The book includes six meditations and he refers to each previous meditation as "yesterday", but he began work on the book in 1639. Descartes uses the method of doubt (a process of skepticism about the truth of a belief) in order to determine which of his beliefs he can be completely sure of and which could be debunked by mere doubts; “I realized that it was necessary to… tear everything down completely and start from the ground up if I wanted to establish something in the sciences that was stable and would last.” In Meditation II, The Nature of the Human Mind and How It Is Better Known than the Body, Descartes finds truths that he knows with certainty and discovers that it exists and is essentially a thinking thing (sum nes cognitas). Descartes believes that the self is essentially a “thinking thing” (82) – a thing that “doubts, understands, affirms, denies, is willing, is unwilling, and also imagines and has sense perceptions.” He distinguishes between mind and body, or thinking and extended substances. Through his reflections, Descartes proposes that the “self” refers only to the soul or mind, not the body. “It is certain that I am truly distinct from my body and can exist without it” (115). He may doubt that his hands are moving, but he cannot doubt that he is
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