Plato arrives at his apportionment of functions by a method which is old-fashioned, and which anybody versed in modern psychology would regard as a “rationalization.” Plato is trying to give a firm basis to the division of classes which he favored; and so he compares the community to a human being, possessed of the virtues of wisdom, valour, temperance, and justice. Each of these virtues Plato relates to a particular class of people. Wisdom is appropriate to the rulers of the city. Thus arises the class of guardians. Valour is the characteristic of the defenders of the city and hence a military class, called auxiliaries, appears. Temperance, or agreement, is the virtue which relates to all classes. Finally, there comes justice. “Justice is the ultimate cause and condition of all of them.... If a question should arise as to which of these four qualities contributed most by their presence to the excellence of the State whether the agreement of rulers and subjects or the preservation in the soldiers of the opinion which the law ordains about the true nature of dangers, or wisdom and watchfulness in the rulers would claim the palm, or whether this which I am about to mention,” namely, “everyone doing his own work and not being a busybody--the question would not be easily determined.” Nevertheless, it is plain that justice is the keystone of the Platonic utopia. We must not misunderstand Plato’s division of classes. Aristotle criticizes Plato in terms of a more simple system of democracy; but Plato did not mean to institute a fixed order; within his Republic the Napoleonic motto--_la carrière est ouverte aux talents_--was the guiding principle. What lay beneath Plato’s argument was a belief which present-day studies in psychology seem likely to confirm; a belief that children come into the world with a bent already well marked in their physical and mental constitutions. Plato advocated, it is true, an aristocracy or government by the best people; but he did not believe in fake aristocracies that are perpetuated through hereditary wealth and position. Having determined that his city was to contain three classes, rulers, warriors, and workers, his capital difficulty still remained to be faced; how was each individual to find his way to the right class, and under what conditions would he best fulfill his functions there? The answers to these questions bring us to the boldest and most original sections of the Republic: the part that has provoked the greatest amount of antagonism and aversion, because of its drastic departure from the rut of many established institutions--in particular, individual marriages and individual property. In order to perpetuate his ideal constitution Plato relies upon three methods: breeding, education, and a discipline for the daily life. Let us consider the effect of these methods upon each of the classes.