Brian Cutter & Dustin Crummett (University of Notre Dame), “Psychophysical Harmony: A New Argument for Theism"
Forthcoming, Oxford Studies in Philosophy of Religion
Dustin Crummett and I have a new paper, “Psychophysical Harmony: A New Argument for Theism,” forthcoming in Oxford Studies in Philosophy of Religion. It concerns a puzzle about consciousness that, according to Philip Goff, is “going to change the world.” In this post, I’ll explain what psychophysical harmony is, why it seems to call for explanation, and why it seems especially puzzling from the standpoint of naturalistic atheism. Dustin and I aren’t the first to discuss the puzzle of psychophysical harmony. Versions of it have been discussed by Adam Pautz, Philip Goff, David Chalmers, Hedda Hassel Mørch, Brad Saad, among others. Nor are we the first to suggest that it poses a prima facie threat to naturalistic atheism. Pautz writes, concerning one kind of psychophysical harmony, “What—short of an intelligent designer—might explain why the psychological laws are actually ‘fine-tuned’ to result in normative harmony?” Noa Latham writes, concerning another kind of psychophysical harmony that seems to be implied by David Chalmers’ views in The Conscious Mind, that it’s “in need of a benevolent God to make it credible” and that “actual theists might herald this as a new argument from design.” But unlike most other philosophers who have discussed the puzzle of psychophysical harmony, we draw the natural inference. We think of the psychophysical harmony argument as loosely analogous to the more familiar cosmological fine-tuning argument for theism, focused on the psychophysical laws (laws linking physical states to phenomenal states) rather than laws of physics and cosmology. But the psychophysical harmony argument has one major advantage: it’s not vulnerable to multiverse responses (or so we argue—see sect. 4 of paper).
For an initial presentation of the problem, it will be convenient to make two metaphysical assumptions about consciousness. The problem remains even if we drop both, for reasons I’ll discuss below, but the assumptions make it easier to get an initial handle on the issue.
The first assumption is dualism. Experiences are not identical with physical processes in the brain, dispositions to behave in certain ways, or anything like that. Nor do the physical truths metaphysically necessitate the truths about experience. Experiences are linked to physical states of matter by fundamental, metaphysically contingent “psychophysical laws.” The second assumption is the causal closure of the physical. The physical events involved in behavior and brain processing have exclusively physical causes. Taken together, our two assumptions amount to something like epiphenomenalist dualism, a view that many naturalistically minded dualists have found attractive (e.g., David Chalmers, Frank Jackson, and Thomas Huxley). On this view, experience is a byproduct of physical activity in the brain, but experience doesn’t exert “top-down” causal influence on brain processing or behavior. Since experience is not causally responsible for our behavior, our behavior would presumably have been the same if the psychophysical laws had mapped physical states onto phenomenal states in different ways.
Given dualism, it’s natural to suppose that more-or-less any conceivable way of systematically mapping physical states onto experiences corresponds to a possible set of psychophysical laws. It will be helpful to get a sense of the range of possibilities here. First, there will be zombie worlds—worlds physically like ours but without experience—which are governed by our physical laws but feature no psychophysical laws. There will also be worlds with psychophysical laws different from our own. Some possible laws would yield spectrum inversion, giving us greenish experiences in the physical circumstances that produce reddish experiences in the actual world. Some possible psychophysical laws would have made us “partial zombies,” giving us (say) visual phenomenology but no auditory phenomenology, or neutral sensory experience but no affectively valenced experience, or sensory and affective phenomenology but no cognitive phenomenology. Some possible psychophysical laws would have assigned experience to different physical systems, as in worlds physically like ours where only rocks are conscious, or worlds where elementary particles are conscious but all macroscopic physical systems are zombies. Some possible psychophysical laws draw from a more impoverished palate of phenomenal qualities, associating all physical states with the same boring gray phenomenology, or with a small set of slightly different ringing sensations. Some possible psychophysical laws are only sensitive to micro-scale physical patterns, not higher-level functional/computational patterns, as in worlds where each specific microphysical configuration of the particles in your brain is associated with a slightly different TV-static-like experience.
