Monday, April 13, 2009

Descartes’ “clear and distinct perception” argument

The “clear and distinct perception” argument is one of two arguments for mind-body dualism Descartes gives in the sixth of his famous Meditations on First Philosophy. It can be summarized as follows:

1. Whatever I have a clear and distinct idea of is capable of existing just as I understand it, at least in principle (e.g. if God creates it that way).

2. I have a clear and distinct idea of myself as simply a thinking, non-extended thing.

3. I have a clear and distinct idea of my body as simply an extended, non-thinking thing.

4. So I and my body are capable, at least in principle, of existing apart from each other.

5. So I am distinct from my body.

Does the argument work? Most contemporary philosophers would say No. I would say No and Yes and No.

Huh? Bear with me.

Here’s the first “No” part. For one thing, Descartes is, by all accounts, wrong to think of extension as the essence of matter, and thus as the essence of the human body. From an Aristotelian-Thomistic perspective (which is my perspective) there is obvious reason to reject this view, since A-T rejects the entire modern mechanistic conception of matter of which it is just a variation. But even those who accept this mechanistic conception – which includes almost all contemporary philosophers, even if (usually) only implicitly and unreflectively – would allow that “extension” (i.e. those properties of matter which can be defined geometrically, more or less) is too crimped a way of spelling out the mechanistic idea. They would allow all sorts of other mathematically quantifiable properties to feature in our characterization of matter as well. (What they share with Descartes is the insistence that, whatever matter is, formal causes and, especially, final causes will simply not be allowed to count as part of the material world.)

For another thing, A-T would also obviously reject Descartes’ implied assimilation of the self to the mind. Though the mind (specifically the intellect) is immaterial, “I” am nevertheless not distinct from my body from the A-T point of view, certainly not without serious qualification. In fairness to Descartes, he did not – contrary to the standard caricature (one now being vigorously combated by Descartes scholars) – actually hold that the body is non-essential to a human being, as if we were all really just ghosts trapped in machines (to allude to Ryle’s famous parody). He explicitly denies that “I” am in my body the way a pilot is in a ship, as if the body were an inessential excrescence. On the contrary, he believed that soul and body form a kind of organic unity, that a human being was an irreducible composite of the two, having attributes (namely appetites, emotions, and sensations) which cannot be predicated of either the soul alone or the body alone. The trouble is that, having abandoned the Aristotelian idea that the soul is the form of the body, and emphasizing as he does that it is the ego itself (and not just some part of the person) which is distinct from the body, he had a devil of a time explaining just how such an organic unity was possible. Hence it is no surprise that the “ghost in the machine” conception of human nature came to be seen as paradigmatically Cartesian, whatever Descartes’ own intentions. (Notoriously, what a thinker wants to conclude is not always what his premises actually imply.)

So, to the extent that Descartes’ argument depends on these assumptions, it is open to criticism. But it can fairly easily be fixed up to avoid these problems. For “myself” in step 2 and “I” in steps 4 and 5, just read “the mind” or (more exactly – and as we’ll see in a moment, as much in line with Descartes’ understanding of the mind as with the A-T view) “the intellect.” For “extension” just plug in either the Aristotelian view of matter or your favorite mechanistic conception. (It makes no difference for this specific argument.) Even if the resulting argument does not get us to precisely Descartes’ brand of dualism, it will definitely get us to some form of dualism, if it is otherwise unobjectionable.

Is it otherwise unobjectionable? Here we come to the “Yes” part of my initial reply. The main objection contemporary philosophers have to Descartes’ argument concerns its second premise, and it is an objection Hobbes raised in the Third Set of Objections to the Meditations. Even if it is conceded that Descartes has a clear and distinct idea of himself as a thinking thing, how can he be so sure that that which is doing the thinking is non-extended or, more generally, non-corporeal? The fact that he doesn’t conceive of corporeality when he conceives of thinking doesn’t show that thinking isn’t corporeal, any more than conceiving of triangularity without conceiving of trilaterality shows that something could be triangular without being trilateral.

So, Descartes needs some way of showing that thought can occur in the absence of anything corporeal or bodily. How about (after the fashion of some contemporary dualists) an appeal to metaphysical possibility, in particular to possible worlds? As in: “It is metaphysically possible for the mind to exist apart from the body” or “There is at least one possible world where mind exists apart from the body”? Nix that. From an A-T point of view, anyway, while these statements are perfectly true, they presuppose dualism and thus cannot be used to establish it. You cannot know what is possible for a thing, or what it might be like in various possible worlds, until you know its nature or essence. (Contemporary philosophers who try to define essence in terms of possible worlds thus have things backwards.) Hence, you cannot assert that there is a possible world in which mind exists apart from body, or that it is metaphysically possible for mind to exist apart from body, until you know the mind’s nature. And its nature is exactly what the Hobbesian objection calls into question.

A better way to show that thought can be incorporeal is just to show that it cannot be corporeal. This is a better way for two reasons. First, it establishes an even stronger claim than the one in question – always nice work if you can get it. Second, it is easy to do.

