"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 think, therefore I am."

"I am accustomed to sleep, and in my dreams to imagine the same things that lunatics do when awake."

"I suppose therefore that all I see is false. I believe that none of what my deceptive memory represents to me ever existed."

"I desire to live in peace and to continue the life I have begun, adopting as my motto 'to live well, one must live concealed'."