If one man believes that the earth is round and another believes that it is flat, they can set off on a joint voyage and decide the matter reasonably. But if one believes in Protestantism and the other in Catholicism, there is no known method of reaching a rational conclusion. For such reasons, I had come to agree with Santayana that there is no such thing as ethical knowledge. Nevertheless, ethical concepts have been of enormous importance in history, and I could not but feel that a survey of human affairs which omits ethics is inadequate and partial.
Source: The Autobiography of Bertrand Russell, v.3 chap. 1: Return to England, 1969
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