Moral principle explanations of supervenience

Abstract

Here's a very common challenge for defenders of non-naturalism about morality. The moral facts supervene upon the natural facts -there cannot be a change moral facts without a change in the natural facts. More specifically, a certain action with certain moral properties couldn't have had some other moral properties without having different natural properties (including, perhaps extrinsic or relational natural properties). And similarly for other bearers of moral properties, not just actions.Here's a common formalization of this idea:where M is the set of moral properties and N is the set of natural properties. This principle says that: For every moral property F, if something has F then it has a natural property G such that it's metaphysically necessary that anything that is G is F.Perhaps some nuances need to be added to this formulation (see, for example, Atiq (2020)), but those don't matter for our purposes.Explaining supervenience is a central challenge for the non-naturalist. The supervenience principle we just wrote down describes a very specific type of moral choreography -the moral and the natural properties dance together in a highly regimented way. But, the non-naturalist says, moral properties are sui generis. They are completely distinct from the natural properties. So, on the face of it, it's not easy to see what explains this choreography. 1 But there is a non-naturalist strategy which purports to explain supervenience rather simply. So simply, in fact, that Fogal and Risberg (2020, p. 177) say that, in light of it 'the attention garnered by Strong Supervenience (and its ilk) in recent decades looks rather misplaced'. They call it the Divide and Conquer strategy, and I will follow them in that terminology.* Thanks to Daniel Fogal, Olle Risberg and two anonymous reviewers.1 Perhaps explaining supervenience is also a challenge for other views of the metaphysics of morality, but I'll focus on non-naturalism.The divide and conquer strategy was most influentially defended by Scanlon (2014). 2 The strategy starts with claiming that particular moral facts are explained by general moral principles, along with matters of natural fact. The way that Fogal and Risberg (p. 175) put it is that moral explanations have this structure:Explanans: particular natural fact(s) (e.g. a is a lie).Principle: general explanatory moral principle (e.g. lying is wrong).Explanandum: particular moral fact (e.g. a is wrong).Given that all particular moral facts are explained in this way there is a quick argument to supervenience. Moral facts are either general explanatory moral principles or particular moral facts. If we assume, as seems reasonable to most, that the general moral principles are necessary, then, trivially, they can't change without the natural facts changing, because they can't change at all. 3 Particular moral facts, on the other hand, are determined by the moral principles and the natural facts, as per the structure of moral explanations just described. And since the moral principles can't change, this implie...