"I have always held that the two questions, God and the Soul, were the chief of those which ought to be demonstrated by the help of philosophy rather than of theology."

"I concluded that I was a substance whose whole essence or nature consists in thinking, and whose being does not depend on any place or any material thing."

"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 resolved to seek no other knowledge than that which I might find within myself, or in the great book of the world."

"I am a thing that thinks, that doubts, that affirms, that denies, that wills, that refuses, that imagines also, and that perceives."