CS Lewis in Mere Christianity on Ethical Relativism
There are two reasons for saying it belongs to the same class as mathematics. The first is, as I said in the first chapter, that though there are differences between the moral ideas of one time or country and those of another, the differences are not really very great — not nearly so great as most people imagine — and you can recognize the same lay running through them all: whereas mere conventions, like the rule of the road of the kinds or clothes people wear, may differ to any extent. The other reason is this. When you think about these differences between the morality of one people and another, do you think that the morality of one people is ever better or worse than that of another? Have any of the changes been improvements? If not, then of course there could never be any moral progress. Progress means not just changing, but changing for the better. If no set of moral ideas were truer or better than any other, there would be no sense in preferring civilized morality to savage morality, or Christian morality to Nazi morality. In fact, of course, we all do believe that some moralities are better than others. We do believe that some of the people who tried to change the moral ideas of their own age were what we would call Reformers of Pioneers — people who understood morality better than their neighbors did. Very well then. The moment you say that one set of moral ideas can be better than another, you are, in fact, measuring them both by a standard, saying that one of them conforms to that standard more nearly than the other. But the standard that measures two things is something different from either. You are, in fact, comparing them both with some Real Morality, admitting that there is such a thing as a real Right, independent of what people thing, and that some people’s ideas get nearer to that real Right than others. Or put it this way. If your moral ideas can be truer, and those of the Nazis less true, there must be something — some Real Morality — for them to be true about. The reason why your idea of New York can be truer of less true than mine is that New York is a real place, existing quite apart from what either of us thinks. If when each of us said ‘New York’ each means merely ‘The town I am imagining in my own head’, how could one of us have truer ideas than the other? There would be no question of truth or falsehood at all.