Ryle's claim is that Descartes (and, presumably, every other dualist, whether interactionist or not) makes a category mistake in supposing that the mind is something over and above the body.
Examples of Category Mistakes:
- Asking to see A&M-Corpus Christi after seeing FC, CI, S&T, CCH, UC, etc.
- Asking to see the parade after watching the clowns and fire-engines go by.
- Asking to see the player responsible for team-spirit in a baseball game.
Ryle's Test:
X and Y are in the same category if 'X' and 'Y' can be conjoined or disjoined without absurdity.
For example:
I have classes in CCH and CI. (Not absurd, hence CCH and CI are in the same category.)
I have classes in CCH, CI and A&M-Corpus Christi. (Absurd, hence A&M-Corpus Christi is not in the same category as CCH and CI.)
Another example:
I have a pain in my left-leg and my right-arm. (Not absurd.)
I have a pain in my left-leg, my right-arm, and my mind. (Absurd.)
Hence, the mind is not in the same category as the body. It makes no sense to speak of the mind as a substance either like or distinct from the body.
What, then is the relationship between Mind and Body if they are not distinct substances?