Beversluis, Kim, and C. S. Lewis on causal closure
Here is an interesting passage in Beversluis chapter on the argument from reason:
JB: Naturalists believe that everything that happens within the total system is caused by something internal to it, so that nothing is independent in a way that enables it to escape this vast interlocking causal web. In short, nature is a self-contained and closed system. By "closed" Lewis means causally closed. So defined, naturalism is a form of determinism--the philosophical theory that everything that happens, happens necessarily as a result of antecedent causes given which nothing could else could have happened. So by naturalism, Lewis means deterministic naturalism. thus, he declares, "no thoroughgoing naturalist believes in freee will (M1, 17). It is important to notice that his argument depends on the assumption that there are ony two alternatives: deterministic naturalism and supernaturalism. If other choices exist, the refutation of the former would not entail the truth of hte latter, as Lewis claims it does.
VR: So in this passage Beversluis commits Lewis to understanding naturalism as deterministic, with the implication that forms of naturalism that deny determinism are not naturalistic. Intereesing Lewis does discuss the denial of determinism through quantum-mechanical indeterminism and says that this would be a rejection of strict natruralism but not an affirmation of supernaturalism, since it would admit a Subnatural realm rather than a supernatural realm. I have discussed this in a couple of posts, but what I had not seen before was the fact that Beversluis seems to think that causal closure entails determinsm.
As defined by contemporary philosophers such as Jaegwon Kim, closure does not entail determinism. Kim writes:
JK: The first of these is the principle that the physical world constitutes a causally closed domain. For our purposes we may state it as follows:The causal closure of the physical domain. If a physical event has a cause at t, then it has a physical cause at t.
There is also an explanatory analogue of this principle (but we will make no explicit use of it here): If a physical event has a causal explanation (in terms of an event occurring at t), it has a physical causal explanation (in terms of a physical event at t).8 According to this principle, physics is causally and explanatorily self-sufficient: there is no need to go outside the physical domain to find a cause, or a causal explanation, of a physical event. It is plain that physical causal closure is entirely consistent with mind-body dualism and does not beg the question against dualism as such; it does not say that physical events and entities are all that there are in this world, or that physical causation is all the causation that there is. As far as physical causal closure goes, there may well be entities and events outside the physical domain, and causal relations might hold between these nonphysical items. There could even be sciences that investigate these nonphysical things and events. Physical causal closure, therefore, does not rule out mind-body dualism--in fact, not even substance dualism; for all it cares, there might be immaterial souls outside the spacetime physical world. If there were such things, the only constraint that the closure principle lays down is that they not causally meddle with physical events--that is, there can be no causal influences injected into the physical domain from outside. Descartes's interactionist dualism, therefore, is precluded by physical causal closure; however, Leibniz's doctrine of preestablished harmony and mind-body parallelism, like Spinoza's double-aspect theory,9 are perfectly consistent with it. Notice that neither the mental nor the biological domain is causally closed; there are mental and biological events whose causes are not themselves mental or biological events. A trauma to the head can cause the loss of consciousness and exposure to intense radiation can cause cells to mutate.
VR: In short, the causal closure principle doesn't imply that there are determining physical causes for every event, only that there are no non-physical causes for any event. The argument from reason, on the other hand, if successful, intends to show that there are non-physical causes for the mental states involved in rational inference. The causal closure principle that Kim presents is sufficient to generate argument from reason. If Lewis had had Kim's definition of causal closure to work with, he would not have saddled the naturalist with determinism, but the argument from reason would not have been effected, since if the AFR works, it requires not merely the denial of physical determinism but also of the causal closure principle as defined by Kim.