At the beginning of the thirteenth century the recovery by western Christendom from the Arabs, Jews and Greeks of the metaphysical treatises of Aristotle, and their translation into Latin, caused a ferment in the intellectual world comparable to that produced by Darwin in the nineteenth century. To vindicate traditional methodoxy Albertus Magnus undertook to harmonize the doctrines of the Church with the Peripatetic philosophy, and this work was carried to its conclusion by his pupil, St Thomas Aquinas, with such success that the latter has become the official philosopher of Roman Catholicism. The system of Aquinas centres in his conception of God, to the exposition and criticism of which this book is devoted.