The Summa Theologiae of Saint Thomas Aquinas (1265-1274)

The context: Thomas Aquinas and the pedagogical challenge of his time

When Thomas Aquinas begins the Summa around 1265, he is forty years old, and he teaches at Rome, at the Dominican convent of Santa Sabina, on the Aventine. The Dominican Roman province has charged him with organising a studium provinciale — an internal higher school of the order, intended for young friars who will not all go to Paris. This teaching is not academic in the Parisian sense: it is addressed to religious destined for preaching, confession and the care of souls.

It is precisely in this pedagogical context that Thomas conceives the Summa. The existing manuals do not satisfy him. The Four Books of Sentences of Peter Lombard had become, over the course of the 13th century, the reference manual of the theology faculties, through progressive use and not by a decree of the Fourth Lateran Council (1215); but their thematic structure — God, creatures, Incarnation, sacraments — remains fragmented. The earlier Summae (Sentences of Alexander of Hales, Summa Aurea of William of Auxerre, Summa de Bono of Albert the Great) are rich but imperfectly ordered^[5].

Thomas, in the prologue of his work, judges these works deficient for the incipientes, beginners in theology: multiplication of useless questions, articles, distinctions and arguments, an order dictated by occasion or by the chance of the commented text, and not by the subject matter itself; and tedious repetition^[6]. His project is therefore new: to rebuild all of theology according to an order intrinsic to the subject matter itself.

« Le docteur de la vérité catholique doit non seulement instruire les avancés, mais aussi former les commençants, selon la parole de l'Apôtre : « Comme à des enfants en Christ, je vous ai donné du lait à boire, non une nourriture solide » (1 Co 3, 1-2). Notre intention dans cet ouvrage est de présenter ce qui appartient à la religion chrétienne de la manière qui convient à l'instruction des commençants. » — Saint Thomas Aquinas, prologue of the Summa Theologiae, c. 1265-1266^[7]

Three cities, eight years: the chronology of composition

The Summa was written over eight years, in three successive cities, as Thomas moved according to the needs of the Dominican order and the decisions of the Holy See^[8]:

Thomas does not write alone. According to William of Tocco in his Ystoria (ch. 18), reporting the truthful testimony of Thomas's companion (socius), his students and his copyists, he dictated at the same time, in his room, to three scribes — sometimes four — texts on different subjects, which Tocco presents as a manifest miracle^[9]. His principal secretary is Brother Reginald of Piperno, his faithful companion since Orvieto, who remained at his bedside until his death and later compiled the Supplementum^[10].

The prologue: a new order for theology

Thomas's major innovation is architectonic in nature. Instead of following the order of Peter Lombard's Sentences (which had imposed on all theologians for a century a structure dictated by an external book), Thomas rebuilds theology according to a scheme he draws from Saint Augustine and systematises: everything starts from God as principle (Prima Pars), passes through the movement of the rational creature towards God through its acts (Secunda Pars), and is fulfilled in Christ as the way to God (Tertia Pars).

This scheme has a name: exitus et reditus — going forth from God and return to God. It is the great Neoplatonic meditation (Plotinus, Proclus) received by the Greek Fathers (Saint Dionysius the Areopagite), Christianised, and structured by Thomas into a complete rational architecture. « Parce que le but principal de cette doctrine sacrée est de communiquer la connaissance de Dieu, et non seulement en ce qu'il est en lui-même, mais aussi en tant qu'il est le principe et la fin des choses, et spécialement de la créature rationnelle, » writes Thomas, « nous traiterons d'abord de Dieu, ensuite du mouvement de la créature rationnelle vers Dieu, et enfin du Christ qui, en tant qu'homme, est notre voie pour aller vers Dieu. »^[11]

Overview: three parts, 512 questions, over 2,600 articles

The Summa is divided into three parts (partes), the second of which is itself subdivided into two sections. Here is the map of the whole^[12]:

The Summa properly so called — without the posthumous Supplementum — comprises 512 questions (119 + 114 + 189 + 90) distributed over about 2,669 articles, in which Thomas examines and resolves nearly 10,000 objections^[13]. With the Supplementum (99 questions compiled by Reginald of Piperno), the whole reaches 611 questions — 612 according to the count of the Catholic Encyclopedia, which counts one subdivision — and about 3,120 articles^[14]. No other theological work of the medieval West attains this synthetic scope.

The Trinitarian rhythm: exitus, motus, reditus

The great architectural beauty of the Summa is its intentional Trinitarian structure, which is not a scholastic grid but a Christian meditation on the mystery of God and the return to him:

• Prima Pars — God as principle: one starts from the summit (God in himself, his simplicity, his Trinity), and descends through creation (angels and men). The doctrine of God is treated first not because it would be obvious, but because it grounds all theological intelligibility.
• Secunda Pars — man on the way to God: the rational creature, created in the image of God, acts to attain the end for which it is made. This part is by far the most voluminous (303 questions out of 512) because the moral and spiritual life is the proper object of Dominican preaching. It is divided into the Prima Secundae (general principles of human acts) and the Secunda Secundae (application to the particular virtues).
• Tertia Pars — Christ as the way: the return to God is possible only through the incarnate Word, and through the sacraments which prolong in the Church the work of the Incarnation and the Redemption.

It is this ordering that leads the Dominican historian Marie-Dominique Chenu to say that the Summa is not an "extended catechism" but a theologal work in the strong sense: an understanding of the faith that unfolds according to the very movement of God towards the creature and of the creature towards God^[15].

