Americans need rest, but do not know it. I believe this to be a large part of the explanation of the crime wave in the United States.

It is not what the man of science believes that distinguishes him, but how and why he believes it. His beliefs are tentative, not dogmatic; they are based on evidence, not on authority or intuition.

All exact science is dominated by the idea of approximation.

Orthodoxy is the grave of intelligence, no matter what orthodoxy it may be.

Be isolated, be ignored, be attacked, be in doubt, be frightened, but do not be silenced.

There's a Bible on that shelf there. But I keep it next to Voltaire - poison and antidote.

Ever since men became capable of free speculation, their actions, in innumerable important respects, have depended upon their theories as to the world and human life, as to what is good and what is evil. This is true in the present day as at any former time. To understand an age or a nation, we must understand its philosophy, and to understand its philosophy we must ourselves be in some degree philosophers. There is here a reciprocal causation: the circumstances of men s lives do much to determine their philosophy, but, conversely, their philosophy does much to determine their circumstances.