"Not to be absolutely certain is, I think, one of the essential things in rationality."

"'Change' is scientific, 'progress' is ethical; change is indubitable, whereas progress is a matter of controversy."

"The good life, as I conceive it, is a happy life. I do not mean that if you are good you will be happy - I mean that if you are happy you will be good."

"The true spirit of delight, the exaltation, the sense of being more than Man, which is the touchstone of the highest excellence, is to be found in mathematics as surely as in poetry."

"To be able to fill leisure intelligently is the last product of civilization, and at present very few people have reached this level."

"We have, in fact, two kinds of morality side by side: one which we preach but do not practice, and another which we practice but seldom preach."

"Knowledge is expensive."

"It usually takes more than three weeks to prepare a good impromptu speech."

"Time is on the side of the oppressed today, it's against the oppressor. Truth is on the side of the oppressed today, it's against the oppressor. You don't need anything else."

"The more things a man is ashamed of, the more respectable he is."

"Not everybody has to sing the melody."

"Many people weigh the guilt they will feel against the pleasure of the forbidden action they want to take."