Anatomy of an article: the scholastic quaestio

Each question (quaestio) treats a theme (for example: "De l'existence de Dieu", Ia, q. 2) and is divided into articles (articuli), each posing a precise sub-question. The structure of an article follows a rigorous scholastic logic, inherited from the university disputatio and systematised by Thomas^[16]:

1. Interrogative title — always in the form Utrum..., « Si oui ou non... ». Example: « Utrum Deus sit », « Si Dieu existe » (Ia, q. 2, a. 3).
2. Videtur quod... — « Il semble que (oui ou non)... »: statement of the objections in their strongest version, generally three or four. Thomas himself formulates the adversarial arguments, sometimes better than his adversaries.
3. Sed contra... — « Mais au contraire... »: a contrary authority (Scripture, Father of the Church, recognised philosopher) which contradicts the objections and orients the solution.
4. Respondeo dicendum quod... — « Je réponds qu'il faut dire... »: the body of the article, Thomas's positive and personal exposition, which establishes the doctrine.
5. Ad primum, ad secundum, ad tertium... — resolution objection by objection, showing why each adversarial argument was insufficient, leaving nothing unanswered.

This method has an unequalled pedagogical virtue: it teaches the reader to think the difficulty through before the solution, to steelman the adversary before answering. A quick reading of the Summa may give the impression of formal rigidity; an attentive reading reveals that in each article Thomas reformulates the best arguments against his own thesis — and resolves them without evasion.

This probity in objection — formulating it at its strongest before resolving it — is one of the reasons why Étienne Gilson's Thomisme remains, since its first edition in 1919, the French reference introduction to the thought of Thomas^[17].

The sources brought to bear

The Summa is also remarkable for the density and diversity of its sources. For each article, Thomas summons:

• Sacred Scripture as the first source (through the sed contra and the bodies of articles). Thomas cites the Bible in about 9,000 occurrences throughout his work.
• The Fathers of the Church: Saint Augustine in the first rank (cited more than 5,000 times in the Summa), Saint Jerome, Saint Gregory the Great, Saint Ambrose, Saint John Damascene, Pseudo-Dionysius the Areopagite, Saint Anselm.
• The pagan philosophers: above all Aristotle (whom Thomas simply calls Philosophus, « le Philosophe »), but also Plato, Cicero, Seneca, Boethius.
• The Muslim and Jewish commentators on Aristotle: Avicenna (Ibn Sina), Averroes (Ibn Rushd) — often corrected, sometimes followed —, and Maimonides (Moses Maimonides, the Rabbi Moyses).
• The medieval canonists and theologians: Peter Lombard, Hugh of Saint-Victor, Bernard of Clairvaux, Albert the Great (Thomas's master).

This synthesis — Scripture, Fathers, Aristotle, the Arab-Muslim, Jewish and Latin worlds — is without equivalent in the history of Western thought. Thomas receives the whole of the received tradition and reorders it in a single movement.

The five ways: rationally demonstrating God's existence

At the very beginning of the Prima Pars, after establishing that theology is a science (q. 1), Thomas poses the fundamental question: « Utrum Deus sit » — does God exist? (Ia, q. 2, a. 3). He answers it with the famous five ways (quinque viae), rational proofs of God's existence founded on the observation of the sensible world. Thomas does not hold Saint Anselm's ontological proof to be rigorously valid; he prefers an a posteriori approach, which starts from what the senses know and ascends towards the cause^[18].

Here are the five ways, as Thomas sets them out:

1. First way — from motion: whatever is in motion is moved by another. One must ascend to a first unmoved mover, « et tous comprennent que c'est Dieu ». Argument drawn from Aristotle (Physics VIII).
2. Second way — from efficient causality: one cannot ascend to infinity in the chain of efficient causes. There must be a first efficient cause, to which all give the name of God. An equally Aristotelian argument.
3. Third way — from the contingent and the necessary: the things of the world can be or not be; hence if everything were contingent, there could have been a moment when nothing existed, and then nothing would exist now. There must be a being necessary through itself. Argument enriched by Avicenna and Maimonides.
4. Fourth way — from degrees of perfection: we observe degrees (more or less good, more or less true, more or less noble). Now degrees refer to a maximum which is the cause of the others. There is therefore a supremely true, good, noble being: God. An argument of predominantly Platonic and Augustinian character.
5. Fifth way — from finality: things devoid of intelligence act towards an end with regularity, which supposes an intelligent being ordering nature. « C'est ce qu'on nomme Dieu. » A major teleological argument.

« La première voie, la plus manifeste, est tirée du mouvement. Il est certain et constant aux sens que dans le monde, des choses sont mues. Or, tout ce qui est mû est mû par autre chose... Il est donc nécessaire d'arriver à quelque premier moteur qui n'est mû par rien, et tous comprennent que c'est Dieu. » — Saint Thomas Aquinas, Summa Theologiae, Ia, q. 2, a. 3, body of the article^[19]

These five ways do not demonstrate a complete Christian God (Trinitarian, free creator, incarnate). They establish rationally, from the sensible world, that an ultimate being exists and that it has at least these five attributes. The rest — Trinity, free creation, Incarnation — belongs to Revelation, which Thomas then receives in the same Summa. Rational demonstration is therefore not a rival of faith; it prepares the ground on which faith can unfold without contradiction.

The divine attributes: simplicity, perfection, infinity

After establishing that God is (Ia, q. 2), Thomas examines what he is (Ia, qq. 3-26) — more exactly, what he is not, since the divine being escapes all direct positive grasp. He develops the negative attributes (God is not composed, has no body, is not in time) before being able to predicate by analogy positive perfections (goodness, truth, life, justice, mercy).

