The effort to distinguish clearly between the philosophical and the scientific problem, and to understand the relation between the two, is a strictly modern product. The earlier Greeks thought nothing of having a cosmological theory that was in ?at contradiction to their metaphysis. The former was Opinion It was inductive, realistic, concrete, sensory: the latter was truth it was deductive, rational. The cosmology could be understood by anybody; the real truth only by the initiated. Even Parmenides had highly complex teachings as to the movements of the heavenly bodies; on the other hand he was perfectly certain from a rational standpoint that motion was quite impossible. And if many people even today seem to have analogous water-tight compartments in their minds, we shall probably have to admit that it is a more sophisticated distinction, not a naive one. But we have not yet told the whole story. Not only did the ancient and medieval thinkers entertain at the same time a priori truth and scientific opinion, but they complicated matters generally by the introduction of an a priori science which therefore occupied a sort of intermediate position so far as subject-matter and general validity was concerned. It was in this a priori science, however that the evolution theory in modern times arose.14 On the side of pure philosophical thought there had been, since the time of Plato, no room for talk of ontological development; the orthodox thinkers were bound by the whole movement of history to deny that change could be ultimate. But, it seems, from every other manner of man there came now and then suggestions of world develop ment Of a more or less definite sort, which found expression in Astronomy, Botany, Biology, etc., as well as in philosophies such as that of Leibnitz mentioned above.