2. _The Practical Need of Knowledge._ But mere curiosity will not entirely explain the Greek intellectual movement. There had grown up an imperative practical need for knowledge. In Athens and other Greek cities the democracy of the fifth century B. C. had supplanted the tyranny of the sixth century. Duty and inclination together forced the citizen into active participation in public affairs. In these democratic cities family tradition and character were no longer sufficient for success; but it became generally recognized that the most useful and successful man was the educated man. The complex relations existing between states and between the citizens in the states made education absolutely necessary for the politician. Nowhere was the need of an education more imperative than in Athens; nowhere was the need more easily filled. In a very short time after the Persian Wars the social position of science changed to one of power; and the inner character of science changed from the study of nature to the study of ethical and political problems. Scientists became teachers of eloquence, for the citizen now needed to be an orator and a rhetorician. Statesmen and generals must know how to persuade. Courts of law were public, their proceeding oral, and personal attendance was therefore required. There was no man in Athens who might not be condemned, if he could not personally in court refute falsehoods and disentangle sophistries. Besides, to be beaten in debate was as disgraceful in the eyes of the public as to lose one’s cause. Two classes of men, with an importance hitherto unknown, appear in Greek history,――the rhetoricians and the dialecticians. _Rhetoric_ was public oratory, necessary for the public defense of one’s rights, or for the maintenance of one’s dignity, or for the gratification of one’s ambition. The _dialectic_ was, on the other hand, argument employed in private between two persons, usually friends, to unravel an obscurity, to reduce an opponent to silence, to exercise one’s self in the mastery of a subject, or to sift evidence. The dialectic, therefore, became a distinct mental pursuit for men who had a natural defect in public speaking or rhetoric. Besides rhetoric and dialectic, there grew up somewhat later what was called the eristic. _Eristic_ was polemical argument consisting of catch-phrases and logical subtleties. It was taught as an art of adroit argument.