Frank Kogan

(Dredged from fallible memory and speed-reading on the bus -- then ett by computer and painfully reconstructed)

Concepts are a priori while intuitions are a posteriori
No, plenty of -- most? -- concepts are also a posteriori, in Kant's scheme of things. He is on the hunt for concepts that are a priori, because they are the key to his proof that inside and outside -- in the schemes conjured up by his proto-modern predecessors (from Descartes via Locke and Berkley to Hume and Leibniz), these seem to have been sundered from one another. He amplifies the division in order to bridge it more successfully and completely -- at least, that's the intention of his project, though this rhetorical amplification ends up with a far greater role in subsequent "philosophy as it should be practiced" than it ought to, if he had indeed successfully built the bridge. (Because what was adopted was the technique?)
The concepts Kant concludes are a priori are cap-T Time and cap-S Space -- my caps, to be clearer shortly. Small t-time and small-s space are of course given us via intuitions: cf such sentences as "Look, there's still space in this cupboard" and "The train is on time". Kant's argument is that Space and Time the a priori concepts do NOT simply emerge as conceptualised aggregates of all the spca-and-time intuitions we're given., Because we need them in advance, as conditions of possibility of consciousness at all. Without a pre-constituted armature of structure through which our experiences, intuitions, perceptions and a posteriori concepts all pass, consciousness as we experience simply couldn't happen.
He goes further. Cap-t Time and Cap-s Space are not given to us, as such. They're NOT inherent Iin the great out there. They're what we bring to the experience picnic, to structure our experiences. The hard-wired bridging mechanism, if you like, between living thought and not-necessarily living matter. These seems very peculiar -- and I believe (as he did) entirely original to Kant. The corollary of this is his science-fictional nightmare: the noumenal vs the phenomenal. Which again seems hugely to stress a separation, the very separation he is urgently striving to overcome.
It's a little unjust to say he just asserts, re the nature of the noumenon. (I'm tempted to argue he confuses matters by discussing noumena plural, since plurlity is surely a phenomenal quality...) Basically he defines it -- as that which we can perhaps understand (in the abstract) to exist, and the forms it must take, but can't imagine viewing or really grasp. I think the noumenon seems less peculiar if we get down to cases (but what follows is me trying to firm up his idea, not him).
Right, so we are hairless mammals in a hostile world. We are yea-high and to orientate ourselves and judge what is to hand that's dangerous or good for us, we use an evolved perceptual machinery which is highly selective. We can see an object's front as it presents to us, for example -- but not the entirely of its insides, or (without optical aids) whatever parts are facing away from us. We encounter a moving or changing object as a succession of intuitions -- we do not and cannot see its whole, from beginning to end, in one go, complete with all in-between stages. Both these ideas are comprehensible -- the idea of them is imaginable -- but the machineries of our perception prevent us (or have not evoled to allow us?) from "seeing" in this manner. (Mathematics -- geometry especially -- allows us other ways to explore such notions, of course.)