However little Greek philosophy as a whole developed during the fourth century along the lines of its subsequent expansion, still the speculations of Plato and Aristotle necessarily helped to prepare for the coming charge. The antagonism between the ideal and phenomenal worlds which Plato set up, and Aristotle vainly attempted to bridge over, leads ultimately to a contrast between the outer and the inner life, between thought and the object of thought. The generic conceptions or forms, which Plato and Aristotle regard as most truly real, are, after all, fabrications of the human mind. The conception of reason, even in its expanded form as the divine Reason, or reason of the world, is an idea formed by abstraction from the inner life. And what is really meant by identifying form in itself with what is, and matter with what is possible, or even (as Plato does) with what is not, or by placing God outside of and in contrast to the world, but the admission that man finds in his own mind a higher and more real existence than any which he finds outside of it, and that what is truly divine and unlimited must be in the mind as an idea, apart from and independent of all impressions from without? Plato and Aristotle in fact declared that reason constitutes the real essence of man—reason coming from above and uniting itself with the body, but in itself superior to the world of sense and life in time—and that man’s highest activity is thought, turned away from all external things, and meditating only on the inner world of ideas. It was only one step further in the same direction for the post-Aristotelian philosophy to contemplate man in complete severance from the outer world, and to refer him to himself for that satisfaction which he can find nowhere else in life. [B. Common characteristics of the post-Aristotelian philosophy.] This step was taken by the Schools of the Stoics, Epicureans, and Sceptics which appeared in the first half of the third century before Christ, superseded the influence of the older Schools, and asserted their supremacy without great variation in their teaching until the beginning of the first century. In whatever else these three Schools may differ, at least they agree in two fundamental points, (1) in subordinating theory to practice, and (2) in the peculiar character of their practical philosophy. [(1) Theory subordinated to practice.]