The Summa Theologiae is Aquinas's vast unfinished systematic theology — over three thousand articles structured as scholastic disputations, the most ambitious single work of Christian theology ever attempted.
summa-theologiae
Aquinas's vast unfinished masterwork of systematic theology, comprising over three thousand articles structured as Scholastic disputations and constituting the most ambitious single work of Christian theology in the Western tradition.
Composed 1265–1274, left unfinished at Aquinas's death; the missing sections of Part III were assembled by his secretary Reginald from earlier writings.
Introduction
The Summa Theologiae is Thomas Aquinas's vast systematic theology, composed between 1265 and 1274 and left unfinished at his death. Comprising over three thousand articles distributed across three Parts (the second of which is itself divided into two parts), it is the most ambitious single work of Christian theology ever attempted in the Latin tradition. The work's structure — every question treated through the formal mechanism of the Scholastic quaestio (objections, sed contra, response, replies to objections) — is also the most fully realized expression of medieval philosophical-theological method.
The Summa became the standard reference work for Catholic theology after the Council of Trent and the official philosophy of the Catholic Church after Pope Leo XIII's Aeterni Patris (1879). Outside Catholicism, contemporary analytic Thomism (Anthony Kenny, Eleonore Stump, Brian Davies, Edward Feser) has integrated its arguments into mainstream anglophone philosophy.
Form, length, date, language
The Summa Theologiae is structured in three Parts:
- Prima Pars (First Part, Ia): God, creation, the angels, the human person. 119 questions, 584 articles.
- Secunda Pars (Second Part, divided into Prima Secundae and Secunda Secundae): the human person's return to God; ethics and the virtues. The Prima Secundae (Ia-IIae) treats the general structure of human action and the virtues; the Secunda Secundae (IIa-IIae) treats the individual virtues in detail. Together, 303 questions, approximately 1,600 articles — by far the longest section.
- Tertia Pars (Third Part, IIIa): Christ, the sacraments. 90 questions, 549 articles, left unfinished. The missing sections (the Supplementum) were assembled posthumously by Aquinas's secretary Reginald of Piperno from Aquinas's earlier commentary on the Sentences.
The total work runs to approximately 1.5 million words in Latin — longer than the King James Bible. It was composed between 1265 and December 1273, when Aquinas had what appears to have been a mystical experience that left him unable to continue writing. He died three months later, in March 1274.
The original language is medieval scholastic Latin in Aquinas's distinctive style: technical, precise, often dry, structured rigorously by the quaestio format.
Why it was written
The Summa was composed as a teaching text for beginners in theology (ad eruditionem incipientium, as Aquinas's prologue states). The standard theological textbook of the time was Peter Lombard's Sentences, structured by topic and difficult for students to navigate as a coherent introduction. Aquinas's Summa aimed to provide a systematically organized alternative.
The larger philosophical-theological purpose is the integration of Aristotelian philosophy with Christian theology. The recently translated Aristotelian corpus had reached the Latin West through Arabic and Hebrew intermediaries, posing the question of whether Aristotle could be integrated with Christian doctrine or had to be rejected. The Summa is Aquinas's mature demonstration that integration is possible. Aristotelian categories (substance, accident, form, matter, potentiality, actuality, the four causes) structure the metaphysics; the Aristotelian account of virtue, phronesis, and eudaimonia structures the ethics; the Aristotelian psychology of the De Anima structures the philosophy of the human person.
Structure and argument
Prima Pars (Ia): God, creation, the human person. Opens with the Quinque Viae — the Five Ways of demonstrating God's existence (Ia q.2 a.3), proceeding from motion, efficient causation, contingency, gradation of perfections, and the orderliness of natural processes. The doctrine of God proper (Ia qq.3–26) develops the divine attributes (simplicity, perfection, goodness, infinity, eternity, unity). Subsequent questions treat the Trinity, creation, the angels, and finally the human person as a unified composite of body and soul.
