"The two operations of our understanding, intuition and deduction, on which alone we have said we must rely in the acquisition of knowledge."
"I am indeed amazed when I consider how weak my mind is and how prone to error."
"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."
"Each problem that I solved became a rule which served afterwards to solve other problems."