At the heart of this section stands a decisive metaphysical thesis — the real distinction between essence and existence. Every creature is composed of an essence (what it is) and an existence (the fact that it is). These two principles do not coincide: a man may cease to exist without ceasing to be a man in his essence. But in God alone, essence and existence are identical. God is subsistent Being itself (ipsum esse subsistens) — he is his existence (Ia, q. 3, a. 4)^[20]. It is the metaphysical explanation of the name revealed to Moses at the burning bush: "I am who am" (Ex 3:14). All subsequent Christian metaphysics — down to Étienne Gilson in the 20th century — meditated on this identification.

The Trinity, creation, the angels, man

The Prima Pars continues with:

• The Trinity (qq. 27-43): processions, relations, missions of the divine Persons. Thomas takes up and synthesises the whole patristic tradition (Augustine, Cappadocians, Damascene).
• Creation (qq. 44-49): God as first cause, creatio ex nihilo, distinction between creation and conservation, goodness of creation and the problem of evil.
• The angels (qq. 50-64) — a long treatise in which Thomas, following Pseudo-Dionysius, ranks the nine angelic choirs, and examines their mode of knowledge and their free choice. This density long surprised readers; it is explained because the angels are the purae substantiae intellectuales — the created archetype of all non-sensible knowledge.
• Man (qq. 75-102): the subsistent spiritual soul (q. 75), the substantial union of soul and body (q. 76), the faculties (intellect, will, sensibility), the state of innocence before the fall.

It is in question 75 that Thomas refutes Platonism (the soul is not a complete substance shut up in a body like a pilot in his ship) and Averroism (the agent intellect is not numerically separate, one for all mankind). His solution: the human soul is the substantial form of the body, the principle of unity of a single composite. It is Aristotelian hylomorphism, taken up and Christianised^[21]. This doctrine became dogma at the Council of Vienne in 1311-1312 — direct proof of Thomas's magisterial influence less than forty years after his death.

The Prima Secundae: general principles

The Prima Secundae (Ia-IIae, 114 questions) treats the common principles of all human acts. It is, in Thomas's work, the great treatise of moral anthropology.

The starting point is beatitude (qq. 1-5): man's last end. Taking up Aristotle, Thomas shows that man necessarily seeks an end — he does not act without reason — and that all partial ends are subordinated to an ultimate end. This end can be neither riches, nor honour, nor glory, nor power, nor health, nor pleasure, nor even a created good: only the beatific vision of God, that is, the immediate knowledge of the divine essence in Heaven, can fill the unlimited desire of the human intellect and will (q. 3, a. 8).

Thomas then examines, in a rigorous order:

• Human acts in the strict sense (qq. 6-21): voluntary, free, imputable, distinct from acts merely of man (digesting, growing old).
• The passions (qq. 22-48): love, desire, joy, sorrow, hope, fear, daring, anger — eleven passions classified according to the concupiscible and the irascible. Thomas rehabilitates the passions against a certain Stoic dualism: they are not bad in themselves, but orderable.
• Habits (qq. 49-54): stable qualities inclining to act well or badly.
• The virtues (qq. 55-67) and the vices (qq. 71-89), opposed genera of habits.
• Law (qq. 90-108): a full treatise in its own right, on the nature and types of law.
• Grace (qq. 109-114): the conclusion opening onto the work of Christ.

Natural law: participation in the eternal law

In the Treatise on Law (Ia-IIae, qq. 90-108), Thomas distinguishes four laws: eternal, natural, human and divine. The eternal law is God's reason governing the world; the natural law is the participation of this eternal law in the rational creature (q. 91, a. 2). Every man, as a rational being, bears engraved within him first precepts — good must be done and pursued, evil avoided (q. 94, a. 2) — which dictate the fundamental human goods: preserving one's life, transmitting life, living in society, knowing God, attaining truth.

This doctrine of natural law, inherited from Saint Paul (Rom 2:14-15), Saint Augustine and Roman law (Cicero), is the philosophical framework of the modern social teaching of the Church. Leo XIII (Rerum Novarum, 1891), Pius XI (Quadragesimo Anno, 1931), John XXIII (Pacem in Terris, 1963), Paul VI (Humanae Vitae, 1968), John Paul II (Veritatis Splendor, 1993), Benedict XVI (Caritas in Veritate, 2009) mobilise it directly. The whole contemporary debate on bioethics, marriage, abortion or the death penalty takes root in it.

The Secunda Secundae: the virtues in detail

The Secunda Secundae (IIa-IIae, 189 questions) is the most voluminous section of the Summa. It examines the virtues in their proper content, one after another — for the Dominican pastoral ministry of preaching and confession, a practical manual of unequalled precision.

Thomas follows a rigorous scheme for each virtue: nature, subject (which human faculty receives it), proper object, opposed vices (by defect and by excess), corresponding gifts of the Holy Spirit, beatitudes and fruits attached to it. This precision is why the Secunda Secundae remains, seven centuries later, the moral compass of Catholic theology. The Catechism of the Catholic Church (1992), at §§1803-1845, structures its treatise on the virtues directly on this Thomist scheme.

The incarnate Word, the way to God

The Tertia Pars opens with a major question (q. 1, a. 1): « Convenait-il que Dieu s'incarne ? ». Thomas answers with the beauty of the divine order: it was fitting that the Supreme Good communicate itself, and the highest communication is the union of a human nature to the Person of the Word.

