Thomas Aquinas

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Thomas Aquinas (1225–1274) was an Italian Dominican friar, theologian, and philosopher whose attempt to reconcile Aristotle with Christian doctrine became, after his death, the dominant intellectual framework of the Catholic Church. Born to a noble family near Aquino, in the Kingdom of Sicily, he was sent as a child to the abbey of Monte Cassino and later studied at Naples, where he encountered both the Aristotelian texts then newly arriving in Latin and the young Order of Preachers. His decision to join the friars rather than take a comfortable abbacy provoked his family to seize him near Aquapendente and confine him at the family fortress of Roccasecca for the better part of two years, while relatives worked by every means — a famous episode has them sending a courtesan to his room, whom he is said to have driven out with a brand from the fire — to break his vocation. He held to it, and the order won. Sent north, he came under Albertus Magnus at Cologne around 1248; when the hulking, taciturn young man defended a hard thesis, Albert reportedly told the class that they called him the dumb ox, but his bellowing would one day resound throughout the world.

The setting: a new Aristotle

The setting matters. Aristotle’s full corpus had only recently reached Latin Christendom, by way of Arabic and Greek intermediaries, and much of it looked dangerous — an eternal cosmos with no beginning, a remote first mover indifferent to particulars, and an account of the intellect that seemed to leave no room for a personal immortal soul. The texts arrived freighted with the great Muslim commentators who had already digested them: Avicenna (Ibn Sina), whose emanationist metaphysics and distinction of essence from existence gave the Latins a vocabulary, and Averroes (Ibn Rushd), whose reading of the unity of the intellect across all humanity threatened the soul outright. This was the inheritance of the great twelfth-century translation movement centered on Toledo — Gerard of Cremona, Dominicus Gundissalinus, Michael Scot — that carried the philosophy of the falsafa tradition, alongside its Greek sources, into the Latin schools. The conservative response in Paris was to ban or quarantine the new learning: the Aristotelian books on nature were repeatedly prohibited in the arts faculty across the first half of the thirteenth century.

Aquinas took the harder road. He argued that reason rightly used and revelation rightly received cannot finally contradict, since both descend from the same divine source; a truth of philosophy and a truth of faith may differ in how they are known, but they cannot collide as truths. The slogan that organizes the whole project is that grace does not destroy nature but perfects it — and, in the same key, that the light of natural reason is itself a participation in the divine light, not a rival to it. To make the case he did the laborious thing: he wrote line-by-line commentaries on the Physics, the Metaphysics, the Nicomachean Ethics, the De Anima, the Posterior Analytics, and the Politics, working from the fresh, accurate translations of his Dominican confrère William of Moerbeke, so that the Latin West could read Aristotle close rather than at second hand. He was not baptizing a pagan; he was thinking with him, and against him where faith required.

The two Summae

His two great unfinished summaries set out the synthesis at length. The earlier, the Summa contra Gentiles (1259–1265), is the more apologetic in cast — four books that argue from reason as far as reason can go (the existence and nature of God, creation, providence) and then turn to the truths reason cannot reach unaided (the Trinity, the Incarnation, the sacraments, the last things). The later and greater, the Summa Theologiae (begun 1266 and left unfinished at his death), is a teaching architecture of staggering scale, built in the formal scholastic quaestio form: a question is posed, objections marshalled, a governing authority cited in the sed contra, the master’s own determination given in the respondeo, and each objection then answered in turn. Its three parts move in a great circle — from God and creation (the Prima Pars), out through the moral life of the rational creature returning to God (the Prima Secundae and Secunda Secundae), to Christ and the sacraments as the road back (the Tertia Pars) — the Neoplatonic figure of procession and return, exitus and reditus, recast in Aristotelian terms. He composed it not for masters but for beginners, and it became the most studied work of Christian theology after the Bible.

The metaphysics: being, essence, and existence

At the foundation lies a metaphysics of being. For Aquinas, God is not a being among other beings, not even the largest or first; God is being itself, ipsum esse subsistens, the sheer act of existing in which everything else participates. The hinge of the system is the real distinction, in every creature, between essence — what a thing is — and existence, the esse by which it actually is. A unicorn and a horse have intelligible essences; only the horse has existence added to its essence, received from elsewhere. In God alone essence and existence are identical: God does not have being, God is being. This distinction Aquinas inherited, through the Latin calque essentia / esse, from Avicenna’s mahiyya and wujud, transmitted via Gundissalinus to Albertus Magnus and then refined into a Thomistic cornerstone. From it follows the analogy of being: when one says God is good or wise, the words are used neither univocally (as if God’s goodness were the same in kind as a creature’s) nor equivocally (as if they shared only a sound), but analogically — what is called good in creatures preexists in God in a higher and unlimited mode, as effect resembles cause. This single move lets Aquinas speak of God meaningfully without collapsing the infinite distance between creator and creature, and it keeps company with the apophatic caution he drew from Pseudo-Dionysius: what God is exceeds what any name can capture.

