes would make already in the banal conditions where no one has foreseen his actions. It is based on a certain, limited causality, where the choice of taking one or two boxes does not change the content. The second is dependent on Laplacian determinism; more precisely, it is dependent on Noumenes' belief in this determinism. It is based on another causality, whereby Noumène's choice determines the contents of the boxes, by retroactively determining the sum that the Zlork placed in them!

In the framework of Laplacian determinism, it is impossible to separate these two causalities; only the real, unique world exists, where everything happens but nothing causes.

The contradiction that Noumenes arrives at concerns two prescriptive assertions: (1) “Take one box!” and (2) “Take both boxes!” The contradiction disappears, of course, if we refuse to consider that the prescriptive assertions have any real meaning; if they are only illusions, the contradiction is only illusory. Again, it is because it is impossible for us not to believe in the reality of the meaning of prescriptive assertions that we must reject the assumptions that allow for the existence of such a contradiction. More specifically, I think it is necessary to reject the assumption that it is possible, at least in principle, for a Zlork to predict, by means of a computer, or by any other means, the choice we are about to make. We must therefore, at the very least, reject Laplacian, computable determinism.

Why Elodie doesn't jump out of the window

A third case will show more clearly the need to believe in some reality of counterfactual worlds. Let's assume that Elodie is on the top floor of a skyscraper. The window is open. Elodie has no suicidal tendencies. Why doesn't she jump out of the window?

The question is silly, of course: she doesn't jump out of the window because if she did, she would fall and kill herself.

But she won't jump, she knows that. So what reality can she give to the sentence “If I jumped out of the window, I would fall”?

Here we find the contradiction already mentioned concerning the cause of the falling stone; but this time, we are talking about future events, not past ones. Elodie is faced with the choice of jumping or not; if she doesn't jump, it's because she believes the sentence “if I jumped, I would fall” to be true. If she believes it to be true, it is because it describes something real. If, however, the world in which Elodie jumps is in no way real, this sentence cannot make sense, cannot be true.

Deliberation is a situation where we have several possibilities. We have to believe in the reality of these possibilities, and in the consequences of each of them, for our deliberation to make sense. This implies giving a reality of some kind to all these future situations. This is still true in situations where our choice is already made, such as Elodie's facing the window, as long as we retain the possibility of choosing otherwise. Elodie is free to jump, even if she has no intention of doing so. Because of this freedom, the situation in which Elodie will jump retains a certain reality, and it is this reality that gives meaning to the assertion she can only believe: “If I jumped, I would fall.”

The deliberative situation we are in thus implies a belief in our freedom. This freedom is real even when our choice is “self-evident”. It is this freedom that gives meaning to the deliberative situation, but also to causality and laws.

Let us return to the situation of Elodie with her stone; but let us suppose that the choice of her act is not yet made. She can choose to throw the stone while saying “pumpkin”; to throw it without saying that; to say “pumpkin” without throwing the stone; and finally, to do neither. If we assume that these four possible future worlds are in any way real, it is without ambiguity that we can say that it is the act of throwing the stone, and not the fact of saying “pumpkin”, that causes its fall. Indeed, in the two worlds where Elodie throws the stone, it falls, whether or not she says “pumpkin”; in the other two, the stone does not fall.

As soon as physical laws are not confined to a description of a single MR world, but are constrained by the need to describe a plurality of possible worlds, their arbitrary character falls away. Since we can say “556841278025 pumpkins”, as well as all such sentences – even if we have no intention of doing so! – the worlds in which we utter these sentences each have a measure of reality; in each of these worlds, the stone falls (despite our sentence), and therefore none of the modified laws I have suggested – where uttering such sentences causes the stone to float – is true.

The fantastic

I am aware that these conclusions are both “fantastic” and ill-defined. What can this “partial reality” mean? This “plurality of worlds”?

I have chosen not to delve into the question of quantum mechanics in this article. I will simply state the following points, which any specialist in the field will agree with:

The postulates of quantum mechanics possess, in the eyes of common sense as well as in the eyes of our Laplacian habits of thought, a quite fantastic character.

Quantum mechanics implies, or at least strongly suggests, the possible existence of a “plurality of worlds”; be it the evanescent quantum superposition limited to the “microscopic” world, the enduring but fragile plurality of the “Schrödinger cat” type, or the limitless multiplicity of many-worlds theories (Hugh Everett).

Counterfactuality has a different status in quantum mechanics than in the Laplacian perspective; in some experimental situations, counterfactual assertions even seem testable.

The standard interpretation of quantum mechanics (Copenhagen interpretation) empties the notion of reality of its meaning; if we want to reconstruct this notion, it seems conceivable that it would be different from what was conceived before.

The standard interpretation of quantum mechanics gives a key role in lifting the quantum superposition to the notion of observer; a notion not defined within this interpretation (or implicitly defined as a human being), but whose most immediate interpretation in realistic terms is that of subjectivity. The standard interpretation escapes this conclusion only by denying the notion of reality.

I certainly do not claim that quantum mechanics, a non-Laplacian theory (in its standard interpretation) represents a solution to the problem of the existence of ethics, freedom and other subjective objects. On the contrary, it is by starting from the subjective that we have been able to conclude that it is necessary to believe in the existence of a reality, of “something”; an existence that the standard interpretation of quantum mechanics denies. Moreover, the latter does not give substance to a plurality of “sustainable” worlds. Finally, the interpretation in terms of multiple worlds, the one that would seem to best suit some of our conclusions, represents a return to a Laplacian conception; we have seen that it is precisely not suitable48.

We can think of the points listed above more as clues in a police investigation; as elements suggesting that we are on the right track, without yet knowing how to assemble them into a whole picture.

Penrose, for his part, does not believe in the many-worlds interpretation at all. On the other hand, he has individualised certain very particular structures within the nervous tissue – the microtubules – which, according to him, are capable of maintaining quantum coherence (between “multiple worlds”) for long enough for certain phenomena, which he assumes to be deterministic but not calculable, to operate49 . It would be these phenomena, linked to quantum gravitation, which would produce the “reduction of the wave function” and thus, in a way, a non-computable choice of the real future world among the various possibilities. Now, if our deliberative situation is one that involves making sense of a plurality of future worlds, it is also one that chooses among these worlds.

Again, these are considerations that do not even constitute the beginnings of a completed and satisfactory theory. However, they do suggest at least this: it may be that certain characteristics of the subjective are part of the fundamental laws of physics, with the nervous tissue representing a privileged locus for the use of these laws in the sense of an efficient resolution of the problems that an organism must face in order to survive, and that subjectivity itself, with its qualia, pleasures and pains, results from this use.

7. The reality of sentience

(...) noticing that this truth: I think, therefore I am, was so firm and so assured that all the most extravagant suppositions of the Sceptics were not capable of shaking it, I judged that I could receive it without scruples for the first principle of the philosophy I was looking for.50

If in this Cartesian approach we substitute simple perception for the act of thinking, we can argue that our own character as sentient beings is a primary evidence; and that consequently sentience itself exists as a fact of the world. This self-recognising sensibility is, however, somewhat autistic; Descartes is then obliged to appeal to the idea of God in an attempt to demonstrate the existence of the world itself.

We have seen (section 4) that all action, all deliberation, is fundamentally altruistic, in the sense that it is not concerned with what the sensibility feels at the very moment of deliberation, but projects itself onto the consequences of the act, which are necessarily future, unperceived, but foreseen, assumed. Descartes starts from the evidence of what is directly perceived. I propose another path, which starts from the impossibility of not believing in certain things that are not directly perceived.

Indeed, we have seen that we cannot nonbelieve that it makes sense to ask ourselves “What to do?”; and that therefore we cannot nonbelieve in the truth in itself of the answers we seek, which are of the form “Do such and such a thing!” Finally, if it makes sense to seek such answers, it is necessarily that these answers are true by virtue of criteria or rules that may be accessible to us. If it were a priori impossible for us to determine the right answer, there would be no point in looking for it.