There follows a christological treatise of impressive density (qq. 1-59):

• The hypostatic union (qq. 2-15): two natures, divine and human, in a single Person; Thomas follows Chalcedon (451) against Eutyches and Nestorius.
• The properties of Christ (qq. 16-26): capital grace, holiness, knowledge (Thomas attributes to the man Christ beatific knowledge from conception), power.
• The mysteries of Christ's life (qq. 27-59): the Virgin Mary (her Immaculate Conception is not yet dogmatically defined, Thomas remains nuanced), childhood, public life, passion (qq. 46-52, a capital treatise on Redemption as satisfaction), resurrection, ascension, second coming.

On the Redemption, Thomas develops and refines the doctrine of Saint Anselm (Cur Deus homo, c. 1098): Christ redeems mankind through his Passion as satisfaction offered to the Father's justice, in our name. But Thomas tempers Anselm: satisfaction was not strictly necessary (God could have forgiven without it), it is fitting to divine wisdom and mercy (q. 46, aa. 2-3). This finesse is characteristic.

The sacraments and the great treatise on the Eucharist

The second great section of the Tertia Pars (qq. 60-90) treats the sacraments. Thomas systematises the notion: a sacrament is a signum sensibile rei sacrae quatenus est sanctificans homines — a sensible sign of sacred reality insofar as it sanctifies men (q. 60, a. 2).

He then develops each sacrament (baptism, confirmation, Eucharist, penance — the four completed treatises) with its matter, form, minister and effects. The Eucharist receives the longest and deepest treatment (qq. 73-83): Thomas sets out there the doctrine of transubstantiation (q. 75), taken up from the Fourth Lateran Council (1215). The substance of bread and wine is converted wholly into the substance of the Body and Blood of Christ; only the sensible species (appearance, taste, physical properties) remain^[22]. It is this analysis which was retained at session XIII of the Council of Trent (1551, Decretum de SS. Eucharistia, ch. 4 and can. 2)^[23].

« Cette conversion, qui a lieu dans le sacrement de l'autel, ne peut être saisie ni par les sens, ni par l'imagination, mais par l'intellect seul, soutenu par la foi divine. C'est pourquoi saint Cyrille dit : « Ne doute pas que cela soit vrai, mais accueille plutôt avec foi les paroles du Sauveur, car comme il est la Vérité, il ne ment pas. » » — Saint Thomas Aquinas, Summa Theologiae, IIIa, q. 75, a. 1, body of the article^[24]

It is also to Thomas that we owe, outside the Summa, the great Eucharistic hymns — Adoro Te devote, Pange lingua, Lauda Sion, Tantum Ergo — composed for the feast of Corpus Christi instituted by Urban IV in 1264.

The interruption: 6 December 1273 at Naples

Thomas does not finish his work. On 6 December 1273, feast of Saint Nicholas, in the chapel of Saint Nicholas of the Dominican convent of Naples, as he celebrates Mass, something happens within him. He then remains strangely silent. Reginald of Piperno, his secretary and companion, seeing that Thomas does not resume dictation, presses him to continue. Thomas refuses. Reginald insists. Thomas finally answers with this phrase, which has become famous^[25]:

« Je ne puis plus écrire. Tout ce que j'ai écrit me semble paille à côté de ce que j'ai vu et qui m'a été révélé. » — « Non possum, quia omnia, quae scripsi, videntur mihi paleae respectu eorum, quae vidi et revelata sunt mihi. » — Saint Thomas Aquinas, words reported by Reginald of Piperno, testimony of Bartolomeo da Capua at the canonisation trial, Naples, 1319^[26]

This saying — « mihi videtur ut palea » — has spilt much ink. Three classic interpretations:

1. Mystical interpretation: Thomas received a direct vision of God (intuitive vision, raptus), which showed him the radical inadequacy of all theological language. This reading is that of most ancient biographers (William of Tocco, Bartolomeo da Capua) and of the Dominican tradition.
2. Medical interpretation: Thomas is said to have suffered a cerebral accident or total exhaustion (the historian J.-P. Torrell mentions it without deciding); his silence would be pathological. This reading, defended by some moderns, is a minority one and contested.
3. Theological interpretation: Thomas, having reached the highest threshold of his meditation on the sacraments and on Christ, perceives that all theology remains mortgaged on the beatific vision, and that his 2,000 articles are but a stammering approach to what will be given face to face.

Whatever interpretation is retained, the fact remains: Thomas writes not one more line of the Summa after this date. The Tertia Pars stops at question 90, in the treatise on penance, before the questions on extreme unction, holy orders, marriage, the resurrection and eternal life, which were to close the work. The author's silence speaks as loudly as his words.

The Supplementum: posthumous compilation by Reginald of Piperno

After Thomas's death, his Dominican brethren, and particularly Reginald of Piperno, judge that the unfinished work cannot remain as such. Sacramental theology (extreme unction, holy orders, marriage) and eschatology (resurrection, judgement, heaven, hell, purgatory) are indispensable to a complete manual of Catholic doctrine. Reginald then compiles, from Thomas's youthful commentary on the Sentences of Peter Lombard (written between 1254 and 1256), a sequel to the Tertia Pars. It is the Supplementum (Supplementum tertiae partis), 99 questions^[27].

This Supplementum is therefore not, properly speaking, from the hand of the mature Thomas — it takes up the Thomas of thirty, still strongly marked by the structure of the Sentences. Later theologians always carefully distinguish it from the body of the Summa. But it circulated in medieval manuscripts with it, and all modern printed editions (including the Leonine) include it.

