APRIORI

[B:xvii] Kant opposes a priori and empirical knowledge. He distinguishes between pure theoretical reason, pure practical reason, and mathematics, all of which are sources of a priori knowledge, and he also claims that we have a peculiar kind of a priori knowledge of the self. For Kant, a priori knowledge is certain, and the possibility of a priori knowledge about concepts and intuitions is grounded on his so-called "Copernican Revolution", according to which "we suppose that objects must conform to our knowledge"--Kant argues that the "rules" of sensibility and the understanding are "in me prior to being given to me, and therefore as given a priori". It is the possibility of such a priori knowledge, he thinks, that "promises to metaphysics...the secure path of a science". His programme involves (1) "explaining how there can be knowledge a priori" and (2) "furnishing satisfactory proofs of the laws which form the a priori basis of nature" (thereby showing in what sense objects must conform to our knowledge). He insists that a priori speculative (theoretical) knowledge is limited to possible experience (and thus to the realm of appearances, and their construction by the faculties of our minds); however, it is possible through practical a priori knowledge to "pass beyond the limits of all possible experience" [A2/B3] Kant gives the general definition of a priori knowledge as "knowledge absolutely independent of all experience. Opposed to it is empirical knowledge, which is knowledge possible only a posteriori , that is, through experience. A priori modes of knowledge are entitled pure when there is no admixture of anything empirical [but not all a priori propositions are pure, e.g., the causal maxim is a priori but not pure]".