Aquinas 101

Who was Aquinas?

Born to Italian nobility, Thomas shocked his family by joining the newly-founded Dominican order rather than pursuing a comfortable career in the Church hierarchy. He studied under St. Albert the Great, taught in Paris and Naples, and produced an enormous body of work — most famously the Summa Theologiae, a systematic exploration of God, creation, morality, and Christ, still studied by seminarians and philosophers today. The Church honors him as a Doctor of the Church and calls him the Doctor Angelicus — the "Angelic Doctor" — for the clarity and holiness of his thought.

Aquinas's great project was to show that the truths discoverable by human reason — the kind of truths a philosopher could reach through careful observation and logic — are not opposed to the truths God reveals through Scripture and the Church. Grace, he taught, does not destroy nature; it perfects it.

The Five Ways

In the Summa, Aquinas offers five philosophical arguments ("the Five Ways") for God's existence, each starting from something observable in the world and reasoning back to a necessary first cause:

1. The Argument from Motion — whatever moves is moved by another; this cannot regress infinitely, so there must be an unmoved mover.
2. The Argument from Efficient Cause — nothing causes itself; tracing causes back requires a first, uncaused cause.
3. The Argument from Contingency — everything that exists could have not existed; there must be a necessary being that grounds all contingent ones.
4. The Argument from Gradation — we recognize degrees of goodness and perfection, which implies a standard of perfect goodness against which we measure.
5. The Argument from Design (Teleology) — natural things act toward ends even without minds of their own, pointing to an intelligence that directs them.

Each "way" concludes simply: "and this we call God." They are not meant to produce faith by themselves, but to show that belief in God is reasonable — a conclusion reason can reach on its own, before revelation ever begins to speak.

The Virtues

Aquinas gave classic shape to the Church's teaching on virtue — good habits that make it easier to do what is right. He distinguishes the four cardinal virtues, accessible to human effort and reason alone: prudence (practical wisdom), justice (giving each their due), fortitude (courage), and temperance (self-mastery) — from the three theological virtues, which can only be received as gifts of grace: faith, hope, and charity. Charity, he taught, is the "form" of all the other virtues — without love, even courage or generosity can curdle into something else.

Natural Law

Aquinas taught that God has written a moral law into human nature itself, discoverable by reason even apart from revelation — summarized in the basic precept "do good and avoid evil." Because every person shares the same rational human nature, the natural law is, in principle, knowable by anyone, of any culture or era — which is why Aquinas's ethics has shaped not only Catholic moral theology but centuries of Western legal and political thought.

The Transcendentals

Following Aristotle, Aquinas held that being itself has certain properties that transcend every category — most famously truth, goodness, and beauty. Anything that fully is is, in that measure, also true, good, and beautiful, because all being flows from God, who is Truth, Goodness, and Beauty itself. It is why the pursuit of truth in the sciences, the pursuit of goodness in ethics, and the pursuit of beauty in art are not three separate projects for a Catholic — they are three paths up the same mountain.

Go deeper

The Thomistic Institute offers a free, guided walk through the entire Summa Theologiae, and countless Catholics have been introduced to Aquinas through the "Pints with Aquinas" podcast, which pairs a beer with a question from the Summa each week.

Read the Summa Theologiae ↗ Pints with Aquinas ↗