Descartes’ Argument from Divisibility
Works Cited Missing
Reneì Descartes’ treatise on dualism, his Meditations on First Philosophy, is a seminal work in Western intellectual history, outlining his theory of the mind and its relation to the rest of the world. The main argument running through the Meditations leads from his universal methodic doubt through his famous cogito, to proofs of dualism, God, and the world. The Cartesian dualism is one of the most influential ideas to come out of the work; the style of the Meditations, however, is one of personal rumination, following what appears to be Descartes’ stream of consciousness , and it allows for mild tangential discussions. Hence alongside his more famous argument for dualism, which is based on doubt and then the properties of his mind as he discerns them, Descartes devoted a small space to outlining a very simple and straightforward supplementary argument for dualism, designed to be an independent verification of his ideas.
This separate argument in support of dualism hinges on the concept of divisibility. As Descartes himself put it,
we cannot understand a body to be anything but divisible, whereas we cannot understand the mind to be anything but indivisible. For we cannot conceive of half of a mind, as we can conceive of half of any body whatever, no matter how small. From this we are prompted to acknowledge that the natures of mind and body…are different from one another. (Meditations, p. 8-9)
We can state the argument schematically to make it easier to work with:
(1) If something is true of A that is not true of B then A and B are distinct.
(2) Any body, being an extended thing, is divisible, at least in theory.
(3) The mind, being immaterial and non-extended, is completely indivisible,
even in theory.
(4) Therefore, something is true of the mind that is not true of the body—
namely, that it is indivisible—and hence no mind is a body.
Stated in this way the argument is valid, but for it to be sound we must be able to accept all of its premises.
The first premise is uncontroversial, as it follows from the concept of numerical identity that if two things are numerically identical then anything that is true of one is true of the other, as both things are actually only one thing being referred to in two different ways. We can therefore accept it as true. Moving to the second premise, it should be noted that physical bodies may not, in fact, be infinitely divisible, but as they are still divisible to some extent, this does not invalidate the argument and is only a tangential concern. At any rate, that material bodies are divisible seems almost self evident. The third premise is really the crux of the argument and the point of uncertainty. Is the mind really indivisible? Upon initial reflection it would certainly seem so; Descartes’ claim that one cannot conceive of “half of a mind” seems intuitively true on the face of it.
However, one must remember that by...