Mind and body · Quiz question 24/35
Descartes' Divisibility Argument
Lose an arm and you don't lose part of yourself. So is the thinking 'you' a different kind of thing from your body? Descartes's divisibility argument from Meditation VI, and its critics.
Say you lose an arm in an accident. Part of your body is gone, but it doesn't feel like part of you is gone. A body can be split into pieces, but it's hard to even picture half a self.
The 'me' that thinks is a non-physical thing (a soul), separate from my brain and body.
René Descartes, in the Sixth Meditation of his Meditations on First Philosophy (1641). The body, he argued, is by its very nature always divisible, while the mind is utterly indivisible. When he considers himself purely as a thinking thing, he can't pick out any parts; and if a foot or an arm is cut off, nothing is taken away from the mind. Willing, understanding and perceiving aren't parts of the mind either: it's one and the same mind doing all of them. Descartes thought this one argument alone was enough to show the mind is completely different from the body. It's a separate line of argument from the conceivability argument in the same Meditation (→ The Disembodied Mind).
If you agreed, you lean toward substance dualism: the thinking, feeling 'you' isn't just one aspect of brain activity but a non-physical thing in its own right. That's what separates it from property dualism, which says consciousness doesn't reduce to physics but there's no separate soul. Most other questions on this axis (→ Mary's Room, The Philosophical Zombie) ask what consciousness is like; this one asks what it is that's conscious.
The best-known challenge comes from split-brain cases. In patients whose corpus callosum (the bridge between the two hemispheres) was cut, the two halves seemed to handle information separately, and Thomas Nagel concluded in a 1971 paper that there's no answer to how many minds are involved in such cases. That shakes Descartes's premise that the mind is always a single, indivisible whole. And the interaction problem — how a non-physical mind moves a body (→ The Disembodied Mind) — is still there.
The thinking 'me' is a single, indivisible substance, different in kind from the divisible body.
Key names: Descartes, Plato, William Hasker (unity-of-consciousness argument)Consciousness may not reduce to physics, but its subject needn't be a separate non-physical substance.
Key names: David Chalmers, Thomas NagelThe subject of consciousness is the brain and body. The mind feels like one thing because the brain integrates information.
Key names: Paul Churchland, Daniel Dennett