=The Sophists.=--About the time of Pericles there came to Athens men who professed to teach wisdom. They gathered many pupils and charged fees for their lessons. Ordinarily they attacked the religion, customs, and institutions of Greek cities, showing that they were not founded on reason. They concluded that men could not know anything with certainty (which was quite true for their time), that men can know nothing at all, and that nothing is true or false: "Nothing exists," said one of them, "and if it did exist, we could not know it." These professors of scepticism were called sophists. Some of them were at the same time orators. =Socrates and the Philosophers.=--Socrates, an old man of Athens, undertook to combat the sophists. He was a poor man, ugly, and without eloquence. He opened no school like the sophists but contented himself with going about the city, conversing with those he met, and leading them by the force of his questions to discover what he himself had in mind. He sought especially the young men and gave them instruction and counsel. Socrates made no pretensions as a scholar: "All my knowledge," said he, "is to know that I know nothing." He would call himself no longer a sage, like the others, but a philosopher, that is to say, a lover of wisdom. He did not meditate on the nature of the world nor on the sciences; man was his only interest. His motto was, "Know thyself." He was before all a preacher of virtue. As he always spoke of morals and religion, the Athenians took him for a sophist.[82] In 399 he was brought before the court, accused "of not worshipping the gods of the city, of introducing new gods, and of corrupting the youth." He made no attempt to defend himself, and was condemned to death. He was then seventy years old. Xenophon, one of his disciples, wrote out his conversations and an apology for him.[83] Another disciple, Plato, composed dialogues in which Socrates is always the principal personage. Since this time Socrates has been regarded as the "father of philosophy." Plato himself was the head of a school (429-348); Aristotle (384-322), a disciple of Plato, summarized in his books all the science of his time. The philosophers that followed attached themselves to one or the other of these two masters: the disciples of Plato called themselves Academicians,[84] those of Aristotle, Peripatetics.[85]