The exact words
The search for one certain thing
René Descartes wanted to put knowledge on a foundation that could not be shaken. He had been taught many things at school that turned out to be uncertain, and he decided that the only way forward was to doubt everything that could possibly be doubted and see whether anything survived.
In Part IV of his Discourse on the Method, published in French in 1637, he describes the process. His senses sometimes deceive him, so he set aside everything they told him. People make mistakes in reasoning, even in geometry, so he set aside his proofs. And since dreams can feel completely real, he supposed that everything that had ever entered his mind was no more true than a dream.
The one thing he could not doubt
Then he noticed something. While he was trying to think that everything was false, it was necessary that he, the one doing the thinking, should be something. “I think, therefore I am” was so certain that “no ground of doubt, however extravagant,” could shake it. He took it as the first principle of his philosophy and tried to rebuild everything else on top of it.
The phrase first appeared in French, “je pense, donc je suis.” The Latin version everyone knows, “cogito, ergo sum,” appears in his Principles of Philosophy of 1644. In his Meditations of 1641 he puts the same insight as “I am, I exist,” true each time he thinks it.
How to use it
The line is the best-known sentence in philosophy and is often used as a joke (“I shop, therefore I am”). In serious writing, explain that it is about certainty under doubt; that is what made it the starting point of modern philosophy.
What people get wrong
“I think, therefore I am” means thinking makes you exist, or that intelligence proves your worth.
It is about certainty. Descartes was looking for one thing he could not possibly doubt, and found it in the fact that he was doubting.
Timeline
- 1619Shut in a stove-heated room in Germany during a winter military campaign, Descartes resolves to rebuild all his knowledge from the ground up.
- 1637Discourse on the Method is published in French in Leiden. Part IV contains “je pense, donc je suis.”
- 1641The Meditations on First Philosophy develop the argument as “I am, I exist.”
- 1644The Principles of Philosophy, written in Latin, gives the famous form “ego cogito, ergo sum.”
Use it in a speech
Questions people ask
What does “I think, therefore I am” mean?
Even if I doubt everything else, I cannot doubt that I am doubting. Doubting is thinking, and something that thinks must exist. So I exist.
Where did Descartes write it?
First in French, “je pense, donc je suis,” in his Discourse on the Method (1637). The Latin “cogito, ergo sum” appears in his Principles of Philosophy (1644).
Why is it important?
It became the starting point of modern Western philosophy, which begins from the thinking self and asks what we can know for certain.
Cite this quote
These cite the original source directly, so you can use them in an essay or paper. Always check your teacher's required style.