"It is precisely because I am in the habit of using my senses to think of things that I find it difficult to think of anything else."

"The first precept was never to accept a thing as true until I knew it as such without a single doubt."

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

"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 am accustomed to take my sleep for granted, and I often imagine that I dream of the most important things, when after all I am only dreaming."