The mouse in the log

To make things even clearer, let's suppose that I have built a fire in the open air, and I am about to add a log. I notice that there is a cavity in the log, and at the bottom of the cavity is a mouse. I have a second log at my disposal, but it is stained with mud, and I prefer not to get my fingers dirty. I therefore plan to set fire to the first log, the one where a mouse is hiding.

I tell my friends about it, and I get three reactions:

1. Romain tells me: “it's only a mouse, so it's a body without a soul; we know this because we've never seen a mouse talk. So it doesn't feel anything, and if it screams when it roasts, it will be like the screeching of wood; so you must choose this log over the other. This choice is less cruel to the mouse than it is kind to your fingers, which it will save from getting dirty”51.

2. Peter said to me, “It is a mouse that has a nervous system, a brain, like us, and can therefore feel pain; it will suffer terribly if you put it in the fire. So take the other log, even if it makes your fingers dirty.”

3. Edward says to me: “from our own experience we each know that we can suffer, and by analogy we know this about other humans. But to ask how far down the scale of animal species there is still some form of sentience is gratuitous speculation; these are questions that cannot be answered and should be left to idle dreamers. So it makes no sense to ask whether the mouse can suffer. Therefore, you are right to choose this log over the other, and to keep your hands clean.”

Both Romain and Peter accept that the sentience or non-sentience of the mouse is a fact. They also both think that this fact is decisive for the answer to “What to do?”. Their difference lies in a disagreement about this fact itself.

Both also believe that they have reached their conclusion about the (non-)sentience of the mouse on the basis of reasoning, based on data. These data are factual, in the classical sense: the absence of speech in mice, the presence of nerve tissue, etc.

Edouard, on the other hand, concludes neither that mice are sentient nor that they are not; he considers this question meaningless. “Therefore,” says he, “we can pretend that it is not”.

This is a frequently held line of reasoning, but it is really a non-reasoning. From the fact that a certain assertion A (”the mouse is sentient“) is (according to him) meaningless, Edward concludes that we must act as if it were false.

Yet if an assertion is meaningless, so must be its negation. The same reasoning, if valid, therefore implies that we must also act as if not-A were false; and hence, as if assertion A were true.

In fact, I think Edward is right: if A is meaningless, we must act as if A were true, and also as if A were false. Only, as I shall explain, it is impossible to act by satisfying these two conditions. It follows that, contrary to Edward's assertion, A is not meaningless. The mouse is, or is not, sentient.

So what are these meaningless assertions? I think we can say at least this: an assertion is meaningless if it can be assumed to be true or false, without actually changing the world. If A is meaningless, a world where A is true and another where A is false are really the same world. Normal, non-meaningless assertions, on the other hand, I will call “substantive assertions”.

Suppose that a meaningless assertion implies another assertion which is substantive. This cannot happen, one might say. Yet Edward, like Roman and Peter, admits that if the mouse were sentient, it should not be burned; it is because it makes no sense to say that it is sentient that he concludes that it can be burned. So he admits that A (”the mouse is sentient“) implies B (”the mouse should not be burned“), while thinking that A does not make sense, and that we cannot therefore conclude B.

However, if we accept my conclusion that prescriptive assertions have meaning, and are therefore substantive, then the prescriptive assertion B (”you must not burn the mouse“) is substantive.

If A is meaningless, we can imagine it false, or true, without really changing the world. But in the ”version“ of the world where A is true, we must also assume B to be true, since A ⇒ B. In the other ”version“ of the world, where A is false, B must also be true, since it is in fact the same world, and B is a substantive assertion.

In sum, if a meaningless assertion implies a substantive assertion, the latter is necessarily true.

As already indicated, if A is meaningless, so is not-A. Therefore, we can say:

Any substantive conclusion that would follow either from the truth or from the falsity of a meaningless assertion is true.

In this case, however, we have A ⇒ B, but also not-A ⇒ not-B; we must conclude that B is both true and false, i.e. that we must not burn the mouse, and that we must burn it. If we believe in the substantive character of prescriptive assertions, it is impossible for us to have such a contradiction. It follows that our hypothesis cannot be true: it cannot be true that A is meaningless. The fact that the mouse is or is not sentient is therefore a substantive fact, a real fact of the world.

This applies to mice, but also, of course, to any other animal; indeed, to any material system enclosed in the log. It makes sense to ask whether the bacteria, wood or stones embedded in the log are sentient; the answer may be that they are not, but it cannot be that the question is meaningless.

Selfishness and non-hedonism

To reach this conclusion, I assumed that the right answer to the question ”What to do?“ depends on the eventual pleasure or suffering that our choice will cause. More precisely, I had to assume that it depends on the eventual pleasure and suffering caused to the mouse. However, there are two other possibilities:

— that the right answer depends only on my own possible pleasure or suffering (selfish assumption);

— that the correct response does not depend on anyone else's pleasure and suffering (non-hedonistic hypothesis52).

Let us first consider the egoistic hypothesis. As I have already noted, the ”myself“ towards whom this ethic shows concern is necessarily a future ”myself“. If we redo our ”mouse“ reasoning with this future self in place of the mouse, we still come to this conclusion: it makes sense to assume the existence of a sentience that is in fact alien to me. This is, in fact, the sensibility of this future self; it is a sensibility that I do not experience, nor have I ever experienced, whose existence I do not notice any more than I notice the existence of the sensibility of others.

The only support I know of for solipsism is the problematic character of otherness, of the existence of another sensibility than my own. By definition, a sensibility is felt; how can I believe in the existence of a sensibility that I do not feel? But this reasoning cannot stop there, since the same applies to my own future sensibility. If the problem of otherness is to drive us to solipsism, it must be to the point of instantaneous solipsism, which considers as non-existent any sensibility other than my own present one.

But this is precisely a conclusion that we cannot accept, once we admit that there is necessarily a right answer to the question ”What to do? and that this answer depends on some pleasure or suffering that has occurred, even if it depends only on “my” future pleasure or suffering. Instant solipsism cannot therefore be right. Despite its problematic nature, otherness exists, and this conclusion removes the main basis for solipsism in general.

The same is true of the logic behind the frequently stated thesis of the radical impossibility of true altruism, which is based on the question: what does it matter to me to make another suffer? The answer, of course, is “nothing”, except insofar as this suffering may affect my own well-being, in which case we find a selfish motivation. However, the same question arises in relation to any concern for my own suffering: my suffering tomorrow (or in five minutes' time), so what can it do to me now? The answer, again, is “nothing”, an absolute “nothing”, this time, insofar as the effect cannot precede the cause. This logic, which should justify egoism (and even make altruism impossible), would imply that nothing can be a just motivation for my choices; and to this we have seen that we cannot believe.

Conversely, once we realise the absence of a direct perception of our future feeling by our present feeling, this future feeling of ourself is in the same relationship with our present feeling as the feeling of any other individual: a relationship of complete otherness. If, despite this otherness, our future pleasure and unhappiness are a fair motivation for our present choices, there is no reason why the same should not be true of the future pleasure and unhappiness of others.

I have probably not strictly speaking demonstrated the falsity of the egoistic hypothesis, but only removed its basis, and shown that its truth would not fundamentally change my conclusion: that it makes sense to suppose the objective existence of a sensibility other than that which we perceive at the moment of deliberation.

Finally, we have to consider the non-hedonist hypothesis, which is that the right motivation for my actions may not depend on anyone's pleasure or suffering. Let us first note that this is a hypothesis that we do not actually believe in, and that I do not think anyone has ever believed in. It would imply that pain is in no way a fair motivation to try to stop it; that the discomfort experienced if we stop breathing is in no way a fair motivation to continue doing so. Yet it is for these reasons that we protect ourselves from pain from birth onwards, and that our ancestors have been doing the same for millions of years, as have all sentient beings who protect themselves from pain and suffering. Believing in this hypothesis would not necessarily imply stopping breathing53 ; breathing could continue to be the right act for other reasons. But this would be somewhat coincidental; believing in this hypothesis would therefore imply being prepared to stop breathing if these other reasons simply disappeared, regardless of the suffering of asphyxiation, which would count for nothing as motivation.

