Primary texts

St. Thomas' Writings

Aquinas wrote across genres: systematic syntheses, disputed questions, biblical commentaries, sermons, and short treatises. Read him by form, because each kind of writing teaches in a different rhythm.

Core languages

Latin and translation

Main forms

Summae, quaestiones, commentaries

Reading habit

Slow, comparative, source-first

How the corpus is ordered

Read Aquinas by literary form

The Summae

The large syntheses show how Thomas orders many questions into one architecture. They are best read with attention to sequence, not as quote collections.

Disputed questions

These texts make the argumentative method visible. Objections, distinctions, and replies are not decoration; they are the way the issue is clarified.

Commentaries and short treatises

Biblical commentaries, Aristotelian commentaries, and works like De ente et essentia sharpen vocabulary and show how Thomas reads authorities with precision.

Parallel reading

Latin with a facing translation

These brief passages are aligned so you can move line by line through Thomas’s Latin while keeping the sense of the argument in view.

Opening lines

De ente et essentia

Thomas begins with the danger of confusion at first principles.

  1. Latin

    Quia parvus error in principio magnus est in fine, secundum Philosophum in I Caeli et mundi, ens autem et essentia sunt quae primo intellectu concipiuntur, ut dicit Avicenna.

    English translation

    Because a small error at the beginning becomes great at the end, as the Philosopher says in On the Heavens, and because being and essence are what the intellect first conceives, as Avicenna says.

  2. Latin

    Ideo, ne ex eorum ignorantia errare contingat, ad horum difficultatem aperiendam dicendum est quid nomine essentiae et entis significetur.

    English translation

    Therefore, so that ignorance about them does not lead us into error, we must explain what is signified by the names essence and being.

Book I, chapter 2

Summa contra Gentiles

Thomas states the aim of showing what the Catholic faith professes about God.

  1. Latin

    Intendit autem nostrae intentionis studium ea manifestare quae de Deo veritas catholica profitetur, errorem eliminando contrarium.

    English translation

    The purpose of our study is to make clear what the Catholic truth professes about God, while excluding the contrary error.

  2. Latin

    Inter ea vero quae de Deo confitemur, duplex veritatis modus invenitur. Quaedam namque vera sunt de Deo quae omnem facultatem humanae rationis excedunt.

    English translation

    Among the things we confess about God, two modes of truth are found. Some truths about God surpass every capacity of human reason.

I, q. 2, a. 3

Summa theologiae

Thomas turns to the question of whether God exists and frames the famous five ways.

  1. Latin

    Respondeo dicendum quod Deum esse quinque viis probari potest.

    English translation

    I answer that the existence of God can be proved in five ways.

  2. Latin

    Prima autem et manifestior via est, quae sumitur ex parte motus. Certum est enim, et sensu constat, aliqua moveri in hoc mundo.

    English translation

    The first and more evident way is taken from motion. For it is certain, and evident to the senses, that some things are moved in this world.

Catalog

Major works catalog

Open a dedicated page for each major work, with reading guidance and links back to the arguments that depend on it.

Systematic theology

Summa Theologiae

1265-1274, unfinished

Aquinas's most famous synthesis, ordered from God and creation through human action, Christ, the sacraments, and final beatitude.

Open this work

Apologetic synthesis

Summa contra Gentiles

c. 1259-1265

A major work explaining truths knowable by reason and truths received by revelation, especially about God, providence, and salvation.

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Metaphysical treatise

De ente et essentia

c. 1252-1256

A short treatise on being, essence, existence, substance, accident, form, matter, and individuation.

Open this work

Disputed questions

Quaestiones disputatae de veritate

1256-1259

A large set of disputed questions on truth, knowledge, conscience, good, free choice, grace, and related topics.

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Disputed questions

Quaestiones disputatae de potentia

1265-1266

Disputed questions on divine power, creation, the Trinity, divine simplicity, and the relation of God to creatures.

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Disputed questions

Quaestiones disputatae de malo

c. 1269-1271

A major treatment of evil, sin, free will, temptation, demonic action, and moral disorder.

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Disputed questions

Quaestiones disputatae de anima

1265-1266

Aquinas's mature disputed treatment of the soul, intellect, embodiment, and human operations.

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Academic disputations

Quodlibetal Questions

1256-1272

Public university disputations on theological, philosophical, moral, and ecclesial questions raised from many directions.

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Doctrinal summary

Compendium Theologiae

1265-1267, unfinished

A concise summary of Christian doctrine arranged around faith, hope, and charity.

Open this work

Natural philosophy

De principiis naturae

c. 1252-1256

An early short work explaining matter, form, privation, generation, and the four causes.

Open this work

Philosophical treatise

De aeternitate mundi

c. 1270

Aquinas asks whether reason can prove the world had a temporal beginning and argues that temporal beginning is known by faith.

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Polemic treatise

De unitate intellectus contra Averroistas

1270

Aquinas defends the individuality of the human intellect against Latin Averroist readings of Aristotle.

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Political theology

De regno / On Kingship

c. 1267

A political work on rule, kingship, tyranny, civic order, and the common good.

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Patristic Gospel commentary

Catena Aurea

1263-1268

A chained commentary on the four Gospels that gathers interpretations from Church Fathers.

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Theological commentary

Commentary on the Sentences of Peter Lombard

1252-1256

Aquinas's early major theological work, written as part of his academic formation on Lombard's standard textbook.

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Scriptural commentary

Biblical Commentaries

1250s-1270s

Commentaries on books including Job, Psalms, Isaiah, Matthew, John, Romans, 1 Corinthians, Galatians, Ephesians, Philippians, Colossians, and Hebrews.

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Aristotelian commentary

Commentary on Aristotle's Nicomachean Ethics

1271-1272

Aquinas's commentary on Aristotle's central ethical work, treating happiness, virtue, prudence, friendship, and justice.

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Aristotelian commentary

Commentary on Aristotle's Metaphysics

1269-1272

A major commentary on being, substance, causality, act and potency, and wisdom.

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Aristotelian commentary

Commentary on Aristotle's Physics

1268-1269

Aquinas's commentary on motion, nature, change, time, place, and causality.

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Aristotelian commentary

Commentary on Aristotle's De Anima

1267-1268

A commentary on soul, life, perception, imagination, and intellect.

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Aristotelian commentary

Commentary on Aristotle's Politics

1271-1272, incomplete

An incomplete commentary on Aristotle's account of the city, citizenship, regimes, and political life.

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Liturgical theology

Office and Hymns for Corpus Christi

1264

Liturgical texts traditionally attributed to Aquinas, including hymns associated with Corpus Christi and Eucharistic devotion.

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Ecumenical theology

Contra errores Graecorum

1263-1264

A work addressing theological disputes between Latin and Greek Christians, especially Trinitarian and ecclesial questions.

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Apologetic treatise

De rationibus fidei

1265

A short apologetic work explaining Christian doctrines in response to objections from Muslims, Greeks, and others.

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Philosophical theology

Expositio super Boethium De Trinitate

1257-1259

A commentary important for Aquinas's account of theology, philosophy, science, and the relation between faith and reason.

Open this work

Continue with the 24 Thomistic Theses

Once the voice of Thomas is in view, the theses become more useful as a doctrinal map rather than an isolated checklist.

Go to the 24 Thomistic Theses