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Who really said it

Three things are necessary for the salvation of man: to know what he ought to believe; to know what he ought to desire; and to know what he ought to do

Written by Thomas Aquinas c. 1225–1274 · Italian Dominican friar, theologian & philosopher; Doctor of the Church
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Genuinely Aquinas. It opens the prologue of his Lenten sermon-conferences on the Ten Commandments (“De duobus praeceptis caritatis et decem legis praeceptis”), preached at Naples in 1273 and recorded by Reginald of Piperno. The Latin — “Tria sunt homini necessaria ad salutem…” — is faithfully rendered here; note that this exact English wording is one translation among several (the widely-circulated Joseph B. Collins 1939 version reads “Three things are necessary for man to be saved…”).

Last verified 8 Jul 2026 · how we verify · spot an error?

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“Three things are necessary for the salvation of man: to know what he ought to believe; to know what he ought to desire; and to know what he ought to do” — Thomas Aquinas, The Two Precepts of Charity and the Ten Commandments (prologue), Naples, 1273

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Provenance

The source

Work
De duobus praeceptis caritatis et decem legis praeceptis (The Two Precepts of Charity & the Ten Commandments)
Passage
Prologue — the opening sentence
Composed
Lent 1273, Naples; reported by Reginald of Piperno
Translation
This exact English is an older, unattributed literal rendering; the widely-hosted Joseph B. Collins (1939) version reads “Three things are necessary for man to be saved…”

Three things are necessary for the salvation of man: to know what he ought to believe; to know what he ought to desire; and to know what he ought to do. The first is taught in the Creed; the second in the Lord’s Prayer; the third in the Law.

The second sentence, which Aquinas gives immediately after, maps the three onto the Creed (belief), the Lord’s Prayer (desire) and the Law/Commandments (action) — the framework for his whole set of Lenten conferences.

Aquinas on the Ten Commandments (prologue), isidore.co

How we traced it

  • The line is genuinely Aquinas: it is the prologue of his Lenten conferences on the Ten Commandments (Collationes in decem praeceptis), whose Latin opens “Tria sunt homini necessaria ad salutem…” The Collins (1939) English translation ↗ reproduces that prologue.
  • The companion sermon-set was preached at Naples in 1273 and taken down by Reginald of Piperno, per Nicholas Ayo’s Latin-English edition of the Apostles’ Creed conferences (Notre Dame, 1988).
  • The exact popular English wording is preserved on Philip Guston’s 1952 painting in the Smithsonian’s Great Ideas of Western Man series, which credits “St. Thomas Aquinas, Two Precepts of Charity, 1273.”

The 13th-century Latin is long in the public domain, but rights attach to the exact English wording displayed. That wording is a specific translation whose translator and first-publication date we could not pin down — it is not the widely-hosted Joseph B. Collins (1939) rendering, which differs. Because we cannot document a pre-1931 appearance or identify the translator, we assert no copyright status. (A faithful literal rendering of the public-domain Latin can of course be made freely.)

Fact-check

Misquote & mis-sourcing watch

The attribution to Aquinas is correct — this is a rare case where the popular line is genuinely the author’s. The pitfalls here are about which work and which translation, not who.

Thomas Aquinas Correct author, loose sourcing

The line is often quoted with no source, or filed vaguely under the “Apostles’ Creed” sermons. It actually opens the prologue to his conferences on the Ten Commandments (“De duobus praeceptis caritatis et decem legis praeceptis”); the Smithsonian’s label “Two Precepts of Charity, 1273” names that same work correctly.

Anonymous translator One translation of several

“To know what he ought to believe…” is one English rendering; the scholarly Joseph B. Collins (1939) version reads “Three things are necessary for man to be saved: knowledge of what is to be believed…” (see isidore.co). Both track the same Latin; neither is “the” original English.

Bottom line: really Aquinas — the opening of his 1273 Naples sermons on the Ten Commandments, faithfully rendered from “Tria sunt homini necessaria ad salutem…” (Latin/English at isidore.co).

Context

Why it mattered

In 1273, at the end of his life, Aquinas set aside the technical Latin of the Summa to preach a course of plain Lenten sermons for the ordinary people of Naples. This sentence is the doorway to that whole course: he tells his hearers that a saved life needs three kinds of knowledge — what to believe, what to desire, and what to do.

He then hands each to a familiar text: the Creed teaches belief, the Lord’s Prayer trains desire, and the Commandments direct action. It is Aquinas’s entire catechetical scheme compressed into one balanced tricolon.

Belief, desire, action — the Creed, the Our Father, and the Law.

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Filed under

More provenance-checked quotes on the same theme, each with its reuse status.

Wisdom Character Knowledge

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Dig deeper

Trusted places to keep pulling the thread — primary archives, fact-checks, and scholarship. We show how we used each one before you leave.

Aquinas, The Ten Commandments (prologue), Collins (1939) Englishisidore.co

The prologue of the Lenten conferences in the Collins (1939) English translation.
Guston, “Three things are necessary…” (Great Ideas of Western Man)americanart.si.edu

1952 painting bearing the exact popular wording, crediting Aquinas’s “Two Precepts of Charity, 1273.”
The Sermon-Conferences on the Apostles’ Creed (Ayo, 1988)archive.org

Nicholas Ayo’s Latin-facing English edition of the companion 1273 Naples conferences; notes Reginald of Piperno’s record.
Aquinas, De decem praeceptis (Latin/English reader)aquinas.cc

Side-by-side Latin and English of the Ten Commandments conferences containing this prologue.
Thomas Aquinasen.wikipedia.org

Biography and works of the author, including his 1273 Lenten catechetical sermons.

The true author

About Thomas Aquinas

Thomas Aquinas

c. 1225–1274 · Italian Dominican friar, theologian & philosopher · Doctor of the Church

Thomas Aquinas (c. 1225–1274) was an Italian Dominican friar whose synthesis of Aristotelian philosophy and Christian theology — above all the Summa Theologiae — became foundational for Western thought. In the last year of his life he preached a set of plain-language Lenten catechetical conferences at Naples on the Creed, the Lord’s Prayer, the Hail Mary and the Ten Commandments; this line opens the program for those sermons. He was canonized in 1323 and named a Doctor of the Church.

For writers & researchers

Cite this

Primary source — Chicago

Thomas Aquinas, De duobus praeceptis caritatis et decem legis praeceptis (Collationes in decem praeceptis), prologue, delivered Naples, 1273. Latin: “Tria sunt homini necessaria ad salutem: scilicet scientia credendorum, scientia desiderandorum, et scientia operandorum.”

MLA (9th ed.)

Aquinas, Thomas. De duobus praeceptis caritatis et decem legis praeceptis (Collationes in decem praeceptis). Naples, 1273.

APA (7th ed.)

Aquinas, T. (1273). De duobus praeceptis caritatis et decem legis praeceptis [Sermon collection].

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Quotle.info. “Who really said ‘Three things are necessary for the salvation of man: to know what he ought to believe; to know what he ought to desire; and to know what he ought to do’?” Last verified 8 Jul 2026. https://quotle.info/who-said/three-things-are-necessary-for-the-salvation-of-man-to-know

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