All is to be doubted.

I hope that posterity will judge me kindly, not only as to the things which I have explained, but also to those which I have intentionally omitted so as to leave to others the pleasure of discovery.

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.

For how do we know that the thoughts which occur in dreaming are false rather than those others which we experience when awake, since the former are often not less vivid and distinct than the latter?

I am accustomed to sleep and in my dreams to imagine the same things that lunatics imagine when awake.

Because reason...is the only thing that makes us men, and distinguishes us from the beasts, I would prefer to believe that it exists, in its entirety, in each of us.

It is not enough to have a good mind. The main thing is to use it well.