Lately I’ve been fiddling with a thought experiment that seems to suggest the causal efficacy of higher-level properties and objects, and have been wondering how such causal efficacy may be compatible with causal closure of the physical (more exactly microphysical) domain. Since I am gullible and prone to make mistakes I present my half-baked ideas on these matters, in search of further criticism and illumination.
As a non-reductive physicalist, I want to maintain the existence and causal efficacy of higher-level objects, properties, and events (that is, at levels higher than the microphysical). And since I am also a physicalist, I am required to acknowledge the causal closure of the microphysical, i.e., that if a microphysical event has a cause, then it has a microphysical cause. But there is a tension between these two positions: if higher level entities have non-redundant causal powers, then this leads to downward causation (the microphysical level is open to causal input from higher levels). Downward causation, in turn, seems to violate the causal closure of the microphysical. Kim‘s causal exclusion argument and Merricks‘s overdetermination argument exploit this tension in favor of reductive or eliminative physicalism.
I believe that the tension ought to be resolved without giving up the causal efficacy of higher level entities. Now I have a thought experiment which convinces me of their causal efficacy. The basic idea behind the thought experiment is this. Our social world is rife with conventions, and these conventions are arbitrary. For instance, it is the convention everywhere to drive on one side of the road (right or left), but each country could just as well have adopted the alternative convention of driving on the other side of the road. Hence the movements of hundreds of millions of car-wise arrangements of microparticles could have been vastly different. This seems to indicate that our traffic conventions (in addition to microphysical laws) determine the movements of these microparticles, which is an instance of downward causation.
My thought experiment builds on the basic idea that the movements of microparticles this way or that way depend causally on the adoption of this or that rule of convention. So, consider the game pieces on the chess board, moved about in accordance with the rules of chess. These pieces are composed of microparticles, and the movements of these microparticles on the board are microphysical events which have microphysical causes. Sure, these game pieces are moved about in accordance with the rules of chess. But given the causal closure of the microphysical, the movements of the microparticles composing the pieces would be fully determined by the laws of microphysics.
Now here’s the twist. Take the game of kness, which is exactly like the game of chess, except that the knight can only jump over pawns (I suppose the clergy and the royalty might appreciate this rule). Whenever we sit down to play a game of chess, we might decide to play kness instead. And if we decide to play kness instead chess, everything else remaining the same up to the moment of the decision, then the movements of the knight-wise arranged atoms on the board would be systematically different from those in the game of chess.
So, what accounts for this systematic difference between the kness game we play and the chess game we could have played in this scenario (and in the correspondingly different movements of knight-wise arranged atoms)? It cannot be the laws of microphysics, since they remain the same regardless of whether we play in accordance with the rules of chess or kness. It cannot be the initial positions, velocities, and other intrinsic/extrinsic properties of the microparticles at the start of the game, since we have stipulated these to be the same in our ceteris paribus clause, “everything else remaining the same”. Therefore, the systematic difference can only be accounted for by the difference in the rules of chess and kness, which govern the movement of chess pieces. These rules, when rigidly followed by the players, dictate the systematically differential movements of knight-wise arranged microparticles in kness as opposed to chess.
Objection 1. By now, of course, you will have noticed a gaping loophole in my ceteris paribus clause, which allows us to get around the conclusion just reached. The physicalist who affirms the causal closure of the microphysical domain will surely insist that everything could not have remained the same up to the moment of our decision to play kness instead of chess. There would have been differences in the microphysical states underlying the intention to play kness and the intention to play chess. Moreover, the determinist would add that I am assuming, in that ceteris paribus clause, the libertarian position that free choice uninfluenced by physical causes and influencing physical events is possible. This libertarian assumption begs the question against causal closure of the physical domain, and renders the argument in the previous paragraph circular.
My Response. Now, I believe these physicalist responses are red herrings (I especially do not want to mix up the issue of the causal efficacy of higher level entities with the debate between determinists and libertarians on the free will). The loophole can easily be mended, as follows. Instead of human players, imagine two computers playing against one another in a room. These are programmed to move about the game pieces on the board in accordance with the rules of chess or kness. This eliminates the room for human error. And let’s rig up the room to a setup like that of the Schroedinger’s Cat: a Stern-Gerlach device measures the spin of a quantum object in a superposition state, and according as the measured spin turns out to be up or down, the computers play chess or kness. This allows us to get around the issue of human free choice. Whether the computers play chess or kness depends on the probabilistic outcome of the measurement, everything else remaining the same up to the moment when the measurement takes place. Then our old conclusion still stands. The laws of microphysics and the initial states of the microparticles cannot account for the systematic difference in the movements of knight-wise arranged microparticles in chess and kness. Only the different rules of chess and kness do that. (There is, of course, a difference in the spin of the quantum object which triggers a game of kness as opposed to chess. But this only explains why the computers play kness instead of chess. It doesn’t explain the systematically different movements of knight-wise arranged microparticles in chess and kness.)
In later posts in the same series, I hope to anticipate and address some further objections that a redutive physicalist is likely to make, and suggest a way of resolving the tension between causal closure and downward causation. But quite likely I will face insurmountable objections. So, more half-baked ideas on the way in the next few days!