It often happens that the universal belief of one age of mankind — a belief from which no one was, nor without an extraordinary effort of genius and courage could at that time be free — becomes to a subsequent age so palpable an absurdity, that the only difficulty then is to imagine how such a thing can ever have appeared credible.

Challenging the orthodoxy

At any given moment there is an orthodoxy, a body of ideas which it is assumed all right-thinking people will accept without question. It is not exactly forbidden to state this or that or the other, but it is “not done” … Anyone who challenges the prevailing orthodoxy finds himself silenced with surprising effectiveness. A genuinely unfashionable opinion is almost never given a fair hearing, either in the popular press or in the highbrow periodicals.