Hence, despite the fact of philosophy being only divisible into two principal parts, the theoretical and the practical, and despite the fact of all that we may have to say of the special principles of judgement having to be assigned to its theoretical part, ie to rational cognition according to concepts of nature: still the critique of pure reason, which must settle this whole question before the above system is taken in hand, so as to substantiate its possibility, consists of three parts: the critique of pure understanding, of pure judgement, and of pure reason, which faculties are called pure on the ground of their being legislative a priori.