The Problem with Metaphysical Naturalism (According to Victor Reppert)

Victor Reppert and I have had a long series of exchanges (thirty five years) dating back to when we were both graduate students at Emory University. I do not think that we would come to agreement even if we were granted another thirty five years to debate, but I am determined at least to get clear on the grounds of some of our disagreements. As always, philosophical debate is impeded by the slipperiness of definitions. You think that you have ably refuted an opponent’s claim that X is Y, and he replies, “Ah, if I had meant by “X” and “Y” what you mean, your argument would succeed, but what I mean by “X” and “Y” is…” And so it goes, if not ad infinitum, at least ad nauseam. Could souls be natural entities? Well maybe if by “natural” you mean… Let me try then to draw a definitional line in the sand so that Victor and I can avoid frustration and not pull out the little hair each of us has left.
metaphysical naturalism (MN) is like the slogan “What happens in Vegas stays in Vegas”: “The causes of effects in the natural world stay in the natural world.” The “natural world” (which I also call “the physical universe”), in its broadest characterization, I understand to be space/time itself plus the matter and energy it contains and the fundamental laws that hold within this totality. MN as I understand it holds (1) that the total cause of any effect that occurs in the physical universe is also part of the physical universe (or perhaps just is the whole physical universe), and so the physical universe is causally closed. (2) The physical universe itself, in its most general, fundamental, or primordial features neither has nor needs a cause. (3) Putative non-physical entities, like Platonic forms, might exist, but they have no power to cause anything in the natural world.