In saying this, I have neither demonstrated that pain and pleasure are the right motivations for our actions, nor that this is an assertion we can only believe in. Perhaps, however, we can take the problem in reverse. We have seen that we cannot but believe that the question “What to do?” has a meaning, and that the search for the right answer has a meaning, and finally that the criteria and rules for determining this answer cannot a priori be beyond our reach. There must therefore be something that can constitute a goal for our actions. This something must also appear to us as a goal in itself, and not as a means to another end. And this is precisely how suffering and pleasure appear to us: as things to be avoided or sought immediately.

It would not be right to define suffering and pleasure as the immediate negative and positive terms of our ends; this would be to give a sort of operational definition to objects that exist in themselves. Rather, the reasoning is that there must be something like a primary motivation, and that on the other hand we find that suffering and pleasure are that primary motivation.

It is worth recalling here that the suffering and pleasure we experience at a certain moment are not strictly speaking the motivation that guides our deliberation at that same moment, since it can only have an effect on future suffering and pleasure. Rather, they constitute a “sample” of that other suffering and pleasure; they make them known to us, in short. It is also true to say that we have direct knowledge of our own immediate sensibility; but if that were all there was to it, nothing would prevent us from locking ourselves into instantaneous solipsism. It is the deliberative situation from which we cannot escape that implies that we step outside ourselves, that we believe in the existence (at least possible) of other sensibilities, and also, that we believe it is possible for us to determine their existence, and to act upon them.

It is thus the deliberative situation that implies that we believe in an “external” world, in an objective reality. Within this reality there are necessarily causal, “mechanical” relations, without which we would have no possibility of acting; and there are also, as equally objective entities, subjectivities, connected in one way or the other to the “material”, “mechanical” world, without which we could not know them and act on them. Or rather: these subjectivities are part of the “material” world, are part of the same physical world, even if we do not yet know how to pinpoint them and understand their interactions with the rest of the physical world.

Sentience and the deliberative situation

I have argued that we are placed in the deliberative situation, and that this makes us ethical beings (moral agents), and free beings (endowed with free will). We are also sentient beings. Can we say that every sentient being is in the deliberative situation, and that every being in the deliberative situation is sentient?

On the basis of the above developments, I think it is very plausible to say that every deliberative being must also be sentient. Believing does seem to be a feeling. Moreover, deliberation implies a primary motivation; we have seen that it is suffering and pleasure that play this role in us. If something else played this role in another being – say, zeal and pleasure – it seems that it should make no difference to his behaviour; he would beg us to preserve him from zeal, and/or to grant him pleasure, without perhaps even perceiving these “things” (if he is not a sentient, but only a deliberative being). We would find ourselves in the situation of radical impossibility of determining the sentient character of being, a radical impossibility that we cannot believe in.

I believe that the reverse is also likely. It seems to me that suffering always has the value of a primary motivation to stop it, and that the existence of such a motivation only makes sense if it is part of a deliberative process.

One could imagine a sensibility that does not perceive any suffering or pleasure; that perceives only neutral qualia, such as colours, textures, sounds, that do not give it pleasure or displeasure. It would then become aware of reality, but would not know any motivation to deliberate or act. It seems to me, however, that knowledge of reality only makes sense to us through our possibilities of acting on it; such a situation may be temporarily possible, but I doubt that it corresponds to a lasting state in which any real being would be placed.

It should not be believed, however, that it is possible to establish a simple, quantitative and reliable relationship between a being's capacity for action and its degree of sentience. We can be paralysed – under the effect of certain substances, for example, or in a nightmare – and still experience intense suffering. This does not imply that we do not deliberate; it just means that this deliberation does not actually lead to anything.

Nevertheless, I think that very generally sentient beings – even insects and earthworms, if they are sentient – are in the deliberative situation, and therefore are ethical agents, at least in a minimal sense.

8. Reality and virtuality

Our technophilic culture tends ever more to spread as a matter of course the notion of a purely logical nature of reality, and of the equivalence between the virtual and the real. I have mentioned (section 5) the myth of the thinking robot predicted by Turing. A more modern example is the Matrix film series, where the characters (if I have understood well) cannot themselves determine whether they are real or merely the result of the execution of some sub-programme in a giant computer. Yet they suffer, desire and struggle. The implicit assumption is that since any reality can be simulated by a programme – and modern achievements are often strikingly successful in simulating landscapes, airplanes, textures and so on – subjective perception itself can be simulated, and thus becomes quasi-real, indistinguishable from real subjectivity.

Is “virtual suffering” really equivalent to real suffering? Does it hurt?

I believe the answer is both yes and no: yes, in the sense that any existing virtual suffering would indeed be equivalent to real suffering, by virtue of the rejection of epiphenomenalism (section 5). It would be equivalent in an ethical sense: we would have the same moral obligation to make it cease. But this would lead us, as we shall see, to an absurd situation. Therefore, virtual suffering cannot exist.

But what are these “virtual” things? We have seen (section 5) that in the Laplacian perspective, the totality of the world can at any moment be described by a set of numbers, and that its evolution, starting from this description, is subject to a calculable determinism, that is can be predicted by the application of an algorithm. This is true of the world as a whole, at least in theory; it is also true of any part of the world. If I know at a time t1 the complete state of a human being, which would mean, to use our billiard ball model, knowing the position and speed of each of the billiard balls that make up that human being, I can calculate what state the human being will be in (or was in) at any other time t2, provided that I add one more piece of information: I also need to know all the external influences that may have affected the system in the time interval [t1, t2]. In the case of a human being, I must know all the verbal or other interactions he may have had with other humans, all the things he saw and so on; but it is not enough for me to know their general content, I must know these interactions molecule by molecule, billiard ball by billiard ball.

Given these conditions, which are implausible for a system as complex as a human being, but which can be fulfilled in principle, the calculation that will allow us to know the state of the system at t2 from its state at t1 will be a simulation. The computer will initially contain in its memory a binary representation of each of the numbers describing the system; this set of binary representations will form a model of the simulated system. The calculation will be carried out step by step, by applying the laws of evolution over very short time intervals; the shorter these are, the greater the precision of the calculation. At each step, therefore, the model will be the representation of the system at a certain instant; after a certain number of steps, it will represent the system at t2.

This procedure is a simulation of the real system by virtue of there being a correspondence between each part of the real system and a counterpart in the model. Each billiard ball has a set of six numerical representations, describing its three positional parameters and three velocity parameters. Any set of billiard balls also corresponds to a set of numerical representations; any relationship between billiard balls corresponds to a relationship between numerical representations. The elementary time intervals of the real system correspond to the calculation steps that make the model evolve. In short, any characteristic of the real system has its “virtual” correspondent within the model that simulates it; and this remains true when it is a non-instantaneous feature, relating states of the system at different times.

If the world is Laplacian, sentience is necessarily the product of certain relationships between the “billiard balls” – molecules, fields, etc. – inside our brain. If our brain is simulated by a model as we have described it, which is always possible in principle (if the world is Laplacian), this sentience too has its virtual correspondent within this model. If the human being suffers, the model “experiences” at the “same moment” (at the corresponding stage in the algorithm's progress) a “virtual suffering”.

This is the notion of virtual suffering. We have asked ourselves whether such suffering is equivalent to real suffering; we can rephrase this question, in line with the characterisation of suffering introduced in section 7: does such virtual suffering constitute a primary motivation in our deliberations? Do we have a moral obligation to stop it?

