All animals, except man, know that the principal business of life is to enjoy it - and they do enjoy it as much as man and other circumstances will allow.

There are two classes [of scientists], those who want to know, and do not care whether others think they know or not, and those who do not much care about knowing, but care very greatly about being reputed as knowing.

The course of true anything never does run smooth.

An obstinate man does not hold opinions, but they hold him; for when he is once possessed with an error, it is, like a devil, only cast out with great difficulty.

Science is being daily more and more personified and anthromorphized into a god. By and by they will say that science took our nature upon him, and sent down his only begotten son, Charles Darwin, or Huxley, into the world so that those who believe in him, &c.; and they will burn people for saying that science, after all, is only an expression for our ignorance of our own ignorance.

The youth of an art is, like the youth of anything else, its most interesting period.

They say the test of [literary power] is whether a man can write an inscription. I say, "Can he name a kitten?" And by this test I am condemned, for I cannot.