What about the placebo effect, then? Those are examples of 'top-down causation' which would mitigate against a physicalist explanation, would they not? — Wayfarer
Mental causation is such a widespread phenomenon that one hardly needs to appeal to such things as the placebo effect to exemplify it. I decide to raise my hand and, lo and behold, my hand rises. The decision might have been the result of a deliberative process (and hence of 'mental events') while the outcome is a material process. There would appear to be a complete explanation couched in terms of low-level material/physiological processes that explains in causal terms why it is that my hand rose there and then. Those two explanatory levels pertain to two different domains (i.e. the intentional level of description of behavior, and the physiological level of description of biological processes) that still can be construed to relate to one another by an asymmetrical supervenience relation. You might (counterfactually) have decided to raise your hand earlier, or later, or not at all, but, in such cases, some of the antecedent circumstances of the physical motion of your hand necessarily would (counterfactually) have been different. We can count 'brain states' as part of those antecedent circumstances. Those are (low-level) neurophysiological states which instantiate, or realize, the (high-level) 'reasons' (roughly construed as beliefs and desires) why you would have decided to raise your hand there and then. (I am not actually endorsing this internalist representationalist view of mental content but it is good enough for the sake of simplicity and doesn't prejudge the present argument.)
So, the mere exemplification of mental causation, as an instance of (apparent) downward-causation, in the real world isn't threatening to the supervenience story. Someone who endorses Kim's causal exclusion argument might still acknowledge that the downward-causal story in terms of mental-causation constitutes a useful coarse-grained explanation of the observed event. In spite of its usefulness, Kim would argue that such an explanation is causally redundant because the genuine cause of the 'event' that occurred, as described fine-grainedly in terms of the low-level physiological or physical description, is operative independently of the high-level characterization of the process.
It's true that if we define the outcome (such as someone's arm raising) fine-grainedly in terms of underlying physiological or physico-chemical processes then the outcome is fully determined to occur in a causal sense. From this fact, Kim derives his causal-exclusion conclusion. He argues, on the basis of supervenience, that the outcome could not have been different unless the low-level causal antecedent had been different. And hence, the low-level explanation is deemed to be complete. And hence, the high level explanation, albeit useful for making coarse-grained predictions in the absence of specific knowledge of the underlying low-level properties, is causally redundant. We may thus conclude that 'the mental' (that is, the high-level intentional/psychological functional properties that supervene of the domain of physical states) is epiphenomenal.
The conclusion is unwarranted and very few critics of Kim manage to uproot the fundamental ground of his confusion, and hence the core flaw in his argumentation, although Peter Menzies and Christian List may have come closest in my opinion.
The main flaw in Kim's conception, I think, is that he tends to tacitly and uncritically rely on a metaphysical-realist stance towards low-level material constituents and, on the other hand, on an empiricist or nominalistic stance towards high-level composite entities that are materially constituted by those low-level constituents. While the individuation criteria by means of which we single out (coarse-grainedly) the high-level entities and define their (high-level) powers and properties are somehow defined pragmatically, or theoretically, the low level constituents (such a atoms and molecules, or whatever) are assumed to be causally efficient irrespective of our categorizations of them.
This is a picture that is very strongly indebted to the modern conception of classical mechanics: of objectively real particles and the objectively real forces being exerted between them (or the force fields mediating those forces). 'Objectively real' here is meant to signify that something exists independently of contextual factors or high-level relational characterrizations. The fundamental ground for all genuine causation in the material world consists in the intrinsic properties of corpuscules, and their intrinsic powers to affects the properties of other particles. Everything else that is being defined in terms of aggregates or emergent relational properties is supervenient on this fundamental 'objective' description.
How is Kim's argument affected if we relax those metaphysical assumptions and grant the same ontological status to relational properties that we accord to (putative) intrinsic properties of elementary material constituents? It collapses entirely, on my view. And the reason for that is very simple. If we acknowledge the idea that what makes something what it is isn't exhausted by what it is that this thing is materially constituted of but also is defined by its functional relations to other things, and also by the pragmatic context relative to which this thing is being single out as being representative of a definite category, of instantiating some definite property, then the distinction between the low-level basis of supervenience and the higher-level supervenient domain is abolished. Complete knowledge of the intrinsic properties of the material constituents, and of they elementary mutual interactions, would still constitute an incomplete knowledge of the world since it is fully abstracting away from
what it is that those material constituents are constituents of.
Hence, for instance, the low-level explanation for the putative 'event' that was the occurrence of an upward movement of a hand doesn't constitute any kind of a rival
causal explanation of the intentionally described event of someone's raising her hand. If what makes this action the action that it is precisely is a context of prior deliberation (for instance) then such actions must be distinguished from upward motions of a hand that might be the result of a stroke, or a strong gust of wind, or whatever. It is thus quite irrelevant that a strict supervenience relation still holds between the domain of intentional behavior and the material-physical domain. The low level explanation can't compete with the high-level one because it abstracts away from the very fact that the low-level outcome (the hand motion) happens to be an instantiation of the phenomenon that we sought to explain, and hence it doesn't even begin to explain why it is that a voluntary
action intelligibly occurred.