«Cogito ergo sum[a]» is a philosophical proposition by René Descartes. The simple meaning is that thinking about ones existence proves - in and of itself - that an «I» exists to do the thinking. This proposition became a fundamental element of Western philosophy, as it was perceived to form a foundation for all knowledge. While other knowledge could be a figment of imagination, deception or mistake, the very act of doubting one's own existence arguably serves as proof of the reality of one's own existence, or at least of one's thought. (source: en.wikipedia.org)
