Terry Horgan & Mark Timmons have posted Analytical Moral Functionalism Meets Moral Twin Earth on PhilPapers. Here is the abstract:
In Chapters 4 and 5 of his 1998 book From Metaphysics to Ethics: A Defence of Conceptual Analysis, Frank Jackson propounds and defends a form of moral realism that he calls both ‘moral functionalism’ and ‘analytical descriptivism’. Here we argue that this metaethical position, which we will henceforth call ‘analytical moral functionalism’, is untenable. We do so by applying a generic thought-experimental deconstructive recipe that we have used before against other views that posit moral properties and identify them with certain natural properties, a recipe that we believe is applicable to virtually any metaphysically naturalist version of moral realism. The recipe deploys a scenario we call Moral Twin Earth.
And from the paper:
Now consider Moral Twin Earth, which, as you might expect, is very much like good old Earth: same geography and natural surroundings, with people who live in Twin Australia and by and large speak Twin English, etc. Of particular importance here is that Moral Twin Earthers have a vocabulary that works very much like human moral vocabulary: they use the terms ‘good’ and ‘bad’, ‘right’ and ‘wrong’ to evaluate actions, persons, institutions, and so forth (at least those who speak Twin English use these terms, whereas those who speak some other Twin language use terms orthographically identical to the terms for good, etc., in the corresponding Earth language). In fact, were a group of explorers from Earth ever to visit Moral Twin Earth they would be strongly inclined to translate the Moral Twin Earth terms ‘good’, ‘right’, and the rest as identical to their own orthographically identical English terms. After all, the uses of these terms on Moral Twin Earth bear all the formal marks that are usually taken to characterize moral vocabulary and moral practice. In particular, the terms are used to reason about considerations bearing on the well being of persons on Moral Twin Earth; Moral Twin Earth people are normally disposed to act in certain ways corresponding to judgments about what is ‘good’ and ‘right’; they normally take considerations about what is ‘good’ and ‘right’ to be especially important, even of overriding importance in most cases, in deciding what to do; and so on.
Let us suppose that investigation into Twin English twin-moral discourse and associated practice reveals that Twin Earthers all would converge, under ideal reflective inquiry, to a mature folk morality that is nonconsequentialist, and thus is distinct from the consequentialist mature folk morality to which (we are supposing) Earthers would all converge. Suppose too that Twin Earthly mature folk morality is best systematized by some specific deontological normative theory; call this Td. The theory Td, although importantly different from Tc, nonetheless is similar enough to Tc to account for the fact that twin-moral discourse operates in Twin Earth society and culture in much the manner that moral discourse operates on Earth. (We have already noted that if explorers from Earth ever visit Moral Twin Earth, they will be inclined, at least initially, to construe persons on Moral Twin Earth as having beliefs about good and right, and to translate Twin English uses of these terms into orthographically identical English terms.) The differences in the respective mature folk moralities of Earthers and Twin Earthers, we may suppose, are due at least in part to certain species-wide differences in psychological temperament that distinguish Earthers from Twin Earthers. (For instance, perhaps Twin Earthers tend to experience the sentiment of guilt more readily and more intensively, and tend to experience sympathy less readily and less intensively, than do Earthers. )
Given all these assumptions and stipulations about Earth and Moral Twin Earth, what is the appropriate way to describe the differences between moral and twin-moral uses of ‘good’, ‘right’, ‘fair’, etc.? Two hermeneutic options are available. On one hand, one could say that the differences are analogous to those between Earth and Twin Earth in Putnam’s original example, to wit: the moral terms used by Earthers designate the unique natural properties that respectively satisfy the respective Lewis-style conceptual analyses of those terms obtainable from theory Tc, whereas the twin-moral terms used by Twin Earthers designate distinct unique natural properties that respectively satisfy the respective conceptual analyses obtainable from Td; hence, because corresponding moral and twin-moral terms have different, incompatible, conceptual analyses, moral and twin-moral terms differ in meaning, and are not intertranslatable. On the other hand, one could say instead that moral and twin-moral terms do not differ in meaning or reference, and hence that any apparent moral disagreements that might arise between Earthers and Twin Earthers would be genuine disagreements—i.e., disagreements in moral belief and in normative moral theory, rather than differences in meaning.
We submit that by far the more natural and plausible mode of description, when one considers the Moral Twin Earth scenario, is the second.
Highly recommended.