"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."

"The soul is not in the body as a pilot in his ship, but intimately joined and intermingled with it."

"It is proper to a philosopher to doubt everything, at least once."

"To know what is true is to know what is good."

"Except our own thoughts, there is nothing absolutely in our power."