Descartes vs. Aquinas (and other scholastics) on the senses, the imagination, God, and the soul

In Summa theologiae, Ia, q. 75, a. 1, Aquinas writes:

[A]d inquirendum de natura animae, oportet praesupponere quod anima dicitur esse primum principium vitae in his quae apud nos vivunt animata enim viventia dicimus, res vero inanimatas vita carentes. Vita autem maxime manifestatur duplici opere, scilicet cognitionis et motus. Horum autem principium antiqui philosophi, imaginationem transcendere non valentes, aliquod corpus ponebant; sola corpora res esse dicentes, et quod non est corpus, nihil esse. Et secundum hoc, animam aliquod corpus esse dicebant.

In Discours de la méthode, AT, 37, Descartes writes:

Mais ce qui fait qu'il y en a plusieurs qui se persuadent qu'il y a de la difficulté à le connaître [i.e., God], et même aussi à connaître ce que c'est que leur âme, c'est qu'ils n'élèvent jamais leur esprit au delà des choses sensibles, et qu'ils sont tellement accoutumés à ne rien considérer qu'en l'imaginant, qui est une façon de penser particulière pour les choses matérielles, que tout ce qui n’est pas imaginable leur semble n'être pas intelligible.

But then, after seeming to express the same insight as Aquinas, Descartes goes on to suggest that people who accept the dictum according to which “n'y a rien dans l'entendement qui n'ait premièrement été dans le sens” (“nihil est in intellectu quod non sit prius in sensu”) have the same problem. Indeed, the dictum itself is an indicator of that problem!

Ce qui est assez manifeste de ce que même les philosophes tiennent pour maxime, dans les écoles, qu'il n'y a rien dans l'entendement qui n'ait premièrement été dans le sens, où toutefois il est certain que les idées de Dieu et de l'âme n'ont jamais été. Et il me semble que ceux qui veulent user de leur imagination, pour les comprendre, font tout de même que si, pour ouïr les sons, ou sentir les odeurs, ils se voulaient servir de leurs yeux : sinon qu'il y a encore cette différence, que le sens de la vue ne nous assure pas moins de la vérité de ses objets, que font ceux de l'odorat ou de l'ouïe; au lieu que ni notre imagination ni nos sens ne nous sauraient jamais assurer d'aucune chose, si notre entendement n'y intervient.

Descartes is either unaware of the scholastic explanation of the dictum (cf. e.g., De veritate, q. 2, a. 3, ad 19) or doesn’t accept it. My hunch is that it’s the latter. But not being an expert on Descartes, I would be glad for help on this.

Aquinas's brain in a vat?

Prima facie some people might think that Aquinas’s epistemology is susceptible to the brain in a vat (BIV) objection. Two things could suggest this: (1) Aquinas is a direct realist (in something like John Searle’s sense of the term minus the biologism and perhaps a few other things) and (2) he believes that, for human beings, it is our senses that first put us into cognitive contact with the world (and in which all our subsequent natural knowledge of things is rooted).

But I don’t think that Aquinas really needs to worry about BIVs. He doesn’t need to because nobody needs to, that is, no reasonable person does. But before I tell you why I think this, let’s consider the objection.

If I may, I shall use Hilary Putnam’s formulation of the objection as he presents it in Reason, Truth, and History. Putnam, of course, thinks he has an argument that shows that the BIV objection is self-refuting. I’m not going to adopt Putnam’s argument or evaluate it. I’m just going to use his account of the objection. Here it is:

Imagine that a human being (you can imagine this to be yourself) has been subjected to an operation by an evil scientist. The person's brain (your brain) has been removed from the body and placed in a vat of nutrients which keeps the brain alive. The nerve endings have been connected to a super-scientific computer which causes the person whose brain it is to have the illusion that everything is perfectly normal. There seem to be people, objects, the sky, etc.; but really, all the person (you) is experiencing is the result of electronic impulses travelling from the computer to the nerve endings. The computer is so clever that if the person tries to raise his hand, the feedback from the computer will cause him to “see” and “feel” the hand being raised. Moreover, by varying the program, the evil scientist can cause the victim to “experience” (or hallucinate) any situation or environment the evil scientist wishes. He can also obliterate the memory of the brain operation, so that the victim will seem to himself to have always been in this environment. It can even seem to the victim that he is sitting and reading these very words about the amusing but quite absurd supposition that there is an evil scientist who removes people’s brains from their bodies and places them in a vat of nutrients which keep the brains alive.

Against direct realists like Aquinas, who hold that, in general, our senses reliably deliver an extra mentem world to us, the objection is supposed to show that they can never be certain that this is the case, they can never be certain that such a knowable extra mentem world exists. Cue the dark chuckling of the skeptic.

But why are Aquinas and other direct realists condemned to this uncertainty? I take it that it is essential to the BIV objection that, by hypothesis, there would be no noticeable difference between the worlds experienced by us whether the ontological/epistemic situation is as the direct realist thinks or whether we are BIVs. In other words, in both worlds, things would look exactly the same. This being so, the poor direct realists just can’t say for sure that they aren’t BIVs. And, presumably, they should give up their direct realism or, at the very least, not be too smug about it.

I’m afraid, however, that I’m just not convinced that direct realists should be all that anxious in the face of the BIV objection. The reason why I think this way is easy to state. According to the hypothesis, you could never have any evidence that you are a BIV, for if you did, you could know you were a BIV. You might understand that it is a logical possibility, but it is a logical possibility for which you have zero evidence and (again, according to the hypothesis) never could have any evidence. In the Enquiry Concerning Human Understanding, David Hume tells us that “[a] wise man ... proportions his belief to the evidence.” Who could disagree? But if I should proportion my belief to the evidence, then I should never take seriously the proposal that I am a BIV. And if I am a direct realist, I should never give up my direct realism because of it.

Consider an analogous case. The controversy over Shakespeare’s real identity is well-known. It seems to me to be logically possible that the real Shakespeare is a Norwegian playwright who became proficient in English. But suppose no evidence ever turns up that suggests that this is more than a logical possibility. Without any evidence, the Shakespeare scholar who takes the Norwegian possibility seriously is a perfect fool.

Aquinas and other direct realists need not worry about BIVs (nor need anybody else).