Summa Theologica

The Summa Theologica is Aquinas's attempt to organize the whole of Christian theology into a single rational structure. It proceeds by questions, each divided into articles, each article raising an objection, stating a counter-position, and resolving the issue. The method is Aristotelian; the ambition is encyclopedic. Over the course of three parts and thousands of articles, Aquinas treats God's existence and nature, the structure of creation, the moral life of rational creatures, the virtues, the sacraments, and the person of Christ.

The First Part (Prima Pars) establishes God as pure act, simple, eternal, and the cause of all that exists. It then descends through the hierarchy of creation: angels, the human soul, the material world. The Second Part, divided into two halves, is the heart of the moral theology. The Prima Secundae treats the general principles of human action: happiness as the ultimate end, the passions, habits, virtues, law (eternal, natural, human, divine). The Secunda Secundae takes up each virtue and vice in particular, from faith, hope, and charity through justice, prudence, temperance, and fortitude. The Third Part, left unfinished at Aquinas's death, treats Christ and the sacraments.

What makes the Summa more than a compendium is its architectonic coherence. Every question connects to every other through the underlying metaphysics of act and potency, form and matter, participation and causality. The treatment of law alone draws together theology, ethics, and political philosophy in a framework that shaped centuries of natural-law thinking. Virtually every idea in the Great Conversation finds some articulation here, which is why the Summa touches more entries in this collection than any other single work.