Abstract

Terence Horgan and Mark Timmons's Moral Twin Earth thought experiment poses a serious challenge for an influential kind of moral realism. It presents us with a case in which it is intuitive that two speakers are expressing a substantive disagreement with one another. However, the meta-semantics associated with this relevant form of moral realism entails that the speakers' moral predicates express different semantic contents, and thus, the moral sentences they utter do not express conflicting propositions. Consequently, this variety of moral realism implies, wrongly, that the speakers do not express substantive disagreement after all. Some philosophers have objected to the Moral Twin Earth argument on the grounds that is possible for two speakers to express disagreement with one another, even if the moral sentences they utter do not express conflicting propositions. Heimer Geirsson supports this claim by appeal to the distinction between semantic reference and speaker reference. David Merli supports the same claim by noting that speakers whose moral sentences do not express conflicting propositions may nevertheless express a non-moral, practical disagreement over what to do. In this article, I argue that neither Geirsson nor Merli provides moral realists with a satisfying response to the Moral Twin Earth argument