 For when we reason, the memory acts; and where there is memory, there can be error, should there be some evil genius on whom we depend in our knowledge who amuses himself by deceiving us…. [But] I am quite persuaded that he could not deceive me in my knowledge through simple perception…. For even if I should really suppose such a God, a God as powerful as I can imagine, I feel that in this extravagant supposition I could not doubt that I am, or that twice two equals four, because I perceive these things through simple perception without the use of memory. (Search 6.2.6, OC 2:370; LO 480–1)