Cogito, ergo sum Cogito, ergo sum This proposition became a fundamental element of Western philosophy, as it purported to form a secure foundation for knowledge in the face of radical doubt. While other knowledge could be a figment of imagination, deception, or mistake, Descartes asserted that the very act of doubting one's own existence served—at minimum—as proof of the reality of one's own mind; there must be a thinking entity—in this case the self—for there to be a thought. Descartes first wrote the phrase in French in his 1637 "Discourse on the Method". He referred to it in Latin without explicitly stating the
Descartes number Descartes number In number theory, a Descartes number is an odd number which would have been an odd perfect number, if one of its composite factors were prime. They are named after René Descartes who observed that the number would be an odd perfect number if only were a prime number, since the sum-of-divisors function for would satisfy, if 22021 were prime, where we ignore the fact that reveals that 22021 is composite. A Descartes number is defined as an odd number where and are coprime and , whence is taken as a 'spoof' prime. The example given is the