 The philosophical modernism at issue in postmodernism begins with Kant's “Copernican revolution,” that is, his assumption that we cannot know things in themselves and that objects of knowledge must conform to our faculties of representation (Kant 1787).  Ideas such as God, freedom, immortality, the world, first beginning, and final end have only a regulative function for knowledge, since they cannot find fulfilling instances among objects of experience. With Hegel, the immediacy of the subject-object relation itself is shown to be illusory. As he states in The Phenomenology of Spirit, “we find that neither the one nor the other is only immediately present in sense-certainty, but each is at the same time mediated” (Hegel 1807, 59), because subject and object are both instances of a “this” and a “now,” neither of which are immediately sensed. So-called immediate perception therefore lacks the certainty of immediacy itself, a certainty that must be deferred to the working out of a complete system of experience.  However, later thinkers point out that Hegel's logic pre-supposes concepts, such as identity and negation (see Hegel 1812), which cannot themselves be accepted as immediately given, and which therefore must be accounted for in some other, non-dialectical way. 