The Work
The Summa Theologica (also Summa Theologiae, 'Summary of Theology') was composed by Thomas Aquinas between 1265 and 1274, left unfinished at his death. Written in Latin, it is organized into three major parts (the Prima Pars, Secunda Pars - itself divided into Prima Secundae and Secunda Secundae - and Tertia Pars), containing 512 questions, 2,669 articles, and approximately 10,000 objections with responses. The total length exceeds 1.5 million words, making it one of the longest works of systematic thought ever composed. A supplement compiled by Aquinas's students from his earlier commentary on the Sentences of Peter Lombard completes the unfinished third part.
The work was initially intended as a textbook for Dominican students - 'beginners,' as Aquinas says in the prologue - but became the definitive expression of Catholic systematic theology. The first complete printed edition appeared in 1485. Pope Leo XIII's encyclical Aeterni Patris (1879) declared Thomistic philosophy the official philosophy of the Catholic Church, and the Summa was placed on the altar alongside the Bible at the Council of Trent (1545-1563). The standard critical edition is the Leonine edition (1882-present). Major English translations include those by the English Dominican Fathers (22 vols., 1911-1925) and the Blackfriars bilingual edition (61 vols., 1964-1981).
Biblical Engagement
Despite its philosophical architecture, the Summa is fundamentally a work of biblical theology. Aquinas cites Scripture more than any other source - far more than Aristotle. Modern scholars have counted over 12,000 biblical citations across the work. Every article begins with scriptural sed contra ('on the contrary') arguments, and the body of each article typically synthesizes philosophical reasoning with biblical exegesis.
The opening question - whether theology is a science - establishes Scripture as the foundational authority. Aquinas argues that sacred doctrine proceeds from the articles of faith revealed in Scripture, just as a subordinate science proceeds from the principles of a higher science (I, q.1, a.2). His proof of God's existence in the famous 'Five Ways' (I, q.2, a.3) begins from natural reason but is framed by Exodus 3:14 ('I AM WHO I AM') and Romans 1:20 ('the invisible things of him from the creation of the world are clearly seen').
Genesis 1:1 ('In the beginning God created the heaven and the earth') grounds the extensive treatise on creation (I, qq.44-119). John 1:1 ('In the beginning was the Word') provides the basis for Aquinas's Trinitarian theology, particularly his treatment of the divine processions and the Word as the intellectual emanation of the Father (I, qq.27-43). The treatise on law draws on Romans 2:14-15 (the natural law written on the heart), Psalm 4:6 ('the light of thy countenance, O Lord, is signed upon us'), and the Decalogue (Exodus 20). The treatise on grace (I-II, qq.109-114) is built on Pauline texts: Romans 3:24, Ephesians 2:8-9, and 2 Corinthians 12:9.
The Secunda Secundae, on the virtues, draws on 1 Corinthians 13:13 (faith, hope, and charity as the theological virtues), Matthew 5:3-12 (the Beatitudes), and the Wisdom literature (especially Proverbs and Sirach). The Tertia Pars, on Christ and the sacraments, is grounded in the Christological hymns (Philippians 2:5-11, Colossians 1:15-20) and the institution narratives (Matthew 26, Mark 14, Luke 22, 1 Corinthians 11).
Author & Context
Thomas Aquinas (1225-1274) was born into a noble family at Roccasecca in the Kingdom of Sicily (modern-day Italy). He was educated at the Benedictine monastery of Monte Cassino and at the University of Naples, where he encountered the works of Aristotle - newly translated from Arabic into Latin - that would transform his intellectual life. Against his family's strong objections (they kidnapped and confined him for a year), he joined the Dominican Order, a mendicant order dedicated to preaching and teaching.
Aquinas studied under Albert the Great at Cologne and Paris, then taught at the University of Paris, the Roman curia, and various Dominican houses in Italy. His intellectual project was the integration of Aristotelian philosophy with Christian theology - a synthesis that was controversial in his time, since many traditionalists viewed Aristotle with suspicion as a pagan philosopher whose ideas threatened Christian doctrine. The condemnations of 1277, issued by the Bishop of Paris just three years after Aquinas's death, targeted several Thomistic propositions.
Aquinas composed the Summa during the last decade of his life, primarily in Italy (Rome, Viterbo, Orvieto, and Naples). On December 6, 1273, while celebrating Mass, he had a mystical experience after which he stopped writing entirely, telling his companion Reginald of Piperno: 'All that I have written seems to me like straw compared to what has now been revealed to me.' He died three months later, on March 7, 1274, en route to the Council of Lyon. He was canonized in 1323 and declared a Doctor of the Church in 1567.
Structure and Argument
The Summa follows a grand circular structure modeled on the Neoplatonic scheme of exitus-reditus (going forth and return). The Prima Pars treats God in himself (the divine essence, the Trinity) and God as the source of creation (angels, the material world, human beings). The Secunda Pars treats the human being's return to God through moral action: the Prima Secundae addresses the general principles of morality (happiness as the ultimate end, the passions, virtues, vices, law, grace), while the Secunda Secundae treats the individual virtues and vices in detail. The Tertia Pars treats Christ as the way of return - the Incarnation, the life of Christ, and the sacraments as the means of grace.
The biblical architecture is clear: the movement from Genesis (creation) through the Wisdom literature and the Law (moral life) to the Gospels (Christ) and the epistles (grace and sacraments) mirrors the canonical order of Scripture. Aquinas is not merely using the Bible as a proof-text repository; he is structuring his entire theological vision on the narrative arc of Scripture.
