It is with logic that one proves; it is with intuition that one invents.

All the scientist creates in a fact is the language in which he enunciates it. If he predicts a fact, he will employ this language, and for all those who can speak and understand it, his prediction is free from ambiguity. Moreover, this prediction once made, it evidently does not depend upon him whether it is fulfilled or not.

If one looks at the different problems of the integral calculus which arise naturally when one wishes to go deep into the different parts of physics, it is impossible not to be struck by the analogies existing.

Deviner avant de démontrer! Ai-je besoin de rappeler que c'est ainsi que se sont faites toutes les découvertes importantes.

Science is built up with facts, as a house is with stones. But a collection of facts is no more a science than a heap of stones is a house.

It is far better to foresee even without certainty than not to foresee at all.

The scientist does not study nature because it is useful; he studies it because he delights in it, and he delights in it because it is beautiful.