The Methodological Implications of Reference Magnetism on Moral Twin Earth

The Moral Twin Earth challenge to ethical naturalism threatens to undermine an otherwise promising metaethical view by showing that typical, naturalist-friendly theories of reference determination predict diverging reference in Twin Earth scenarios, making it difficult to account for substantive moral disagreement. Several theorists have recently invoked David Lewis’s doctrine of reference magnetism as a solution, claiming that a highly elite moral property—a moral “joint in nature”—could secure shared reference between ourselves and our twins on Twin Earth, despite our diverging usages of moral terms. This paper argues that this move has significant methodological implications: namely, it entails that a certain sort of simplicity is truth-conducive. Consequently, when applied to moral theories, this gives certain views, specifically monist ones like utilitarianism and contractualism, an advantage over their more complicated rivals, forms of pluralism and particularism. Thus, ethical naturalists cannot invoke reference magnetism without a substantial impact on first-order theorizing.