Science is what you know, philosophy what you don't know.

Can a society in which thought and technique are scientific persist for a long period, as, for example, ancient Egypt persisted, or does it necessarily contain within itself forces which must bring either decay or explosion?

In science men have discovered an activity of the very highest value in which they are no longer, as in art, dependent for progress upon the appearance of continually greater genius, for in science the successors stand upon the shoulders of their predecessors; where one man of supreme genius has invented a method, a thousand lesser men can apply it.

In America everybody is of opinion that he has no social superiors, since all men are equal, but he does not admit that he has no social inferiors.

In all affairs it's a healthy thing now and then to hang a question mark on the things you have long taken for granted.

The whole problem with the world is that fools and fanatics are always so certain of themselves, but wiser people so full of doubts.

Three passions simple but overwhelmingly strong, have governed my life; the longing for love, the search for knowledge, and unbearable pity for the suffering of mankind.

All human activity is prompted by desire.

There is no need to worry about mere size. We do not necessarily respect a fat man more than a thin man. Sir Isaac Newton was very much smaller than a hippopotamus, but we do not on that account value him less.

This idea of weapons of mass exterminations utterly horrible and is something which no one with one spark of humanity can tolerate. I will not pretend to obey a government which is organizing a mass massacre of mankind.