As men begin to grow civilized, they cease to be satisfied with mere taboos.

But as the work proceeded I was continually reminded of the fable about the elephant and the tortoise. Having constructed an elephant upon which the mathematical world could rest, I found the elephant tottering, and proceeded to construct a tortoise to keep the elephant from falling. But the tortoise was not more secure than the elephant, and after some twenty years of very arduous toil, I came to the conclusion that there was nothing more that I could do in the way of making mathematical knowledge indubitable.

A habit of finding pleasure in thought rather than action is a safeguard against unwisdom and excessive love of power, a means of preserving serenity in misfortune and peace of mind among worries. A life confined to what is personal is likely, sooner or later, to become unbearably painful; it is only by windows into a larger and less fretful cosmos that the more tragic parts of life become endurable.

War grows out of ordinary human nature.

The satisfaction to be derived from success in a great constructive enterprise is one of the most massive that life has to offer.

What will be the good of the conquest of leisure and health, if no one remembers how to use them?

Science may set limits to knowledge, but should not set limits to imagination.