1. _The Cosmological Period_ begins with the birth of Greek philosophical reflection (625 B. C.) and has a nominal ending with the Persian wars (480 B. C.). This does not mean that the interest of the Greeks in cosmology stopped in 480 B. C., but that it was no longer their prominent interest. Cosmology is the study of the reality of the physical universe (the cosmos). The particular cosmological question occupying the minds of the Greeks in this period may be stated thus: What, amid the changes of the physical world, is permanent? This will be seen to be a philosophical question and not the same as a question in natural science. The theatre of philosophical activity was the colonies and not the motherland. Two important aspects of this period must be considered besides the philosophical,――the political situation and the religious mysteries. 2. _The Anthropological Period_ begins in the motherland before the cosmological movement ended in the colonies. It starts with a great social impulse just after the victories of the Persian wars (480 B. C.) and ends with the death of Socrates (399 B. C.). Athens is the centre. This period includes the most productive intellectual epoch of Greece as a whole, although not its greatest philosophers. Socrates is the most striking personality in the period. The period is called anthropological, because its interest is in the study of man and not of the physical universe. The word anthropology means the study of man. 3. _The Systematic Period_ begins with the death of Socrates (399 B. C.) and ends with the death of Aristotle (322 B. C.). Alexander the Great died 323 B. C. The period is called systematic because it contains the three great organizers or systematizers of Greek philosophy. These were Democritus, Plato, and Aristotle. The spread of Greek culture beyond its own limits through the conquests of Alexander is of great importance for the history of thought in the Hellenic-Roman Period, which follows this period. CHAPTER II THE COSMOLOGICAL PERIOD (625–480 B. C.): THE PHILOSOPHY OF NATURE When we enter upon the one hundred and fifty years of philosophical beginnings of Greece, which are called the Cosmological Period, we find ourselves confronted with an extremely interesting social situation, which has been brought about partly by the political and geographical environment of the Greek, partly by his inherited genius. On the one hand, during this century and a half, the political troubles of the Greeks became increasingly aggravated by the growth of Persia on the east and of Carthage on the west. On the other hand, we find that the Greek religion took a sudden turn to mysticism, and by its side a slow but increasing interest in philosophical questions. All through this period Greek politics and Greek religion were a constant peril to Greek life. Greek philosophy proved to be its safety.