Thomas Aquinas

About Thomas Aquinas

The Summa Theologiae — abandoned unfinished in December 1273 after its author reported a mystical experience he would describe only as palea, "straw" — stands as the central theological monument of Latin Christianity; its author, Thomas Aquinas (c. 1225 – 7 March 1274), was a Dominican friar from the minor Sicilian nobility whose synthesis of Aristotelian philosophy with Christian revelation defined Catholic thought for seven centuries. Born at the castle of Roccasecca, near Aquino in what was then the Kingdom of Sicily, he was one of the youngest sons of Count Landulf of Aquino — a minor noble family whose orbit included the Benedictine abbey of Monte Cassino and whose imperial connections tied the household to the court of Frederick II. Around the age of five or six he was sent as an oblate to Monte Cassino, following the common path for the younger sons of such families; he was expected to rise to become Abbot of Monte Cassino and return the family to ecclesiastical influence in the kingdom. Early biographers describe a grave, studious child whose questions to his masters — what is God? — already pointed toward his later life's work.

The oblate plan broke in 1239 when Frederick II's quarrel with the Benedictines sent Thomas to the newly founded studium generale at the University of Naples. There he encountered two things that reshaped his life: the full Aristotelian corpus, including works recently transmitted through Arabic commentary and fresh Latin translations from Arabic and Greek, and the Dominican Order — the Order of Preachers — whose combination of poverty, preaching, and university learning represented a radically different vocation from Benedictine monasticism. In 1244, against his family's plans, he joined the Dominicans. His brothers, acting at their mother's behest, kidnapped him on the road and held him at the family castle of Roccasecca for about a year in an effort to force him back to Monte Cassino. One late hagiographical strand adds that they sent a prostitute to test his chastity and that he drove her off with a firebrand from the hearth — modern biographers (Torrell, Weisheipl) treat this episode cautiously as probably later embellishment. When the family finally released him, his Dominican superiors sent him north.

He entered the intellectual center of Latin Christendom in 1245, studying at Paris under Albertus Magnus, the German Dominican who had begun the systematic assimilation of the Aristotelian corpus into Christian theology. From 1248 to 1252 Thomas followed Albert to Cologne, where Albert founded the Dominican studium generale; the two together worked through the Nicomachean Ethics, the Metaphysics, and the Dionysian corpus. It was at Cologne that Albert, told by fellow students that their silent, heavy-set classmate was a dull ox, reportedly answered that the bellowing of this ox would one day be heard throughout the world. Thomas returned to Paris between 1252 and 1256 for his theological license and took the Dominican magister's chair over the resistance of the secular masters, who were trying to exclude the mendicants from the Paris faculty. He held two Paris regencies (1256–1259 and 1268–1272), separated by almost a decade in Italy (Orvieto, Santa Sabina in Rome, and the papal court at Viterbo under Urban IV and Clement IV) during which he began the Summa Theologiae. A third period in Naples (1272–1273), where he was founding a new Dominican studium, continued the Summa and concluded in the mystical event that has defined his spiritual reputation ever since.

On 6 December 1273, during Mass in the chapel of St. Nicholas at the Dominican convent in Naples, Thomas underwent an experience that ended his writing. To his long-time scribe and companion Reginald of Piperno he said afterward, according to William of Tocco's later vita, that everything he had written now seemed to him like straw (palea) compared to what had been revealed. He never dictated another word of the Summa; the Third Part stops at question 90, on penance, mid-argument. Summoned by Pope Gregory X to the Second Council of Lyon — which was to address reunion with the Greek Church — he fell ill on the journey — reportedly after striking his head on a low-hanging branch along the Appian Way — and was taken to the Cistercian abbey of Fossanova in Lazio, where he died on 7 March 1274. Reports of his final days describe intense devotion to the Eucharist and a brief dictation on the Song of Songs. He was canonized by Pope John XXII at Avignon in 1323, declared a Doctor of the Church by Pius V in 1567, and proclaimed the model of Catholic theology by Leo XIII's 1879 encyclical Aeterni Patris. That document launched the neo-Thomistic revival whose lineage includes Gilson, Maritain, Chenu, Congar, Pieper, the transcendental Thomists Rahner and Lonergan, and the analytic Thomists and Radical Orthodox writers of the present. He is the backbone of Catholic theological education to this day, and the figure Dante placed in the Heaven of the Sun (Paradiso 10–14) as the exemplary theological mind of the Latin West.

