According to Socrates, the ultimate object of human activity is happiness, and the necessary means to reach it, virtue. Since everybody necessarily seeks happiness, no one is deliberately corrupt. All evil arises from ignorance, and the virtues are one and all but so many kinds of prudence. Virtue can, therefore, be imparted by instruction.
The disciple of Socrates, Plato (427-347 B.C.) declares that the summum bonum consists in the perfect imitation of God, the Absolute Good, an imitation which cannot be fully realised in this life. Virtue enables man to order his conduct, as he properly should, according to the dictates of reason, and acting thus he becomes like unto God. But Plato differed from Socrates in that he did not consider virtue to consist in wisdom alone, but in justice, temperance, and fortitude as well, these constituting the proper harmony of man's activities. In a sense, the State is man writ large, and its function its function is to train its citizens in virtue. For his ideal State he proposed the community of goods and of wives and the public education of children.
Though Socrates and Plato had been to the fore in this mighty work and had contributed much valuable material to the upbuilding of ethics; nevertheless, Plato's illustrious disciple, Aristotle (384-322 B.C.), must be considered the real founder of systematic ethics. With characteristic keenness he solved, in his ethical and political writings, most of the problems with which ethics concerns itself.
Unlike Plato, who began with ideas as the basis of his observation, Aristotle chose rather to take the facts of experience as his starting-point; these he analysed accurately, and sought to trace to their highest and ultimate causes. He set out from the point that all men tend to happiness as the ultimate object of all their endeavours, as the highest good, which is sought for its own sake, and to which all other goods merely serve as means. This happiness cannot consist in external goods, but only in the activity proper to human nature - not indeed in such a lower activity of the vegetative and sensitive life as man possesses in common with plants and brutes, but in the highest and most perfect activity of his reason, which springs in turn from virtue. This activity, however, has to be exercised in a perfect and enduring life. The highest pleasure is naturally bound up with this activity, yet, to constitute perfect happiness, external goods must also supply their share. True happiness, though prepared for him by the gods as the object and reward of virtue, can be attained only through a man's own individual exertion. With keen penetration Aristotle thereupon proceeds to investigate in turn each of the intellectual and moral virtues, and his treatment of them must, even at the present time, be regarded as in great part correct. The nature of the State and of the family were, in the main, rightly explained by him. The only pity is that his vision did not penetrate beyond this earthly life, and that he never saw clearly the relations of man to God.