Aristippus and the Cyrenaics laid stress on the cheerfulness of Socrates and his capacity for reasonable enjoyment when an opportunity presented itself. They taught accordingly, a hedonis tic ethic, with pleasure as the highest good. (See CYRENAICS.) Antisthenes and the Cynics on the other hand, were impressed chiefly with Socrates' indifference to hardships of every kind, his readiness to go without things when necessary. They accord ingly preached the simple life, and Diogenes carried it so far as to reduce it almost to the life of a dog. (See CYNICS.) Euclid and the Megarians were interested mainly in Socrates' conception of the nature of real knowledge, namely, that it con sists of properly formed concepts, as distinguished from mere opinions based on mere observation. Accordingly, they adopted a rather sceptical attitude towards sense-perception and sense objects, and developed, in connection with this sceptical propa ganda, a form of disputation or eristic which became notorious for its excessive subtlety. But by far the most important of the informal disciples of Socrates was Plato, who, to some extent, shared the views of the Megarians. (See MEGARIAN SCHOOL.) Plato B.c•) first studied philosophy under a follower of Heraclitus. At the age of 20 he came under the influence of Socrates and remained in close touch with him until his death in 399. Plato then travelled for a while in southern Italy where he came into contact with the Pythagoreans. All these influences may be discerned in his philosophy, which they helped to shape. When in 387 Plato opened a school (the Academy) in Athens, the Pythagorean spirit betrayed its presence in the inscription : "Let no one who knows no Geometry come under my roof." Plato's philosophy is one of epistemological and ontological idealism. The way in which he arrived at it may be briefly indi cated as follows: He agreed with Heraclitus that all objects of sense-perception are in ceaseless flux, undergoing incalculable changes. No universal truth can therefore be asserted about this "ever-rolling stream." On the other hand, Plato also agreed with Socrates that real knowledge is possible, but only in the form of concepts or universal truths. So he concluded that the objects of real knowledge are not the ever-changing things of the sensible world, but supra-sensible objects which are immutable and eter nal. These supra-sensible, eternal, immutable objects he called "Ideas" or "Forms." The world of change is not, indeed, a mere illusion. But it consists of things that have only a lower degree of reality, things that are but poor imitations of the corresponding "Ideas" after which they are named. Plato thus distinguished two principal types of object and two principal types of cognition corresponding to them. Real knowledge (or science, or the higher kind of cognition) has "Ideas" for its objects. Sense-perception is but "opinion," a lower kind of cognition, which has the world of change for its objects. Or, again, knowledge is concerned with the world of (eternal) Being; "opinion" is concerned with the world of mere "becoming" and passing away.
It is possible that what Plato really meant by his "Ideas" was the "laws" of things and events; that when he described the ordinary things of the sensible world as "copies" of the "Ideas" he simply meant that they conform more or less to those laws ; and that the "copies" are poor in the sense that their conformity to law is only approximate, not exact. However this may be, Plato's con ception of the world is that of a real system. But it is a teleologi cal system, not a merely mechanical system. He gives expression to this conception by identifying the essence of the universe with "the Good." The conception was probably the result of Socratic influence. Socrates had identified the real character, or essence, of a thing with what it is good for. He had made enemies by his insistence that rulers and generals, etc., are not merely people who catch enough votes to be elected to office, but people who really know the business of a ruler, or of a general, etc., who really are "good for" the end in view. By extending this conception to all things, Plato conceived all things as adapted to various ends, these ends as subordinated or adapted to higher ends, and so on to a final end, "the Good," which is the purpose or ultimate end of the universe as a whole. (See ACADEMY, GREEK ; ETHICS, HISTORY OF;
KNOWLEDGE, THEORY OF; PSYCHOLOGY, HISTORY OF.) Philosophy is an attitude of mind as well as a system of ideas. As an inspirer of the philosophic attitude Plato has never been surpassed, and but rarely equalled, if at all. Philosophy needs both the ideas and the attitude. Great philosophic ideas, indeed, are impossible without the philosophic attitude. But there is a kind of enthusiastic attitude that seems to be possible without ideas. And the teaching of philoophy has often suffered from it.
For zo years Aristotle studied in Plato's Academy and his own philosophy, though different in many ways from that of Plato, contains important Platonic elements. Undoubtedly Aristotle was more realistic, more empirical than Plato; and that will account for most of the other differences between them. But even that primary difference must not be exaggerated.
The general tendency of Plato's philosophy was to divide the universe into two parts, the relation between which he did not make clear. On the one hand, there was the world of becoming, of change, of sense, enjoying an inferior sort of reality; on the other hand, the world of being, the world of ideas, eternal and supremely real, and only remotely "copied" by the inferior world of change. Such, at all events, was Aristotle's interpretation of Plato, and he did not agree with such a disruption of the cosmos. While agreeing with Socrates and with Plato on the importance of ideas in the sense of concepts, if there is to be real knowledge, he felt that Plato's conception of "Ideas," and their aloofness from the particular objects of sense-perception, offered no ex planation at all, for the relation of "copying" was a mere meta phor. Yet the primary business of "ideas" is to explain the world of experience, not merely to constitute an additional world.
The fundamental ontological conceptions in the philosophy of Aristotle are those of Matter and Form. The term Form is essentially equivalent to Plato's "Idea," which was itself an off spring of the Pythagorean "Form." The early Ionians were only concerned with the problem of primary matter; Pythagoras had been so preoccupied with "Form" that he almost forgot matter, or regarded "Form" as the primal matter or stuff of all things; Plato had removed the "Forms" or "Ideas" from the material world into a heaven of their own; Aristotle endeavoured to get a right conception of both matter and form, and of the relation between them. The conclusion at which he arrived was that form is immanent in matter, the ideal is immanent in the material, the universal is immanent in the particular; they are not generally divorced from each other, they are distinguishable but not sep arable. To understand Aristotle's view it is well to remember that he was the greatest biologist of antiquity, perhaps of all times. Plato was a geometrician, and that before the invention of co-ordinate geometry. His preoccupation was with ideal geo metrical figures, eternal and static. His "Ideas" were conceived by his mind after the pattern of these eternal and static figures. Aristotle was a biologist preoccupied with the phenomena of growth and development, the transition from the potential to the actual, from the seed to the embryo, and from the embryo to the fully developed form of animal.