Stoic apathy, Epicurean self-contentment, and Sceptic imperturbability, were the doctrines which suited the political helplessness of the age, and they were therefore the doctrines which met with the most general acceptance. There was yet another which suited it—viz., the sinking of national distinctions in the feeling of a common humanity, the severance of morals from politics which characterises the philosophy of the Alexandrian and Roman period. The barriers which kept nations apart had been swept away, together with their national independence: East and West, Greeks and barbarians, were united in large empires, brought into communication and forced into comparison with one another in matters the most important. Philosophy declared that all men are of one blood and are equally privileged citizens of one empire, that morality rests on the relation of man to man, and is independent of nationality and position in the state; but in so doing it only explicitly stated a truth which was partly realised and partly implied in actual life. [(2) Intellectual causes.] The very course which philosophy itself had taken during the previous century and a half had prepared the way for the turn which now set in. Socrates and the Sophists, in different ways no doubt, had each devoted themselves to the practical side of life; and thus the Cynic School was the precursor of Stoicism, the Cyrenaic of Epicureanism. These two Schools are, however, only of minor importance in the general progress of philosophy in the fourth century, and sophistry by the close of the same century was already a thing of the past. Socrates, it is true, would have nothing to do with physical enquiries; yet he felt the desire for knowledge far too keenly to bear comparison with the post-Aristotelian philosophers. Proposing to concern himself only with subjects which were of practical use in life, he yet put forth a theory of knowledge which involved a reform quite as much of speculative as of practical philosophy, and that reform was accomplished on a grand scale by Plato and Aristotle.