“The love of wisdom” was the name which, from the fifth century B.C. onwards, the Greeks bestowed on any kind of intellectual endeavour which was diverted from the practice and directed to the theory of life. The scope of this striving naturally varied in different periods. In the infancy of Greek speculation, _i.e._, in the sixth and fifth centuries B.C., men pored with wide, childlike eyes over the marvels of nature that lay about them and tried to find in natural science the solution of the riddle of existence. Philosophy was then mainly the embodiment of scientific and mathematical research, that is to say, it was what we nowadays call “Science.” A troublous period followed, represented by the Sophists, a time of youthful storm and stress, out of which the mature philosophy of ideas developed towards the end of the fifth century. The term “philosopher” begins to acquire a professional meaning. Side by side with the Sophist, who supplied “culture” in return for money, stood the philosopher, who directed the course of education without remuneration. At first, it is true, this education was confined to morals. But in Plato it proceeded to expand into a study that comprised mathematics, logic, physics, and ethics, as well as politics, forming a pyramid built on the broadest of possible bases and culminating in the idea of Good. By that time a “philosopher” had come to mean one who is capable of grasping the eternal idea (Plato, Rep. VI, 484 A). Next, in the Universal Encyclopædia of Aristotle, this platonic structure is completed and made habitable within and fitted to human requirements. Under him the idea and the term “philosopher” attained its maximum extension. Thereafter both begin to narrow down. The end of the fourth century witnessed the collapse of the Greek state, to the insecure structure of which the philosophers had never been blind. With the fall of the Hellenic municipal system and the rise of the Macedonian sovereignty a new world comes into being, in which the leaders are monarchs and no longer individual citizens. The outlook and sphere of action of the individual is restricted. Men grow to be eminent in practical affairs, experts in the art of living, less eager to solve the riddle of the universe than that of the personal Ego, by withdrawing men from the tumult of external affairs and guiding them into the imperturbable calm of philosophic conviction as into a sure haven. Hence in the systems of the Stoa and of Epicurus and Pyrrho the designation of philosopher assumes the meaning of a counsellor in the conduct of life, who, in the lack of political liberty then prevailing, held up an ideal of liberty within, which no tyrant could menace.