Descartes was possessed by an extreme desire to distinguish truth from falsehood. In his admiration of the sheer clarity of mathematics, Descartes wanted to construct an indestructible system of beliefs established on principles of absolute certainty. Perfect knowledge is that which cannot be doubted, indubitable, "clear and distinct" ideas, and a type of knowledge that is incorrigible, such as the knowledge of one's own mental life. Descartes considered what seemed to be immediate experience as …showed first 75 words of 433 total…

…showed last 75 words of 433 total…doubt that he doubted. Find a self-professed skeptic and ask him/her if he/she can doubt that he/she is doubting. The application of universal doubt left Descartes' existence intact. No matter how persuasive and convincing the evil demon deceived poor Descartes, he could not deceive Descartes about his existence because he had to exist in order to be deceived. The cogito is self-evident and indubitable because every attempt to doubt it affirms it.