This paper is trying to display basic moments of Critique of Pure Reason as a philosophical project of transcendental foundation of metaphysics. The idea of this project has been introduced in philosophical thinking under the name of Copernican revolution in philosophy, in which instead of our cognition being determined by its objects, the cognizing power of subject itself is seen in its constitutive character for the possibility of objects of cognition. Central question on which transcendental inquiry is directed is possibility of metaphysical cognition as cognition of objects a priori, the question which Kant formulates as that of possibility of synthetic judgements a priori. For that reason, paper displays Kant’s understanding of structural elements of cognition a priori which is itself enabled by understanding and sensibility as two autonomous cognitive powers. The pure concepts of understanding and spacio-temporal form of sensibility represent a priori structures of our cognition, which are conditions of possibility of every object for us. In respect to finitude of human cognition, understanding is with its concepts necessarily directed to content of intuition as the only mean on which it can apply its concepts and therefore produce cognition, and intuition gives objects to us only under the a priori conditions of sensibility. Understanding and sensibility are producing cognition a priori only in their unity, and that cognition is by means of sensibility limited on the objects of possible experience. Transcendental standpoint is formed in such manner in which a priori structures of subject's cognizing powers are discovered as that by means of which the objective being of possible objects is being constituted, so that it is only object of possible experience in its form given by our cognizing powers that is a priori cognizable. Transcendental subject understood in its foundation as self-conscious I is discovered as source of objecthood of objects.