Penrose's positions A, B, C and D

Penrose distinguishes the following four positions concerning the physical status of sentience:

A: All thought is algorithmic; in particular, the sensations of conscious perception arise from the mere act of executing the appropriate algorithm.

B: Consciousness is a property of the physical actions of the brain; but although any physical action can be algorithmically simulated, an algorithmic simulation cannot by itself bring about consciousness.

C: Some specific physical actions in the brain produce consciousness, but these actions cannot be simulated by an algorithm.

D: Consciousness cannot be explained in physical or algorithmic terms or in any scientific way.

D is the mystical position; I think we can leave it aside, since it implies outright the impossibility of determining by physical means – the only ones available to us – whether a given object is or is not conscious, and thus the impossibility of finding an answer to the question “What to do?”.

In a Laplacian worldview, our choice is between positions A and B. Both accept that an algorithmic simulation of our brain is possible, a consequence that follows from the Laplacian vision, as we have seen. They differ in the answers they give to our question about the equivalence between virtual and real suffering; A answers positively, B negatively. A is the so-called “strong artificial intelligence” position; it is the one implicitly embraced by Turing (see section 5). B by contrast represents the “weak artificial intelligence” position, and rejects the operationalist position on subjectivity, both as a definition and as a criterion. It assumes that a computer can exist that would fully pass the Turing test, without being truly sentient.

Position C rejects the Laplacian paradigm. It is the position held by Penrose, who argues for the possibility of a non-computable determinism (see Section 5). It is also the position that I defend in this article.

I explained in Section 6 why I believe Laplacian determinism to be incompatible with the deliberative situation. Penrose gives other arguments against computable determinism, based on Gödel's theorem, which I will quickly summarise. I will add a specific argument against position A, which is in line with some of Penrose's and Searle's remarks, and which has to do with the arbitrariness of the relationship between the model and the system it simulates. Finally, I will argue against position B because it appears to imply epiphenomenalism.

The conclusion will be that it is impossible to simulate algorithmically at least some physical phenomena. Finally, I will argue that it seems likely that such physical phenomena are in fact not simulatable either algorithmically or in any other way; that is, that it is not possible, in general, to take a complete copy of a physical system.

Penrose's argument

Penrose develops in the two books I have cited an argument against the possibility of simulating specifically the human capacities for mathematical thinking. He does so on the basis of a modified form of Gödel's theorem. I refer to these books for a full exposition of his arguments and for the answer he gives to a large number of objections that have been made against them. I will limit myself to a brief outline.

Gödel's famous theorem (1931) concerns the possibility of a complete formalisation of mathematical reasoning. The conclusion of his theorem is that such a formalisation is not possible. Penrose uses a variant of this theorem in algorithmic terms.

The human brain is capable of proving mathematical theorems. If the world is Laplacian, everything that happens in it can be simulated by an algorithm. This algorithm will then be a theorem proving algorithm.

What does this mean? We will assume that we can give the following characterisation. A theorem proving algorithm A will be such that:

A operates on a countably infinite class of mathematical problems. This can be a class indexed by a natural number. An example of such a class might be: “Is there a prime number greater than the number n? Algorithm A takes as input the number n, and either eventually reaches a final state and gives us an answer (in our example: either “yes” or “no”), or keeps calculating forever without reaching a final state and giving an answer.

— We know from our mathematical insight that A is sound, in the sense that when it does give us an answer, that answer is always correct. We do not require that it always give us an answer. To take the previous example, it could be the following algorithm, described in plain language: ”test whether n + 1 is prime; if so, give the answer “yes”; if not, test the next number, and so on“. Because of the structure of this algorithm, we can see that if it answers us, the answer will necessarily be correct. In general, it will be our mathematical understanding of the structure of A that allows us to see (i.e. prove) that A is sound.

Penrose then considers the case where algorithm A acts on a very general class of mathematical problems, each of which is of the form: ”Take as an input an algorithm and a number; does this algorithm, applied to this number, lead to a final state or not?”. Thus the input of A is a pair (algorithm, number), encoded as a number.

By applying a modified form of Gödel's theorem (due to Turing), Penrose shows us54 that we can determine a certain algorithm G and a certain number n such that we can prove that G applied to n leads to a final state, but which is such that A does not give an answer concerning the pair (G, n).

Penrose's conclusion is that such an algorithm A cannot encompass the entire human capacity to solve this class of problems, or that if it does, we cannot know it, or know that it is sound. For if we know this, and know that A is sound, we can immediately construct the algorithm G for which we know the answer, but for which A cannot give the answer.

This last conclusion itself follows directly from Gödel's theorem, and is disputed by no one55. What is disputed – by proponents of strong artificial intelligence, in particular – is Penrose's willingness to conclude that no algorithm A can encompass the whole of our mathematical understanding. The objection to Penrose's reasoning is that our mathematical understanding may well be encompassed by such an algorithm, without that algorithm being known (by us) to be sound; and that it is, indeed, not sound. We know that humans can make mistakes, including in their mathematical reasoning.

It is not without consequences, however, to accept that human mathematical understanding can be wrong, not simply because of our distraction, but in principle. This implies that there must be some theorem that contains a reasoning error, but which is otherwise such that we are unable, even in principle (through the application of the algorithm on which our general mathematical reasoning is based), to perceive this error; we will declare the result stated by this theorem to be true, with certainty, while it is in fact false. Penrose notes56 :

But is it really plausible that our unassailable mathematical beliefs might rest on an unsound system – so unsound, indeed, that “1 = 2” is in principle part of those beliefs? Surely, if our mathematical reasoning cannot be trusted, then none of our reasoning about the workings of the world can be trusted. For mathematical reasoning forms an essential part of all of our scientific understanding.

Penrose's argument57 thus ends with a rhetorical question to which he suggests that we answer negatively, without, however, offering a rigorous justification. I believe this argument to be correct in its substance, and capable of being more solidly grounded on the necessity of taking the internal view seriously, the very necessity that has served as my guiding thread throughout this article and which I believe is implicit in many of Penrose's own reasonings. I will not develop this point further here, for lack of space and time.

It serves to note, however, that what seems to be at stake in this whole line of reasoning is the substantive character of mathematical understanding. The “theorem proving” algorithm does not prove, or even assert, anything by itself; it only proves theorems because our independent mathematical judgement perceives it, through examination of its structure, to be sound. Whenever we do mathematics, we cannot but believe that our mathematical understanding is that of a truth independent of our assertions; if we assume that it is really no more than the execution of an algorithm, hence of a process incapable, by itself, of asserting anything about truth, our whole mathematical understanding loses all meaning. I don't think it is really possible, therefore, for us to believe that our mathematical perceptions result from the execution of an algorithm.

What I find remarkable about Penrose's approach is that it draws on mathematical understanding, a faculty often seen as the epitome of human rationality, to support the substantive character of all understanding. The mathematician and the earthworm are put fundamentally on the same level. Both perceive, understand and participate in essentially the same situation in the world.

Penrose says little about ethics. The animal question is, however, present in his writings; he is careful to note, in each of the two books I have cited, that he does not believe that sentience is limited to the human species58, and seems open to some ethical consequences.

Algorithmics and counterfactuality

I will now return to this issue of the relationship between algorithms and sentience from another angle, that of the abstract nature of algorithms. Penrose devotes several pages to this question59 in connection with John Searle's argument on the “Chinese room”60. I will develop this theme here in my own way.

Position A implies that the mere execution of an algorithm can induce subjective sensations. The sensations produced are real, not just appearances of sensations, external behaviours (driven by the results of the calculation) that would be “as if” the machine running the algorithm were sentient, without it really being so (the latter would be position B).

However, an algorithm is itself a mere abstract mathematical object; as such, it has no location in time or space. How then can it give rise to a feeling, which is a real physical object?

