The unity of knowledge was thus purchased at a price.  Things must cease to be studied in themselves, and must be allegorized into types, in order that they might be reduced to a unity.  Perhaps the purchase of unity on terms such as these is a bad bargain; and it is at any rate obvious that in such an atmosphere scientific thought will not flourish, or man learn to adjust himself readily to the laws of his environment.  From the standpoint of natural science we may readily condemn the Middle Ages and all their works; and we may prefer a single Opus of Roger Bacon to the whole of the Summa of St. Thomas.  But it is necessary to judge an age which was destitute of natural science by some other criterion than that of science; nor must we hasten to say that the Middle Ages found the Universal so easily, because they ignored the Particular so absolutely.  The truth is, that though mediaeval thinkers knew far more of the writings of Aristotle than they did of those of Plato, they were none the less far better Platonists than they were Aristotelians.  If they had been better Aristotelians, they would have been better biologists; but as they were good Platonists, they had a conception of the purpose and system of human life in society, which perhaps excuses all, and more than all, the defects of their biology.  Any survey, however brief, of the political theory of the Middle Ages will show at once its Platonic character and its incessant impulse towards the achievement of unity.

III

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,