=The Comprehensiveness of the Aim of Democritus.= The reconstruction of the philosophy of Democritus has always been difficult for the historian because, from the originally great mass of his writings, only fragments remain. The fragments show, however, many interesting things: that he covered the entire range of experience in his investigations; that he was quite as much interested in psychical as in physical problems; that his contribution to epistemology was even greater than to physics; and that he was interested in the atomic theory because he believed that it was a working hypothesis for the explanation of experience of every kind. This last characteristic shows the systematic nature of his work and his right to stand with Plato and Aristotle. Democritus fully realized that the task of science was to explain experiences through a conception of reality. So he constructed his conception of the atom in order that he might explain phenomena intelligibly. He saw that no conception strange to experience or against experience, like the Eleatic Being, would answer scientific demands. A rational conception of absolute reality will have value only as experience testifies to it and, on the other hand, as it explains experience. Democritus valued his theory of the atoms because it seemed to explain all phenomena. This construction of a single fundamental rational principle for all kinds of phenomena shows how much more of a systematic scientist he was than the Cosmologists. =The Enriched Physics of Democritus――Hylozoism becomes Materialism.= There is so great enrichment in elaboration and generalization in the physical doctrine of Democritus over that of Leucippus that it amounts to a change in principle. In all probability Leucippus, like other Cosmologists, was a hylozoist, and did not differentiate matter and life. He is to be grouped with the Reconcilers, or even with the Eleatics, rather than with Democritus. Democritus was a materialist. The period of forty years between himself and Leucippus had been the rich period of the introduction of psychological investigation and of the discrimination of psychical from physical processes. Materialism or spiritualism is not possible in the historical development of the human mind until it passes through just such a period of differentiation as the Sophistic Enlightenment. Before such a period there is animism and hylozoism; after such a period there is materialism and spiritualism of various sorts. Matter must be discriminated from spirit before one of the terms can be reduced to the other. So the hylozoistic pluralism of Leucippus became in the hands of Democritus a realistic materialism, pluralistic as well.