A reader encountering Aquinas only through the textbook image of the scholastic system-builder misses what his own contemporaries and the 6 December 1273 event make plain. He is a Christian mystic as much as a philosopher, and the devotional practice of fellow Dominicans recorded him as a man often in tears at the altar and frequently in hours of silent contemplation between bouts of disputation. The Summa is ordered throughout to the beatific vision; Dionysius the Areopagite is cited more often than any patristic authority except Augustine; the Corpus Christi hymns he composed for the feast instituted in 1264 remain the musical center of Latin Eucharistic devotion. His theological-rational architecture was always ordered toward a reality he judged, at the end, to exceed it.

Contributions

Aquinas's contributions cluster around a single project: showing that the Aristotelian intellectual revolution then reshaping the universities could be fully absorbed into Christian theology without diluting either. The results are a set of doctrines that together define the shape of Catholic philosophical theology.

The Five Ways (Summa Theologiae I.2.3) are five distinct demonstrations of God's existence, not variations on a single cosmological argument. The first argues from motion (change requires a first unmoved mover); the second from efficient causality (ordered causal series require a first uncaused cause); the third from contingency (if everything could fail to exist, at some point nothing would have existed, so something must exist necessarily); the fourth from gradation of perfection (degrees of a perfection require a maximum); the fifth from teleology (the end-directed behavior of natural bodies requires an intelligent orderer). None is original to Aquinas — Aristotle, Avicenna, and Maimonides provide antecedents for each — but their compressed presentation became the reference version for subsequent Western philosophical theology.

The analogia entis (analogy of being) is Aquinas's answer to the apophatic-cataphatic problem that Maimonides had driven to an extreme. If divine names are predicated univocally (with the same sense) of God and creatures, God is reduced to a being among beings; if equivocally (with unrelated senses), theological language collapses into silence. Aquinas argues in Summa contra Gentiles I.32–34 and ST I.13 that predication is analogical: God is truly named as good, wise, just, but the perfections named exist in God in a different and infinitely fuller mode than in creatures. The analogy holds because creatures participate derivatively in perfections that exist per se in God. This is the precise hinge between apophatic theology (God is unknowable) and cataphatic theology (God is truly revealed), an answer that does not collapse either pole.

The metaphysics of act and potency, combined with the real distinction between essence (essentia) and existence (esse), yields Aquinas's characterization of God as ipsum esse subsistens — subsistent being itself. In every creature, essence (what a thing is) is really distinct from existence (that it is), so every creature is a composite whose existence is received. In God alone, essence and existence are identical: God is not a thing that exists but the pure act of existing. The transcendentals — being (ens), one (unum), true (verum), good (bonum), and on some accounts beautiful (pulchrum) — are coextensive with being itself; every being is one, intelligible, and good, and these are not added properties but the same reality under different formal aspects.

Natural law (lex naturalis), treated in ST I-II.94, defines the rational creature's participation in eternal law. The first precept is that good is to be done and evil avoided; specific precepts are reached through practical reason's reflection on the fundamental human inclinations (to preservation, to procreation and child-rearing, to truth and life in society). Natural law became the foundation of Catholic moral philosophy and a central resource for modern human-rights theory and international law, especially through the Salamanca School of Vitoria and Suárez in the sixteenth century.

The virtue ethics of the Secunda Secundae integrates the four Aristotelian cardinal virtues (prudence, justice, fortitude, temperance) with the three theological virtues (faith, hope, charity). Virtues are stable dispositions acquired through habituation and, in the case of the theological virtues, infused by grace. The account remains the operative reference for Catholic moral theology and a major influence on the contemporary virtue-ethics revival (MacIntyre, Foot, Hursthouse).

Contemplation as the highest human activity (ST II-II.179–182) follows Aristotle's Nicomachean Ethics X: the beatific vision is contemplation brought to completion. The Dominican formula contemplata aliis tradere — to hand on to others what has been contemplated — integrates contemplation and action in a mixed life that Aquinas judges superior to pure contemplation because it overflows from fullness rather than hoarding it.

