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.”
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