Prima Secundae (Ia-IIae): General ethics and the structure of human action. The treatise on happiness opens by establishing that the ultimate human end is the beatific vision of God (qq.1–5). Subsequent questions analyze human action, the passions, habit, virtue and vice, law (including natural law), and grace. The treatise on natural law (qq.90–108) is one of the most influential single sections of the Summa.
Secunda Secundae (IIa-IIae): The particular virtues. The longest section of the Summa. The three theological virtues (faith, hope, charity) are treated first; then the four cardinal virtues (prudence, justice, fortitude, temperance), each with extensive subordinate virtues and vices. The treatise on justice (qq.57–122) is the foundational text of Catholic moral theology on right, law, and political community.
Tertia Pars (IIIa): Christology and the sacraments. Treats the Incarnation (qq.1–26), the life of Christ (qq.27–59), and the sacraments (qq.60–90). The work breaks off in the middle of the treatise on the sacrament of penance.
Key passages
- Ia q.2 a.3 — the Five Ways for the existence of God.
- Ia q.3 a.4 — the doctrine that in God essence and existence are identical.
- Ia q.13 — the analogy of being and the doctrine of analogical predication.
- Ia q.75–89 — the unified treatment of the human person as body-soul composite.
- Ia-IIae q.1–5 — the treatise on happiness as the ultimate human end.
- Ia-IIae q.94 — the natural law as the rational creature's participation in the eternal law.
- IIa-IIae q.57–79 — the treatise on justice.
- IIIa q.75 — the doctrine of the Eucharistic real presence, deploying the technical category of substance.
Reception history
The Summa was contested in its first generation. Several of Aquinas's theses were condemned at Paris and Oxford in 1277, three years after his death. The Dominican order defended him; the Franciscans, defending the Augustinian alternative, opposed. He was canonized in 1323, and his work became the standard reference of the Dominican school.
The Council of Trent (1545–1563) reportedly conducted its deliberations with the Summa on the altar. The Counter-Reformation made the Summa the foundational text for Catholic theology and seminary training. The Second Scholastic in Spain (Francisco Suárez, Domingo de Soto, Cajetan's massive commentary) extended and applied it.
Pope Leo XIII's encyclical Aeterni Patris (1879) made Thomism the recommended philosophy of Catholic education. The resulting Neo-Thomist movement (Étienne Gilson, Jacques Maritain, Réginald Garrigou-Lagrange) shaped Catholic intellectual life for nearly a century. The Second Vatican Council (1962–1965) loosened the strict requirement, opening Catholic theology to more pluralistic engagement, but the Summa remains a major reference.
The most striking recent reception is analytic Thomism, initiated by Anthony Kenny's The Five Ways (1969) and developed by Peter Geach, Elizabeth Anscombe, Brian Davies, Eleonore Stump (whose Aquinas, 2003, is the standard contemporary commentary), and many others. Analytic Thomism has integrated the Summa's metaphysics, philosophy of mind, and ethics into the mainstream of anglophone philosophy.
Contemporary engagement
The standard scholarly Latin edition is the Editio Leonina (the Leonine Commission's century-long critical edition, still in progress). The standard English translation is the Dominican Fathers' translation, available freely online and in the Christian Classics edition. Major recent scholarly monographs include Brian Davies's The Thought of Thomas Aquinas (1992) and Thomas Aquinas's Summa Theologiae: A Guide and Commentary (2014), Eleonore Stump's Aquinas (2003), and the Cambridge Companion to Aquinas's Summa Theologiae (Philip McCosker and Denys Turner, eds., 2016). Active scholarly debates concern the interpretation of the Five Ways, the structure of the doctrine of analogy, the relation between natural law and divine command, and the contemporary application of Thomist categories in metaphysics, ethics, and philosophy of religion.
Further reading
- Aquinas — the author
- Scholasticism — the method the work fully realizes
- Christian Theology — the tradition
- Aristotelianism — the philosophical framework integrated with theology
- Augustine — the other great authority
- Virtue — the central ethical category of the Secunda Secundae
The most ambitious single work of Christian theology in the Western tradition. The foundational text of Catholic philosophy.