Discourses: Book 3 3 : 1
The subject-matter with which the good and excellent man has to deal is his own governing principle, that of a physician and the masseur is the body, of a farmer is his farm; but the function of the good and excellent man is to deal with his impressions in accordance with nature. Now just as it is the nature of every soul to assent to the true, dissent from the false, and to withhold judgement in a matter of uncertainty, so it is its nature to be moved with desire toward the good, with aversion toward the evil, and feel neutral toward what is neither evil nor good. For just as neither the banker nor the greengrocer may legally refuse the coinage of Caesar, but if you present it, whether he will or no, he must turn over to you what you are purchasing with it, so it is also with the soul. The instant the good appears it attracts the soul to itself, while the evil repels the soul from itself. A soul will never refuse a clear sense-impression of good, any more than a man will refuse the coinage of Caesar, On this concept of the good hangs every impulse to act both of man and of God.