I have a basic understanding of Kant's philosophy which revolves mostly around how human mind synthesizes valid knowledge, that is, the forms of understanding unifying perceptions, and forms of sensibility conditioning sense data, etc.
But from what I have read, it appears to me that Kant has totally ignored questions about the nature of the mind. Well, maybe I have missed the point of Kant's philosophy because he actually argues how any purely rational ontology, including that of mind, consists in "transcendental application of the categories" hence an invalid intellectual business. But I still can't see why the following questions may be invalid: how do pure concepts come to be in the first place and what do they tell us about the nature of mind?
A question about the genesis of those concepts may be directed to Kant's stuff on how they are deduced from forms of judgement, but my question is deeper: how can there be any pure concepts considering they are unlike anything in the sensible world? Are we born with them? Or do they magically appear in our mind once we form our first judgements during infancy? What do the fact that such concepts occur in our mind at all tell us about the nature of our mind?