If then Democritus, Plato, and Aristotle do not reflect the time in which they live, what relation do they bear to Greek civilization? They are not isolated and out of all relation to the life of the Greek people. On the contrary, they are the most comprehensive and the most profound expression of Greek life. One turns to them as the most perfect representation of Greek culture. They are the intimate expression of Greek thought, even if not of contemporaneous Greek thought. They are the final statements of the two preceding periods, projected into a time that had other interests. Democritus brought the Cosmological movement to a close, was its final expression, and gave it systematic form. Plato did the same for the Anthropological Period. In Aristotle the systematic cosmology of Democritus and the systematic ethics of Plato find a new meaning, in a closer union, under a more coördinating principle. Aristotle was the last possible word of Greek philosophy, for he systematized every branch known to the Greeks. He not only evolved a speculative theory of the whole, but he organized the special sciences. It must be further said that no one of these three great Greeks could have produced the results each did produce, if each had not been the leader of a school of many workers. Within each school there must have been vigorous coöperation along lines according to the inclination of the individual members. Thus each school collected a vast amount of material which was worked over according to the method and purpose of the leader. =The Fundamental Principle of the Systematic Period.= At the beginning of this book attention was called to the difference between Greek, Mediæval, and Modern thought. Greek thought was characterized as objective. It is important to reiterate this objective significance of Greek thought at this point, when we are about to discuss the teachings of Democritus, Plato, and Aristotle. Plato’s theory is often called an idealism and Democritus’ theory materialism, but they are not the idealism and materialism of modern times. No terms have fluctuated in their meanings more than such philosophical terms as these, as can be judged from the fact that in the Middle Ages Plato’s doctrine was called realism. The Greeks were not idealists in the sense that Berkeley and Hegel were idealists. In general, it should be remembered that when we speak of Greek art, Greek politics, Greek philosophy as idealistic, they are not idealistic in the modern sense.[19]