His sacramental theology, especially the systematic account of transubstantiation in ST III.75 (the term itself is eleventh- and twelfth-century; Aquinas provides the Aristotelian-metaphysical exposition), and his Corpus Christi Eucharistic hymns composed for the feast instituted by Urban IV in 1264 — Pange Lingua, Adoro Te Devote, Lauda Sion, Tantum Ergo, O Salutaris Hostia — combine in Latin Christianity the most technical theology with the most sung and prayed liturgy.

The Augustinian-Thomistic shift in epistemology is among his subtlest contributions. Augustine's theory of knowledge depended on an inner divine illumination: the mind sees eternal truths because the divine Teacher illumines them. Aquinas preserves Augustine's grace-theology intact but replaces the illumination epistemology with an Aristotelian account of abstraction from phantasms: the human intellect knows by abstracting intelligible species from the sense images formed in the imagination. Knowledge begins in the senses; nothing is in the intellect that was not first in the senses (except the intellect itself). The shift is a real revision of Augustinian anthropology, even as Augustine remains constantly quoted as a doctrinal authority.

Works

Aquinas's literary output, composed in roughly twenty-two years of active writing (c. 1252–1273), is vast — the Leonine critical edition begun under Leo XIII in 1882 runs to more than fifty folio volumes and is still incomplete.

The Summa Theologiae (the Leonine editors prefer this title over Summa Theologica), composed c. 1265–1274, is his unfinished masterwork. It is organized in three parts: the Prima Pars on God and creation, the Secunda (subdivided into Prima Secundae on general moral theology and Secunda Secundae on specific virtues and vices), and the Tertia Pars on Christ and the sacraments. The Tertia breaks off at III.90 when Aquinas stopped writing in December 1273; the Supplementum was compiled posthumously by Reginald of Piperno from Aquinas's earlier Scriptum super Sententiis. Each article follows the disputational form of the medieval universities: objections, a sed contra, a respondeo, and replies to objections. The Leonine critical edition is standard; the Blackfriars Latin-English facing-page edition in sixty-one volumes (1964–1981) is the most useful scholarly translation.

The Summa contra Gentiles, composed c. 1259–1265 across four books, is a more philosophical treatise that argues from reason to propositions about God, creation, providence, and the beatific vision, and then treats specifically revealed truths in Book IV. The tradition that it was commissioned for Dominican missionaries engaging Muslim and Jewish interlocutors in Spain goes back to Peter Marsilio's fourteenth-century Vita of Raymond of Peñafort; modern scholarship treats this provenance with caution.

The Scriptum super Sententiis Petri Lombardi is his bachelor-level commentary on Peter Lombard's Sentences, composed c. 1252–1256 at Paris. The Disputed Questions — De Veritate (1256–1259), De Potentia (1265–1266), De Malo (c. 1269–1272), De Anima, De Spiritualibus Creaturis, and the Quaestiones Quodlibetales — record the formal public disputations that were the characteristic academic exercise of the thirteenth-century Paris theological faculty.

The Aristotle commentaries — on the Physics, Metaphysics, De Anima, Posterior Analytics, Nicomachean Ethics, Politics, De Caelo, De Generatione et Corruptione, and several smaller treatises — were made possible by William of Moerbeke's new Greek-to-Latin translations that began arriving during Aquinas's career. They treat Aristotle as a living philosophical interlocutor rather than a historical curiosity.

The scriptural commentaries include extensive Lectura on Isaiah, Jeremiah, Job, the Psalms, and the Pauline epistles, along with the Catena Aurea — a gospel commentary stitched together from the Greek and Latin Fathers. Aquinas personally cites Dionysius the Areopagite (whom he accepted, with his age, as the Pauline convert of Acts 17) nearly 1,700 times across the corpus; Augustine is cited even more often.

Smaller treatises include De Unitate Intellectus contra Averroistas (1270) against the Latin Averroist thesis of a single intellect shared by all humans, De Aeternitate Mundi, and the incomplete Compendium Theologiae. The Eucharistic hymns — Pange Lingua, Adoro Te Devote, Lauda Sion Salvatorem, Tantum Ergo, O Salutaris Hostia, Verbum Supernum Prodiens — were composed for the Feast of Corpus Christi (instituted by Urban IV in 1264) and remain the musical and devotional backbone of Latin Eucharistic worship.

Controversies

The reputation of Aquinas as smooth Catholic consensus is a retrojection from the Leonine revival of the late nineteenth century. In his own lifetime and in the half-century following his death, his theology was one position among many, and several of his theses were formally condemned.

