One does not ask whether a scientific theory is true, but only whether it is convenient.

Mathematicians do not deal in objects, but in relations between objects; thus, they are free to replace some objects by others so long as the relations remain unchanged. Content to them is irrelevant: they are interested in form only.

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.

Tolstoi explains somewhere in his writings why, in his opinion, “Science for Science's sake” is an absurd conception. We cannot know all the facts, since they are practically infinite in number. We must make a selection. Is it not better to be guided by utility, by our practical, and more especially our moral, necessities?

It is by logic that we prove, but by intuition that we discover. To know how to criticize is good, to know how to create is better.

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

Experiment is the sole source of truth.