The Eleatic Philosophers.—About 500 B.C., and nearly contemporary with the Pythagoreans, flourished the Eleatic philosophers, among whom Xenophanes, Parmenides, Zeno, and Melissus were the principal leaders. They speculated about the nature of the mind, or soul, and departed from the speculations respecting the origin of the earth. The nature of the infinite and the philosophy of being suggested by the Ionian philosophers were themes that occupied the attention of this new school. Parmenides believed in the knowledge of an absolute being, and affirmed the unity of thought and being. He won the distinction of being the first logical philosopher among the Greeks, and was called the father of idealism.

Zeno is said to have been the most remarkable of this school. He held that if there was a distinction between being and not being, only being existed. This led him to the final assumption that the laws of nature are unchangeable and God remains permanent. His method of reasoning was to reduce the opposite to absurdity.

Upon the whole, the Eleatic philosophy is one relating to knowledge and being, which considered thought primarily as dependent upon being. It holds closely to monism, that is, that nature and mind are of the same substance; yet there is a slight distinction, for there is really a dualism expressed in knowledge and being. Many other philosophers followed, who discoursed upon nature, mind, and being, but they arrived at no definite conclusions. The central idea in the early philosophy up to this time was to account for the existence and substance of nature. It gave little consideration to man in himself, and said little of the supernatural. Everything was speculative in nature, hypothetical in proposition, and deductive in argument. The Greek mind, departing from its dependence upon mythology, began boldly to assert its ability to find out nature, but ended in a scepticism as to its power to ascertain certainty. There was a final determination as to the distinction of reality as external to mind, and this represents the best product of the early philosophers.

The Sophists.—Following the Eleatics was a group of philosophers whose principle characteristic was scepticism. Man, not nature, was the central idea in their philosophy, and they changed the point of view from objective to subjective contemplation. They accomplished very little in their speculation except to shift the entire attitude of philosophy from external nature to man. They were interested in the culture of the individual, yet, in their psychological treatment of man, they relied entirely upon sense perception. In the consideration of man's ethical nature they were individualistic, considering private right and private judgment the standards of truth. They led the way to greater speculation in this subject and to a higher philosophy.

Socrates the First Moral Philosopher (b. 469 B.C.).—Following the sophists in the progressive development of philosophy, Socrates turned his attention almost exclusively to human nature. He questioned all things, political, ethical, and theological, and insisted upon the moral worth of the individual man. While he cast aside the nature studies of the early philosophy and repudiated the pseudo-wisdom of the sophists, he was not without his own interpretation of nature. He was interested in questions pertaining to the order of nature and the wise adaptation of means to an end. Nature is animated by a soul, yet it is considered as a wise contrivance for man's benefit rather than a living, self-determining organism. In the subordination of all nature to the good, Socrates lays the foundation of natural theology.

But the ethical philosophy of Socrates is more prominent and positive. He asserted that scientific knowledge is the sole condition to virtue; that vice is ignorance. Hence virtue will always follow knowledge because they are a unity. His ethical principles are founded on utility, the good of which he speaks is useful, and is the end of individual acts and aims. Wisdom is the foundation of all virtues; indeed, every virtue is wisdom.

Socrates made much of friendship and love, and thought temperance to be the fundamental virtue. Without temperance, men were not useful to themselves or to others, and temperance meant the complete mastery of self. Friendship and love were cardinal points in the doctrine of ethical life. The proper conduct of life, justice in the treatment of man by his fellow-man, and the observance of the duties of citizenship, were part of the ethical philosophy of Socrates.

Beauty is only another name for goodness, but it is only a harmony or adaptation of means to an end. The Socratic method of ascertaining truth by the art of suggestive questioning was a logical mode of procedure. The meeting of individuals in conversation was a method of arriving at the truth of ethical conduct and ethical relations. It was made up of induction and definition. No doubt the spirit of his teaching was sceptical in the extreme. While having a deeper sense of the reality of life than others, he realized that he did not know much. He criticized freely the prevailing beliefs, customs, and religious practice. For this he was accused of impiety, and forced to drink the hemlock. With an irony in manner and thought, Socrates introduced the problem of self-knowledge; he hastened the study of man and reason; he instituted the doctrine of true manhood as an essential part in the philosophy of life. Conscience was enthroned, and the moral life of man began with Socrates.

Platonic Philosophy Develops the Ideal.—Plato was the pupil of Socrates and the teacher of Aristotle. These three represent the culmination of Greek philosophy. In its fundamental principles the Platonic philosophy represents the highest flight of the mind in its conception of being and of the nature of mind and matter, entertained by the philosophers. The doctrine of Plato consisted of three primary principles: matter, ideas, and God. While matter is co-eternal with God, he created all animate and inanimate things from matter. Plato maintained that there was a unity in design. And as God was an independent and individual creator of the world, who fashioned the universe, and is father to all creatures, there was unity in God. Plato advanced the doctrine of reminiscences, in which he accounted for what had otherwise been termed innate ideas. Plato also taught, to a certain extent, the transmigration of souls. He was evidently influenced in many ways by the Indian philosophy; but the special doctrine of Plato made ideas the most permanent of all things. Visible things are only fleeting shadows, which soon pass away; only ideas remain. The universal concept, or notion, is the only real thing. Thus the perfect globe is the concept held in the mind; the marble, ball, or sphere of material is only an imperfect representation of the same. The horse is a type to which all individual horses tend to conform; they pass away, but the type remains. His work was purely deductive. His major premise was accepted on faith rather than determined by his reason. Yet in philosophical speculations the immortality of the soul, future rewards and punishments, the unity of the creation and the unity of the creator, and an all-wise ruler of the universe, were among the most important points of doctrine.