This is a hard lesson, but it must be learned: there is no virtue that does not become a vice if it is carried to extremes; there is no virtue that does not become a vice if it is applied at the wrong time, or under the wrong circumstances, or at the wrong stage of human development. In fact, we may say that most vices are virtues misapplied. The so-called natural vices are simply natural impulses carried to excess, while the unnatural vices result from the suppression and distortion of natural impulses. The Greeks had as their supreme virtue what they called "sophrosune." It is a beautiful word, worth remembering; it means a beautiful quality called moderation. We shall find, as we come to investigate, that life is a series of compromises among many different needs, many different desires, many different duties; and reason sits as a wise and patient judge, and appoints to each its proper portion, and denies to it an excess which would starve the others. Such is true morality, and it is incompatible with the existence of any fixed code, whether of human origin or divine. The fixed morality is a survival of a far-off past, of the days of instinct and servitude. Human reason has developed but slowly, and perhaps only a few people are as yet entirely capable of taking control of their own destiny; perhaps it is really dangerous to think for oneself! But if we investigate carefully, we may decide that the danger is not so much to ourselves as it is to others. The most evil of all the habits that man has inherited from his far-off past is the habit of exploiting his fellows, and in order to exploit them more safely the ruling castes of priests and kings and nobles and property owners have taken possession of the moralities of the world and shaped them for their own convenience. They have taught the slave virtues of credulity and submission; they have surrounded their teachings with all the terrors of the supernatural; they have placed upon rebellion the penalties, not merely of this world, but of the next, not merely of the dungeon and the rack, but of hellfire and brimstone.