The 1277 Paris Condemnation is the most significant. On 7 March 1277 — by coincidence exactly three years after Aquinas's death — Étienne Tempier, Bishop of Paris, issued a syllabus of 219 propositions drawn from the Arts Faculty's Aristotelian teaching and condemned them under pain of excommunication. Some of the condemned propositions touched Thomistic positions directly, most famously the thesis that immaterial substances are individuated only by their species (so that each angel constitutes its own species) and certain propositions on divine omnipotence and the uniqueness of the created order. The condemnation was political as much as theological: Tempier was asserting Augustinian-Franciscan theology against the perceived naturalism of the Aristotelians. The Thomistic clauses were formally revoked in Paris in 1325, two years after Aquinas's canonization. A narrower, earlier Tempier condemnation of 1270 had targeted thirteen specifically Aristotelian theses (the eternity of the world, the unity of the intellect, rational determinism) without directly naming Aquinas; his De Unitate Intellectus contra Averroistas (1270) was his formal response against the most provocative Latin Averroist of the day, Siger of Brabant.

The Franciscan opposition was sustained and serious. John Pecham, the Franciscan Archbishop of Canterbury, backed the composition of William de la Mare's Correctorium Fratris Thomae (1278), which identified 118 Thomistic propositions the Franciscans judged suspect or erroneous. Richard of Middleton, Roger Marston, and the later Franciscan tradition through Duns Scotus maintained the Augustinian-Bonaventurean alternative — giving priority to will over intellect, defending divine illumination, and, in Scotus's case, articulating a univocal rather than analogical theory of being. The Dominican-Franciscan theological difference became one of the defining medieval distinctions and never fully closed.

The Reformation response was fierce. Luther regarded scholastic theology as a trap that had replaced the gospel with Aristotelian metaphysics; his disdain for Aquinas specifically was vehement, expressed in the 1517 Disputation against Scholastic Theology and the 1518 Heidelberg Disputation. Protestant scholasticism of the seventeenth century (Turretin, the Westminster divines) nonetheless reincorporated much Thomistic structure, and the twentieth-century Protestant Thomistic revival has softened the confessional boundary.

The Averroist question — whether Aquinas preserves or deforms Aristotle — remains a real scholarly debate. Étienne Gilson argued that Aquinas transcended Aristotle by introducing existence as act (esse as actus essendi), yielding a metaphysics of existence rather than of essence. Others argue that Aquinas's Christianizing moves (the subordination of philosophy to sacra doctrina, the elevation of contemplation to the beatific vision, creation ex nihilo) move so far from Aristotle's own framework that the label 'Aristotelian' obscures more than it clarifies.

Religious coercion and the treatment of heretics are among the parts of Aquinas most difficult for modern readers. Summa Theologiae II-II.10 on unbelief and II-II.11 on heresy treat obstinate heretics as deserving, after two warnings, excommunication and handover to the secular arm for execution. The argument is that heretics, unlike Jews and pagans, have corrupted what they once received and therefore owe the faith they profess; the state, under a Christian prince, has the same duty to protect the spiritual order that it has to protect the civil order. This was consensus medieval theology, not Aquinas's innovation, and it was the theoretical scaffolding of inquisitorial procedure. The Second Vatican Council's Dignitatis Humanae (1965) repudiated the conclusion while much of the underlying virtue framework was retained. An honest account of Aquinas registers both that these questions are integral to his theological system as he wrote it and that the Church that canonized him has formally judged the conclusions wrong.

Notable Quotes

'Everything I have written seems like straw to me compared to what has now been revealed to me.' — reported by William of Tocco, Vita of Aquinas, of Aquinas to Reginald of Piperno after the Mass of 6 December 1273 in Naples. The Latin word rendered 'straw' is palea. Aquinas never dictated another word after this.

'Lord, you are what I have written about you.' — part of the same Naples vision, as reported in Tocco's Vita, said before the crucifix in the chapel of St. Nicholas.

'Adoro te devote, latens deitas.' — 'I devoutly adore you, hidden deity'; opening line of the Eucharistic hymn Adoro Te Devote, composed by Aquinas for the Feast of Corpus Christi instituted by Urban IV in 1264.

