  In any case, even if the nature of disagreements lends some plausibility to cognitivism, moral realists need also to respond to the error theorist's contention that the arguments and disagreements all rest on some false supposition to the effect that there are actually facts of the sort there would have to be for some of the claims to be true. And, however moral realists respond, they need to avoid doing so in a way that then makes a mystery of the widespread moral disagreement (or at least difference) that all acknowledge.