Cogito, Ergo Sum

Possibly the most famous sentence in philosophy, René Descartes’s cogito, ergo sum—I think, therefore I am—appears in the 1641 work Meditations on First Philosophy, written in Latin by the French philosopher René Descartes (1596–1650). Descartes’s famous conclusion came at the end of a project to subject all of his beliefs to radical doubt. In other words, Descartes set out to reject any belief he could not know for certain to be true.

For instance, he rejected his belief in the world of sensory experience because he believed his senses could be deceived. However, he found one belief he could not doubt—that he was thinking. Descartes claimed it was impossible for him to doubt that he was thinking, because in doubting this, he would be thinking. Then Descartes declared, if he knew for certain that he was thinking, he knew for certain that he existed. Thus, Descartes had found one unquestionable belief —belief in his own existence.

Descartes’s cogito argument is a common jumping-off point for what philosophers call the problem of self-knowledge: What is unique about our awareness of ourselves from the inside? That is, in what ways is it different to think about our own thoughts, feelings, and desires as opposed to anything else? Some people think one difference is that we cannot be mistaken when we honestly report what we are thinking or feeling. This idea seems plausible if you consider the case of pain. If you feel that you are in pain, it seems impossible that you could be wrong in believing that you are in pain.


  1. Descartes believed that he had given a proof for the existence of God that was so strong it could not possibly be doubted

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