The vitality of thought is in adventure. Ideas won't keep. Something must be done about them. When the idea is new, its custodians have fervor, live for it, and if need be, die for it.

Inventive genius requires pleasurable mental activity as a condition for its vigorous exercise. "Necessity is the mother of invention" is a silly proverb. "Necessity is the mother of futile dodges" is much closer to the truth. The basis of growth of modern invention is science, and science is almost wholly the outgrowth of pleasurable intellectual curiosity.

Nature is probably quite indifferent to the aesthetic preferences of mathematicians.

True courage is not the brutal force of vulgar heroes, but the firm resolve of virtue and reason.

Every really new idea looks crazy at first.

To see what is general in what is particular, and what is permanent in what is transitory, is the aim of scientific thought.

In all education the main cause of failure is staleness.