"I found myself constrained to believe that there are certain principles which the human mind spontaneously accepts as true."

"I have never had any experience that was not accompanied by some thought."

"If you would be a real seeker after truth, it is necessary that at least once in your life you doubt, as far as possible, all things."

"I shall proceed by setting aside all that in which I can suppose there to be the slightest doubt, just as if I had discovered that it was wholly false."

"I suppose therefore that all the things I see are false imaginations; I believe that nothing ever existed of all that my fallacious memory represents to me."