What is morality in any given time or place? It is what the majority then and there happen to like and immorality is what they dislike.

The art of progress is to preserve order amid change and to preserve change amid order.

No Roman ever died in contemplation over a geometrical diagram.

I regret that it has been necessary for me in this lecture to administer a large dose of four-dimensional geometry. I do not apologize, because I am really not responsible for the fact that nature in its most fundamental aspect is four-dimensional. Things are what they are.

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.

The purpose of education is not to fill a vessel but to kindle a flame.

Everything of importance has been said before by somebody who did not discover it.