Cogito, ergo sum (See CSMK III 159, 161.) Another predecessor was Avicenna's "Floating Man" thought experiment on human self-awareness and self-consciousness. The 8th century Hindu philosopher Adi Shankara wrote in a similar fashion, No one thinks, 'I am not', arguing that one's existence cannot be doubted, as there must be someone there to doubt. The central idea of "cogito, ergo sum" is also the topic of Mandukya Upanishad. Spanish philosopher Gómez Pereira in his 1554 work "De Inmortalitate Animae", published in 1749, wrote ""nosco me aliquid noscere, & quidquid noscit, est, ergo ego sum"" ("I know that I know something, anyone who knows
Cogito, ergo sum "Meditations", Descartes phrases the conclusion of the argument as "that the proposition, "I am, I exist," is necessarily true whenever it is put forward by me or conceived in my mind." ("Meditation" II) At the beginning of the second meditation, having reached what he considers to be the ultimate level of doubt—his argument from the existence of a deceiving god—Descartes examines his beliefs to see if any have survived the doubt. In his belief in his own existence, he finds that it is impossible to doubt that he exists. Even if there were a deceiving god (or an evil demon),