I recently completed an independent study with a student interested in Mackie’s error theory, and we spent a good deal of time discussing Mackie’s argument from relativity or disagreement. For those unaware, the late Australian philosopher John Mackie favored an error theory of morality, according to which, although our ordinary moral language presupposes that our moral beliefs can correspond to moral facts, there are not moral facts with which those beliefs correspond. So as Mackie understood it, if Matilda believes that capital punishment is wrong and Nancy believes capital punishment is not wrong, their disagreement is in reality only an apparent disagreement, since there is no fact about the wrongness of capital punishment that would render their disagreement intelligible. Mackie held that this error-theoretical account offers a better explanation of the apparent widespread intra- and intersocietal moral disagreement than the alternative, namely, that either Matilda or Nancy is guilty of irrationality, ignorance, misperception, etc., with respect to the alleged moral facts. Moral discourse is thus akin to fairy discourse: The parties to a moral disagreement are arguing, literally, about nothing, just as those who argue about whether fairies’ wings are translucent or opaque are arguing about nothing.
I’ve often felt that the disagreement argument is an important advance over the sophomoric and soft-headed “anthropological” argument that simply says (a) there’s lot of moral disagreement in the world, so (b) there are no objective moral facts or truths. Mackie’s point is that deep-seated disagreement is rationally intractable disagreement, resulting not from any failure of rationality by one of the parties but from the parties holding conflicting normative attitudes toward one and the same sort of act or policy. This is what distinguishes moral disagreement from factual or scientific disagreement: In a factual or scientific disagreement, we have a good idea about what sort of evidence would rationally settle the matter, but with fundamental moral disagreements, we not only can’t point to what sort of evidence would rationally settle the matter, there doesn’t seem to be *any* evidence that might settle it.
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