You may read any quantity of books, and you may almost as ignorant as you were at starting, if you don't have, at the back of yourminds, the change for words in definite images which can only be acquired through the operation of your observing faculties on the phenomena of nature.

Of moral purpose I see no trace in Nature. That is an article of exclusively human manufacture and very much to our credit.

I doubt the fact, to begin with, but if it be so even, what is this but in grand words asking me to believe a thing because I like it.

Not far from the invention of fire we must rank the invention of doubt.

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.

Proclaim human equality as loudly as you like, Witless will serve his brother.

I would rather be the offspring of two apes than be a man and afraid to face the truth.