Actually, A does not imply that the algorithm itself gives rise to feelings; it is the execution of the algorithm that is said to have this effect61. So the question arises: what counts as the execution of an algorithm?

The typical case of the execution of an algorithm is that done on a computer. The algorithm is represented in the computer's memory as a programme, in the form of voltages and electrical charges; so too is the data on which the algorithm operates, forming a physical representation of our model of reality.

Through the laws of physics governing the electrical circuits that make up the computer, this data will be modified step by step in the manner specified by the algorithm. It is this physical process that constitutes the execution of the algorithm.

It is perfectly possible, however, to view the same physical process in another way: as the meaningless playing out of the laws of electronics, as sets of billiard balls colliding, which, starting from a certain initial configuration, evolve after a certain time to another configuration. To see this evolution as the execution of an algorithm it is necessary to add a meaning to this physical process.

This meaning is first of all that which allows a certain configuration of electrical charges to represent the model, that is, a collection of numbers. But this relationship is established by us! The current representation of a number in a computer is made by a series of electronic circuits capable of taking two stable states. We call one of these states “0” and the other “1”. We agree that a certain collection of, say, 64 of these binary memories scattered sometimes in the four corners of the computer represents, in an order also fixed by convention, the binary writing of a certain number among all those which form the model.

In short, the contents of the computer, without the arbitrary conventions we establish, represent nothing at all. This contradicts the real, unconventional character of the suffering and pleasure that the execution of the algorithm is supposed to induce.

It may be said that it is the program itself that “forces” a certain interpretation of the computer's memory states in terms of numbers. For example, when adding two numbers, the binary carry is propagated in a certain order between the different binary memories; it is this order that sets the order of interpretation of these binary memories as numbers.

I don't think this objection is sufficient. Perhaps the program can fix one interpretation as the most “reasonable”. Other interpretations are always possible. We can interpret the collection of 64 binary memories in any order, even if the operation performed on these numbers is of an absurd character. The execution process will then probably not be the representation of any physical process; it will however still correspond to the execution of an algorithm, which will not be the initial algorithm we wanted to see executed, but another, useless one. The problem of the arbitrariness of the relationship between the representation and the represented number is not solved.

The same can be said of the status of the program, also coded by binary memories, and supposed to represent the algorithm. But there is another problem concerning this representation of the algorithm. The concrete execution, which is supposed to induce sensations, necessarily takes place on a set of starting data. But an algorithm, as an abstract mathematical object, is capable of operating on a plurality of sets of starting data; in principle, even on an infinity. For example, the algorithm for adding two numbers in their decimal representation is capable of adding any set of two numbers from the infinite set of integer pairs. It is this infinity of possible values for the starting data that constitutes the algorithm as a representation of a certain logic. An algorithm capable only of adding two and two can be stated simply by the instruction “print four”; nothing distinguishes it from a multiplication algorithm also limited to the same data. It does not incorporate any addition logic. Any algorithm capable of operating only on a finite set of data is equivalent to a finite enumeration of the results of that operation, an enumeration that does not incorporate any general logic.

Now, as I said, the concrete execution of an algorithm by a computer starts with a single set of starting data. One may say: yes, but this execution is done according to laws of physics which make it possible on any set of starting data; it is these laws which institute the program in memory as a representation of the algorithm.

Here we find the problem of counterfactuality: the concrete process is the execution of the algorithm by virtue, not of itself, but of what would also happen in worlds other than the real world!

To make this problem more concrete, suppose a computer is executing a certain algorithm on a certain set of starting data D. Suppose that this algorithm and these data are such that this execution generates, by virtue of A, certain sensations. Assume a second identical computer, running the same algorithm on the same set of data D, except that we have added a small external device measuring the data entering the microprocessor, and a hot plate underneath. This external device is set up in such a way that if it saw other values than those in D entering the microprocessor, it would turn on the hot plate, which would melt the microprocessor. It would thus trigger in a world other than the real world; in the real world it does not interfere with the execution of the algorithm.

However, because the complete computer + external device system could not execute the algorithm on any other data than D, it no longer actually executes the algorithm. Therefore, by virtue of an external device that does not interfere in any way with what is actually happening in the computer (since it is not triggered), this second computer no longer generates the sensations that the first one did.

So it seems that the fact that a certain device generates certain sensations depends not on what happens in the real world, but on what happens in worlds other than the real world...

This is just one of the astonishing, and indeed incredible, consequences of the abstract nature of an algorithm and the arbitrary nature of the correspondence between the representation of data in a machine and the data itself. Without going into detail, it seems likely to me that the following assertion is true: in a Laplacian world, any physical process at any time can, given the right mapping rules, represent the execution of any algorithm on any data set. It would follow that, depending on the correspondence rules we choose to consider, suffering and pleasure, as well as any sensation, would be anywhere, anytime.

It seems clear to me, then, that if A were true, the purpose of reducing suffering and increasing pleasure could make no sense. This would render meaningless the deliberative situation, to which we cannot fail to attach meaning. Therefore, we cannot believe that A is true.

The B position and epiphenomenalism

Position B also places itself in the Laplacian framework, and thus assumes that the algorithmic simulation of any phenomenon is possible, and thus, in particular, that of the entire brain of a sentient being. It postulates, however, contrary to A, that such a simulation would not generate the sensations of which the simulated system is the seat. Sensibility is not linked to the execution of an algorithm, but to this execution within a certain type of matter.

This is Searle's position, but he does not explain what this link might be. The advantage of this thesis is that sentience is not derived from the abstract object of the algorithm, but from the concrete object within which the algorithm is executed. The computer simulation of a hurricane, says Penrose (following Searle), is certainly not itself a hurricane62.

It seems to me that this position implies epiphenomenalism (which I defined in section 5) quite directly, and should therefore be rejected. Indeed, sentience is present in the simulated system, but absent in the simulating system. The result of the evolution of the simulating system cannot therefore be caused by a sentience. For example, let us suppose that the computer simulating a human being is placed in the skull of an android robot, and that the result of its execution activates the motor organs of the robot, so as to give it the same behaviour as the simulated human being. If the human being screams in pain, the android will scream, but without pain; it will still be the same scream. In the human being, unless we assume the epiphenomenalist thesis to be true, pain is the cause of the cry; at least, it participates in its determination. In the android, no pain is the cause of the cry. The latter will be entirely determined by the execution of the algorithm on the data modelling the human brain; the causal relationship between the cry and this data is the same as the causal relationship between the human cry and the parameters represented by this data within its brain, namely the position and speed of the various billiard balls. The pain, absent in the android, seems superfluous in the human being, seems to be added to an already complete causal relationship; there is nothing left to cause. We thus find the epiphenomenal situation.

Can all physical systems be simulated?

The conclusion is that a sensible physical system cannot be simulated algorithmically; for we have argued against A that such a simulation cannot be sensible, and against B that it must be.

If this conclusion is true, it implies that physics cannot be Laplacian.

Penrose speculatively seeks to develop a non-Laplacian physics, where a non-computable determinism would come into play. A priori one can imagine that within such a physics, the simulation of one system by another would remain possible, provided that the system simulating a system subject to non-computable determinism is itself non-computationally determined; in particular, it could not be a computer.

In Section 6 I showed that the possibility of simulating a sentient being led to a contradiction, in particular in the context of Newcomb's paradox. I had assumed that this simulation would be done by computer; in reality, however, the algorithmic character of the simulation was not involved. My conclusion, if valid, implies the impossibility of any simulation of a sentient being.

My reasoning about Newcomb's paradox was related to the impossibility of not believing in our own freedom. It seems to me that the problem we have with the very definition of free will is at least partly due to the inveterate and largely unconscious habit we have of assuming that any physical system can, necessarily, be simulated by another. If we accept that this is not the case, we may be able to retain determinism – at least some form of non-computable determinism – without the possibility of acquiring at a certain point in time all the information defining a system in order to “replay” its evolution elsewhere. Our free decisions could retain their uniqueness and unpredictability, without being determined by anything.

