Progress is the exploration of our own error. Evolution is a consolidation of what have always begun as errors. And errors are of two kinds: errors that turn out to be true and errors that turn out to be false (which are most of them). But they both have the same character of being an imaginative speculation. I say all this because I want very much to talk about the human side of discovery and progress, and it seems to me terribly important to say this in an age in which most non-scientists are feeling a kind of loss of nerve.

The world can only be grasped by action, not by contemplation.

Astronomy is not the apex of science or of invention. But it is a test of the cast of temperament and mind that underlies a culture.

We are all shot through with enough motives to make a massacre, any day of the week that we want to give them their head.

It doesn't matter whether you're talking about bombs or the intelligence quotients of one race as against another if a man is a scientist, like me, he'll always say Publish and be damned.

To me, being an intellectual doesn't mean knowing about intellectual issues; it means taking pleasure in them.

The symbol and the metaphor are as necessary to science as to poetry.