The control of learning and education by the Church is the most peculiar and essential aspect of her activity. The control of war and peace was a matter of guiding the estate of the baronage; the control of trade and commerce was a way of directing the estate of the commons; but the control of learning and education was nothing more nor less than the Church's guidance of herself and her direction of her own estate. _Studium_ may be distinguished from _sacerdotium_ by mediaeval writers; but the students of a mediaeval university are all 'clergy', and the curricula of mediaeval universities are essentially clerical. All knowledge, it is true, falls within their scope; but every branch of knowledge, from dialectic to astronomy, is studied from the same angle, and for the same object--_ad maiorem Dei gloriam_. Here, as elsewhere, the penetrating and assimilative genius of the Church moulded and informed a matter which was not, in its nature, easily receptive of a clerical impression. The whole accumulated store of the lay learning of the ages--geometry, astronomy, and natural science; grammar and rhetoric; logic and metaphysics--this was the matter to be moulded and the stuff to be permeated; and on this stuff St. Thomas wrought the greatest miracle of genuine alchemy which is anywhere to be found in the annals of learning. The learning which the Church had to transform was essentially the learning of the Hellenic world. Created by the centuries of nimble and inventive thought which lie between the time of Thales and that of Hipparchus, this learning had been systematized into a _corpus scientiae_ during that age of Greek scholasticism which generally goes by the name of Hellenistic. In its systematized Hellenistic form, it had been received by the Roman world, and had become the culture of the Roman Empire. By writers ranging from Ptolemy to Boethius the body of all known knowledge had been arranged in a digest or series of pandects; and along with the legal codification of Justinian it had been handed to the Christian Church as the heritage of the ancient world. The attitude of the Church to that heritage was for long unfixed and uncertain. The logic, and still more the metaphysics, of Aristotle were not the most comfortable of neighbours to the new body of Christian revelation committed to the Church's keeping. In the hand of Berengar of Tours the methods of Greek logic proved a corrosive to the received doctrine of the Mass. In the hands of Abelard, in the _Sic et Non_, they served to suggest the need of criticism of the text of Christian tradition. If unity was to be preserved, a bridge must be built between the secular science of the Greeks and the religious faith of the Church. In the thirteenth century that bridge was built. Aristotle was reconciled with St. Augustine; the _Organon_, the _Ethics_, and the _Politics_ were incorporated in the body of Christian culture; and the mediaeval