I do not believe that a moral philosophy can ever be founded on a scientific basis. … The valuation of life and all its nobler expressions can only come out of the soul’s yearning toward its own destiny. Every attempt to reduce ethics to scientific formulas must fail. Of that I am perfectly convinced.

Do not grow old, no matter how long you live. Never cease to stand like curious children before the Great Mystery into which we were born.

I do know that kind fate allowed me to find a couple of nice ideas after many years of feverish labor.

The most incomprehensible thing about the world is that it is comprehensible.

One strength of the communist system of the East is that it has some of the character of a religion and inspires the emotions of a religion.

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.

Show me a satisfied man, and I'll show you a failure.