Besides its influence on the formation and direction of political eloquence, the doctrine professed by Protagoras had a far-reaching effect on the subsequent development of thought. Just as Cynicism was evolved from the theory of Hippias, so also did the teaching which denied Nature and concentrated all study on subjective phenomena, with a tendency towards individualistic isolation, lead on to the system of Aristippus. The founder of the Cyrenaic school is called a Sophist by Aristotle, nor can the justice of the appellation be doubted. He was, it is true, a friend and companion of Socrates, but intellectually he is more nearly related to Protagoras. Aristippus rejected physical studies, reduced all knowledge to the consciousness of our own sensations, and made immediate gratification the end of life. Protagoras would have objected to the last principle, but it was only an extension of his own views, for all history proves that Hedonism is constantly associated with sensationalism. The theory that knowledge is built up out of feelings has an elective affinity for the theory that action is, or ought to be, determined in the last resort by the most prominent feelings, which are pleasure and pain. Both theories have since been strengthened by the introduction of a new and more ideal element into each. We have come to see that knowledge is constituted not by sensations alone, but by sensations grouped according to certain laws which seem to be inseparable from the existence of any consciousness whatever. And, similarly, we have learned to take into account, not merely the momentary enjoyments of an individual, but his whole life’s happiness as well, and not his happiness only, but also that of the whole community to which he belongs. Nevertheless, in both cases it is rightly held that the element of feeling preponderates, and the doctrines of such thinkers as J. S. Mill are legitimately traceable through Epicurus and Aristippus to Protagoras as their first originator. Notwithstanding the importance of this impulse, it does not represent the whole effect produced by Protagoras on philosophy. His eristic method was taken up by the Megaric school, and at first combined with other elements borrowed from Parmenides and Socrates, but ultimately extricated from them and used as a critical solvent of all dogmatism by the later Sceptics. From their writings, after a long interval of enforced silence, it passed over to Montaigne, Bayle, Hume, and Kant, with what redoubtable consequences to received opinions need not here be specified. Our object is simply to illustrate the continuity of thought, and the powerful influence exercised by ancient Greece on its subsequent development.