The only use of a knowledge of the past is to equip us for the present. The present contains all that there is. It is holy ground; for it is the past, and it is the future.

War can protect; it cannot create.

The point about zero is that we do not need to use it in the operation of daily life. No one goes out to buy zero fish.

The study of mathematics is apt to commence in disappointment.

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

The guiding motto in the life of every natural philosopher should be, seek simplicity and distrust 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.