"I desire to live in such a way that I can spend the rest of my life without having committed any fault."

"Cogito, ergo sum. (I think, therefore I am.)"

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

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

"I confess that I have never been able to find out what is the 'substantial form' of a human body, or how it differs from the form of a statue."