'Pange, lingua, gloriosi Corporis mysterium.' — 'Sing, tongue, the mystery of the glorious Body'; opening of the Corpus Christi processional hymn Pange Lingua, among the most widely sung pieces in the Latin liturgical tradition.

In the commentary on Dionysius's Divine Names (In De div. nom. IV), Aquinas teaches that in the final approach to God love completes what intellect cannot grasp — a paraphrase of his position rather than a direct quotation; the Latin tag sometimes circulated as his own (Ubi desinit intellectus ibi incipit amor) is not traceable in his corpus.

'Grace does not destroy nature but perfects it.' — Gratia non tollit naturam sed perficit; Summa Theologiae I.1.8 ad 2, the operative formula of the Thomistic synthesis and one of his most cited lines.

Legacy

Aquinas's legacy is less a line of disciples than a series of recurring rediscoveries. The first recovery began within a generation of his death with John Capreolus (c. 1380–1444), the princeps Thomistarum, whose Defensiones Theologiae Divi Thomae Aquinatis defended Thomistic theses against Scotist and nominalist critics. The Dominican commentatorial tradition — Cajetan (Thomas de Vio, whose 1507–1522 commentary on the Summa is printed in the Leonine edition), Francisco de Vitoria at Salamanca, Domingo Báñez, John of St. Thomas (Poinsot) — sustained Thomistic scholarship through the sixteenth and seventeenth centuries and produced in Vitoria the founding document of international law (the Relectiones on the Indians and on the law of war, 1539).

The Counter-Reformation adopted Aquinas as the official theologian of the Council of Trent: the Summa was later said to have been placed on the altar alongside Scripture and papal decretals during the Council of Trent (1545–1563) — a Counter-Reformation tradition rather than documented council practice, but one that captures the authority Aquinas held. Pius V declared him Doctor of the Church in 1567 and ordered a complete edition of his works (the 1570 Piana).

The neo-Thomistic revival of the nineteenth and twentieth centuries transformed Aquinas from one theological voice among many to the central reference for modern Catholic thought. Leo XIII's 1879 encyclical Aeterni Patris commanded the restoration of Thomistic philosophy in Catholic seminaries and universities, launching what would become the dominant Catholic intellectual project for nearly a century. Manual Thomism — the Roman textbook tradition exemplified by Reginald Garrigou-Lagrange — reduced the system to propositions for seminary memorization. Existential or historical Thomism, developed by Étienne Gilson (The Christian Philosophy of St. Thomas Aquinas, 1948) and Jacques Maritain (The Degrees of Knowledge, 1932), recovered the metaphysics of esse and pressed Aquinas into dialogue with modern philosophy and politics. Transcendental Thomism, pioneered by Joseph Maréchal and developed by Karl Rahner, Bernard Lonergan, and Emerich Coreth, engaged Kantian and Hegelian philosophy through Thomistic categories.

The French Dominican ressourcement movement — Marie-Dominique Chenu (Introduction à l'étude de Saint Thomas d'Aquin, 1950), Yves Congar, Henri-Marie Féret — returned to the historical Aquinas behind the scholastic manuals and reread him as a contemplative theologian embedded in a medieval spiritual and historical context. Josef Pieper's popular expositions (The Silence of St. Thomas, Leisure the Basis of Culture) extended Thomistic thought into cultural criticism. Jean-Pierre Torrell's two-volume Saint Thomas Aquinas (1993, 1996) is the contemporary definitive biography.

The analytic Thomist tradition, beginning with Peter Geach and Elizabeth Anscombe at Cambridge and developing through Norman Kretzmann, Eleonore Stump (Aquinas, 2003), Brian Davies, and Fergus Kerr, reads Aquinas in conversation with analytic philosophy of mind, action theory, and philosophy of religion. Radical Orthodoxy — John Milbank and Catherine Pickstock's Truth in Aquinas (2001), along with Graham Ward — rereads Aquinas as a participatory-Platonic thinker as much as an Aristotelian, recovering the mystical and liturgical depth that Leonine manual Thomism had flattened.

Within the Catholic Church, Aquinas's status was codified by the 1917 Code of Canon Law (canon 1366.2) requiring his method and doctrine in philosophical and theological formation; the 1983 Code softened the requirement while preserving his central place. Every significant post-Vatican II Catholic theologian — Hans Urs von Balthasar, Henri de Lubac, Joseph Ratzinger, Robert Barron, David Bentley Hart — engages him, even when critically.

