of the sources of metaphysics

"....knowledge lying beyond experience. It can therefore have for its basis neither external experience, which is the source of physics proper, nor internal, which is the basis of empirical psychology. It is therefore a priori cognition, coming from pure understanding and pure reason."



What Kant is trying to say in this section is that metaphysics as well as mathematics are an a priori because those are things that one learn through pure understanding and reasoning instead of knowledge or experience. For instance how 7+5=12. Kant says that mathimatical judgments are all synthetic, they are a priori and not empirical.