Sometimes one pays most for the things one gets for nothing.

When I examine myself and my methods of thought, I come to the conclusion that the gift of fantasy has meant more to me than any talent for abstract, positive knowledge.

A country cannot simultaneously prepare and prevent war. I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones. The distinctions separating the social classes are false; in the last analysis they rest on force.

You imagine that I look back on my life's work with calm satisfaction. But from nearby it looks quite different. There is not a single concept of which I am convinced that it will stand firm, and I feel uncertain whether I am in general on the right track.

It is the theory which decides what we can observe

The stakes are immense, the task colossal, the time is short. But we may hope - we must hope - that man's own creation, man's own genius, will not destroy him.

Our entire much-praised technological progress, and civilization generally, could be compared to an axe in the hand of a pathological criminal.