Cogito, ergo sum

Possibly the best known of all philosophical quotations; this is from the French philosopher René Descartes in Discourse on Method, 1637, where he attempted to prove his existence as a thinking being, by thinking. ‘I think, therefore I am’ comes to us in English via two translations.

Descartes’ original statement in French was “Je pense, donc je suis”.

This is such a well-known line that it has spawned humorous alternatives, not least:

“I’m pink, therefore I’m spam”
“René Descartes was a drunken fart – I drink therefore I am”.