I have no faith, very little hope, and as much charity as I can afford.

The only question which any wise man can ask himself, and which any honest man will ask himself, is whether a doctrine is true or false.

The known is finite, the unknown infinite; spiritually we find ourselves on a tiny island in the middle of a boundless ocean of the inexplicable. It is our task, from generation to generation, to drain a small amount of additional land.

If the twentieth century is to be better than the nineteenth, it will be because there are among us men who walk in Priestley's footsteps....To all eternity, the sum of truth and right will have been increased by their means; to all eternity, falsehoods and injustice will be the weaker because they have lived.

As for your doctrines I am prepared to go to the Stake if requisite ... I trust you will not allow yourself to be in any way disgusted or annoyed by the considerable abuse & misrepresentation which unless I greatly mistake is in store for you... And as to the curs which will bark and yelp - you must recollect that some of your friends at any rate are endowed with an amount of combativeness which (though you have often & justly rebuked it) may stand you in good stead - I am sharpening up my claws and beak in readiness.

Life is too short to occupy oneself with the slaying of the slain more than once.

The struggle for existence holds as much in the intellectual as in the physical world. A theory is a species of thinking, and its right to exist is coextensive with its power of resisting extinction by its rivals.