The reason is one we have examined in several earlier posts (such as this one). The objects of the intellect are abstract concepts, which are universal rather than particular, and determinate or exact rather than indeterminate or inexact. And the thoughts in which these concepts feature are (at least often) as universal, determinate, and exact as the concepts themselves. Yet nothing material has or can have these characteristics. Material objects and processes are inherently particular rather than universal, and also inherently indeterminate or inexact. Hence thoughts cannot possibly be identified with anything material. The point can be and has been developed at greater length (by writers like James Ross, and by me in The Last Superstition and Philosophy of Mind and in the earlier post just linked to) but the basic idea is fairly simple, is as old as Plato and Aristotle, and was endorsed and developed by various Scholastic writers.

The irony is that Descartes himself at least hints at this very argument when, earlier in the Sixth Meditation, he draws a rigid distinction between imagination on the one hand – which he apparently takes to be corporeal – and intellect on the other, which alone he identifies with the self he takes to be incorporeal. (The famous example of the chiliagon – which the intellect understands even though the imagination cannot form an image of it – is presented in this context.) This parallels the Aristotelian-Scholastic doctrine that intellect is immaterial while sensation and imagination are material. It is often supposed that Descartes assimilates sensation, imagination, and intellect into an amorphous something called “the mind,” but this is not the case. His view of their relationship is actually fairly close to that of his Scholastic predecessors. Here as elsewhere Descartes is, as contemporary Descartes scholars have made an industry of documenting, far more Scholastic than one would expect the Father of Modern Philosophy to be. (If only he had been consistently Scholastic, he would have really had something! – though he would not have had this claim to paternity. But we’d all have been better off, and Descartes could have spared himself a few millennia in purgatory.)

The thing is, once this Platonic-Aristotelian-Scholastic point has been developed in support of (our reformulated version of) premise 2, it more or less establishes dualism all by itself, so that the rest of the argument becomes otiose. Hence, Descartes’ argument works, but only if reformulated to such an extent that it amounts to little more than a restatement of an idea that had more or less already been around for millennia. The distinctively Cartesian bits – the stuff about “clear and distinct perception,” the assimilation of the self to the intellect, and the conception of matter as extension – are either wrong or irrelevant. So, as a Cartesian argument for dualism, the argument doesn’t really work after all. What is true in it isn’t new, and what is new isn’t true.

How typically modern!


  1. As much as I may disagree with Descartes on certain issues, I really do admire his honesty and his humility in many respects.

    He is by far one of my favorites if not my favorite. I don't think this comment was relevant to the topic at hand, but I felt like saying that.

  2. Ricky 'The Hitman' HattonApril 14, 2009 at 4:13 PM

    Hi Dr. Feser,
    I'm trying to understand the argument.
    Why is "the assimilation of the self to the intellect" wrong? Is it because according to the A-T view there is a true and complete union between the body and the mind/soul? And therefore the self can't assimilate to the intellect (mind?) leaving behind the body?

  3. Some overconfident blogger named Will Wilkinson is in need of an opponent to debate his blithe assertion that none of the arguments for God's existence work. You'd fit the bill. Check out this post and comments to see what the kerfuffle is about.

  4. looks like its cutting out some of the address.
    here it is again with hopefully none of it missing.

  5. Different anonymous here.

    Frankly, there is no lack of penny-ante bloggers - certainly new atheists - shooting their mouths off and dismissing arguments they don't even understand, and certainly are ill-equipped to seriously tackle. Will doesn't want a serious opponent or even a debate. He likely just wants to vent or, at most, get attention.

    I think Ed's got bigger fish to fry, should he care to.

  6. Hello Ali,

    Yes, I've always had a soft spot for Descartes myself, despite my many differences with him. Far greater than any of the other early moderns (except Leibniz). His system is endlessly fascinating, and a thing of beauty. But it's wrong! Oh well...

    Hello Ricky,

    From the A-T point of view, the self or person is the whole thing, soul and body together, since the soul, being by definition the form of the body, is essentially tied to the body it informs. (That doesn't mean it can't survive the death of that body, only that its identity is always determined by its having been the form of that body, and that until it is reunited with it is at best an incomplete substance, not a complete substance in its own right.)

  7. Hello Anonymous 1 and Anonymous 2,

    I've tangled with Will before, in contexts where he knew what the hell he was talking about. He should stick to those.

  8. Ed Feser writes:

    Yes, I've always had a soft spot for Descartes myself, despite my many differences with him. . . His system is endlessly fascinating, and a thing of beauty. But it's wrong! Oh well...Ed,
    I think we're going to have to do something about that 'soft spot'. See my comment at WWWtW.

  9. George, the soft spot is only so soft. What I mean is that as an intellectual system, Descartes' philosophy has obvious attractions, as all hyper-rationalist positions going back to Parmenides and Plato inevitably do for any philosopher. But they are attractions that must be firmly resisted. And (as you indicate over at the W4 combox) considered theologically (as opposed to merely philosophically) Descartes' system is awful.