I'm grateful for your comments. The idea of a priori knowledge goes back to Plato and Hume and Kant are as guilty as almost all other philosophers to his time of being overly influenced by Plato's conception of a transcendent intelligible realm that gives our minds its contents. That said, in defense of Kant's schema, he is talking about a priori structures of mental capability, not actual knowledge. He acknowledges, correctly, that we need something by which to process experiences, but that all knowledge comes from experience.