From no other personage in history, aside from the founders of universal religions, has there flowed such a stream of moral influence as issued from the life and teachings of Socrates, the son of Sophroniscus. All the chief ethical systems of the Greco-Roman world were the development of germs found in his doctrines. The Cyrenaic and Eleatic, the Cynic, Stoic, and Epicurean, the Platonic, Neoplatonic, and Aristotelian systems had their sources here. The Stoic and Neoplatonic systems contributed important elements to early Christian ethics, while the Aristotelian system exercised a profound influence upon the scholastic ethics of medieval times. In the contribution which these various systems, especially the Stoic, have made to the world’s common fund of ethical thought and feeling is found in large part the measure of the ethical debt which modern civilization owes to Hellenism. Socrates’ aim was to replace the artificial conventional conscience of his contemporaries by a natural rational conscience; in other words, to replace customary communal morality by reflective individual morality.[497] His fundamental doctrine was that virtue is dependent upon knowledge; indeed he almost or quite made knowledge and virtue one and the same thing. He maintained that one can no more see the right without doing it than one can see a proposition to be true without believing it. Therefore without knowledge--insight--there can be no true virtue.[498] But clearness of vision requires the purification of the intellect, the getting rid of all false intellectual and moral notions; hence the aim and purpose of Socrates’ unique method of cross-examination was to show his interlocutor the baseless and mutually contradictory character of his inherited chance-acquired ideas and beliefs, and to bring him to that self-knowledge which is the beginning of real knowledge.[499] This practical identification by Socrates of knowledge and virtue, this doctrine of his that it is impossible that one should not will to do that which he sees to be good and right, overlooks the saddest and yet most certain fact of human experience, namely, that perversity of the human will which causes man though seeing the good to choose the evil. But it is a theory of human nature which, in the case of such happily constituted souls as Socrates, in whom the authority of conscience is sacrosanct and inviolable, is nearly or quite accordant with fact. With such persons to see an act to be right is to do it. With them dissonance between knowledge and volition is a moral impossibility.