Almost immediately after posting Downward Causation II, I had realized that my response to Objection 2 is flawed. I will briefly discuss that here. Then I will present my proposal for resolving the tension between downward causation and causal closure. Namely, I will argue for the conceptual possibility of downward causation in the same way that Pascal argued for the conceptual possibility of God as a simple and yet omnipresent entity. If God is simple in the sense of being unextended and hence indivisible, how is it conceivable that God is present throughout space at any given moment? Pascal’s answer: think of an indivisible point moving in all directions at infinite speed. Now, Einstein’s special relativity shows that the existence of such an entity is physically impossible, but we may grant Pascal that he succeeds in showing it conceptually possible. Similarly, I will try to show the conceptual possibility of downward causation on the supposition of causal closure.
Objection 2 suggested that the difference between the arrangements of microparticles composing into a computer running chess or kness can explain the systematic difference between the movements of knight-wised arranged microparticles in chess and kness. This obviates the need to posit the laws of kness and chess regulating the movements of microparticles in addition to the laws of microphysics.
In response I had noted that even on this suggestion there should be a nomic correlation between microparticles arranged chess- or kness-program-wise and other microparticles moving systematically according to chess or kness rules. And there must be indefinitely many nomic correlations like this, since there are indefinitely many conventional rules. So much I have argued in the previous post, and in the present post I had intended to use multiple realizability considerations to argue that these nomic correlations themselves are best subsumed under irreducible and higher-level conventional rules than under base-level microphysical laws.
But now it seems to me terribly misguided and confused to accord the status of law to rules of convention. There’s a world of difference between laws which regulate the behavior of objects with natural necessity, and rules of convention which do not. The computer is a mechanism that operates with natural necessity in accordance with the laws of mechanics, designed to produce output that covaries with input. The rules of chess or kness are part of the input, i.e., instructions that we feed to the mechanism on how it should process incoming data. The mechanism then carries out these instructions with nomic necessity, not because its behavior is governed by these instructions, but because it is governed by the laws of mechanics. In general, if computers and brains can be modeled abstractly as universal Turing machines, rules of convention should be understood as instructions fed to the machines as input, rather than as laws regulating the physical implementations of such machines.
My final assessment, then, is that the thought experiment fails to establish downward causation. As this is not the desired result, I am a bit disappointed. At least I know now that an argument aiming to show downward causation should appeal to irreducible laws which operate with natural necessity rather than to rules of convention.
Now let me explain why I think there need not be unacceptable conflict between downward causation and causal closure. This is often presented as a matter of conceptual impossibility: if there is causal closure of the microphysical, then it is impossible or inconsistent to conceive that downward causation occurs.
Let me suggest one conceivable way of reconciling downward causation with causal closure of the microphysical. This is by adopting a pluralistic account of causation in the real world. Now, there are many different accounts of causation available: e.g., various regularity accounts dating back to Hume, the counterfactual analysis due to Lewis, the recent manipulationist account of Woodward, probabilistic accounts, conserved quantity theories (Salmon, Dowe), etc. I think the best account of the nature of causation in the real world will combine a nomic subsumption account with a conserved quantity account. Namely, actual instances of causation will involve the propagation and transfer of universally conserved quantities (like mass-energy) in natural processes in accordance with laws of the form “in relevantly similar circumstances, similar things will happen”. By laws here I don’t mean just laws of nature which are exceptionless, but also the invariances captured by ceteris paribus generalizations made in the special sciences. We can also add qualifications to allow for probabilistic laws.
If we accept such a pluralistic account of causation, we see that the claims of downward causation and causal closure of the microphysical are ambiguous, and that there is a disambiguation of the two claims which can reconcile both with one another. When I accept the causal closure of the microphysical domain, what I accept is that the domain as a whole is one in which matter-energy (and other universally conserved quantities) are conserved. But I deny that matter-energy is conserved only in accordance with microphysical laws. The conservation is also in accordance with higher-level laws. And when I accept that higher-level laws make a difference in the collective behavior of microparticles, I am not claiming that higher-level objects and properties generate new fundamental forces which inject additional energy into the microphysical domain. I am only claiming that new laws emerge at higher levels which channel the fundamental forces in the microphysical domain in new ways. So I deny what Terry Horgan says about causal emergentism, i.e., that it views higher level properties “as fundamental force-generating properties [which] generate new forces over and above those generated by the causal properties of physics, so that the net force affecting the distribution of matter is different from the net physical force.” The net force is the same, there is a difference only in the nomically patterned ways of channeling the fundamental forces at the microphysical level. To continue in this figure of speech, the microphysical laws are coarsely patterned, whereas the laws at higher levels are more finely patterned. This figure of speech may not be very helpful, but it is the only way in which I can conceive the compatibility of downward causation and causal closure.
Footnotes to Hume 