Each problem that I solved became a rule, which served afterwards to solve other problems.
Except our own thoughts, there is nothing absolutely in our power.
I am accustomed to sleep and in my dreams to imagine the same things that lunatics imagine when awake.
I am indeed amazed when I consider how weak my mind is and how prone to error.
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 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.
It is not enough to have a good mind the main thing is to use it well.
Perfect numbers like perfect men are very rare.
The reading of all good books is like a conversation with the finest minds of past centuries.
The senses deceive from time to time, and it is prudent never to trust wholly those who have deceived us even once.
The two operations of our understanding, intuition and deduction, on which alone we have said we must rely in the acquisition of knowledge.
When it is not in our power to follow what is true, we ought to follow what is most probable.