As Art is intuition, so Philosophy is the pure concept: it is easy to see that all the formal definitions of Philosophy that have ever been given, as science of the first principles, of the ultimate causes, of the origins of things, of norms, of values, of categories, are mere verbal variants of the pure concept. Even the most materialistic and realistic philosophies, since matter itself or nature or reality are assumed by them as principles of universal validity, as concepts or ideas, fall within the limits of this definition. In this sense there is no philosophy which is not idealistic: the differences between one philosophy and another are nothing but differences in the elaboration of the pure concept. What follows from this identification cation of philosophy with the pure concept is that all philosophies are, of necessity, systematic, inasmuch as it is impossible to think the pure concept as a singular or particular one, outside its relations with the whole. This systematic character belongs to every philosophical proposition, and not only to the actual systems of philosophy: the solution of every particular philosophical problem implies a vision of that problem in its universality, that is, in the system. We are constantly reminded of this exigency by the fact that a new and original elaboration of particular problems does actually react on the whole of our thought; and that we are often compelled to revise our fundamental opinions by the discovery of a difficulty which at first presents itself in one sphere of thought only.