It is remarkable that this conclusion also “says something” to anyone familiar with the structure of quantum mechanics. This is because quantum mechanics also makes it impossible, in the general case, to measure a system completely and reproduce it identically without destroying the original system. As I said at the end of Section 6, I am not saying that quantum mechanics as it exists is the solution to our problem, but I see this convergence as a sign that we may be on the right track.

9. Some tentative conclusions

This is by far the longest article I have written, and the one that cost me the most effort. The main difficulty has been the impression that I was tackling a little-recognised field, particularly in France, and had to face contradictory but strongly held convictions, which implied developing considerations that do not fit into any established discursive register. Activists usually prefer ideas that are immediately effective. Philosophers typically know little about physics, which they presume to be irrelevant to their field. Physicists, symmetrically, look down at all philosophy, especially if it claims to have implications for their own domain. I have had to defend a point of view – mine – that contrasts with the orthodoxy of each of these fields, because of its ethical realism, and also, paradoxically, because of its physical realism.

I would never have developed these reflections if I had not discovered, three years ago, the work of Roger Penrose; and if the team of the Cahiers had not given its active and patient support to the project of a thematic issue on this subject. One of my greatest fears was, and remains, the accusation of “mysticism” that will inevitably be launched at my theses. I believe it is useful to explain below why I see such an accusation as unfounded.

First, however, I would like to round up a few practical conclusions that I think can already be drawn from the theses I have developed; conclusions that, I believe, can be grounded only in considerations that break with the dominant physical and philosophical conceptions.

Sentience: what criteria?

Admittedly, the criteria of sentience that can be derived from my theses are not far from those that are suggested by intuition. What then is the practical point of all these developments? It lies, as argued in section 1, in the hope of better grounding these criteria. For we only listen to our intuition if we choose to; we have seen that large sectors of the population prefer not to, moving back and forth between a convenient attribution of sentience all the way to carrots or even to stones – in order to declare that anything can be said, hence nothing can be concluded – and an equally convenient restriction of sentience to the human species alone.

The mere fact of managing to talk about sentience without feeling that any discussion on this subject must necessarily lead to a dead end on the scientific level, or to dissolving the issue into a functionalism dependent on the arbitrariness of human descriptions or a natural teleology – both of which are unlikely to provide a ground for serious ethical consideration – seems apt to lend strength to our discourse when we say that yes, pigs and hens are sentient, and no, carrots are not plausibly sentient, and finally, if we do not know today if and to what extent insects are sentient, we may know one day, and that in any case, the question does have a meaning, since it has an ethical one.

A first criterion we can put forward is that of intelligence. I believe that intelligence – the capacity to understand the world – is necessarily linked, at least at the evolutionary level, to sentience. This statement is both consistent with our intuition and surprising in the light of the usual views of anti-speciesism. Does a more intelligent being deserve more consideration for its interests? Certainly not; it is sentience, not intelligence, that justifies taking a being's interests into account; or more precisely, that makes a being have interests to take into account. However, it is not contradictory with this position to affirm that a correlation exists between intelligence and sensibility.

Intelligence, the ability to understand the world, is not a specifically human characteristic. It is a necessary ingredient of the deliberative situation. If decisions could be made by a three-neuron impulse comparator, there would be no need for suffering or pleasure, no need for deliberation, no need for understanding the world. I believe that the deliberative situation involves non-algorithmic mechanisms, the outcome of which cannot be predicted “mechanically”. Indeed, it is the debate about whether or not animals are “mechanical” that has historically been, and still is in many discourses, tantamount to deciding if they are sentient. If they are mere machines, Descartes told us, then they do not feel; their cries are not caused by suffering and by an attempt to act on the world to put an end to this suffering, but only by the inexorable, infinitely reproducible and predictable course of a clockwork mechanism. Conversely, the ability to “innovate” seems a specific feature of the deliberative situation; and we have seen that this most likely involves sentience.

A certain discourse on plants tends to attribute sentience to them simply because they sometimes react to grazing by “telling” other plants, through the production of a certain gas (ethylene), that they need to protect themselves. In fact, this “communication” can be explained by entirely automatic mechanisms that never involve a deliberative situation; it cannot therefore be seen as an indication of sentience.

A system may certainly be more or less intelligent; I believe the same to hold for sentience. However, it is not obvious that the correlation between intelligence and sentience is direct or constant. Moreover, in the absence of a clearer understanding of both intelligence and sentience, we have no accurate way of measuring either. I don't think it absurd, however, to assume that a fly may be sentient, but less so than an adult human or elephant.

Concerning this question of the possibility of “more” or “less” sentience, I believe we will have to admit that our consciousness is not an indivisible whole; or that it is less so than we tend to think. Cases of “split brain” – where the communication between the two hemispheres of the brain has been cut – suggest that it may be possible, for example, for one hemisphere to be happy and the other sad. If the suffering of the whole – of both hemispheres together – ethically counts as 1, then the suffering of each hemisphere must count as 1/2. In any event, we can hope one day to quantify suffering and happiness when we better understand these phenomena. Again, however, we must beware of simplistic conclusions that would have that a larger brain suffers more than a smaller brain!

Another feature probably correlated with intelligence and the existence of deliberative situations in general, and therefore with sentience, is the organism's capacities for action. A plant can do nothing against a predator; if it suffered at every bite, this suffering would be vain. It would urge the plant to deliberate; but this deliberation could never lead anywhere. It is worth noting that deliberation, in the only beings that we know deliberate – in animals, therefore, in their nervous tissue – is a great consumer of energy, of that very energy which is very generally, for life, the limiting factor. Using the “brain muscles” is tiring, and we avoid doing it for no reason. One may surmise that deliberation by its nature involves a great deal of energy consumption. Evolution is unlikely to develop such a phenomenon if it has no positive effect on survival and reproduction.

Evolutionary reasoning cannot be absolute, however. A characteristic may well remain in an organism after it has become useless or even harmful. I have in mind, for example, mussels and oysters (bivalves); they have nervous tissue and belong to a phylum (molluscs) of which some members (octopuses, etc.) are certainly sentient and highly intelligent. In bivalves, sentience may be useless; their capacity for action seems to be limited to the opening and closing of their shells according to simple external factors (immersion, temperature...). However, one may imagine that in their case sentience has not regressed to the point of disappearing.

I think it is indeed interesting to consider sentience in the context of evolution. Suffering, it is often said, is “merely” a mechanism invented by evolution to elicit avoidance behaviour, for example. A certain view of Darwinism, known as adaptationism, ultimately reduces all features of an organism to their function alone, regardless of their conditions of possibility. However, wings on birds are not reducible to their utility for escaping predators; their existence involves also specifically physical phenomena, such as the lift of the air, which render flight possible. If the air were less massive, for example, the wings would have to be larger to do the same job; their development might not have been “worth it” in evolutionary terms.

Suffering and pleasure are clearly mechanisms that increase the survival and reproduction of organisms! I propose, however, that sentience, as well as intelligence – the possibility of non-algorithmically determined deliberation – may have represented, somewhat like flight, possibilities offered by physics; evolutionary mechanisms would have “taken advantage” of these possibilities, while remaining dependent on the physics that underlies them. Sentience and deliberation are therefore not “mere” mechanisms set up by evolution, but physical phenomena in their own right, with their own constraints.

One such constraint may be the energy cost, which I have noted. Another is the sluggishness of our thoughts. This is not a characteristic of nervous tissue in general; consider the speed with which we integrate the mass of visual information representing a face or a landscape and recognise its elements almost instantly. But these are automatic, unconscious operations. In contrast, as soon as we try to understand the meaning of even a simple sentence that presents some novelty – for example, an unfamiliar mathematical assertion – it takes us seconds, even sometimes weeks. We understand and think slowly. If it were possible for us to do the same much faster, we can assume that evolution would have found the way.