Beyond Catholicism, Aquinas's influence is pervasive. Alasdair MacIntyre's After Virtue (1981) and its sequels rehabilitated Aristotelian-Thomistic virtue ethics for secular moral philosophy. Anglican theology through Austin Farrer, Eric Mascall, and more recently Sarah Coakley and Rowan Williams engages him steadily. The mystical Aquinas — the figure of 6 December 1273 — was largely obscured for a century by the Leonine rationalist image but has been steadily recovered by Torrell, Pieper, the Radical Orthodox writers, and Bernard McGinn's multivolume Presence of God history of Christian mysticism.

Significance

For a reader approaching Aquinas from outside Latin Christianity — from another contemplative tradition, from the comparative study of religion, or from secular philosophy — his importance is easy to miscalibrate in either direction. Devotional Catholic presentations can make him sound like a finished oracle whose every word is dogma. Secular modern dismissals can make him sound like a medieval scholastic whose arguments collapse under post-Humean scrutiny. Both images miss what he is.

Aquinas is the figure who did, for Christian theology, what Ibn Rushd did for Islamic philosophy and what Maimonides did for Jewish thought — absorbed the full Aristotelian system into a revealed-religion framework without either dissolving the religion into philosophy or dismissing the philosophy as a threat. The three projects are structurally parallel and were in dialogue: Aquinas cites Maimonides as 'Rabbi Moses' and Avicenna and Averroes by name, and the analogia entis is in part his answer to what he took to be Maimonides's overshoot into pure negative theology. For cross-tradition study, Aquinas is the worked example of how a medieval revealed tradition absorbs a Greek philosophical inheritance without surrendering its contemplative core.

His theory of analogy matters beyond its Christian setting. The problem of how the language of a contemplative tradition can be both true of ultimate reality and inadequate to it is the problem every apophatic tradition faces. Hindu Advaita distinguishes Saguna Brahman (with attributes) from Nirguna Brahman (without attributes); Islamic kalam distinguishes tanzih (incomparability) from tashbih (likeness); Kabbalah distinguishes Ein Sof (the Infinite) from the sefirot (the attributes through which the Infinite relates to creation). Aquinas's analogia entis operates in the same structural slot: truly naming the divine without capturing it, holding apophatic humility and cataphatic praise together in the same utterance.

His metaphysics of esse — the claim that God is not a being but the pure act of existing, with every creature participating in existence as a gift — is the ontological correlate of the contemplative insight that the ground of reality is not a thing. The Ein Sof of Kabbalah, the Nirguna Brahman of Vedanta, the Tao that cannot be named — all name a ground that exceeds 'being' understood as one entity among others. Aquinas's ipsum esse subsistens is the Latin Christian articulation of the same recognition, stated in Aristotelian metaphysical terms.

The 6 December 1273 event — the Mass after which he judged his writing to be straw — is the indispensable corrective to the textbook image. Aquinas ended his career as a mystic who had seen what his theology had been trying to describe and recognized the distance. The Summa is the most technically elaborate theological architecture Western Christianity has produced, and its author closed his working life with the statement that what had been revealed to him during Mass exceeded it beyond comparison. This is not anti-intellectualism; Aquinas had written the Summa. It is the testimony of a first-rank theological mind about the relation between even the best conceptual system and the reality it points toward.

For contemporary moral philosophy, his natural law and virtue ethics provide a framework that survived the twentieth-century ethical crises that dismantled deontological and utilitarian systems. Alasdair MacIntyre's After Virtue and its successors, Elizabeth Anscombe's Modern Moral Philosophy, and the broader virtue-ethics revival owe him a direct debt. For anyone approaching Christian contemplative practice from outside, Aquinas is the figure who demonstrates that intellectual rigor and mystical depth are not opposed. He wove Dionysius the Areopagite through the Summa more than any patristic source apart from Augustine; he composed Eucharistic hymns sung for seven hundred years; he wrote some of the most technical metaphysics of the medieval period; and he ended in a mystical experience he judged beyond everything he had written. The integration is the point.

Connections

Aquinas sits at a crossroads: backward to Aristotle, Augustine, Dionysius, and Boethius; sideways to Maimonides, Avicenna, and Averroes; forward to the Franciscan and later scholastic traditions, to Dante, to Eckhart, and to the neo-Thomist and analytic-Thomist lineages of modernity. He is also — for readers approaching him from other contemplative traditions — structurally connected to the apophatic-cataphatic synthesis that every revealed tradition has had to work out.