The first challenges: Étienne Tempier (1277) and John Pecham (1284)

Three years after Thomas's death, on 7 March 1277 — by a troubling coincidence, the anniversary of his death — the bishop of Paris Étienne Tempier promulgates a condemnation of 219 philosophical and theological propositions taught in the Paris faculty of arts. The main target is the Latin Averroism of the secular masters (Siger of Brabant, Boethius of Dacia). But a few articles indirectly touch Thomist theses, notably the unicity of the substantial form in man (corollary of hylomorphism), or the doctrine of individuation by matter^[28].

The condemnation creates a climate of suspicion around Thomas. At Oxford, on 30 October 1284, the Franciscan archbishop John Pecham, primate of England, renews earlier condemnations of his predecessor Robert Kilwardby and explicitly targets Thomist theses (substantial form, Eucharist, intellect). These censures provoke a powerful Dominican reaction: William de la Mare (a Franciscan) writes a Correctorium fratris Thomae, and several Dominicans answer with Correctoria corruptorii^[29].

The situation quickly reverses. On 14 February 1325, Étienne Bourret, bishop of Paris, repeals the portion of the 1277 condemnation that targeted Thomas, « en tant qu'elle paraissait toucher ou affecter sa doctrine ». Two years earlier, Thomas had been canonised: a canonised saint could no longer be condemned. The way was open for the full magisterial recognition of the Summa.

Canonisation by John XXII (1323) and the Neapolitan trial

Thomas was canonised on 18 July 1323 at Avignon by Pope John XXII, forty-nine years after his death. The cause was instructed by two great inquiries: a first at Naples in 1319, where dozens of witnesses were heard (Dominican friars of Saint Dominic of Naples, relatives, neighbours, servants who had known Thomas); a second at Fossanova from 10 to 27 November 1319, on the very place of his death, to question the Cistercian monks who had assisted Thomas in his last days^[30].

At the Neapolitan trial, a decisive witness intervenes: Bartolomeo da Capua, archbishop of Capua, logothete of the kingdom of Naples, who had gathered from the very mouth of Reginald of Piperno (died 1290) the account of the vision of 6 December 1273. It is through him that the phrase « mihi videtur ut palea » is officially recorded^[31].

The year 1323 thus marks the official end of suspicions. Thomas is not only orthodox; he is a saint. His doctrine can henceforth circulate as a positive reference throughout the Church.

Saint Pius V: Doctor of the Church in 1567

After the Council of Trent (1545-1563), which marks the great dogmatic ordering of the Church in the face of the Protestant Reformation, the Dominican Saint Pius V (Michele Ghislieri, pope from 1566 to 1572) performs two decisive acts for Thomas:

• 11 April 1567 — By the bull Mirabilis Deus, he proclaims Thomas Aquinas Doctor of the universal Church^[32]. After the four great Latin doctors (Ambrose, Jerome, Augustine, Gregory the Great) and the great Greek Fathers, this is one of the first additions to this restricted college. The title is not honorary: it means that Thomas is recognised as a doctrinal authority of reference for the whole Church.
• 1570 — Pius V has published at Rome the first great official edition of the complete works of Thomas, the Editio Piana (17 in-folio volumes), produced by the Dominicans at the convent of the Minerva.

The effect is immense. All of post-Tridentine scholasticism — the great commentators Cajetan (1469-1534), Francis of Vitoria (1483-1546), Domingo Bañez (1528-1604), Francisco Suárez (1548-1617) — gravitates around the Summa as its reference text. The moral and sacramental theology of Trent, the teaching of the Society of Jesus and that of the great Catholic universities (Salamanca, Coimbra, Louvain) make it their framework.

The Summa at the Council of Trent: tradition and historical reality

A tradition reported by Leo XIII in Aeterni Patris (1879) holds that the Fathers of the Council of Trent, when debating in session, placed Thomas Aquinas's Summa on the altar — beside Sacred Scripture and the pontifical decrees — to seek counsel and reasons there^[33]:

« C'est un éloge unique de Thomas, et qu'il ne partage avec aucun autre docteur catholique, que les Pères de Trente, au cœur de leur assemblée, aient voulu, avec les livres de l'Écriture divine et les décrets des Souverains Pontifes, exposer sur l'autel même la Somme de Thomas d'Aquin, pour y demander conseils, raisons, oracles. » — Leo XIII, encyclical Aeterni Patris, 4 August 1879^[34]

Modern historians nuance this tradition. No contemporary conciliar document (1545-1563) explicitly mentions such a ritual; the first written attestation dates from the mid-17th century, nearly a century after the council. What is documentarily certain, on the other hand, is that the Summa is constantly cited and discussed at the council, particularly at sessions XIII (Eucharist, 1551), XIV (Penance, 1551) and XXII (Mass, 1562)^[35].

Whether the account is literal or symbolic, its scope remains: Trent thought out its doctrine in constant dialogue with Thomas, and this authority recognised by the conciliar Fathers grounds the later magisterial place of the Summa.

Leo XIII and Aeterni Patris (1879): the neo-Thomist turning point

The 19th-century Catholic world is crossed by a philosophical crisis: rationalism, the positivism of Auguste Comte, German idealism, Marxian materialism, political liberalism seek to emancipate reason from all revealed authority. Catholic theology, divided between ontologism, traditionalism and fideism, struggles to articulate a coherent answer. It is in this context that Leo XIII (Gioacchino Pecci, pope from 1878 to 1903), elected pope with a solid Thomist formation, takes a major decision: to restore in all Catholic schools the philosophy of Saint Thomas as a common intellectual tool.