This lack of speed may be related to Penrose's reflections on certain structures within certain nerve cells, which may be the sites of quantum phenomena requiring a certain minimum amount of time. These reflections also appear to suggest that it is indeed certain kinds of tissue, and not others, that can be the seat of sentience; the obvious candidate being, of course, nervous tissue. It is certainly not the case that all nervous tissue is the seat of sentience; it may well be true, however, that only this tissue, and possibly others possessing similar structures, can be sentient.

Are these considerations mystical?

If it is mystical to consider questions that we do not know how to answer, I accept that my theses here are mystical. I should note, however, that I am not at all asserting the impossibility of ever answering these questions; on the contrary, my efforts have been aimed at ceasing to view sentience as a supernatural object and at starting to create conditions for grasping it within a unified understanding of the world.

If I had been content with setting out the dogmas of modern physics, which actually deny the very possibility of believing in the reality of both stones and feelings, on the one hand, and some Catholic or other religious conviction on the other, I would have incurred far less the reproach of mysticism. It is quite true that my subject is something like “spirit”, or mind, if one considers this word as a synonym for “sentience”. My “mysticism” is mainly due to the fact that I speak of mind outside the recognised frameworks, which allow it to be hermetically cut off from the world of stones.

Lastly, my reflections are completely devoid of one of the most common features of what is generally classified as mysticism, namely, of holism. I do not believe that “the spirit” can be gathered into a great whole. Quite the opposite: sentience appears to me rather divisible. Conversely, a collection of sentient and deliberative beings often behaves in a quite mechanical way. There is nothing more predictable and mechanical than a crowd, in many circumstances where, despite this, each individual remains an intelligent and free being. Thus, while I believe in sentience, and its potential presence in all matter, I do not believe in a great spirit of the universe, in something like a god. I do not believe that the universe is driven by a purpose. At the most I can think that perhaps a tendency present in all sentient beings can lead them, gradually, to harmonise their interests, their actions and their desires.

About the impossibility of not believing, again

I would like to return to the principle that I have made good of several times in this article, that of the “foundation by the impossibility of not believing”. I think it can help us out of some of the dead ends of philosophy and physics. However, it can also easily be perceived as a form of renunciation. If we cannot prove something, but, because of our situation, cannot nonbelieve it, we might as well accept it; in practice, it makes no difference, but we will remain dissatisfied. A higher, more idealistic part of us aspires to ground our beliefs on reason alone.

I do not think that such a view is justified. Philosophy has demanded that everything be based on reason. This is certainly a good thing, when it saves us from mistakes. But, it will be said, it is not to avoid mistakes that one is a philosopher; it is out of love of reason for its own sake!

There is something of an admission here: the love of reason is not just the love of truth. Truth can have an immediate practical significance; reason, on the other hand, has a practical significance only insofar as it allows us to reach the truth. Why, then, should we be in love with reason, rather than with mere truth?

I believe that this passion for reason “for its own sake” is a way of projecting ourselves out of the world. We would like to be elsewhere, in an elsewhere where we would be pure spirits, where nothing is corrupted, where we would not die like beasts die and rot. In order not to rot, we want to be that thing without substance, reason. And just as we disembody ourselves, we disembody the world, reducing it to a senseless game of billiard balls. This is the Platonic, Christian, and finally Cartesian partition of the world, that of absolute speciesism: humans and stones. And the result is that all are dead, both humans and stones.

To acknowledge that we believe what we cannot nonbelieve is not to give up; it is to accept our situation in the world, the situation that makes us exist. We think and feel, but we are mere matter, like stones, bacteria, flies and pigs. That we feel, and the stones do not, remains to be explained; but we are not of a different substance from them. We are in the world as much as they are, we make up the world as they do.

If we must be in love with a notion, I prefer to love truth than reason; and our desire for truth is fully satisfied if we accept my principle.

Let us assume that Morganne believes a proposition A to be true; and at the same time knows that she believes this. Will her desire for truth be satisfied? The answer is yes; for the conditions of satisfaction of this desire are purely subjective. Whether A is, in fact, true or false makes no difference from Morganne's point of view. Since she is certain – rightly or mistakenly – that A is true, and knows this (that she is certain of a proposition she is certain is true), she can but be satisfied.

This reasoning may seem cynical; Morganne is satisfied while perhaps being mistaken. But when it comes to things that we cannot nonbelieve as a result of our position as sentient and deliberative beings, there is no such external viewpoint. As far as these things are concerned, neither we nor anyone else believes Morganne to be mistaken. What more can we ask for?


Gwenva died almost a year ago. He was a cat, as can be observed in figure 1 at the beginning of this article.

The picture shows him in the midst of a physics experiment. His fascinated look fascinates me; he is attempting to understand the world. He is convinced that he can understand something of it, and that at the same time something escapes him; he thinks that the world exists in itself. In this he is right, I believe, unlike many of the founders of quantum mechanics.

He believes in the laws of physics. His paw is raised, hesitant; he knows he is free to hit the water, or not to hit it; he will perceive the result of his choice, in either case. He believes in his freedom, and he believes in causality. He also believes in the reality of the pleasure of living and learning, even for a modest non-human cat.

Gwenva the physicist believed in all those things that our physics and philosophy would want us to renounce. What a clever fellow, this Gwenva!


1. Qualia (singular: a quale) are the purely subjective characteristics of a feeling; they are “what it is like” to experience the colour red, for instance, a “what it is like” that differs from that of seeing green, for instance. The term was coined in 1929 (C.I. Lewis) and is most common in the English speaking world.

2. Shadows of the Mind, 1994; The Emperor's New Mind, 1989.

3. Animal Liberation, 2nd edition, 1990, ch. 1.

4. Animal Liberation, p. 352.

5. Joan Dunayer, «Les poissons: une sensibilité hors de portée du pêcheur», Cahiers antispécistes n°1, octobre 1991.

6. Erwin Schrödinger, Mind and Matter, 1958.

7. Unlike what this quote suggests, it is not obvious that for Schrödinger himself the position described is the rationalist one, since it is not his own. There may be an issue of translation. I noticed in a German translation that the word was rather Verstandesmensch – something like «a positive mind».

8. Florence Burgat with Robert Dantzer, dir. in Les animaux d'élevage ont-ils droit au bien-être?, Paris, INRA Éditions, 2001.

9. Consciousness also is granted “by analogy” to “the most evolved of animals”. A very fragile exception, as we have seen, in the case of INRA researchers for example; in fact, consciousness is only fully granted to humans.

10. See for example chapter 6 of Penrose's The Emperor's New Mind, op. cit.

* I use the term “nonbelief” and its variants, rather than “disbelief”, for the absence of a belief. Nonbelieving an assertion does not imply disbelieving it, that is, believing it to be false.

11. In his famous “wager”, Pascal tries to show us that it is in our interest to believe in God. However, he realises that this is not enough; belief is not a voluntary act. He therefore lists techniques for brainwashing oneself, as it were.

12. Generally speaking, when I say “we” in this article I am not referring specifically to humans, but to all deliberative and sentient beings.

13. I put quotation marks on this term, because prescriptive assertions, as true or false statements, can also be considered to be the descriptions of a state of affairs.

14. Matthew 14:25-31, King James Version.

** As cited by James Rachels in “Moral Philosophy as a Subversive Activity” (Logos: A Journal of Catholic Thought and Culture 5, no. 1 (February 1, 2002)).

15. René Descartes, Discourse on the Method (1637), beginning of the third part (translation John Veitch, Project Gutenberg).

16. Descartes, again (Discourse on the Method, Part III, a little further on): “it appeared to me that, in order to ascertain the real opinions of such, I ought rather to take cognizance of what they practised than of what they said, not only because, in the corruption of our manners, there are few disposed to speak exactly as they believe, but also because very many are not aware of what it is that they really believe; for, as the act of mind by which a thing is believed is different from that by which we know that we believe it, the one act is often found without the other.” (same translation).

