This is the final post in my series of posts on the Moral Twin Earth.
I’m largely unconvinced by Copp’s TSC strategy. During the dialectic, we have been talking of TC and TD as the referents, but once we get to Copp’s strategy, TSC gets imported into the referential intentions of the speaker. This potentially makes it analytic moral naturalism; and The Moral Twin Earth argument is supposed to be against synthetic moral naturalism. Horgan and Timmons might call this another form of chauvinistic conceptual relativism, i.e. it’s my referential intentions or concepts that matter.
Maybe the fair account of the referential intention of the term ‘wrong’ would be ‘not-to-be-doneness’ or something less loaded; but, then, that might be too thin to rule out norms of etiquette or other norms. The ambiguity is not only with the reference but also with the referential intention. Consider the term ‘God.’ If we take a thin enough construal of the referential intentions of speakers to include theists, deists, and pantheists, we’d come up with something like ‘something higher than us’; but theists may say that in thinning the referential intentions we’ve lost what was interesting in the referential intention in the first place.
There’s also an ambiguity in the natural/nonnatural distinction, further complicating the debate between moral naturalists and nonnaturalists. Suppose the natural things are things that science deals with. Once we get to some soft sciences it becomes ambiguous, e.g., is a reason natural or nonnatural? See my post on moral fixed points for a little on this.
I think the better reply by Copp is the point about semantic indeterminacy. Semantic indeterminacy is a general problem that is independent of metaethics. We could construct a Water Twin Earth thought experiment where Earthling water is 100% H2O, while Twin Earthings water is at least 99% H2O–since Twin Earthlings allow for some impurities. (This seems easier on Boyd’s causal theory semantics; or, on Putnam-ish semantics, we could say their referential intentions slightly vary.) Should this lead to relativism about water and everything else?
Horgan and Timmons pose the dilemma: either your reference-fixing relation R is too ambiguous, or it’s determinate but you get objectionable relativism. (For example, ‘human flourishing’ can be seen as ambiguous.) But this seems true for many terms. So why should synthetic moral naturalists be especially concerned?