Physicalism Without Supervenience, Lei Zhong, Phil Studies (2021) 1529-1544
The causal completeness of the physical doesn’t require that every event have a sufficient physical cause: physicalism is quite consistent with genuinely chancy causation. After all, what physicalism ultimately requires is that nothing have a non-physical cause. Once the physicalist has accounted for all the causation going, indeterminism is neither here nor there.
Zhong transfers this insight from the causal relationship to the ontological dependence of higher-level phenomena on the physical. He argues that that dependence, similarly, doesn’t require ontological determination. In other words, higher-level phenomena can wholly depend on the physical without being determined by it.
If true, that would free physicalism from the onerous burden of supervenience. Which means, among other things, it would no be longer threatened by zombie arguments! Nor would it be dogged by the difficulty of establishing supervenience empirically (which I think Zhong over-eggs a bit—both parsimony and induction help with what he calls the “establishment question”).
Zhong is correct, I think, that ontological dependence doesn’t require determination. Those are distinct relationships. But I think he’s wrong that physicalism is compatible with mere ontological dependence.
Zhong (p.1538) mentions a counter-argument from Witmer: if X isn’t sufficient for Y, then something else over and above X is required to make it true that Y. If X is “the physical”, then the something else is extra-physical, and physicalism is false. Zhong thinks Witmer has ignored the possibility of indeterminism: that nothing else besides X makes Y the case, things just turn out that way.
But: even if there is no third party Z that combines with X to produce Y, you still need something over and above X to make it the case that Y obtains. Namely, Y itself! Y is not part of the physical base (by hypothesis), nor is it merely a metaphysical consequence of the physical base (as wholes are to the arrangement of their parts, or realisations to realisers). In Kripke’s famous metaphor, God still has some work to do, after creating X, to put Y in the world.
Interestingly, Zhong mentions the creator-God metaphor (p.1539):
If God rolls dice to see what effects will follow the causes, it should also be okay for God that the higher-level phenomena arise out of the lower-level bases as a matter of probability.
This seems right; God could indeed roll dice for vertical as well as horizontal relations. But notice the shift in agency. God’s role here is limited to “being OK” with high-level phenomena arising chancily. But the point of the metaphor is that God is the creator; things aren’t there unless he puts them there. If God inserts Y after rolling dice—rather than out of some deliberate purpose—he is still doing the extra work.