Every living thing is a sort of imperialist, seeking to transform as much as possible of its environment into itself.

Although it is a gloomy view to suppose that life will die out, sometimes when I contemplate the things that people do with their lives I think it is almost a consolation

Work is of two kinds: first, altering the position of matter at or near the earth's surface relative to other matter; second, telling other people to do so.

It is no credit to the orthodox that they do not now believe all the absurdities that were believed 150 years ago. The gradual emasculation of the Christian doctrine has been effected in spite of the most vigorous resistance, and solely as the result of the onslaughts of freethinkers.

Thinking you know when in fact you don't is a fatal mistake, to which we are all prone

Be scrupulously truthful, even if the truth is inconvenient, for it is more inconvenient when you try to conceal it.

In action, in desire, we must submit perpetually to the tyranny of outside forces; but in thought, in aspiration, we are free, free from our fellowmen, free from the petty planet on which our bodies impotently crawl, free even, while we live, from the tyranny of death.