It is not by coincidence that the concept of difference plays a pivotal role in the architecture of philosophy. Thinking never sets out from mere unity, but always has as its origin a relation of two-valuedness (duplex), which is to say: it is intrinsically related to its objects ab initio. It is this essential duality which supplies the framework in which philosophy creates its concepts. Wolfram Hogrebe pursues the manifestations of this basic duality in the works of some of the most important authors of the 20th century, such as Carl Schmitt and Martin Heidegger. He asserts that in the space formed by duplex, concepts are based on aesthetic rather than scientific decisions. It is here that the characteristic openness of an anarchic sensibility forms itself, like in the writings of Gustav Landauer. In pursuing the movement of difference/duplex from Plato to system theory, Wolfram Hogrebe presents a summary of philosophy from its origins up to its current state.