The encyclical Aeterni Patris of 4 August 1879 is the manifesto of this programme. Leo XIII presents Thomas there as « prince et maître de tous les docteurs scolastiques », having « vénéré au plus haut point les anciens docteurs sacrés » and having « hérité en quelque sorte de l'intelligence de tous »^[36]. The encyclical asks that Thomist doctrine be taught in all Catholic faculties of philosophy and theology.

In practice, there followed:

• 15 October 1879: creation of the Pontifical Academy of Saint Thomas Aquinas (Pontificia Academia Sancti Thomae Aquinatis).
• 18 January 1880: by the motu proprio Placere nobis, Leo XIII officially launches the Editio Leonina, the critical edition of the complete works of Thomas (first volume published in 1882) — a monumental project entrusted to an international Dominican commission (still in progress in 2026 — see below)^[37].
• 4 August 1880: by the brief Cum hoc sit, Thomas is proclaimed patron of all Catholic schools, universities and colleges^[38].

This movement, which would be called neo-Thomism or the Thomist revival, produced in the 20th century major intellectual figures: Reginald Garrigou-Lagrange (1877-1964), Jacques Maritain (1882-1973), Étienne Gilson (1884-1978), Cornelio Fabro (1911-1995), Josef Pieper (1904-1997), Edith Stein (1891-1942, Saint Teresa Benedicta of the Cross). The Second Vatican Council was prepared by these men.

Pius XI and Studiorum Ducem (1923): 600 years after the canonisation

On 29 June 1923, on the occasion of the sixth centenary of Thomas's canonisation (1323-1923, jubilee year), Pope Pius XI (Achille Ratti) publishes the encyclical Studiorum Ducem — « le guide des études ». The document confirms and radicalises Aeterni Patris. Pius XI declares that Thomas did not only teach a doctrine; he shaped Catholic theological method itself^[39].

The encyclical goes further on one decisive point: it affirms that Thomist doctrine is certissimum studiorum ducem — « le très sûr guide des études » — and that it must be followed religiose (religiously) in the formation of priests. It is the summit of magisterial Thomism. The Code of Canon Law of 1917 (canon 1366 §2) had already imposed in obligatory terms on seminaries to « suivre la méthode, la doctrine et les principes du Docteur angélique ». Studiorum Ducem confirms its necessity.

The two Codes of Canon Law (1917 and 1983)

Thomist teaching becomes a canonical norm:

• 1917 Code — canon 1366 §2: « Les professeurs traiteront les matières de la philosophie rationnelle, de la théologie ainsi que la formation des élèves dans ces sciences selon la méthode, la doctrine et les principes du Docteur angélique, et ils s'y attacheront religieusement. » An obligatory formulation.
• 1983 Code — canon 252 §3: « Les disciplines de la théologie dogmatique, fondées toujours sur la parole de Dieu écrite ainsi que sur la tradition sacrée, seront enseignées de telle sorte que les étudiants en pénètrent les mystères du salut, surtout par la spéculation, ayant saint Thomas pour maître. » A somewhat softened formulation (theological pluralism is more recognised), but Thomas remains the master par excellence.

Vatican II, in the decree on priestly formation Optatam Totius (28 October 1965, no. 16), had made the spirit explicit: Thomas remains the guide, but in open dialogue with other traditions, and in connection with contemporary problems.

John Paul II and Fides et Ratio (1998)

Nearly one hundred and twenty years after Aeterni Patris, John Paul II returns to Thomas in his encyclical Fides et Ratio of 14 September 1998, devoted to the relations between faith and reason. In §43, the pope devotes a particular development to Thomas:

« Sur ce long chemin, saint Thomas occupe une place toute particulière, non seulement pour le contenu de sa doctrine, mais aussi pour le dialogue qu'il sut instaurer avec la pensée arabe et la pensée juive de son temps. [...] il eut le grand mérite de mettre au premier plan l'harmonie qui existe entre la raison et la foi. La lumière de la raison et celle de la foi viennent toutes deux de Dieu ; c'est pourquoi elles ne peuvent se contredire. » — Saint John Paul II, encyclical Fides et Ratio, 14 September 1998, no. 43^[40]

The pope then stresses Thomas's double merit: autonomy of philosophical reason (which can seek truth by its own powers) and harmony with faith (which reason receives as a higher light that does not contradict it). It is the antidote, says John Paul II, to the double modern temptation: fideism which despises reason, and rationalism which rejects Revelation. This synthesis is precisely what Thomas built in the Summa.

Faith and reason: harmony without confusion

The central Thomist doctrine, perhaps the most relevant today, is the harmony between faith and reason. Thomas refuses the three extreme positions of his time:

1. Late Augustinian fideism which recognises no autonomy for reason outside faith (Augustinian school).
2. Latin Averroism which radically separates reason and faith (the theory of « double vérité », condemned at Paris in 1277).
3. Stoic or Platonic rationalism which reduces faith to natural reason.

Thomas proposes instead a distinction without separation: natural reason can know God as first principle, demonstrate his existence (five ways), attain certain moral truths (natural law), recognise preambles of faith (existence of a creator God, immortality of the soul). Faith, for its part, accedes to mysteries which reason could not discover by its own powers (Trinity, Incarnation, Redemption, eternal life). But these two orders never contradict each other, for both come from the same God, source of all truth (Ia, q. 1, a. 6 and q. 1, a. 8).