The same Aristotelian grammar of act and potency, form and matter, runs through his account of the created world. Material things are composites of substantial form, the principle that makes a thing the kind of thing it is, and prime matter, pure potentiality with no character of its own. In a living body that substantial form is the soul, the first principle of life — and here Aquinas made one of his boldest and most contested moves. Against the older view that a human being is governed by a plurality of forms stacked one atop another, he held the unicity of substantial form: one soul, intellectual and sensitive and vegetative at once, is the single form of the whole substance. The human intellect knows the world not by innate Platonic vision but by abstracting the intelligible form from the images the senses supply — nothing is in the intellect that was not first in the senses — yet the soul’s power to grasp the universal, which has no bodily organ, shows it to be subsistent and immortal. Against Averroes he insisted that this intellect is the individual’s own, not a single shared mind in which all humanity participates: it is each person’s own understanding that survives each person’s own death.

The Five Ways

The best-known fragment of the system is the quinque viae, the five ways of demonstrating God’s existence, set out with great economy in the Summa Theologiae (Prima Pars, question 2, article 3). Aquinas holds that God’s existence is not self-evident to us and so must be shown from effects we do observe. The first way argues from motion: whatever is moved is moved by another, and the series cannot regress without end, so there must be a first unmoved mover. The second argues from efficient causation to a first cause. The third argues from contingency — that things able not to be cannot all be contingent, or nothing would now exist, so there must be a being necessary of itself. The fourth argues from the gradations of perfection in things to a maximum that is the cause of all lesser degrees. The fifth, the way from governance, argues that natural things without intelligence act toward ends, which requires an intelligent orderer. Each concludes with the same restrained formula — and this is what everyone calls God — claiming only the existence of a first principle, not yet the full God of revelation, whose attributes the following questions unfold.

Ethics, law, and the return to God

The middle of the Summa is a vast moral theology built on the conviction that the human being is made for an end. That end is beatitudo, complete happiness, which Aquinas locates not in any created good — wealth, honor, pleasure, even philosophical contemplation — but finally in the unmediated vision of God, the beatific vision, toward which the whole of human action is ordered. The road there runs through the virtues. The four cardinal virtues — prudence, justice, fortitude, temperance — perfect the natural powers and can be acquired by discipline; the three theological virtues — faith, hope, and charity — are infused by grace and orient the person toward an end exceeding nature’s reach. Here again grace perfects nature: the infused virtues do not replace the acquired ones but raise them.

Underwriting the moral order is the theory of law for which Aquinas is, after the Five Ways, most remembered. The eternal law is God’s own providential governance of all creation; the natural law is the rational creature’s distinctive participation in that eternal law — the light, set in the human mind, by which a person grasps the principles of right action. Its first and self-evident precept is that good is to be done and pursued and evil avoided; from it the further precepts unfold as reason reads off the inclinations of human nature toward life, society, and the knowledge of God. Human law is then a particular determination of the natural law by the practical reason of those who govern, and a human enactment that contradicts the natural law is, in the strict sense, no law at all but a corruption of law. This architecture made Aquinas the principal source of the later natural-law tradition in jurisprudence and political thought.

The Neoplatonic undercurrent

Against the strict Augustinian inwardness that preceded him — the world of Augustine’s divine illumination, where the mind sees truth only in God’s light — Aquinas grants the created order its own integrity and intelligibility: secondary causes really cause, nature really acts, and to honor the world’s own operations is to honor its maker. Yet the Neoplatonic current is present too, and he never disowned it. He read and commented on the works of Pseudo-Dionysius, especially the Divine Names, and his picture of God as the good from which all things flow and to which they return is the Dionysian exitus–reditus carried into the bones of the Summa. Most tellingly, he was the one who, having read William of Moerbeke’s freshly translated Proclus, recognized that the influential Liber de Causis — long circulated under Aristotle’s name — was in fact drawn from Proclus’s Elements of Theology, and said so in his commentary on it. The arch-Aristotelian was thus also the close reader who unmasked a Neoplatonic text hiding behind the Philosopher’s authority. The synthesis was never a flat Aristotelianism; it was Aristotle held within a frame of participation and emanation that owes as much to the Platonic line as to the Lyceum.

