In order to rebut G. E. Moore's open question argument, ethical naturalists adopt a theory of direct reference for our moral terms. T. Horgan and M. Timmons have argued that this theory cannot be applied to moral terms, on the ground that it clashes with competent speakers' linguistic intuitions. While Putnam's Twin Earth thought experiment shows that our linguistic intuitions confirm the theory of direct reference, as applied to 'water', Horgan and Timmons devise a parallel thought experiment about moral terms, in order to show that this theory runs against our linguistic intuitions about such terms. My claim is that the Horgan-Timmons argument does not work. I concede that their thought experiment is a good way to test the applicability of the theory of direct reference to moral terms, and argue that the upshot of their experiment is not what they claim it is: our linguistic intuitions about Moral Twin Earth are parallel to, not different from, our intuitions about Twin Earth.Keywords Ethical naturalism . Moral disagreement . Moral realism . Open question argument . Theory of direct reference . Twin Earth My aim in this paper is to discuss and ultimately reject an objection against ethical naturalism. Ethical naturalism is a form of moral realism: the version of moral realism according to which moral facts (and/or properties) are natural facts (and/or properties). If moral realism can be formulated as the claim that there are moral facts whose obtaining and nature are independent of human beliefs, attitudes, or conventions, naturalists are those realists who claim that these moral facts are natural facts. Naturalism is thus opposed, in meta-ethical debates on moral realism, to two other possible versions of moral realism, according to which moral facts are, respectively, supernatural facts (for example, facts about our immortal souls), or sui generis, i.e. facts of a peculiar kind, distinct from both natural and supernatural facts. Against these views, naturalists claim that moral facts are ordinary natural facts: according to naturalists, ethics deals with the same world as other empirical (natural or social) sciences deal with. As a consequence of this use of the label 'naturalism', Ethic Theory Moral Prac (