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 for thought". In other words, "the only claim that is indubitable here is the agent-independent claim that there is cognitive activity present". The objection, as presented by Georg Lichtenberg, is that rather than supposing an entity that is thinking, Descartes should have said: "thinking is occurring." That is, whatever the force of the "cogito", Descartes draws too much from it; the existence of a thinking thing, the reference of the "I," is more than the "cogito" can justify. Friedrich Nietzsche criticized the phrase in that it presupposes that there is an "I", that there is such an activity as "thinking",