If you had the power to destroy the world, would you do so?

To be able to concentrate for a considerable time is essential to difficult achievement.

The human animal, like others, is adapted to a certain amount of struggle for life [and] the mere absence of effort from his life removes an essential ingredient of happiness. [. . .] He forgets that to be without some of the things you want is an indispensable part of happiness.

Love should be a tree whose roots are deep in the earth, but whose branches extend into heaven.

Indemnity for the past and security for the future.

Mathematics takes us into the region of absolute necessity, to which not only the actual word, but every possible word, must conform.

In astronomy, the law of gravitation is plainly better worth knowing than the position of a particular planet on a particular night, or even on every night throughout a year. There are in the law a splendour and simplicity and sense of mastery which illuminate a mass of otherwise uninteresting details. But in history the matter is far otherwise. Historical facts, many of them, have an intrinsic value, a profound interest on their own account, which makes them worthy of study, quite apart from any possibility of linking them together by means of causal laws.