“None of our beliefs are quite true; all have at least a penumbra of vagueness and error.”

“In science, an observer states his results along with the “probable error”; but who ever heard of a theologian or a politician stating the probable error in his dogmas, or even admitting that any error is conceivable? That is because in science, where we approach nearest to real knowledge, a man can safely rely on the strength of his case, whereas, where nothing is known, blatant assertion and hypnotism are the usual ways of causing others to share our beliefs. If the fundamentalist thought they had a good case against evolution, they would not make the teaching of it illegal.”

“The methods of increasing the degree of truth in our beliefs are well known; they consist in hearing all sides, trying to ascertain all the relevant facts, controlling our own bias by discussion with people who have the opposite bias, and cultivating a readiness to discard any hypothesis which has proved inadequate.”

“Everything is vague to a degree you do not realize till you have tried to make it precise.”

“It seems to me a fundamental dishonesty, and a fundamental treachery to intellectual integrity to hold a belief because you think it's useful and not because you think it's true.”

“What we firmly believe, if it is true, is called knowledge, provided it is either intuitive or inferred (logically or psychologically) from intuitive knowledge from which it follows logically. What we firmly believe, if it is not true, is called error. What we firmly believe, if it is neither knowledge nor error, and also what we believe hesitatingly, because it is, or is derived from, something which has not the highest degree of self-evidence, may be called probable opinion. Thus the greater part of what would commonly pass as knowledge is more or less probable opinion.”

“My own belief is that in most ages and in most places obscure psychological forces led men to adopt systems involving quite unnecessary cruelty, and that this is still the case among the most civilized races at the present day.”