Now, of the two aspects of the Socratic philosophy, the theory of concepts, and the ethical theory, it is easy for us, looking back upon history, to see which it was that influenced the history of thought most, and which, therefore, was the most important. But the men of his own time could not see this. What they fastened upon was the obvious aspect of Socrates, his ethics, and above all the ethical teaching which was expressed, not so {157} much in abstract ideas, as in the life and personality of the master. Both this life and this teaching might be summed up in the thought that virtue is the sole end of life, that, as against virtue, all else in the world, comfort, riches, learning, is comparatively worthless. It is this, then, that virtue is the sole end of life, which forms the point of agreement between all the three semi-Socratic schools. We have now to see upon what points they diverge from one another. If virtue is the sole end of life, what precisely is virtue? Socrates had given no clear answer to this question. The only definition he had given was that virtue is knowledge, but upon examination it turns out that this is not a definition at all. Virtue is knowledge, but knowledge of what? It is not knowledge of astronomy, of mathematics, or of physics. It is ethical knowledge, that is to say, knowledge of virtue. To define virtue as the knowledge of virtue is to think in a circle, and gets us no further in the enquiry what virtue is. But Socrates, as a matter of fact, did not think in a circle. He did not mean that virtue is knowledge, although his doctrine is often, somewhat misleadingly, stated in that form. What he meant was--quite a different thing--that virtue _depends upon_ knowledge. It is the first condition of virtue. The principle, accurately stated, is, not that virtue is the knowledge of virtue, which is thinking in a circle, but that virtue depends upon the knowledge of virtue, which is quite straight thinking. Only if you know what virtue is can you be virtuous. Hence we have not here any definition of virtue, or any attempt to define it. We are still left with the question, "what is virtue?" unanswered. {158}