English abstract. The subjective (consciousness, perception, qualia…) is a reality of this world, and as such belongs to physics; but present-day physics is unable to account for it.
Sentiency is real, is as much a part of the world as any other physical object or property. The author argues that although we cannot prove the reality of sentiency, it is impossible for us not to believe in it; in the same way we cannot prove the reality of the physical world itself, but cannot believe that there is no physical (objective) world at all (whatever its real structure may be).
These inescapable beliefs stem from our situation in the world as deliberative beings, i.e. beings who must, at each moment, decide what to do (or not to do) next, and thus must search for the right answer to the question “What shall I do?”. We cannot seach for an answer to a question without believing that such an answer exists and is right (or true) independently of our finding it. Thus we necessarily believe in the objective truth value of prescriptive propositions, such as “I should drink” or “I should flee”, or “I should stand and defend my young”. This belief in turn founds our inability to disbelieve in the objective existence of both the physical world and sentiency. We must also accept that whenever we cannot disbelieve in something, consistency requires that we acknowledge that belief, and accept its consequences.
The author defines “What shall I do?” as the fundamental ethical question, and argues that there is no difference in type between prudential prescriptive propositions - those regarding the interests of our own future minds - and altruistic prescriptive propositions - those regarding the interests of others’ minds. Consequently, the usual restriction of ethics to the second kind of prescription appears arbitrary. The author thus proposes ethics, the search for the right answer to the question “What shall I do?”, as a foundation for our knowledge of the world.
It is also argued that it is impossible to disbelieve in the reality of free choice, which implies some form of reality for counterfactual propositions, and the reality of causality. The classical view of the physical world, based on what the author calls “Laplacian determinism”, is analysed and is shown to be an empty world, paradoxically devoid of any causality (if only because there is no arrow of time); a world where everything is “determined” but nothing determines and nothing happens, and which precludes any notion of sentiency or even of reality in any meaningful sense. Despite the advent of quantum mechanics, this Laplacian view has remained the paradigm of our scientific worldview, by default, because quantum mechanics gives us no plausible (realist) alternative ontology. But the Laplacian view is itself not credible. The conclusion is that despite the triumphs of modern physics, it is impossible to believe it correct in its fundamental structures.
Roger Penrose’s defense of an alternative, non computational, form of determinism is discussed. Though the Gödel-based argument against the possibility of “artificial” (computational) intelligence does not appear to be rigourously conclusive, it seems conclusive enough if we accept that mathematical truth and proof are more than just ink on paper. Thus the same logic – that of “taking the internal (subjective) point of view seriously” and accepting that we believe whatever in virtue of our position in the world we cannot disbelieve – is at the heart of the author’s argument as it may be at the heart of Penrose’s.
The author argues that the problematic scientific status of sentiency is a major obstacle to a change in the way non human animals are viewed and treated. Human sentiency is generally acknowledged, despite its equally problematic status, but non-human sentiency is systematically discounted as being unprovable, which is (wrongly) considered tantamount to declaring it unreal. However, sentiency appears unprovable only if we accept as final our current conceptions of physics.
One may distinguish three kinds of “reasons to believe” in the truth of an assertion:
A. Demonstrative reasons: informations that prove the assertion or make its truth probable; for instance, to believe that tomorrow it will rain, because the weather forecast has said so and the forecast is usually right.
B. Ethical reasons; for example, in a utilitarian perspective it is right to believe in something whenever that belief will increase the total happiness in the world.
C. Causal reasons: any cause the belief is an effect of. For example, most people believe in the tenets of their religion because they were brought up in that belief.
One may feel that the ideal argument in favor of any assertion is of type A, the model for which is perhaps mathematical reasoning, in which no appeal is made to the utility for the reader to believe in the truth of a conclusion (which would make it an ethical argument, of type B), and no attempt is made to hypnotize the reader into believing the conclusion (which would make it an “argument” of type C). Whether or not the reader is happy that the square of the hypothenuse is the sum of the squares of the two other sides of the right-angled triangle, that is what is proven to him or her.
Only reasons of type A can be valid answers to a question such as “Why do you believe that X?”. An answer of type B — “I believe X because it is better for me (or for someone else) to do so” — cannot replace an argument of type A.  The same goes for explaining that I believe X because of my upbringing, or because of the way my neurons are wired. Such answers may well be true, but they do not answer the question that was asked.
In this article I propose to argue that ethical assertions (prescriptions) are objectively true, and from there argue for the objective reality of sentiency and of freedom. I would be happy if I could found these propositions entirely on reasons of type A. But I cannot.
So will I resort to arguments of type B, and try to make you desire believing what I myself am happy to believe? Or try to trick you into doing so by rhetoric? I will do neither. I feel it justified to appeal in this case to yet another kind of argument. It is an argument that doesn’t attempt to give a reason to believe; it simply aims at pointing out that we already believe a certain proposition, and cannot do otherwise.  If that is so, acknowledging what we believe in is just a matter of consistency.
Such an argument may seem weak, since it is not a form of proof. My answer to this objection is partly ad hominem, while still retaining quite some strength. It consists in noting that it is this same form of argument that ultimately founds all that we believe, starting with our belief in the existence of reality.
This point is actually universally recognized; I will develop that shortly. Quite remarkably, however, very little is generally made of it: the ultimate impossibility to found our belief in a real world on pure reason is seen as a kind of philosophical curiosity that does not detract from the soundness of that belief. On the other hand, the corresponding impossibility in the ethical realm — the ultimate impossibility to found our belief in the truth of ethical assertions on pure reason — is seen as irrefutable proof of the relative or conventional character of ethical assertions, or, for religious-minded people, as the proof of the necessity to base ethics on faith in a god.
I believe instead that the truth value of ethical assertions (prescriptions) is just as soundly based as that of so-called “descriptive” assertions, those that describe for example material facts;  both being founded on the same impossibility for us to not believe in certain things even though we cannot prove them. However weak my argument may be, it cannot be weaker than our belief in the existence of the world; which means it does have some strength.
Before you judge the strength of my argument, I would like you to grasp what it really is about. The impossibility to disbelieve that founds it is not a mere difficulty to disbelieve. It does not refer, for instance, to the psychological suffering that might stem from the disbelief. What I am talking about is an impossibility that is wholly part of our way of being in the world. Please keep in mind that picture: that by virtue of the way we exist in this world, by virtue of our situation as sentient beings, it is impossible not to believe a certain thing. If so, it is vain to pretend not to believe it. Any theory we may build that would contradict that belief cannot then be seen as true without believing both one thing and its opposite; in other words, such a theory cannot be seriously seen as true, as soon as we perceive its implications concerning our inescapable belief. We can still speculate about such a theory, since we can imagine as false what we cannot believe to be false; we may even come to interesting conclusions based on such speculations, but we cannot believe a world based on them to be real.
I will now get to the substance of my argument. My first step will be to point out the impossibility for us to disbelieve in the reality of the truth value of ethical assertions (prescriptions).
 In his famous bet, Pascal argues that it is our better interest to believe in God. He does realize, however, that that is not enough; belief is not a voluntary act. So he then goes on to list the techniques by which we may, so to speak, brainwash ourselves.
 In general in this article when I use the pronoun “we” I am not thinking specifically about humans, but about all deliberative and sentient beings.
 I use quotation marks here because if I am right, prescriptions can be themselves seen as descriptions of a state of affairs.