The Summa Theologica of St. Thomas Aquinas stands as one of the greatest achievements of Christian wisdom, offering a complete and orderly exposition of sacred doctrine in the light of reason perfected by faith. Composed in a methodical question-and-answer format, it guides the reader from the knowledge of God in Himself (First Part, Questions 1–119), through the moral life and man’s return to God (First Part of the Second Part, Questions 1–114; Second Part of the Second Part, Questions 1–189), to the mystery of Christ as the way of salvation (Third Part, Questions 1–90), and finally to the completion of this doctrine in the sacraments and last things (Supplement, Questions 1–99). In this work, St. Thomas unites philosophy and theology under the authority of divine revelation, forming a masterwork of clarity, depth, and fidelity to the teaching of the Catholic Church, and providing students with a sure guide to the study of God, man, and eternal beatitude.
- First Part (Questions 1-119)
The First Part (Prima Pars) of the Summa Theologica treats of God as the first principle of all things. It begins by establishing sacred doctrine, then examines God’s existence and attributes, the mystery of the Trinity, and the work of creation. It concludes with the nature of angels and man, especially man as a rational creature made in the image of God. - First Part of the Second Part (Questions 1-114)
The First Part of the Second Part (Prima Secundae) treats of man’s movement toward his last end, considering the moral life in its principles. It begins with man’s ultimate happiness, then examines human acts as voluntary and moral, the passions of the soul, and the formation of habits. From this foundation, St. Thomas develops the nature of virtue and vice, sin and its causes, and concludes with a treatment of law—especially natural and divine law—and the necessity of grace for attaining eternal life. - Second Part of the Second Part (Questions 1-189)
The Second Part of the Second Part (Secunda Secundae) treats of the moral life in its full perfection by examining the virtues and vices in particular detail. Moving beyond general principles, St. Thomas considers each virtue individually—especially the theological virtues of faith, hope, and charity, and the cardinal virtues of prudence, justice, fortitude, and temperance—along with their opposing vices and related acts. In this way, it provides a concrete and practical guide to the formation of Christian character and the pursuit of holiness through rightly ordered action. - Third Part (Questions 1-90)
The Third Part (Tertia Pars) of the Summa Theologica treats of Christ as the way by which man returns to God. It begins with the mystery of the Incarnation, examining the union of the divine and human natures in Christ, and then considers His life, Passion, Resurrection, and glory. From this, St. Thomas proceeds to the sacraments, through which the grace of Christ’s saving work is communicated to men, especially Baptism, the Eucharist, and Penance. - Supplement (Questions 1-99)
The Supplement to the Third Part (Supplementum Tertiae Partis) completes the Summa Theologica by treating those matters left unfinished at St. Thomas’s death, drawing especially from his earlier writings. It continues the discussion of Penance and then examines the sacraments that perfect the Christian life, including Extreme Unction, Holy Orders, and Matrimony. Finally, it turns to the last things—death, judgment, the resurrection of the body, and the eternal state of the blessed and the damned—bringing the whole work to its fulfillment in man’s final end.
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