Joy in looking and comprehending is nature's most beautiful gift.

A theory can be proved by experiment; but no path leads from experiment to the birth of a theory.

I have not eaten enough of the tree of knowledge, though in my profession I am obligated to feed on it regularly.

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

I know that philosophically a murderer is not responsible for his crime, but I prefer not to take tea with him.

Before God we are all equally wise - and equally foolish.

If one asks the whence derives the authority of fundamental ends, since they cannot be stated and justified merely by reason, one can only answer: they exist in a healthy society as powerful traditions, which act upon the conduct and aspirations and judgments of the individuals; they are there, that is, as something living, without its being necessary to find justification for their existence.