Contested authority, then triumph

His standing was not immediate. The very years of his Paris teaching saw the new Aristotelianism under fire. In 1270 the bishop of Paris, Étienne Tempier, condemned thirteen propositions associated with the radical Aristotelians of the arts faculty; in 1277, three years after Aquinas died, Tempier condemned a far wider net of 219 articles, aimed chiefly at the Averroism of figures such as Siger of Brabant — the eternity of the world, the unicity of the intellect, the notion of a double truth — but sweeping in, by collateral damage, some theses close to Aquinas’s own. In the same year Robert Kilwardby, the Dominican archbishop of Canterbury, condemned at Oxford the very Thomist doctrine of the unicity of substantial form. For a generation Thomism was one school among several, defended chiefly by his own order, contested by the Franciscan Bonaventure’s heirs and later by Duns Scotus and William of Ockham.

The tide turned. He was canonized by John XXII on July 18, 1323, and the canonization brought a quiet rehabilitation: in 1325 the bishop of Paris annulled the 1277 censures insofar as they touched the saint’s teaching. He was named a Doctor of the Church by Pius V in 1567 — the Doctor Angelicus — and at the Council of Trent his Summa is said to have lain open on the altar beside Scripture. In 1879 Leo XIII’s encyclical Aeterni Patris commended Thomism as the model for Catholic philosophy and made it normative in seminary and university, launching the Neo-Thomist revival that shaped Catholic intellectual life for the better part of a century. That endorsement has colored how he is read: as system-builder and arbiter more than as the contemplative he also was.

The straw

For the contemplative is recorded as well. On December 6, 1273, the feast of Saint Nicholas, after some experience while saying Mass at Naples, Aquinas stopped writing, leaving the Summa theologiae unfinished in its treatment of the sacrament of penance. His socius and confessor Reginald of Piperno pressed him to resume; according to the testimony later gathered for his canonization, he answered that he could write no more, for compared with what had been revealed to him everything he had written seemed to him like straw. He died a few months later, on March 7, 1274, at the Cistercian abbey of Fossanova, having collapsed on the journey north to the Second Council of Lyon. The report of the straw is later and shaped, in part, to the purposes of his cult; but it has clung to him with peculiar force — the most exhaustive of medieval reasoners, the man who had written more clear sentences about God than anyone before him, falling silent before something his reasoning could hold up to but not contain.

Texts and scholarship

The Latin corpus is edited critically in the Opera Omnia of the Leonine Commission, established by Leo XIII in 1880 and not yet complete; for the Summa Theologiae the earlier nineteenth-century Vivès Opera Omnia (Paris, 1871–1880), edited by Stanislas-Édouard Fretté and Paul Maré, and the Leonine editio of the Secunda Secundae (Rome, 1897), are both fully in the public domain and scanned in full. The standard English rendering is the Summa Theologica translated by the Fathers of the English Dominican Province (Benziger, New York, 1911–1925), principally the work of Laurence Shapcote, O.P., which is public domain in its first edition and freely available online through New Advent and the Christian Classics Ethereal Library. The fundamental modern biography is Jean-Pierre Torrell’s Saint Thomas Aquinas, Volume 1: The Person and His Work (Catholic University of America Press, 1996; rev. 2005), which reconstructs the chronology of the life and the works; Marie-Dominique Chenu’s Toward Understanding Saint Thomas (Henry Regnery, 1964) remains the classic introduction to reading him in his own terms. The metaphysics of esse received its decisive twentieth-century interpretation in Étienne Gilson’s The Christian Philosophy of St. Thomas Aquinas (Random House, 1956), and the question of essence and existence is treated philosophically in John F. Wippel’s The Metaphysical Thought of Thomas Aquinas (Catholic University of America Press, 2000). The single most influential catalyst of the Thomist revival, Leo XIII’s Aeterni Patris (1879), is the charter document of Neo-Thomism. His commentary on the Divine Names of Pseudo-Dionysius is best read alongside the Areopagite’s own text, available in the Parker translation hosted in the Library.

→ In the library: The Works of Dionysius the Areopagite (Parker, 1899)

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