If (as I said to my friend, furiously brandishing an empty bottle) it is impossible intellectually to entertain certainty, what is this certainty which it is impossible to entertain? If I have never experienced such a thing as certainty I cannot even say that a thing is not certain. Similarly, if I have never experienced such a thing as green I cannot even say that my nose is not green. It may be as green as possible for all I know, if I have really no experience of greenness. So we shouted at each other and shook the room; because metaphysics is the only thoroughly emotional thing.
G. K. Chesterton (from Tremendous Trifles, 1909)