His relationship with Augustine of Hippo is foundational but complex. Aquinas quotes Augustine more than any other authority apart from Scripture and preserves the entire Augustinian grace-theology: the priority of grace, the doctrine of original sin, the seriousness of predestination. What he revises is Augustinian epistemology. For Augustine, the mind sees eternal truths because the interior divine Teacher illumines them. For Aquinas, the mind knows by abstracting intelligible species from sense images (phantasms) — an Aristotelian account that makes human knowledge begin with the senses and work upward rather than beginning with illumination and working downward. The shift is real, and it defines the Augustinian-Thomistic arc.

His use of Dionysius the Areopagite, whom he cites perhaps 1,700 times across his corpus, is the single strongest evidence against the caricature of Aquinas as pure Aristotelian rationalist. Aquinas treated Dionysius as an apostolic-age authority; the attribution to the Athenian convert of Acts 17 was still accepted in the thirteenth century and was only disputed definitively by Lorenzo Valla and Erasmus in the fifteenth and sixteenth. The Dionysian apophatic corpus — the Mystical Theology, the Divine Names — is woven through every treatise on God in the Summa. Aquinas's analogia entis is in effect an Aristotelian mediation of Dionysian apophaticism: the negative theology of the Mystical Theology ('God is neither this nor that') is preserved by denying univocal predication, while the cataphatic theology of the Divine Names ('God is good, wise, just') is preserved by asserting analogical predication.

With Maimonides (cited as 'Rabbi Moses'), Aquinas is engaged in a running dialogue. Maimonides had pushed negative theology to the point that the divine names name only what God is not. Aquinas sees this as collapsing religious language and responds with analogy — the divine names apply positively but analogically. The Jewish-Christian philosophical conversation of the thirteenth century runs directly through this disagreement.

With Avicenna (Ibn Sina), Aquinas inherits the real distinction between essence and existence — a distinction that entered Latin scholasticism through Avicenna's Metaphysics of the Healing. The Avicennian and Thomistic metaphysics of existence are closely related, though Aquinas pushes the esse-essentia distinction further: for Aquinas, existence is not an accident added to essence but the act (actus essendi) by which essence is.

With Averroes (Ibn Rushd), Aquinas is in open controversy. The Latin Averroists at Paris (Siger of Brabant, Boethius of Dacia) read Averroes as teaching a single shared intellect for all humans and the eternity of the world. Aquinas's De Unitate Intellectus contra Averroistas (1270) argues for the plurality of human intellects and the individual immortality of the rational soul.

With his Dominican successor Meister Eckhart, the connection is direct: Eckhart held the same Paris Dominican chair Aquinas had held, and Eckhart's Latin Opus Tripartitum engages Aquinas constantly. Eckhart's mystical theology — the uncreated spark in the soul, the desert of the Godhead, the identity of the ground of the soul with the ground of God — pushes Aquinas's own mystical intuitions in a more Neoplatonic direction and beyond what the institutional church could accept. The 1329 condemnation of Eckhart can be read partly as the boundary-setting that Aquinas's earlier reception had made necessary.

For comparative cross-tradition study, the Advaita Vedantic distinction between Saguna Brahman (Brahman with attributes — Ishvara, the personal God who creates, sustains, destroys) and Nirguna Brahman (the attributeless absolute) maps onto the cataphatic-apophatic distinction that Aquinas's analogy of being mediates. Shankara's Advaita develops the cataphatic register for devotional and worldly purposes and the apophatic register for the highest realization; Aquinas holds both registers simultaneously through the analogy of being. Sufi tawhid — especially in Ibn Arabi's wahdat al-wujud (unity of being) — poses the same question in Islamic metaphysics: how does creation relate to a Real (al-Haqq) that alone exists? Ibn Arabi's resolution, like Aquinas's, uses a participation metaphysics in which creatures participate in a being that God has per se. These are not identical positions, but they are sister positions, and a reader at home in one can enter the other. Within Christian contemplative practice, Aquinas's account of contemplation as the highest human activity (ST II-II.179–182) and his integration of contemplative and active life (contemplata aliis tradere) link him directly to the meditation traditions of East and West.

Further Reading