If people would only talk about what they understood, Earth would be a very quiet place.

I believe serious progress (in the abolition of war) can be achieved only when men become organized on an international scale and refuse, as a body, to enter military or war service.

A problem cannot be solved at the level of consciousness in which it occurs.

Failure is success in progress

Berlin is the place to which I am most closely bound by human and scientific ties.

The individual feels the vanity of human desires and aims, and the nobility and marvelous order which are revealed in nature and in the world of thought. He feels the individual destiny as an imprisonment and seeks to experience the totality of existence as a unity full of significance.

It is a very grave mistake to think that the enjoyment of seeing and searching can be promoted by means of coercion and a sense of duty.