interfere with and mar one another. Emancipation from the outward world would have been far more effectually obtained by a total rejection of physical science than by the construction of a theory whose details were, on any scientific principles, demonstrably untrue. The appeal to natural instinct as an argument for hedonism would, consistently followed out, have led to one of two conclusions, either of which is incompatible with the principle that imperturbability is the highest good. If natural instinct, as manifested by brutes, by children, and by savages, be the one sure guide of action, then Callicles was right, and the habitual indulgence of passion is wiser than its systematic restraint. But if Nature is to be studied on a more specific and discriminating plan, if there are human as distinguished from merely animal impulses, and if the higher development of these should be our rule of life, then Plato and Aristotle and the Stoics were right, and the rational faculties should be cultivated for their own sake, not because of the immunity from superstitious terrors which they secure. And we may add that the attendance on public worship practised by Epicurus agreed much better with the sceptical suspense of judgment touching divine providence than with its absolute negation, whether accompanied or not by a belief in gods who are indifferent to sacrifice and prayer. It was, no doubt, for these and similar reasons that all the most vigorous intellects of Hellas ranged themselves either on the Stoic or on the Sceptic side, leaving the halfhearted compromise of Epicurus to those who could not think out any one theory consistently, or who, like the Romans at first, were not acquainted with any system but his. Henceforth, during a period of some centuries, the whole philosophic movement is determined by the interaction of these two fundamental forces. The first effect of their conflict was to impose on Scepticism an important modification, illustrating its essentially parasitic character. We have seen it, as a general tendency of the Greek mind, clinging to the very texture of mythology, accompanying the earliest systematic compilation of facts, aiding the humanistic attacks on physical science, associated with the first great religious reaction, operating as the dialectic of dialectic itself, and finally assuming the form of a shadowy morality, in rivalry with and imitation of ethical systems based on a positive and substantial doctrine. We have now to trace its metamorphosis into a critical system extending its ramifications in parallelism with the immense dogmatic structure of Stoicism, and simultaneously endeavouring to reach the same practical results by a more elastic adaptation to the infirmities of human reason and the uncertainties of sensible experience. As such, we shall also have to study its influence over the most plastic of Roman intellects, the great orator in whose writings Greek philosophy was