I think; therefore I am.

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

Each problem that I solved became a rule, which served afterwards to solve other problems.

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

A state is better governed which has few laws, and those laws strictly observed.

The two operations of our understanding, intuition and deduction, on which alone we have said we must rely in the acquisition of knowledge.

The senses deceive from time to time, and it is prudent never to trust wholly those who have deceived us even once.

Perfect numbers like perfect men are very rare.

If you would be a real seeker after truth, it is necessary that at least once in your life you doubt, as far as possible, all things.

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.