Biting the Bullet on Moral Twin Earth

Abstract

Terence Horgan and Mark Timmons’ Moral Twin Earth thought experiment shows that realist ethical naturalism entails a kind of conceptual relativism about moral predicates. This conceptual relativism implies, further, that Earthlings and Twin Earthlings do not express substantive disagreement with one another. Because this latter implication clashes with considered linguistic intuitions, Horgan and Timmons conclude that we should reject realist ethical naturalism. Against this, several critics recommend that realists ‘bite the bullet’ with respect to Moral Twin Earth: despite our intuitions, we should accept that the speakers do not disagree. These critics argue that the intuitions elicited by the thought experiment are either the result of a failure on the part of readers to appreciate hidden details of the Moral Twin Earth case, or else they are mere artifacts of readers’ epistemic limitations. In this paper, I show that the Moral Twin Earth argument prevails against this line of attack.