The leading principles of the chief philosophic sects of Greece flowed originally from Socrates--
---- "From whose mouth issued forth Mellifluous streams, that watered all the schools Of Academics, Old and New(359);"
and who has been termed by Cicero(360) the perennial source of philosophy, much more justly than Homer has been styled the fountain of all poetry. Though somewhat addicted to them from education and early habit, Socrates withdrew philosophy from those obscure and intricate physical inquiries, in which she had been involved by the founders and followers of the Ionic school, and from the subtle paradoxical hypotheses of the sophists who established themselves at Athens in the time of Pericles. It being his chief aim to improve the condition of mankind, and to incline them to discharge the several duties of the stations in which they had been placed, this moral teacher directed his examinations to the nature of vice and virtue, of good and evil. To accomplish the great object he had in view, his practice was to hazard no opinion of his own, but to refute prevalent errors and prejudices, by involving the pretenders to knowledge in manifest absurdity, while he himself, as if in contrast to the presumption of the sophists, always professed that he knew nothing. This confession of ignorance, which amounted to no more than a general acknowledgment of the imbecility of the human understanding, and was merely designed to convince his followers of the futility of those speculations which do not rest on the firm basis of experience, or to teach them modesty in their inquiries, and diffidence in their assertions, having been interpreted in a different sense from that in which it was originally intended, gave rise to the celebrated dispute concerning the certainty of knowledge.
The various founders of the philosophic sects of Greece, imbibed that portion of the doctrines of Socrates which suited their own tastes and views, and sometimes perverted his high authority even to dogmatical or sophistical purposes. It is from Plato we have derived the fullest account of his system; but this illustrious disciple had also greatly extended his knowledge by his voyages to Egypt, Sicily, and Magna Græcia. Hence in the Academy which he founded, (while, as to morals, he continued to follow Socrates,) he superadded the metaphysical doctrines of Pythagoras; in physics, which Socrates had excluded from philosophy, he adopted the system of Heraclitus; and he borrowed his dialectics from Euclid of Megara. The recondite and _eisoteric_ tenets of Pythagoras--the obscure principles of Heraclitus--the superhuman knowledge of Empedocles, and the sacred _Arcana_ of Egyptian priests, have diffused over the page of Plato a majesty and mysticism very different from what we suppose to have been the familiar tone of instruction employed by his great master, of whose style at least, and manner, Xenophon probably presents us with a more faithful image.