If concepts are classification rules, and categories are the most general concepts, then Kant s strategy is fairly clear. If the empirical is the clue to the a priori , as Kant supposes, then all three types of transcendental synthesis presuppose sortals. The first two transcendental syntheses seem quite plausible. This does not imply the conscious applying of or even the conscious awareness of such rules, any more than my ability to speak English grammatically implies my awareness of English grammar rules. The third transcendental synthesis is the difficult one.
C take the notorious example of facial recognition.
That we must be able to reidentify objects to have meaningful experience is plausible, but that we must have concepts in order to do so is less clear. C does not seem to follow at all from his argument. And the objective conclusion, that our notion of an object is that of an item in a unitary consciousness, conceptually connected with other such items, seems under motivated. He goes on to discuss what it is to be an object of representation. This seems to have no clear relation to what has come before.