The conception of the 'Summa' was not altogether original. From the earliest days of the Church, men of genius had insisted on the reasonableness of Christian belief by showing that, though supernatural in its origin, it did not conflict with either the facts or the laws of human knowledge. And as these had found their highest expression in Greek philosophy, it was natural that this philosophy should serve as a basis for the elucidation of revealed truth. The early Fathers turned to Plato, not only because his teaching was so spiritual, but also because it could be so readily used as a framework for those theological concepts which Christianity had brought into the world. Thus adopted by men who were recognized authorities in the Church,--especially men like Augustine and the Areopagite,--Platonism endured for centuries as the rational element in dogmatic exposition. Scholasticism inaugurated a new era. Patristic erudition had gathered a wealth of theological knowledge which the Schoolmen fully appreciated. But the same truths were to receive another setting and be treated by different methods. Speculation changed its direction, Aristotle taking the place of his master. The peripatetic system found able exponents in the earlier Scholastics; but Aquinas surpassed them alike in the mastery of the philosopher's principles and in his application of these principles to Christian doctrine. His Commentaries on Aristotle adhere strictly to the text, dissecting its meaning and throwing into relief the orderly sequence of ideas. In his other works, he develops the germs of thought which he had gathered from the Stagirite, and makes them the groundwork of his philosophical and theological speculations. With the subtlety of a metaphysician St. Thomas combined a vast erudition. Quotations from the Fathers appear on nearly every page of his writings, serving either as a keynote to the discussion which follows, or as an occasion for solving objections. Toward St. Augustine he shows the deepest reverence, though their methods differ so widely, and his brief but lucid comments throw light on difficult sayings of the great Doctor. His familiarity with patristic theology is shown particularly in the 'Catena Aurea,' where he links with passages from the Sacred Text numerous extracts from the older commentators. His respect for these interpretations did not prevent him from making a thorough search of Scripture itself. With characteristic clearness and depth he interpreted various books of the Bible, insisting chiefly on the doctrinal meaning. The best of his work in this line was devoted to the Pauline Epistles and to the Book of Job; but his mastery of each text is no less evident where he takes the authority of Scripture as the starting-point in theological argument, or makes it the crowning evidence at the close of a philosophical demonstration.