“Intellectual growth should commence at birth and cease only at death.”

“Growth comes through analogy; through seeing how things connect, rather than only seeing how they might be different.”

“It is only men who are free, who create the inventions and intellectual works which to us moderns make life worth while.”

“Isn't it strange that I who have written only unpopular books should be such a popular fellow?”

“We never cease to stand like curious children before the great mystery into which we are born.”

“A man's ethical behaviour should be based effectually on sympathy, education, and social ties and needs; no religious basis is necessary. Man would indeed be in a poor way if he had to be restrained by fear of punishment and hope of reward after death.”

“People like you and me never grow old. We never cease to stand like curious children before the great mystery into which we were born.”