Cogito, ergo sum
“I think, therefore I am.”
René Descartes, Principia Philosophiae (1644)
What does “Cogito, ergo sum” mean?
Cogito, ergo sum translates as “I think, therefore I am.”
The fact that you think proves that you exist. Descartes’ starting point for certain knowledge, now a symbol of philosophy itself.
“Cogito, ergo sum” word by word
| Latin | English | Grammar |
|---|---|---|
| Cogito | I think | 1st person singular, present tense of cogitare (to think, to weigh in the mind; from co- + agitare, “to turn over”) |
| ergo | therefore | a conclusion word: what follows is proved by what came before |
| sum | I am, I exist | 1st person singular, present tense of esse (to be) |
How to pronounce “Cogito, ergo sum”
In Church Latin a g before i or e turns soft (“j”). In Classical Latin it is always hard, as in “go”.
The story behind it
Descartes first wrote the idea in French, je pense, donc je suis, in his Discourse on the Method (1637). The Latin form became famous through his Principles of Philosophy (1644, Part I, §7), where he calls it the first and most certain thing anyone can know.
His method was radical doubt: question everything that can possibly be doubted – your senses, the world, even mathematics. One thing survives: the very act of doubting is thinking, and someone has to be doing it. So whoever thinks must exist.
The idea has an ancestor: around 1,200 years earlier St Augustine argued “si fallor, sum” – “if I am mistaken, I exist” (City of God 11.26).
Today the line stands for philosophy itself, for rational thinking and for the modern idea of the self. It is also one of the most remixed Latin phrases on the internet.
How to use “Cogito, ergo sum”
Short, famous and instantly recognised: a classic first tattoo for thinkers, a motto for philosophy, science or computer-science graduates, a desk sign for anyone who earns a living by thinking. For something lighter, pick one of the funny variations on the remix page.
- Latin
- Cogito, ergo sum
- English
- I think, therefore I am.
- Source
- René Descartes, Principia Philosophiae (1644)
- Era
- Age of Reason
- Theme
- Philosophy
Common mistakes
- “Cognito, ergo sum” is a common misspelling. Cogito has no n – think of “cogitate”, not “incognito”.
- “Dubito, ergo sum” (“I doubt, therefore I am”) is a later paraphrase of Descartes’ argument, not his own wording.
- The line is from Descartes (1596–1650), not from an ancient Greek or Roman philosopher.
Questions about “Cogito, ergo sum”
Who said “Cogito, ergo sum”?
The French philosopher René Descartes. The Latin wording appears in his Principles of Philosophy (1644); he first wrote it in French in 1637.
Did Descartes write it in Latin or French?
Both. The idea first appeared in French (“je pense, donc je suis”, 1637); the Latin version from 1644 is the one that became famous.
Is it “cogito” or “cognito”?
Cogito. “Cognito” is a frequent misspelling and is not the Latin word for “I think”.
Is “Cogito, ergo sum” a good tattoo?
Yes – it is short, correct Latin and widely recognised. Keep the comma, and double-check the spelling “cogito” before you book.
More to explore
Translation and grammar checked by Latin Quoter · last reviewed November 2026
Latin remixes of Cogito, ergo sum
45 playful twists, e.g. Dormio, ergo sum · Scribo, ergo sum · Curro, ergo sum.
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