of his life; the tyrant Critias, and even the Sophist Protagoras, acknowledged his marvellous power. But I cannot linger longer on the man, with his gifts and peculiarities. More important things demand our attention. I propose briefly to show his contributions to philosophy and ethics. In regard to the first, I will not dwell on his method, which is both subtle and dialectical. We are not Greeks. Yet it was his method which revolutionized philosophy. That was original. He saw this,--that the theories of his day were mere opinions; even the lofty speculations of the Ionian philosophers were dreams, and the teachings of the Sophists were mere words. He despised both dreams and words. Speculations ended in the indefinite and insoluble; words ended in rhetoric. Neither dreams nor words revealed the true, the beautiful, and the good,--which, to his mind, were the only realities, the only sure foundation for a philosophical system. So he propounded certain questions, which, when answered, produced glaring contradictions, from which disputants shrank. Their conclusions broke down their assumptions. They stood convicted of ignorance, to which all his artful and subtle questions tended, and which it was his aim to prove. He showed that they did not know what they affirmed. He proved that their definitions were wrong or incomplete, since they logically led to contradictions; and he showed that for purposes of disputation the same meaning must always attach to the same word, since in ordinary language terms have different meanings, partly true and partly false, which produce confusion in argument. He would be precise and definite, and use the utmost rigor of language, without which inquirers and disputants would not understand each other. Every definition should include the whole thing, and nothing else; otherwise, people would not know what they were talking about, and would be forced into absurdities. Thus arose the celebrated "definitions,"--the first step in Greek philosophy,--intending to show what _is_, and what _is not_. After demonstrating what is not, Socrates advanced to the demonstration of what is, and thus laid a foundation for certain knowledge: thus he arrived at clear conceptions of justice, friendship, patriotism, courage, and other certitudes, on which truth is based. He wanted only positive truth,--something to build upon,--like Bacon and all great inquirers. Having reached the certain, he would apply it to all the relations of life, and to all kinds of knowledge. Unless knowledge is certain, it is worthless,--there is no foundation to build upon. Uncertain or indefinite knowledge is no knowledge at all; it may be very pretty, or amusing, or ingenious, but no more valuable for philosophical research than poetry or dreams or speculations.