The fundamental principle of Plato's philosophy is the belief in an eternal and self-existent cause, the origin of all things. From this divine Being emanate not only the souls of men, which are immortal, but that of the universe itself, which is supposed to be animated by a divine spirit. The material objects of our sight, and other senses, are mere fleeting emanations of the divine idea; it is only this idea itself that is really existent; the objects of sensuous perception are mere appearances, taking their forms by participation in the idea; hence it follows, that in Plato's philosophy all knowledge is innate, and acquired by the soul before birth, when it was able to contemplate real existences, and all our ideas of this world are mere reminiscences of their true and eternal patterns. The belief of Plato in the immortality of the soul naturally led him to establish a high standard of moral excellence, and, like his great teacher, he constantly inculcates temperance, justice, and purity of life. His political views are developed in the "Republic" and in the "Laws," in which the main feature of his system is the subordination, or rather the entire sacrifice of the individual to the state. The style of Plato is in every way worthy of his position in universal literature, and modern scholars have confirmed the encomium of Aristotle, that all his dialogues exhibit extraordinary acuteness, elaborate elegance, bold originality, and curious speculation. In Plato, the powers of imagination were just as conspicuous as those of reasoning and reflection; he had all the chief characteristics of a poet, especially of a dramatic poet, and if his rank as a philosopher had been lower than it is, he would still have ranked high among dramatic writers for his life- like representations of the personages whose opinions he wished to combat or to defend. Aristotle (384-322 B.C.) occupies a position among the leaders of human thought not inferior to that of his teacher, Plato. He was a native of Stagyra, in Macedonia, and is hence often called the Stagyrite. He early repaired to Athens, and became a pupil of Plato, who called him the soul of his school. He was afterwards invited by Philip of Macedon to undertake the literary education of Alexander, at that time thirteen years old. This charge continued about three years. He afterwards returned to Athens, where he opened his school in a gymnasium called the Lyceum, delivering his lessons as he walked to and fro, and from these saunters his scholars were called Peripatetics, or saunterers. During this period he composed most of his extant works. Alexander placed at his disposal a large sum for his collections in natural history, and employed some thousands of men in procuring specimens for his museum. After the death of Alexander, he was accused of blasphemy to the gods, and, warned by the fate of Socrates, he withdrew from Athens to Chalcis, where he afterwards died.