According to the eligibility theory of meaning, often attributed to David Lewis, the referent of a predicate is the property that best balances the twin constraints of charity (i.e. fit with our usage of the term) and eligibility, where eligibility is a function of metaphysical naturalness (i.e. how much of a natural kind the property is). This sort of metasemantics, which is motivated by its ability to resolve problems of indeterminacy and secure shared reference between disputing parties, can be somewhat friendly towards revisionary (i.e. counterintuitive) theories, since highly natural properties can act as “reference magnets,” securing our reference despite some mismatch with usage. In this paper, I apply these considerations to normative ethics and argue that the theory of rule utilitarianism achieves a high balance of charity and eligibility. I proceed by comparing rule utilitarianism to two of its well-known rivals, act utilitarianism and Rossian pluralism (a.k.a. “Commonsense Morality”). I show how the former achieves a high degree of eligibility but only at a significant cost of charity, while the latter does the opposite, fitting very nicely with our considered judgments but at the price of very low eligibility. Rule utilitarianism, on the other hand, strikes a good balance between these extremes; it assigns to our core moral term (‘moral permissibility’) a relatively natural property without doing too much damage to our moral convictions. Thus, rule utilitarianism should be regarded as a promising moral theory by any philosopher who takes seriously considerations of eligibility and naturalness.

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.

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