  Because of this, the Moral Twin Earth objection is often presented as a kind of extension of Moore’s Open Question Argument. The Open Question Argument is, in Moore’s formulation, an attack on the idea that there can be analytic natural-normative property identity claims. But in a larger sense, the Open Question Argument picks out a kind of epistemic shortcoming for moral naturalists. Moral naturalists are committed to the idea that moral facts are a kind of natural fact—but which natural facts are the moral facts? If moral claims are synonymous with certain natural claims, we can know by conceptual analysis which natural facts are the moral facts. And if moral facts are the facts that causally regulate our use of moral terminology, that provides us with another way of investigating which facts are the moral facts. But if neither of those stories are available, it seems that we have no way of identifying which natural facts are the moral ones (Huemer 2005, chapter 4; Bedke 2012). This would be a serious methodological problem for moral naturalists, and would also mark a critical disanalogy between moral epistemology and scientific epistemology. This disanalogy would be crippling to Cornell realists, who hold that there is no such disanalogy.