IT is WIDELY AGREED that normative properties supervene on natural properties. Non-naturalists face a distinctive challenge to explain this relation. Unlike other metanormative contenders, non-naturalists take normative supervenience to be a relation between metaphysically discontinuous kinds: natural properties and sui generis normative properties. As Tristram McPherson forcefully argues, that discontinuity makes it difficult, if not impossible, for non-naturalists to explain supervenience. (1) And it is widely accepted that an inability to explain a necessary relation between distinct kinds--at least insofar as that relation demands explanation--is a significant theoretical cost.
Stephanie Leary argues that non-naturalists can meet this explanatory demand by positing the existence of hybrid normative properties. (2) These properties serve as a kind of "double-sided tape," allowing a natural property to ground a sui generis normative property (e.g., goodness) without violating non-naturalism's commitment to metaphysical discontinuity--i.e., without that grounding relation's holding in virtue of the nature of either the natural properties or the sui generis normative properties themselves. (3) Each hybrid normative property H has two key features: (i) it is part of the (constitutive immediate) essence of H that some natural property G grounds H's instantiation and (ii) it is part of the essence of H that H grounds the instantiation of some sui generis normative property F. (4)
For example, one might claim that being in pain is such a property: that it's part of the essence of being in pain that (a) if one's C-fibers are firing, then one is in pain, and (b) that if x is a painful experience, x is bad. (5) Unfortunately, this proposal does not meet the supervenience challenge. To see this, begin with Leary's formulation of supervenience: (6)
Strong Supervenience: ([for all]F in A)([for all]x)[Fx [right arrow] ([there exists]G in B)(Gx & [[??].sub.]([for all]y)(Gy [right arrow] Fy))] A is the class of normative properties and B is the class of natural properties. Thus, according to Strong Supervenience, for every normative property F, each instantiation of F is metaphysically necessitated by the instantiation of some natural property G. With [A.sub.SG] as the class of sui generis normative properties, Leary's proposal entails:
Hybrid Property: ([for all]F in [A.sub.SG])([there exists]H)([there exists]G in B)[[[??].sub.M](Gx [right arrow] Hx) & [[??].sub.M](Hx [right arrow] Fx)] Hybrid Property does not entail Strong Supervenience. It entails that G is sufficient for F. It does not entail that the instantiation of one or more members of B (i.e., of at least one natural property) is necessary for the instantiation of F, and thus does not entail that F supervenes on the set of natural properties. The latter, Leary claims, is explained by her essentialist metaphysics:
The background essentialist metaphysics explains why it's metaphysically necessary that, if x has some sui generis normative property, x has some natural property that is involved in the essence of whatever hybrid properties ground it. On the essentialist framework, no grounding facts are fundamental--they are all grounded in essences. So, no derivative property F can be instantiated by x unless x has some more fundamental property G and there is an essential connection between being F and being G. (7) Leary makes two key claims about F in this passage. First, she claims that F is a "derivative property"--i.e., is always grounded. Second, she claims that F is always grounded in some natural property. But it is...