I am a metaphysical naturalist (I am also willing to call myself a physicalist or a materialist). I think the simplest characterization of
If Victor is willing to accept my characterization of MN, perhaps we can spell out clearly some of the reasons he thinks that MN is unacceptable. Based on what he says in our most recent exchange, and in many earlier communications, I think that he objects that MN cannot account for four fundamental features of our mental lives:
It seems to me that a physical explanation, if we are sticking with standard definitions and are not expanding the notion of the physical to include things it doesn’t traditionally include, our concept of what it is for something to be a physical explanation, at least at the base level of analysis, is for it to lack four “mentalistic” characteristics. First, the explanation at the base level cannot include a purpose. Second it cannot include any intentionality. What a physical state is about cannot enter into the base-level explanation. Third, it cannot include any reference to normativity. No piece of matter, in the last analysis, goes where it goes because it ought to go there. Fourth, a naturalistic explanation of a material state cannot contain any reference to a first-person perspective.
He further adds that on the hypothesis of naturalism: “…the base level [of causation] is causally closed. This doesn’t mean that it’s deterministic, it means that nothing outside the physical system can affect where a particular atom goes, whether it’s an atom in a rock or an atom in a brain.”
I agree with everything Victor says in the two above quotes. I take it for granted that the brain’s activities, like any other physical effects, can be explained entirely in physical terms. In explaining neurons and their incredibly complex interactions, we will of course make no reference to purpose, intentionality, norms, or first-person experiences—no more than we would in explaining supernovae or the immune system. Yet, as Searle says, our conscious mental life is defined by its qualitative, intentional, and first-person aspects. As I have previously indicated, I see any attempt to deny, diminish, or dismiss the reality of consciousness as deeply pathological, bordering on derangement. Victor reminds me that eliminativists and behaviorists (who did deny, diminish, or dismiss the givens of consciousness) were trying to be consistent naturalists. There is something heroic (or maybe quixotic) about the attempt to buy consistency at the price of denying the undeniable—kind of like a theist who would attempt to circumvent the problem of evil by denying the existence of evil.
Besides, the mock-heroics of eliminativists and behaviorists were totally unnecessary. Can a naturalist consistently countenance explanations in terms of purposes, reasons, norms, etc.? I think so. Consider two alternative accounts of how Sam acquired a belief:
Why does Sam believe that Congressman Ryan’s budget proposals are ludicrous and cruel? Because he read Paul Krugman’s editorial making the argument that those proposals are ludicrous and cruel, and these arguments convinced Sam. Sam was swayed by Krugman’s deft use of logic and command of the economic facts in showing that the Ryan proposal would not alleviate the deficit, and would serve chiefly to further enrich the already fabulously wealthy while adding an extra burden of misery to those already miserable. Sam was particularly impressed by Krugman’s citation of reliable sources such as the Congressional Budget Office. Is this a legitimate explanation of why Sam believes that Congressman Ryan’s budget proposals are ludicrous and cruel? Absolutely. Let’s call this “explanation A.”
Now consider another, far more complex and unfamiliar explanation of why Sam believes that, etc. Actually, it will be an explanation-sketch, since it will be extremely incomplete: From time T1 to time T2 Sam’s brain was in a succession of active states, S1…Sn where that succession of brain states completely realized a succession of mental states, M1…Mn culminating in a mental state, Mn, which was Sam’s conscious conviction that Congressman Ryan’s budget proposals are etc. Each of those brain states S1…Sn will be complexly caused, being conditioned in part by other internal brain states and by the brain’s interaction, via the optic nerve, with light that has reflected from newsprint. That reflected light stimulates the production of nerve impulses in the eye which are carried by the optic nerve to the brain’s visual cortex, where it is complexly processed in intricate connection with other areas of the brain. Now, supposing that this explanation-sketch could be filled out to a reasonable degree of completeness (like events inside a tornado, brain events may be too complex to model completely) would this be a legitimate explanation of why Sam believes that Congressman Ryan’s budget proposals are, etc.? Absolutely. Let’s call this “explanation B.”
I think what really divides us is that Victor holds that explanation A is incompatible with explanation B and I do not. Which of us is right? Victor is right if explanations A and B are mutually exclusive causal explanations of why Sam has his belief. I am right if they are causal explanations but do not mutually exclude. Alternative causal explanations need not compete. Why is it raining hard? Because the atmosphere at cloud level was saturated and the temperature dropped sharply causing the moisture to precipitate rapidly. Another explanation is that a strong cold front collided with a warm, humid, and unstable air mass generating strong thunderstorms. These accounts invoke different causal mechanisms, but are not mutually exclusive, and, indeed, are complementary.
Another possibility is that explanation A and explanation B do not mutually exclude because, though they both are explanatory, one is a causal explanation and the other is not, so they do not make competing claims about what caused Sam’s belief. Not all explanations are causal explanations, not even in science. The classic Hempel/Oppenheim deductive-nomological (DN) model of scientific explanation is a non-causal account. On the DN model, a natural occurrence is explained by subsuming it under a broader nomological. The orbital period of a particular natural satellite is explained by showing that this motion is predicted by Kepler’s Third Law of planetary motion, and by the appropriate initial conditions (the satellite’s distance from the sun). In short, this regularity is explained by showing it to be an instance of a broader regularity; no mention is made of the cause of the planet’s orbital motion. So, might it not be that one of the explanations of Sam’s belief is causal, and the other is non-causal, and they do not make competing claims?
Explanation B is obviously causal. My view is that explanation A is causal too, though in an indirect manner and we have to be very very careful to specify just what is doing the causing. When we say that Sam was convinced by Krugman’s arguments it seems to me perverse to attribute some very (I think in-principally) mysterious kind of causal power to the sense or propositional content of Krugman’s arguments. Attributing causal powers to Fregean Sinn (meaning), if this is what Victor wants to assert, just seems to me a straightforward category mistake. It is like saying that the set of all integers broke the deadlock between NFL players and owners. No, to say that Sam was convinced by Krugman’s arguments means that Sam considered Krugman’s claims, examined the supporting reasons, weighed them in the light of prior knowledge and norms of good reasoning, and judged that these were persuasive. However, considering Krugman’s claims, examining the supporting arguments, evaluating them, and judging them to be persuasive are things that Sam does with his brain, and happenings in Sam’s brain, being physical events, can cause things.
But if Sam’s belief is to be rational, must it not be Krugman’s reasons that convinced him, and is this not, ineluctably, to make a causal claim about the efficacy of those reasons in bringing about Sam’s agreement? No. The reasons qua propositional content (which are abstract objects) did not make Sam believe. Reasons qua propositional content can have no more causal powers than the least prime greater than one billion. Reasons have no causal power but reasoning does. Reasoning is something we do with our brains; it is an activity, a brain activity, just as doing jumping jacks is an activity of our moving limbs. The reasoning process, being fully realized in brain processes can have, qua physically realized, causal efficacy as much as any other physical process. Recognizing that Krugman’s arguments are cogent causes the recognition that his conclusion is supported. Recognizing is a physical process that can cause other recognitions.
But when asked why we believe something, don’t we typically cite reasons, and speak of these reasons as being the cause of our beliefs: “Yes, it was the reliable facts and figures Krugman cited, such as the report of the Congressional Budget Office, that led me [or maybe “compelled me” if I was initially skeptical of his claim] to accept his conclusion.” Terms like “led” and “compelled” imply causes. Yes, we do normally speak this way, as do I. But if I were being philosophically punctilious, I should say that it was not the reasons themselves that compelled me but my becoming aware of those reasons that compelled me—and becoming aware of reasons is something that the brain does.
For these reasons, I see explanations A and B as complementary and not competitors. Indeed, the chain of reasoning that caused Sam to reach his conclusion would be realized in that succession of brain states, S1 to Sn mentioned in explanation B. Now I am sure that absolutely nothing I have said here will settle anything between Victor and me. For one thing, Victor says that physical processes underdetermine mental ones. How does he know this? Has anyone observed two brains in an identical physical state but with different mental states? All the evidence—ALL—seems to support the claim that physical processes are necessary and sufficient for the mental. Where are the counterexamples? Saying “God” or “the soul” would obviously beg the question against me since I see no evidence whatsoever for either of these putative entities.

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