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.

[In many circumstances,] the most important thing about a proposition is not that it be true, but that it be interesting.

Not ignorance, but ignorance of ignorance, is the death of knowledge.

In the history of the world the prize has not gone to those species which specialized in methods of violence, or even in defensive armor. In fact, nature began with producing animals encased in hard shells for defense against the ill of life. But smaller animals, without external armor, warm-blooded, sensitive, alert, have cleared those monsters off the face of the earth.

I have always noticed that deeply and truly religious persons are fond of a joke, and I am suspicious of those who aren't.

There is no more common error than to assume that, because prolonged and accurate mathematical calculations have been made, the application of the result to some fact of nature is absolutely certain.

From the moment of birth we are immersed in action, and can only fitfully guide it by taking thought.