Each article follows a rigorous dialectical format: (1) a question is posed; (2) several objections are presented, often drawing on biblical texts that seem to support the opposing view; (3) a sed contra ('on the contrary') provides an authoritative counter-text, frequently from Scripture; (4) the respondeo ('I answer that') gives Aquinas's own position, integrating reason and revelation; (5) replies to each objection resolve the apparent contradictions.
Key Passages
The Five Ways (I, q.2, a.3) are the most famous passage in the Summa. Aquinas offers five arguments for God's existence drawn from motion, efficient causality, contingency, degrees of perfection, and the governance of nature. Each concludes with the formula 'and this everyone understands to be God' - linking philosophical demonstration to the common understanding grounded in Romans 1:20.
The treatise on the divine names (I, q.13) addresses how human language can refer to God at all. Aquinas's solution - the doctrine of analogy - argues that terms like 'good,' 'wise,' and 'being' are predicated of God neither univocally (with the same meaning as when applied to creatures) nor equivocally (with a completely different meaning) but analogically. This doctrine, grounded in Exodus 3:14 and the biblical tradition of naming God, remains one of the most influential ideas in the philosophy of religion.
The treatise on law (I-II, qq.90-108) distinguishes eternal law (God's providential plan), natural law (the participation of rational creatures in eternal law, per Romans 2:14-15), human law (the application of natural law to particular circumstances), and divine law (revealed in Scripture, both Old and New Testaments). This framework became the foundation of Catholic moral theology and influenced secular legal theory through Grotius, Locke, and the natural rights tradition.
Critical Reception
The Summa was not immediately accepted as the definitive theological text. The 1277 condemnations at Paris and Oxford targeted Thomistic positions, and Franciscan theologians (following Bonaventure and Duns Scotus) offered rival syntheses. It was the Dominican Order's championing of Aquinas, culminating in his canonization in 1323, that established his authority. By the sixteenth century, Dominican commentators Francisco de Vitoria, Cajetan, and John of St. Thomas had made the Summa the standard theological textbook in Catholic universities.
The Reformation brought sharp criticism. Luther called Aquinas 'the fountain and original soup of all heresy, error, and Gospel destruction.' Calvin criticized the natural theology tradition. Protestant theology generally preferred a more purely biblical method. Yet there have always been Protestant Thomists: Richard Hooker drew on Aquinas in his Laws of Ecclesiastical Polity, and the twentieth century saw a significant Protestant engagement through scholars like Arvin Vos, Norman Kretzmann, and Eleonore Stump.
The twentieth-century Thomistic revival, beginning with Leo XIII's Aeterni Patris and continuing through Jacques Maritain, Etienne Gilson, and the Lublin school, restored Aquinas to the center of Catholic intellectual life. The Second Vatican Council (1962-1965) both affirmed Aquinas's importance and opened Catholic theology to other methods. The 'Radical Orthodoxy' movement (John Milbank, Catherine Pickstock) has offered a postmodern retrieval of Thomistic metaphysics.
Theological Significance
The Summa represents the most ambitious attempt in Christian history to integrate faith and reason, Scripture and philosophy, into a single coherent system. Its central conviction - that grace perfects nature rather than destroying it - has profound implications: it means that philosophy, science, art, and politics are not enemies of faith but preparatory stages that find their completion in revelation.
Aquinas's biblical hermeneutics are sophisticated. He distinguishes literal, allegorical, moral, and anagogical senses of Scripture (I, q.1, a.10), insisting that the literal sense - what the human author intended - is the foundation of all interpretation. This commitment to the literal sense, combined with his use of reason to clarify scriptural meaning, makes Aquinas a forerunner of modern biblical scholarship as well as a medieval master.
Legacy
The Summa shaped Catholic theology for seven centuries and continues to do so. The Code of Canon Law (1917, revised 1983) mandates the study of Aquinas in seminary formation. Pope John Paul II's encyclical Fides et Ratio (1998) reaffirmed the Thomistic integration of faith and reason. The work influenced political philosophy (natural law theory in Grotius, Locke, and Jefferson), ethics (the principle of double effect, Just War theory), and metaphysics (the real distinction between essence and existence).
Beyond Catholicism, the Summa has been engaged by Jewish philosophers (Moses Maimonides influenced Aquinas, and later Jewish thinkers responded to him), Islamic scholars (given the shared Aristotelian heritage), and analytical philosophers (Anthony Kenny, Eleonore Stump, Brian Davies). The Thomistic revival in contemporary philosophy of religion represents one of the most significant intellectual movements of the twenty-first century.
Reading Alongside Scripture
Readers should study Exodus 3:14 (the divine name), Romans 1:19-20 (the knowability of God through creation), Genesis 1-2 (creation), Romans 2:14-15 (natural law), 1 Corinthians 13:13 (the theological virtues), Philippians 2:5-11 (the Incarnation), and John 1:1-18 (the Logos). The Wisdom literature - especially Proverbs 8, Sirach 24, and the Wisdom of Solomon - provides essential background for Aquinas's synthesis of faith and philosophy.
Further Reading
- Brian Davies, Thomas Aquinas's Summa Theologiae: A Guide and Commentary (2014) - the best single-volume introduction for readers approaching the Summa for the first time. - Eleonore Stump, Aquinas (2003) - a rigorous philosophical reading by an analytical philosopher. - Jean-Pierre Torrell, Saint Thomas Aquinas: The Person and His Work (1993; English trans. 1996) - the standard scholarly biography.