We thus have altogether two philosophies—the Greek and the Teutonic. As regards the latter we must distinguish the time when Philosophy made its formal appearance as Philosophy and the period of formation and of preparation for modern times. We may first begin Teutonic philosophy where it appears in proper form as Philosophy. Between the first period and those more recent, comes, as an intermediate period, that fermentation of a new Philosophy which on the one side keeps within the substantial and real existence and does not arrive at form, while on the other side, it perfects Thought, as the bare form of a presupposed truth, until it again knows itself as the free ground and source of Truth. Hence the history of Philosophy falls into three periods—that of the Greek Philosophy, the Philosophy of the Middle Ages and the modern Philosophy. Of these the first is speaking generally, regulated by Thought, the second falls into the opposition between existence and formal reflection, but the third has the Notion as its ground. This must not be taken to mean that the first contains Thought alone; it also has conceptions and ideas, just as the latter begins from abstract thoughts which yet constitute a duality. _First Period._—This commences at the time of Thales, about 600 B.C., and goes on to the coming to maturity of the Neo-platonic philosophy with Plotinus in the third century; from thence to its further progress and development with Proclus in the fifth century until the time when all philosophy was extinguished. The Neo-platonic philosophy then made its entrance into Christianity later on, and many philosophies within Christianity have this philosophy as their only groundwork. This is a space of time extending to about 1000 years, the end of which coincides with the migration of the nations and the decline of the Roman Empire. _Second Period._—The second period is that of the Middle Ages. The Scholastics are included in it, and Arabians and Jews are also historically to be noticed, but this philosophy mainly falls within the Christian Church. This period is of something over 1000 years’ duration. _Third Period._—The Philosophy of modern times made its first independent appearance after the Thirty Years’ War, with Bacon, Jacob Böhm and Descartes; it begins with the distinction contained in: _cogito ergo sum_. This period is one of a couple of centuries and the philosophy is consequently still somewhat modern. 2. SOURCES OF THE HISTORY OF PHILOSOPHY.