« La grâce ne supprime pas la nature, mais la porte à son achèvement. » — « Gratia non tollit naturam, sed perficit. » — Saint Thomas Aquinas, Summa Theologiae, Ia, q. 1, a. 8, ad 2^[41]

Essence and existence: the metaphysics of being

The metaphysical heart of the Summa, what distinguishes it from all other scholasticisms (Bonaventure, Duns Scotus, Ockham), is the doctrine of the relation between essence and existence. For Thomas, in every creature there is a real composition between the essence (essentia, what a thing is) and the act of existing (actus essendi or esse, the fact that it is). Essence is in potency; existence actualises it.

In God alone, essence and existence are identical. God is Esse itself subsisting — pure Being, without composition, without potentiality, without becoming. This doctrine is what Étienne Gilson called Thomist existentialism: the primacy of the act of being over every essence, in answer to Neoplatonism which placed essence (the Form, the Idea) before being^[42].

This metaphysics has two major theological consequences:

• The analogy of being: there is a proportional likeness between the being of the creature and the being of God — not univocity (otherwise God would be in the same genus as creatures), not equivocity (otherwise we could say nothing of God), but analogy. It is this doctrine which the Rhenish mystics (Eckhart, Tauler, Suso) prolonged and which Erich Przywara meditated in the 20th century in his great work Analogia Entis.
• Creation as communication of being: the creature receives its being from God at each instant. Creation is not an initial act then stopped; it is a permanent dependence, called conservation. If God ceased for an instant to communicate being to the creature, it would fall back into nothingness.

Natural law and Christian morality

The whole Secunda Pars deploys a morality which is reduced neither to an ethics of rules (Kant, deontologism) nor to an ethics of consequences (utilitarianism) nor to an ethics of subjective fulfilment (modern eudemonism). It is a morality of virtues anchored in:

• A precise anthropology (man as a composite of soul and body, free, ordered to beatitude).
• A universal natural law (inscribed in human nature, accessible to reason).
• Virtues acquired by exercise (cardinal virtues) and infused by grace (theological virtues).
• A transcendent last end (beatific vision of God).

It is this scheme which the Catechism of the Catholic Church (1992) takes up integrally at §§1700-2557 (third part on life in Christ). It underlies the moral teaching of John Paul II in Veritatis Splendor (1993) and Evangelium Vitae (1995).

Transubstantiation and the sacraments

On sacramental ground, Thomas definitively formulates the doctrine which Trent confirmed. Transubstantiation (IIIa, q. 75) is the real, substantial and total conversion of bread and wine into the Body and Blood of Christ — the species (appearance, taste, colour, dimensions) remaining as accidents without their own substance, sustained by divine power. This doctrine is not only preserved but proclaimed dogmatically by Trent in 1551 (session XIII)^[43].

« Quand toute la substance du pain est convertie en toute la substance du Corps du Christ, et toute la substance du vin en toute la substance du Sang du Christ, cette conversion n'est pas formelle, mais substantielle. Elle n'est pas inscrite dans les genres du changement naturel, et peut être appelée par un nom propre : transsubstantiation. » — Saint Thomas Aquinas, Summa Theologiae, IIIa, q. 75, a. 4, body of the article^[44]

Three great schools, three centuries of commentary

Immediately after his canonisation (1323), the Summa becomes a commented text. Three great traditions stand out:

Classical Dominican tradition (15th-16th century) — The mother-commentaries:

• Cajetan (Thomas de Vio, 1469-1534): line-by-line commentary on the Summa, integrated into the Editio Leonina in 1888-1906. The most used until the 20th century.
• Capreolus (John Capreolus, c. 1380-1444): his Defensiones theologiae is a defence of Thomas against the attacks of Duns Scotus, Ockham and their pupils.
• Sylvester of Ferrara (Francesco Silvestri, 1474-1528): commentary on the Summa contra Gentiles.

School of Salamanca (16th century) — Hispanic Thomist renewal:

• Francis of Vitoria (1483-1546): founder of the modern thought of international law from the Secunda Secundae on justice and war.
• Domingo Bañez (1528-1604): confessor of Saint Teresa of Avila, great Thomist, opposed to Molina on grace.
• Cano, Soto, Carranza: other major figures.

Jesuit school (16th-17th century) — Inflected Thomism:

• Francisco Suárez (1548-1617): Disputationes Metaphysicae (1597), systematic reformulation of Thomist metaphysics, which durably influenced the Schools and even Leibniz and Wolff.
• Luis de Molina (1535-1600): doctrine of scientia media (middle knowledge) to resolve the problem of liberty and grace — divergence from the strict Bañezian reading.

Twentieth-century renewal: Garrigou-Lagrange, Gilson, Maritain

With the neo-Thomist relaunch begun by Leo XIII, the 20th century sees a new generation flourish:

• Reginald Garrigou-Lagrange OP (1877-1964) — professor at the Angelicum (Rome). His systematic treatises (La Synthèse thomiste, Le Sens commun) are the classical neo-Thomist reference. He trains a whole generation of theologians, including the future John Paul II.
• Étienne Gilson (1884-1978) — French historian and metaphysician, founder of the Institute of Mediaeval Studies of Toronto. His Thomisme (1st ed. 1919, 6th ed. 1965) remains the great French introduction to Thomas. His rediscovery of the actus essendi marks all existentialist Thomism.
• Jacques Maritain (1882-1973) — philosopher converted by Léon Bloy, who mobilises Thomas to think democracy, art, scientific knowledge (Distinguer pour unir, 1932), human rights.
• Cornelio Fabro (1911-1995) — Italian Stigmatine, rediscovers the doctrine of participation in Thomas (La nozione metafisica di partecipazione secondo S. Tommaso d'Aquino, 1939).
• Marie-Dominique Chenu OP (1895-1990) and Yves Congar OP (1904-1995) — French Thomists, pioneers of a historical reading of Thomas, and intellectual architects of the Second Vatican Council.

