It is a profoundly erroneous truism, repeated by all copy books and by eminent people when they are making speeches, that we should cultivate the habit of thinking of what we are doing. The precise opposite is the case. Civilization advances by extending the number of important operations which we can perform without thinking about them.

You cannot be wise without some basis of knowledge, but you may easily acquire knowledge and remain bare of wisdom.

Common sense is genius in homespun.

Fundamental progress has to do with the reinterpretation of basic ideas.

Life is the enjoyment of emotion, derived from the past and aimed at the future.

Error is the price we pay for progress.

It does not matter what men say in words, so long as their activities are controlled by settled instincts. The words may ultimately destroy the instincts; but until this has occurred, words do not count.