So-called professional mathematicians have, in their reliance on the relative incapacity of the rest of mankind, acquired for themselves a reputation for profundity very similar to the reputation for sanctity possessed by theologians.

We cannot remember too often that when we observe nature, and especially the ordering of nature, it is always ourselves alone we are observing.

Do not say hypothesis, and even less theory: say way of thinking.

The great trick of regarding small departures from the truth as the truth itself - on which is founded the entire integral calculus - is also the basis of our witty speculations, where the whole thing would often collapse if we considered the departures with philosophical rigour.

There is no more important rule of conduct in the world than this: attach yourself as much as you can to people who are abler than you and yet not so very different that you cannot understand them.

Reason now gazes above the realm of the dark but warm feelings as the Alpine peaks do above the clouds. They behold the sun more clearly and distinctly, but they are cold and unfruitful.

Virtue by premeditation isn't worth much.