"I entirely abandoned the study of letters, resolving to seek no other science than that which could be found in myself, or at least in the great book of the world."

"I confess that I have never found in my experience that anything which I once clearly understood could afterwards be called into doubt by me."

"The mind is a substance whose whole essence or nature is to think, and which needs no place, nor depends on any material thing, in order to exist."

"The nature of the mind is entirely distinct from that of the body."

"The first precept was never to accept anything for true which I did not clearly know to be such."