It is often said that experiments should be made without preconceived ideas. That is impossible. Not only would it make every experiment fruitless, but even if we wished to do so, it could not be done. Every man has his own conception of the world, and this he cannot so easily lay aside. We must, example, use language, and our language is necessarily steeped in preconceived ideas. Only they are unconscious preconceived ideas, which are a thousand times the most dangerous of all.

Experiment is the sole source of truth.

It is the simple hypotheses of which one must be most wary; because these are the ones that have the most chances of passing unnoticed.

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

Thus, be it understood, to demonstrate a theorem, it is neither necessary nor even advantageous to know what it means.

The scientist does not study nature because it is useful to do so. He studies it because he takes pleasure in it, and he takes pleasure in it because it is beautiful. If nature were not beautiful it would not be worth knowing, and life would not be worth living. I am not speaking, of course, of the beauty which strikes the senses, of the beauty of qualities and appearances. I am far from despising this, but it has nothing to do with science. What I mean is that more intimate beauty which comes from the harmonious order of its parts, and which a pure intelligence can grasp.

A very small cause, which escapes us, determines a considerable effect which we cannot ignore, and we say that this effect is due to chance.