This document discusses and analyzes René Descartes' famous philosophical statement "Cogito ergo sum" ("I think, therefore I am"). [1] It explains that Descartes came up with this statement in 1637 as part of his philosophical treatise "Discourse on Method" to establish the existence of the self through consciousness and thinking. [2] The document considers different perspectives on this statement, including those who question whether our existence is real or not, and discusses Pierre Gassendi's disagreement with Descartes' reasoning. [3] In conclusion, the author agrees with Descartes' view that if we can think and doubt, then we must truly exist.