17. A few years ago a friend of mine had to undergo a medical examination of a kind that can be painful and that warranted some form of anaesthesia. At the preliminary consultation, the anaesthetist explained to her that she would remain conscious, but that she would not remember anything afterwards; this anaesthesia might not suppress the pain, he said, but since she would not remember it, it amounted to the same. From his point of view, then, the sensations experienced not only by “lower animals” (to paraphrase Schrödinger's “rationalist”), but also by a fully-fledged human, were “gratuitous speculation”, since their memory did not persist (for some unspecified period). They had no reality of their own, and avoiding them should not be an end, even for the person whose future sensations they were. The fact that this discourse can be held, and bring the person herself to hesitate, implies that the reality of a future pleasure or suffering is not always self-evident, even for the person who will to experience it.

18. For an extreme, and somewhat fascistic, form of this individualistic philosophy, see for example the Ayn Rand Institute.

19. I do not believe in the existence of such an entity, at least not in a strong sense: that of the individual as an irreducible whole, enduring unalterably over time. I believe in the existence of sensations, but the “receptacle” of these sensations appears to me much more accidental. For a thorough discussion of the issue of personal identity, see Derek Parfit, Reasons and Persons, Oxford, 1992.

20. Theories of rights have much the same attitude, but often also recognise “duties to ourselves”. However, these are usually not about pleasuring ourselves!

21. The aforementioned Ayn Rand Institute states in the summary of its philosophy (page “Essentials of Objectivism”) the principle: "Ethics: Self-interest". Her followers seem to be very keen that everyone should be selfish. For our own good? We may simply answer: mind your own business!

22. The problem of the “weakness of the will” has received the sweet philosophical name “acrasia”.

23. This expression, like others of the same kind, was and still is used by the proponents of this position; it is certainly in echo of these debates that Schrödinger puts it in the mouth of his “rationalist”.

24. J.M. Coetzee, The Lives of Animals, ed. Princeton University Press, p. 63 of the 2001 paperback edition.

25. Pierre-Simon de Laplace, Essai philosophique sur les probabilités, 1814, ch. “De la probabilité”. My translation.

26. In fact, it is probably sufficient to know this value at a countable infinity of points. This technical detail is not important here.

27. According to Penrose (Shadows of the Mind, section 1.3) it is not clear that this classical model, with its fields and thus an infinite number of variables, is really computable, in the sense defined below (Penrose speaks of “today's physics”, but this amounts to the same, I think, in the context discussed here). Such a possible non-computable character would however represent a discovery, and is therefore not part of the classical paradigm, which hence remains equivalent to a “billiard ball” model.

28. In a famous speech in 1900 ("Nineteenth Century Clouds Over the Dynamical Theory of Heat and Light"), the English physicist Lord Kelvin claimed that physics was then essentially complete, aside from “two small clouds”. That is not how things turned out. One of these small clouds, in particular, was the cause for the first introduction of quanta, and thus for the birth of quantum mechanics and the consequent collapse of the whole edifice of classical physics.

29. The evolution of the state vector is, in quantum mechanics, deterministic and reversible (with a few technical specifications) as long as no “measurement” is performed on the system; and it is precisely this “measurement principle” and its very particular status that prevents quantum mechanics from being a true theory of the physical world. Moreover, I leave aside the irreversible character of the laws of thermodynamics; for these, which would seem to overdetermine those of Laplacian physics, are not laws of evolution in the sense in which I use the expression here. Thermodynamics is far from irrelevant to the subject of this article, but to discuss it would take up too much space.

30. It was such a “Laplacian 2.0” world that Descartes assumed. He believed in the existence of a specific point in the human brain – a point he located in the pineal gland – where the soul enjoyed a two-way communication with the body. In humans and humans alone, therefore, and only at this point, the whole “mechanical”, deterministic laws of physics were violated (information from Daniel Dennett, Consciousness Explained, Little, Brown and Company, 1991, p. 34).

31. Alan Turing, “Computing Machinery and Intelligence”, 1950. The full article is available on the Abelard website.

32. End of section 5. In the setting Turing is discussing the interrogator is confronted both to a human and a computer and knows that one is human and the other a machine, but does not know which is which. The game is to try to find out.

33. Strictly speaking, this implies that non-human animals cannot think, and neither can many humans, as I discuss below. Yet Turing argues in the same article, essentially, that non-human animals are more like humans than like stones. This in itself is a rare position!

34. Temperature is no longer defined today as in the example I have cited. However, thermodynamics is still a choice area for operationalist attitudes; perhaps because the fundamental concepts of thermodynamics, including that of temperature, involve recourse to notions of probability and/or counterfactuality, hence cannot be defined within the framework of Laplacian physics.

35. Section 6, objection 4.

36. Section 2.

37. The Emperor's New Mind, Chapter 10, for example; and Shadows of the Mind, Section 1.9.

38. With the caveat that Penrose makes in Shadows of the Mind, Section 1.3.

39. For a precise definition, see The Emperor's New Mind, Chapter 2.

40. An example of paving from Shadows of the Mind, section 1.9.

41. Shadows of the Mind, Chapter 7.

42. The Emperor's New Mind, Chapter 10, Section 15.

43. Actually, within the framework of the theory of relativity (hence since 1905), the “historical world” point of view is the only legitimate one; it is the instantaneous world that is reduced to a state of fiction, since the notion of “the same instant” in different places in the universe no longer makes sense. This does not change the substance of my presentation, in which the notion of the instantaneous world serves above all to introduce that of the historical world.

44. For reasons that are certainly historical, this expression has a certain religious connotation. However, I will use it occasionally, without giving it a religious meaning, because it is more specific than the simple word “freedom”.

45. Court practice, as well as religious traditions, associate the notion of freedom with guilt and merit. I do not believe in the reality of these notions.

46. In fact, causality does not always imply a relationship of necessity, nor a relationship of sufficiency. It is not necessary for Elodie to throw the pebble for it to fall on the road (Sofia could have done it for her); nor is it sufficient for her to do so (a strong wind could deflect the pebble, causing it to fall on the grass). I leave these complications aside.

47. I thank Estiva for pointing out this paradox; although she does not agree with my conclusion!

48. A good introduction to multiple worlds can be found on the website

49. Shadows of the Mind, Chapter 7.

50. René Descartes, Discourse on the Method, beginning of Part IV.

51. Descartes: “my opinion is less cruel to beasts than it is pious towards men who are enslaved to the superstition of the Pythagoreans [who were vegans] and who are freed from the suspicion of crime whenever they eat or kill animals” (Letter to Morus, 5 February 1649, extract quoted on the website

52. One could also imagine that it does not depend on my own pleasure and suffering, but only on those of others. I leave aside this implausible hypothesis, the examination of which would not, I believe, alter my conclusion.

53. Breathing is a semi-automatic act in human beings. We often breathe without having decided to do so; what I am saying here applies as soon as we ask ourselves the question.

54. Shadows of the Mind, Chapter 2.

55. See Alan Turing, “Computing Machinery and Intelligence”, section 6, objection 3.

56. Shadows of the Mind, section 3.4.

57. See the whole of Chapter 3 for a detailed discussion.

58. The Emperor's New Mind, Section 10.7; Shadows of the Mind, Section 8.6.

59. The Emperor's New Mind, Section 1.5.

60. See Estiva Reus, “Lectures de pensée animale”, page 142 of issue 23 of the Cahiers.

61. “Effect” is not really the right term here, since it suggests an epiphenomenal character of the sensations; just as it should be said, not that the execution induces the sensation, but that it is the sensation, or that it contains it. I will continue to use the usual language, for simplicity's sake.

62. Shadows of the Mind, section 1.3.