Plato (429-347 B.C.), the great Athenian philosopher, was born at Athens in all probability, though it has been said AEgina was his birthplace. His father was Ariston, a descendant of Codrus, and his mother, Perictione, whose family claimed descent from Solon. He was named Aristocles, receiving the name of Plato later, probably from Socrates, in consequence of his broad brow or his fluency of speech; it is difficult to say which. In early life he began to write poems and to study philosophy. He burned his poems and became a disciple of Socrates at the age of twenty, and devoted himself most closely to that sage for ten years. He attended his trial, and after the drinking of the fatal cup (399 B.C.) was obliged to betake himself to Megara, where he stayed with Euclid, who had formerly been one of Socrates' disciples. He then went to Cyrene, and studied geometry under Theodorus, and for some time travelled in Egypt and in southern Italy, where the Pythagoreans still retained some influence. On his return to Athens he taught philosophy in the grove of Academus, giving his services without fee or reward, and soon attracted a large concourse of pupils, among them being Aristotle, and probably Demosthenes. At this time he had many great contemporaries, among them Xenophon, Aristophanes, Thucydides, Euripides, Sophocles, and Praxiteles. In his fortieth year, according to somewhat doubtful testimony, he "visited Sicily, where he incurred the anger of the tyrant Dionysius by the expression of political views obnoxious to that personage. He had a narrow escape from death, and was shipped as a slave to AEgina to be sold in its market-place. He was bought by a Cyrenaic philosopher named Anniceris, who set him at liberty, and he returned to Athens, and with the exception of two visits in later life to the younger Dionysius, stayed there during the remainder of his life. He never married, and took no part in public affairs of any kind. His grave and melancholy aspect gave rise to the saying "As sad as Plato." He died at the age of eighty-two. For a long time his birthday was observed as a festival. His works have been handed down to us complete, and consist of dialogues, in which form of literary composition he has been almost without an equal. Into these dialogues he has often introduced Socrates, and from them we get much of our information about that great philosopher. According to some modern writers, Plato foreshadowed all modern philosophy, and it has been declared that all modern thought has been anticipated by him. Of his greatness there can be no doubt. He sought only truth, and enunciated many noble doctrines. He founded no system, but his services to philosophy are not the less lasting. He divided it into its three parts, which he called dialectics, physics, and ethics, and in the first of these was a master. Dialectics, or the science of ideas, was his strong point. He held that not sensations, but ideas, determined our knowledge. The former merely inform us of the existence of things, but do not explain in the least. He urged this fact most strenuously, and directed it against the sophists, who, thinking man is merely a bundle of sensations, came to the conclusion that to let the senses have their full enjoyment was the chief end of man. Selfishness became in that way the greatest of all personal rights. Plato in his Republic combated this doctrine, holding that virtue was not an imaginary quality, but a reality. He is by no means so clear and cogent in his references to physics; but, after all, his ethical teaching is the most important. He taught the immortality of the soul, and said that the true philosopher should always be prepared for death, as that was not the end. He held that the soul was incarnate, and to the ancients the Socratic dialogue known as the Phaedo, in which he insists upon its immortality, was the best of all his works. It is known that Cato read it just before depriving himself of life. Plato believed firmly in the value of analysis, of inquiry, of questioning the unknown, but he did not depend upon it absolutely. The genuine seeker after truth must have an inherent or intuitive reason, and must recognise those forces of Nature which are not entirely evident to the senses. The idea differs from the sensation in its being that which is, as opposed to that which merely seems. It will be seen that Plato begins with an assumption, and that no one will be convinced of the immortality of the soul who fails to perceive that it is a kind of instinct. Those who have died in the belief, however, as has been well said, had the instinct. Plato argues that nothing whatever can be thought or acted without some kind of assumption, and that this assumption necessarily lies at the root of all moral action.