Mathematicians do not study objects, but the relations between objects.

In the old days when people invented a new function they had something useful in mind.

Intuition is more important to discovery than logic.

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?

Einstein does not remain attached to the classical principles, and when presented with a problem in physics he quickly envisages all of its possibilities. This leads immediately in his mind to the prediction of new phenomena which may one day be verified by experiment.

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

Later generations will regard Mengenlehre (set theory) as a disease from which one has recovered.