Boston was a moral and intellectual nursery, always busy applying first principles to trifles.

Happiness is impossible, and even inconceivable, to a mind without scope and without pause, a mind driven by craving, pleasure, or fear. To be happy, you must be reasonable, or you must be tamed. You must have taken the measure of your powers, tasted the fruits of your passion, and learned your place in the world and what things in it can really serve you. To be happy, you must be wise.

It is a pleasant surprise to him (the pure mathematician) and an added problem if he finds that the arts can use his calculations, or that the senses can verify them, much as if a composer found that sailors could heave better when singing his songs.

One real world is enough.

Prayer is not a substitute for work; it is an effort to work further and be efficient beyond the range of one's powers.

Do not have evil-doers for friends, do not have low people for friends: have virtuous people for friends, have for friends the best of men.

Self-assurance is contemptible and fatal unless it is self-knowledge.