Since the State is to be founded upon reason, its laws must be rational, and rational laws can only be made by rational men, philosophers. The rulers must be philosophers. And since the philosophers are few, we must have an aristocracy, not of birth, or of wealth, but of intellect. The first operative principle of the State is reason, the second is force. For it is not to be expected that the irrational masses will willingly submit to rational laws. They must be compelled. And since the work of the world must go on, the third operative principle will be labour. Plato believed in the principle of division of labour. Only he can excel at any occupation whose life is devoted to it. Hence to the three operative principles correspond three classes, castes, or professions. Reason is embodied in the philosopher-rulers, force in the warriors, labour in the masses. This division of the functions of the State is based upon the threefold division of the soul. To the rational soul correspond the philosopher-rulers, to the nobler half of the mortal soul the warriors, to the appetitive soul the masses. Consequently the four cardinal virtues belong to the State through the functioning of the three classes. The virtue of the philosopher-rulers is wisdom, of the warriors courage, of the masses, temperance. The harmonious co-operation of all three produces justice. The rulers must not cease to be philosophers. Most of their time must be spent in the study of the Ideas, philosophy, and only a portion in the affairs of government. This is rendered possible by the system of taking turns. Those who are not at any particular time {228} engaged upon government retire into thought. The duty of the warriors is the protection of the State, both against its external enemies, and against the irrational impulses of the masses of its own citizens. Normally, the latter will be their chief duty, the enforcement of the decrees of the philosopher-rulers upon the masses. The masses will engage themselves in trade, commerce, and agriculture. Both the other ranks are prohibited from soiling their fingers with trade or agriculture, upon which Plato, as a Greek aristocrat, looked down with unbounded contempt. To what rank a citizen belongs is not determined by birth, nor by individual choice. No individual can choose his own profession. This will be determined by the officers of the State, who will base their decision, however, upon the disposition and capabilities of the individual. As they have also to decide the numbers required for each rank, the magistrates also control the birth of children. Parents cannot have children when they wish. The sanction of the State is required.