Inasmuch as traditional usage and the law of the state are thus tacitly set aside (and on this point Aristophanes judged more correctly in his caricature than the apologists Plato and especially Xenophon will admit) Socrates is the preacher of a new private morality which traverses the public morality of classic antiquity. His death sentence is so far intelligible, though it remains an act of crude, reactionary violence. The greatness of soul, so far beyond the ordinary level of mankind, which, according to all accounts, the philosopher displayed at the near prospect of death, wrought upon a far wider circle than that of his disciples and contemporaries. His martyrdom set the seal upon the victory of the Ideal philosophy in Athens.
Socrates himself represents a complete individuality, hence his method of education has been of service to individualities the most dissimilar. What contrasting types do we find in Xenophon, the bigoted and stupid cavalry officer; and Plato, the witty and profound thinker; the cynic Antisthenes full of the pride of beggary, and the frivolous courtier Aristippus! They all portrayed themselves rather than their master in their writings, and yet each one of them has in some way or other his part in him.
Of all these disciples of Socrates, two only have influenced the afterworld, Antisthenes and Plato, Athenians both, the former a plebeian and founder of the philosophy of the proletariat, the latter, sprung from an old and noble family, an aristocrat of the purest water in all his philosophic ideas. Antisthenes carried the practical and matter-of-fact temper of his master to extremes. Virtue with him is a question of character, and therefore scorns empty words and learning. Logic and mathematics are superfluous, virtue is the only good, vice the only evil; everything else is a matter of indifference. This meagreness of theory is made good by strength of will. Force of character, freedom from the prejudices of conventional custom, conventional religion or conventional government—these are what distinguish the true freeman, the man free in soul, from the slave.
The impression produced by this king in rags in the midst of that age of decadence was striking beyond belief. He with his barking voice seemed to be the warning cry of the proletarian admonishing men to return to nature and to simplicity of life. His acute and witty writings were gladly read. His school, which can show one disciple of world-wide celebrity in the person of Diogenes, was gradually merged into the Stoa, which owes to Cynicism the popular tone of its influential system of ethics. Since the birth of Christ, the Cynic has come to life again, as of old in the guise of the mendicant preacher, proclaiming the gospel of renunciation and holding up the mirror to the corruption of the age. This new Cynicism was one of the most important precursors of the Christian apostolate. It awoke once more in the age of the Renaissance, finding its wittiest exponent in Montaigne, in whose steps J. J. Rousseau afterwards trod. In him we have the best typical example of the strength and weakness of this anti-scientific movement.
Plato, the antithesis of Antisthenes, continued in a direct line the thread of Athenian philosophy. He accomplished, in the widest sense of the term, the task which Socrates had only begun—that of establishing science, now discredited by the Sophist, on a new basis.
We are but imperfectly acquainted with the life of Plato and the phases of his development, for the chronology of his dialogues has not been determined up to this time, either absolutely or relatively, and it is a matter of doubt how far their artistic intention admits of a complete exposition of his system. For Plato’s true work was not his literary productions, which he himself regarded as of secondary importance and which obviously reproduce only a fraction of his researches and speculations, but his Academy, in which, from the eighties of the fourth century onwards, he gathered together the ablest scholars from amongst the youth of Greece for study and life in community. If all the transactions of this Academy had been preserved (like the information Aristotle gives us concerning the latter years), it may be that we should be able to trace distinctly the development of this wonderful man. For Plato is both the most gifted and the most complicated personality of Greek antiquity, and the depths and recesses of his nature were not wholly penetrated by his intimate friends, not even by Aristotle; how much less by us of this latter day. What we do possess is, however, amply sufficient to indicate at least his place in this summary.
If from the ranks of the Greek thinkers we have so far considered, we choose out the most eminent leaders and mark the lines of connection between them, we shall see how they all converge to Plato. He is the focus of ancient philosophy, whither all that went before him tends, and whence bright light and warmth stream forth upon posterity down to our own day.
The range of his achievements alone is enough to make this evident. Like the Ionians his grasp embraces cosmology, physics, and anthropology. Like the Pythagoreans he pursues the study of mathematics with ever increasing devotion, presumably as the basis of his speculations. Like Xenophanes he enters the school of the ancient Orphic Mysticism, and in the Timæus exalts it into a theology culminating in Monotheism. Like the Eleatics he ponders the problems of ontology. Like Heraclitus he inquires into the eternal flow of genesis; he ponders on the ideals of culture and the political theories of the Sophists, he wrestles with the ideal method of Socrates, he strives with hostile philosophers of the Socratic school on this hand and on that (Aristippus, Euclides, and Antisthenes), and, lastly, he strives with himself as his speculation develops more and more along theological and mathematical lines. For, as the genuine servant of Truth, Plato regards himself up to old age as in process of growing and learning. Nothing is so hateful to him as Dogmatism. Nevertheless there are so many opinions to which he held with unwavering constancy that we are probably justified in speaking of the system of Plato.
At the centre of it lies what has crystallised in more living shape out of the dry conceptions of the Socratic method—the domain of ideas. Even as Parmenides perceived Being in the eternal All-Existent, accessible to Reason alone, so Plato sees the being of individual things in that which pertains to them in common and as such can be grasped by the Reason. But even as the Eleatic “One” exists even apart from its recognition as an objective being, so these eternal and unchangeable archetypes (ideai) live in and by themselves as objective essences which exist wholly apart from the individual objects which partake of their form. These archetypes, like the Eleatic All-Existent, bear the name of unit (monad), only in Plato’s scheme there are many such monads, and their unchangeableness does not exclude the idea of causation. Thus his “ideas” are the “units” of Parmenides in multiplicity and the “conceptions” of Socrates endued by metaphysics with the breath of life.
To Socrates the idea of Good and of Virtue lay at the heart of his teaching, and thus the preponderance of the idea of Good is confirmed to his pupil, and in its theological elaboration this abstract idea is converted into the Supreme Reason, the first cause of Being, which is identical with the Deity.