Summa Theologiae

Aquinas designed the Summa, he says in its prologue, for beginners, having found the existing textbooks repetitive and disordered. His remedy was architecture. The First Part treats God in himself, the Trinity, and the procession of creatures from God, including the long treatises on angels and on human nature that made it a compendium of medieval psychology. The Second Part, so large it is divided in two, turns to the movement of the rational creature back toward God: first the general structure of human action, happiness, the passions, habit, virtue, sin, law and grace, then a detailed anatomy of particular virtues and vices, organised around the three theological and four cardinal virtues. The Third Part treats Christ, the sacraments as extensions of the Incarnation, and was to end in the resurrection and last things when death interrupted the work; disciples completed the plan as a Supplement drawn from his earlier writings.

The unit throughout is the article, framed as a disputed question. Each opens with the strongest objections Aquinas can muster against the position he will take, then a countervailing authority, then his own determination, and finally a reply to every objection, a form that obliges the author to inhabit his opponents' arguments before answering them, and that gives the Summa its enduring reputation for intellectual fairness.

On the feast of Saint Nicholas, 6 December 1273, Aquinas underwent an experience while celebrating Mass in Naples after which he stopped writing altogether. Pressed by his companion Reginald of Piperno to continue, he answered, in the account transmitted by the early biographers, that after what he had seen everything he had written seemed to him as straw. The Summa broke off in the middle of the treatise on penance, and Aquinas died three months later on the way to the Council of Lyon. The work's afterlife was turbulent before it was triumphant.

In 1277 the bishop of Paris condemned a list of propositions that touched positions associated with Aquinas; the condemnation was later annulled for his teaching, and his canonisation in 1323 settled his orthodoxy. The Dominican order adopted his doctrine, and by the sixteenth century the Summa had displaced Peter Lombard's Sentences as the text on which theologians lectured, with commentators such as Cajetan writing at its side.

At the Council of Trent it stood among the works consulted on doctrine, and in 1879 the encyclical Aeterni Patris made Thomism the recommended framework of Catholic philosophy, securing the Summa's place at the centre of seminary education. Its questions on law, conscience and just war remain live references in ethics well beyond theology.