"I consider that I possess no senses; I imagine that body, figure, extension, motion and place are but fictions of my mind."

"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."

"Divide each difficulty into as many parts as is feasible and necessary to resolve it."

"For it is not enough to have a good mind, but rather it is necessary to apply it well."

"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."