This, then, is the _summum bonum_, the end of life. For as the excellence or end of any organ or instrument consists in that perfection of its parts, whereby each separately and the whole together work well towards the fulfilling of that which it is designed to accomplish, so the excellence of man must consist in a perfect ordering of all his parts to the perfect working of his whole organism as a {169} [276] rational being. The faculties of man are three: the Desire of the body, the Passion of the heart, the Thought of the soul; the perfect working of all three, Temperance, Courage, Wisdom, and consequently the perfect working of the whole man, is Righteousness. From this springs that ordered tranquillity which is at once true happiness and perfect virtue. [277] Yet since individual men are not self-sufficient, but have separate capacities, and a need of union for mutual help and comfort, the perfect realisation of this virtue can only be in a perfect civic [278] community. And corresponding with the three parts of the man there will be three orders in the community: the Workers and Traders, the Soldiers, and the Ruling or Guardian class. When all these perform their proper functions in perfect harmony, then is the perfection of the whole realised, in Civic Excellence or Justice. [281] To this end a careful civic education is necessary, _first_, because to _know_ what is for the general good is difficult, for we have to learn not only in general but in detail that even the individual good can be secured only through the general; and _second_, because few, if any, are capable of seeking the general good, even if they know it, without the guidance of discipline and the restraints of law. Thus, with a view to its own perfection, and the good of all {170} its members, Education is the chief work of the State.