The greatest minds are capable of the greatest vices as well as of the greatest virtues.

On the one hand I have a clear and distinct idea of myself, in so far as I am a thinking, non-extended thing; and on the other hand I have a distinct idea of body, in so far a this is simply an extended, non-thinking thing. And, accordingly, it is certain that I am really distinct from my body, and exist without it.

I am indeed amazed when I consider how weak my mind is and how prone to error.

Reason is nothing without imagination.

Let whoever can do so deceive me, he will never bring it about that I am nothing, so long as I continue to think I am something.

Divide each difficulty at hand into as many pieces as possible and as could be required to better solve them.

If I found any new truths in the sciences, I can say that they follow from, or depend on, five or six principal problems which I succeeded in solving and which I regard as so many battles where the fortunes of war were on my side.