Summa Theologiae

The Summa Theologiae is Thomas Aquinas‘s attempted complete systematic theology, written between 1265 and 1274 and left unfinished at his death. It is structured as a series of quaestiones, each broken into articles that follow a fixed dialectical form: the question, several plausible objections, a sed contra citing authority on the other side, the respondeo in which Aquinas states his own view, and finally responses to each of the original objections.

For OTS purposes the central material is in the First Part, Question 2, Article 3, where Aquinas presents the Five Ways: the five proofs of the existence of God by way of motion, efficient causation, contingency, gradation, and final causation. The Five Ways are short. They are deliberately schematic. Aquinas treats them as starting points, not finished arguments. They became the starting point for centuries of subsequent debate over the Cosmological Argument and the Teleological Argument.

The Summa breaks off in December 1273. Aquinas had written the bulk of the Third Part, on the Incarnation and the sacraments, but stopped after a religious experience he refused to describe in detail. He died three months later. His secretary Reginald, urged him to keep writing. Aquinas refused.