=The "Mean."=--The crowning importance of wisdom as the rational measure of the ideal life is also illustrated in Aristotle's theory of excellence (or virtue) as a "mean". This phrase is somewhat ambiguous, for some passages would seem to indicate that it is merely striking an average between two kinds of excesses, and finding, as it were, a moderate amount of feeling or action; but there is evidently involved here just the old thought of measure, and "the mean is what right reason prescribes." It is not every one who can find the mean, but only he who has the requisite knowledge. The supreme excellence or virtue is, therefore, the wisdom which can find the true standard for action.[79] =The Wise Man.=--Finally the conception of virtue as wisdom is illustrated in the ideals of the three prominent schools in later Greek thought,--the Sceptics, Epicureans, and Stoics. The wise man among Sceptics is he who suspends judgment where it is impossible to be certain. The wise man among Epicureans is he who chooses the finest and surest and most lasting pleasures. The wise man among Stoics is he who overcomes his emotions. But in every case the ideal is expressed in the same phrase, "the wise man." =Man and the Cosmos.=--We see thus how Greek thought, starting out to challenge all society's laws and standards and bring them to the bar of knowledge, has found a deeper value and higher validity in the true social and moral order. The appeal was to the Cæsar of reason, and reason taken in its full significance carries us beyond the immediate and transient to the broader and more permanent good. Nor can reason in its search for good be content, urges Plato, with the superficial facts of life and society. He who would find and achieve his complete function, his full development, must broaden his horizon still further. As his own particular life is but a part of the ongoing of the larger world, whose forces act upon him, limit him, and determine his possibilities, it becomes absolutely necessary to study not merely his own end and purpose, but the end and purpose of the universe. Human good requires us to know the larger good, _the_ Good, in the full and complete sense. And this perfect Good which is, in truth, the very essence of the universe, is but another term for God, and Plato often uses the two as interchangeable terms.