In the context of transcendental arguments in CPR, What is Kant's reasoning for stating that concepts without intuitions are 'empty'?
I think at this point I understand all the transcendental arguments of CPR except this one - and probably this could considerably change my understanding of Kant as a whole.
Here is my confusion.
Now, if 1 and 2 are true, and Kant can grant 3 (however, this is not crucial to my argument), with what exact reasoning can he state that 4 is 'empty'. I can understand if he says they are 'useless'. But in the transcendental dialectic, his position is more than these metaphysical statements being useless - it is that they are incorrect/erroneous. His position is that it is a mistake to use concepts without intuitions.
For this, in my opinion, he will need to elucidate that concepts CANNOT exist without intuitions, i.e, their content is derived from intuitions. However, it cannot be 'derived' by definition, since they are a priori. On top of that we know they do exist independently in the field of metaphysics - Kant himself claims this.
So while, as a Nietzchean perhaps, I can grant Kant that concepts applied to things that cannot be present in intuition is probably useless (this is an ethical argument, not an epistemological one), I still cannot grant Kant an ontological reason for why I should not use concepts without intuitions in my discussions (which is what metaphysics did before him).
And yes, this argument is a part of Transcendental Deduction, but it's (a) quite unclear and (b) not satisfactory in my opinion because just because categories are a presupposition of experience which also involve intuition in no way mean applying them without intuitions is illegitimate.
EDIT:
I realized this question can be posed in a different way. (This is partly due to the fact the answer might just resort to the fact that synthetic a priori judgements require predicates that we can only get through intuitions).