Often when works at a hard question, nothing good is accomplished at the first attack. Then one takes a rest, long or short, and sits down anew to the work. During the first half-hour, as before, nothing is found, and then all of a sudden the decisive idea presents itself to the mind.

Experiment is the sole source of truth. It alone can teach us something new; it alone can give us certainty.

It is by logic we prove. It is by intuition we discover.

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.

A cat is witty, he has nerve, he knows how to do precisely the right thing at the right moment.

If we wish to foresee the future of mathematics, our proper course is to study the history and present condition of the science.

When the physicists ask us for the solution of a problem, it is not drudgery that they impose on us, on the contrary, it is us who owe them thanks.