 Writers like Brink, Moore, and Stavropoulos propose that when the meaning of expressions in legal rules—and, in particular, the meaning of the moral concepts (like “equality”) that figure in some legal rules—is understood in the same way, then it follows that all rules have determinate applications: either the facts do or do not fall within the extension of the meaning of the key terms in the rule. The meaning of the rule determines its application, but the meaning is fixed by the real referents of the terms in the legal rule. Of course, for this to be a version of S-naturalism, the claim must be that the real referents are themselves things cognizable within a naturalistic framework. So, e.g., it would have to be the case that the legal and moral features of situations picked out by our legal concepts (and the moral concepts embedded in them) must be identical with (or supervenient upon) natural facts: just as there are necessary, a posteriori statements of property identity about water, so too there are such statements about legal and moral facts. For example, perhaps the property of being “morally right” is just identical with the property of “maximizing human well-being,” where the latter may be understood in purely psychological and physiological terms. In that case, whether an action X is morally right is simply a scientific question about whether action X will in fact maximize the relevant kinds of psychological and physiological states in the world. (Most naturalistic moral realisms are based on versions of utilitarianism, precisely because it is easy to see what the naturalistic base of moral properties would be in a utilitarian schema. One peculiar feature of the moral realism of Moore (1992b) is that it is conjoined with a deontological moral theory, yet within a purportedly naturalistic moral realist framework.) The crucial claim, plainly, is that moral facts are to be identified with (or treated as supervenient upon) certain kinds of natural facts. Of course, many philosophers are skeptical that this claim can be made out.