These readings nourished the drafting of Vatican II (1962-1965), most particularly the constitutions Lumen Gentium (Church), Dei Verbum (Revelation) and Gaudium et Spes (Church in the world).

Contemporary Thomists

The tradition continues. Let us cite notably:

• Servais Pinckaers OP (1925-2008) — Fribourg moralist, return to the Secunda Pars against post-Tridentine "casuistic" morality.
• Jean-Pierre Torrell OP — Initiation à saint Thomas d'Aquin (Cerf, 1993, re-ed. 2002, 2008), the French reference biography.
• Eleonore Stump (Saint Louis University) — analytical Thomist, Aquinas (Routledge, 2003).
• Edward Feser — contemporary Thomist apologist, defender of the five ways in analytical philosophy (Aquinas, 2009; Five Proofs of the Existence of God, 2017).

The Editio Leonina: a 140-year worksite

When Leo XIII commissions, in 1879, the critical edition of Thomas's Opera Omnia — the Editio Leonina, whose first volume appeared in 1882 — the aim is to establish, from the medieval manuscripts, the purest possible text of each work, and to replace the disparate printed editions (Piana 1570, Parmensis 1852-1873). It is the Thomist equivalent of the great critical editions of Aristotle (Bekker, Berlin 1831), Plato (Stephanus 1578), the Greek and Latin Fathers (Migne, Patrology 1844-1864), Scripture (Nestle-Aland)^[45].

For the Summa Theologiae specifically, the Leonine edition occupies volumes IV to XII (nine in-folio volumes), published between 1888 and 1906. These volumes include not only Thomas's text, but also Cajetan's commentary set alongside — the « Summa cum Commentariis » which still circulates today in all Thomist libraries.

The Leonine edition is not criticism in the strict sense of the modern word (the critical apparatus is lighter than in current editions of classical texts), but it remains the reference text for all serious Thomist studies. The Commissio Leonina, founded at Rome in 1880 and transferred to Paris since 2012, pursues its work on Thomas's other works (biblical commentaries, Quaestiones disputatae, Quaestiones Quodlibetales) — a worksite which, according to the Dominicans in charge of it, should continue for several more decades^[46].

Modern French translations

Several French reference translations exist:

• Revue des Jeunes edition (Desclée & Cie / Cerf, 60+ volumes, 1925-1973): translation by the French Dominicans, accompanied by notes and glosses; « en regard » format (Latin + French).
• Cerf edition (entitled Somme théologique, 4 volumes in the current edition, directed by A.-M. Roguet, 1st ed. 1984-1986, re-ed. 2013): complete translation, compact format.
• docteurangelique.free.fr digital site (Pages d'Or of the Bibliothèque Numérique): Lachat 1850 translation and later revisions, freely accessible online.

And the Summa is wholly accessible in Latin and English on Corpus Thomisticum (University of Navarre) and New Advent.

The Summa Theologiae is, in the history of Western thought, the most systematic theological work ever composed. It orders into a single body of doctrine the whole of the Christian faith — God, Trinity, creation, angels, man, human acts, virtues, vices, law, grace, Christ, sacraments — in more than 2,600 articles organised into 512 questions and structured according to a Trinitarian rhythm which imitates the movement of God towards the creature and of the creature towards God.

Composed between 1265 and 1274, in three cities (Rome, Paris, Naples), unfinished because of the mystical experience of 6 December 1273 ("all that I have written seems to me as straw"), followed by Thomas's death three months later at Fossanova, the work is complete only with the Supplementum compiled by Reginald of Piperno from the youthful commentary on the Sentences.

First challenged by Étienne Tempier (Paris, 1277) and John Pecham (Oxford, 1284), it is progressively rehabilitated, then triumphs: canonisation of Thomas in 1323, elevation to the rank of Doctor of the Church by Saint Pius V in 1567, symbolic presence at the Council of Trent (1545-1563), solemn restoration by Leo XIII in Aeterni Patris (1879), Pius XI in Studiorum Ducem (1923), John Paul II in Fides et Ratio (1998). The Editio Leonina, commissioned in 1879 (first volume published in 1882), is still its critical reference edition.

At the heart of Thomist doctrine, several key theses durably shaped Catholic thought: the harmony between faith and reason (which never contradict each other for they come from the same God), the real essence/existence distinction (which grounds the metaphysics of being), the doctrine of natural law (which underlies all the social and bioethical teaching of the Church), Eucharistic transubstantiation (which Trent dogmatised), the morality of virtues (which structures the 1992 Catechism of the Catholic Church).

Seven centuries later, Thomas remains the Doctor communis — the common doctor of the Church —, in the words of Pius XI in Studiorum Ducem (29 June 1923, §11)^[47]; the Second Vatican Council, in the decree Optatam Totius (1965, no. 16), gives him as master.

• Read the University of Paris and scholasticism: the intellectual institution which formed Thomas and where he taught his two regencies.
• Read Saint Thomas Aquinas (1225-1274): the complete biography of the Angelic Doctor.
• Read the Council of Trent (1545-1563): the great dogmatic ordering which constantly dialogues with the Summa.
• Read Fides et Ratio, the encyclical of John Paul II (1998): the great modern re-reading of the relation between faith and reason in the light of Thomas.
• Read eucharistic transubstantiation: the doctrine which Thomas systematises and which Trent dogmatically defines.