We know why Mohammedans will not make images of animals or human beings; it is because the Prophet forbade them to do so. We know why orthodox Jews will not eat hare; it is because the Mosaic Law declares that the hare is unclean. Such prohibitions, when accepted, belong to positive morality; but in their origin, at any rate when their origin is known, they belonged to private morality.
Source: Power, a new social analysis, 1938, by Bertrand Russell<
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