To mediaeval thought, as to Plato, the unity of society is an organic unity, in the sense that each member of society is an organ of the whole to which he belongs, and discharges a function at once peculiar to himself and necessary to the full life of the whole. Monasticism, so often misrepresented, attains its true meaning in the light of this conception. The monk is a necessary organ of Christian society, discharging his function of prayer and devotion for the benefit not of himself solely, or primarily, but rather of every member of that society. He prays for the sins of the whole world, and by his prayer he contributes to the realization of the end of the world, which is the attainment of salvation. In the same way the conception of a treasury of merits, afterwards perverted in the system of indulgences, belongs to an organic theory and practice of society. The merits which Christ and the saints have accumulated are a fund for the use of the whole of Christian society, a fund on which any member can draw for his own salvation, just because each is fitly joined and knit together with all the rest in a single body for the attainment of a single purpose. But we need not take isolated instances of the Platonism of mediaeval thought. The whole basic conception of a system of estates, which recurs everywhere in mediaeval life, is a Platonic conception. The estates of clergy, baronage, and commons are the Platonic classes of guardians, auxiliaries, and farmers. The Platonic creed of [Greek: to auton prattein] ('Do thine own duty') is the Christian creed of 'doing my duty in that state of life to which it shall please God to call me'. The Middle Ages are full of a spontaneous Platonism, and inspired by an _anima naturaliter Platonica_. The control which the mediaeval clergy exercised over Christian society in the light of divine revelation repeats the control which the guardians of Plato were to exercise over civic society in the light of the Idea of the Good. The communism of the mediaeval monastery is reminiscent of the communism of the Platonic barracks. And if there are differences between the society imagined by Plato and the society envisaged by the mediaeval Church, these differences only show that the mediaeval Church was trying to raise Platonism to a higher power, and to do so in the light of conceptions which were themselves Greek, though they belonged to a Greece posterior to the days of Plato. These conceptions--which were cherished by Stoic thinkers; which penetrated into Roman Law; and which from Roman Law flowed into the teaching and theory of the early fathers of the Church--are mainly two. One is the conception of human equality; the other, and correlative, conception is that of a single society of all the human race. The equality of men, and the universality of the city of God in which they are all contained, are conceptions which were no less present to Marcus Aurelius than they were to St. Augustine. They are