Everyone knows that moral relativism is impossible. Almost no one has ever knowingly advocated it. A high school kid can crush it. So now what?
All “relativisms” fail because they nominate something absurd as an absolute. Cultural relativism says that some culture is absolute; moral relativism says that someones own opinions, or upbringing, or circumstances are absolute. But they aren’t absolute. So what is? “Nothing” is not an option. This just lands us in the same relativism that no one ever accepted anyway. So what is? Two things? So relativism would make more sense if there were only two people/historical eras/cultures etc? Nonsense. We are forced to a single Absolute, who is nothing like some division of time or finite agent in space.
We know relativism is false because we know something like St. Thomas’s Fourth Way is true. One Cosmos gives a pitch-perfect account of the argument:
To say “progress” is to say “God,” for the very word implies a standard of truth, or beauty, or moral excellence, a standard which cannot exist in the absence of the absolute. Remove the absolute, then truly, nothing is any better or more true than anything else. This is a hierarchical cosmos. Deal with it.
There is some dispute over whether the Fourth Way proves its point by the second sentence. I used to think no, but I lean more towards yes now.
Among beings there are some more and some less good, true, noble and the like. But “more” and “less” are predicated of different things, according as they resemble in their different ways something which is the maximum.