The change from Greek and Roman civilization to the civilization of modern Europe is often represented as having been more abrupt than it really was. We have deduced some of the intermediate stages in the alterations of feeling. In the world of thought there are actual written documents for our information, philosophical treatises and counter-treatises, which, by revealing to us the very moment of impact, enable us to trace more easily the reverberation of thought from mind to mind. Very soon after the break up of Rome, when the Empire was being partially re-organized under Teutonic dynasties and the defunct Latin _Caesar_ rising again as the Germanic _Kaiser_, the great medieval “Schools”, of which the most famous was at Paris, began to arise out of the traditions of monastic learning. Their classical library apparently consisted of one Platonic dialogue and two or three works of Aristotle, all of them translated; but the authority of these translations was absolute. At first Plato was considered the greater “authority”, but from the beginning of the thirteenth century it seems to have been accepted almost as a matter of course that the one great object of all philosophy for all time was the harmonization of Aristotelian logic and Catholic dogma. But though the Aristotelian method (as they understood it) was all in all, the actual Platonic system, with the help of Neoplatonism and the Mystics, lingered in sufficient strength to divide medieval philosophy for several hundred years into two rival camps. The one party, known as “Realists”, held with Plato that “ideas”—now usually called _universals_—had existed before, and could exist quite apart from, things; while the “Nominalists” held that universals had no separate or previous existence. But as time passed, many of the Nominalists went farther still, maintaining that these universals did not exist at all, that they were mere intellectual abstractions or classifications made by the human mind—in fact “ideas” in the sense in which, owing to them, we use the word to-day. One of the reasons—perhaps the chief reason—why so many Schoolmen carried Aristotle beyond himself in this way is a particularly interesting one.