Wednesday, June 4, 2008

Descartes on indivisibility

Descartes gives a strange argument for the real distinction between mind and body. [Philosophical aside: he specifies “real” as in “res,” as opposed to a modal (as in “mode” of substance) distinction, since he recognizes the former as relevant to his substance dualism.]

The argument is one from divisibility.

(1) All extended things are divisible.
(2) No minds are divisible.
(3) No minds are extended things.

Since he believes that extension is characteristic of matter and only matter, it follows that minds cannot be material.

It’s premise (2) that Descartes really needs. What was his reasoning? He claims that he cannot conceive of half of a mind. So he must be going for something really strong, like the inconceivability of a mind’s being divisible.

Well... what would “a portion of a mind” be like, and why would Descartes think that, whatever it is, was inconceivable?

Jonathan Bennett has an interesting conjecture. He says that perhaps Descartes thought that “half a mind” would have to be mind-like in some relevant sense, where perhaps the most obvious sense would be having mentality or consciousness.

It’s very easy to see that “a portion of an extended thing” itself would be extended in a very straightforward, univocal sense of extended.

Descartes does not consider the possibility (perhaps obvious to us today) that the mind is a complex causal result of a factory of simpler, more basic (non-mental) parts. In short, for Descartes, mentality is basic, but he’s not really argued for this.

This helps explain why he instinctively treats mentality and extension as analogously primitive properties of each alleged substance.

Just as splitting and further splitting of an extended object, say, a cat would result in smaller and smaller parts of an extended object, so also should the splitting of a mind result in smaller and smaller thinking portions of a mind, which Descartes took to be absurd. [Another philosophical aside: I think it’s got to be connected also to the special unity of consciousness, which Leibniz later capitalizes on in some profound ways.]

If Descartes were given the example of splitting the cat, what he may not have considered was that mentality should not be analyzed as analogous to the simplicity/basicity of extension but rather more along the lines of the complexity of “being a living animal” or “being a living cat.”

1 comment:

Geoffrey Gorham said...

Perhaps Descartes' reason for not allowing the mind to be composed of non-mental parts can be traced to the second meditation assertion that "i know for certain both that i exist and at the same time that all such images, and in general, everything relating to the nature of body could be mere dreams and chimera". From this he concludes that "my essence consists solely in the fact that I am a thinking thing".When the divisibility argument is made he says it applies "when I consider the mind or myself in so far as I merely a thinking thing". The mind as thinking thing cannot be composed of bodies b/c we can easily suppose that the mind exists even if no bodies exist.

It also seems like one might want to keep separate the question of composition vs. causal dependence. Bodies are composed of only bodies; but they are causally dependent on God. Likewise, even if it turned out that mind is a 'complex causal result' of brain processes, Descartes might insist that it cannot be 'composed of those processes.

Though not divisible into parts in the way bodies are, Descartes does seem to allow two senses in which finite minds are divisible: (i) they have several different faculties: understanding, willing, etc. (Med 4 and 6); (ii) they have temporal parts: 'For a lifespan can be divided into countless parts, each completely independent of the others". (Med 3) God, by contrast, is not divisible in the sense of (i) But has he any reason to say God is indivisible in the sense of (ii)?