The teaching of the Sophists had abolished law. Plato likewise knows no law on the lofty level of his ideal state. But the constraint of law seems superfluous where each individual is trained to be the ideal man. Forced by bitter experience to moderate his demands upon human nature and the state towards the end of his life, he sketched in the _Laws_, a model state on the basis of the old established system of government. But this system, like the metaphysics of his old age, seems, as it were, a desertion of his ideals. All that Plato achieved was the education of a race of pupils in his Academy who far surpassed the common standard of learning and morals, and who, though unable to save the state, yet maintained a high standard of knowledge and an ideal of morality for mankind in the midst of a corrupt society. The greatest of these Academicians is Aristotle of Stagira, who displayed a versatility and thoroughness of research which appears absolutely incomprehensible in our eyes. Like Plato, he steadfastly held that knowledge is never complete, but that truth is to be found by unremitting persistence in inquiry. This is probably the reason why he gave the world some dialogues adapted to the public taste, and with the help of some of his pupils accumulated and published collections of historico-philological and scientific matter in an unpretentious form; but the systematic lectures in which he propounded to the more advanced followers of his school the results of his speculations and of his wide empirical observation, together with a critical treatment of his predecessors, were never published by him. He worked at these papers his whole life long, and many of the didactic writings which were edited by his pupils after his death, and which are all we possess of the whole body of Aristotle’s works, bear evident traces of gradual growth, correction, and amplification. In a sketch like the present it is impossible to give so much as a summary of the contents of this admirably arranged encyclopædia, which ranked as the richest storehouse of every kind of empiric and speculative science from the beginning of the Christian era down to modern times. The essential points in which his life-work makes an advance on that of Plato are as follows: