I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones.

How can he possibly be humble? He hasn't done anything yet.

Man, surrounded by facts, permitting himself no surprise, no intuitive flash, no great hypothesis, no risk, is in a locked cell. Ignorance cannot seal the mind and imagination more securely.

One should guard against preaching to young people success in the customary form as the main aim in life. The most important motive for work in school and in life is pleasure in work, pleasure in its result, and the knowledge of the value of the result to the community.

If the believers of the present-day religions would earnestly try to think and act in the spirit of the founders of these religions then no hostility on the basis of religion would exist among the followers of the different faiths. Even the conflicts and the realm of religion would be exposed as insignificant.

A hundred times every day I remind myself that my inner and outer life are based on the labors of others.

On the left-hand side of the field equation we may add the fundamental tensor guv, multiplied by a universal constant, -λ, at present unknown, without destroying the general covariance.