Morality is both a universal and a surprising fact about human nature. When I say that morality is universal I am not referring to this or that moral code. In fact, I am not referring to an external moral code at all. Rather, I am referring to morality as the voice within, the interior source that Adam Smith called the “impartial spectator.” Morality in this sense is an uncoercive but authoritative judge. It has no power to compel us, but it speaks with unquestioned authority. Of course we can and frequently do reject what morality commands, but when we do...