Now for the puzzle of psychophysical harmony. Psychophysical harmony consists in the fact that experiences are correlated with physical states and with one another in strikingly fortunate ways. One kind of psychophysical harmony is what Pautz calls normative harmony, which occurs when the descriptive role of experience is harmoniously aligned with its normative role. The most straightforward examples involve affectively valenced experiences like pain and pleasure. The descriptive role of pain includes the fact that it is typically associated with withdrawal from the pain-causing stimulus, avoidance of similar stimuli in the future, etc. This behavior tends to lead to the elimination or reduction of pain when we have it and the avoidance of pain in the future. Pain also has a normative role: it is non-instrumentally bad; it is an experience we have reason to avoid and to eliminate/reduce when we have it. The two roles are nicely aligned. Generally speaking, pain is associated with the behaviors it gives us reason to perform, the very behaviors it justifies or rationalizes. The same goes for pleasure.
Given our dualist assumption, it didn’t have to be this way. Imagine a hedonic-inversion scenario, a world where the psychophysical laws swap the descriptive roles of pain and pleasure. (Here I use “pain” and “pleasure” to denote, respectively, unpleasant and pleasant experiences generally, even though “pain” has a somewhat narrower sense in ordinary language.) In this hedonically inverted world, bodily injury results in pleasure, which is followed by withdrawal from the pleasure-causing stimulus and avoidance of similar stimuli in the future. Eating glucose-rich berries results in an unpleasant experience, which is followed by behavior that prolongs the experience and a strengthened disposition to engage in the pain-causing behavior in the future. Here the descriptive roles of pain and pleasure are badly misaligned with their normative roles. We systematically avoid an experience we have reason to pursue and pursue an experience we have reason to avoid.
Or consider a scenario where the psychophysical laws pair all brain states with chaotic, affectively neutral TV-static experience (perhaps a slightly different TV-static experience for each possible microphysical configuration of the brain). In this scenario, we systematically act in ways that promote certain kinds of normatively neutral TV-static phenomenology, and we systematically avoid other kinds of normatively neutral TV-static phenomenology. Here things aren’t as bad as in the hedonic-inversion scenario, but this scenario is still lacking a kind of psychophysical harmony present in our world.
Evolution can’t explain normative harmony. Evolution can explain why we have a brain state that selectively responds to bodily damage and causes withdrawal, avoidance behavior, and the like. But evolution can’t explain why the psychophysical laws of our universe conveniently map this physical state onto an experience whose normative role matches this functional role, an experience that rationally justifies avoidance behavior, withdrawal, etc. Evolutionary forces can’t affect the psychophysical laws, so it’s hard to see how an evolutionary explanation of psychophysical harmony could even get off the ground. And given our causal closure assumption, it’s not like the physical behavior/functioning of organisms would have been any different under alternative psychophysical mappings. Since natural selection only responds to physical behavior/functioning, we’d expect evolution to produce the same physical structures under alternative psychophysical mappings, resulting in disharmony.
Normative harmony seems very lucky. It seems to cry out for explanation. It doesn’t seem to admit of an evolutionary explanation, and in the paper we argue that other naturalism-friendly explanations fail (e.g., the suggestion that experiences have their normative features in virtue of their contingent descriptive roles, so that the experience of pain is bad in virtue of its contingent connection to avoidance behavior).
Beyond hedonic experience
So far I’ve focused on one very specific example of normative harmony: the fact (roughly) that hedonic experiences are paired with behavioral dispositions in ways that respect norms of practical rationality. In the paper, we discuss several other examples of normative harmony that don’t involve hedonic experience, including: (i) cases where sensory experience is paired with behavior/functioning in ways that respect norms of epistemic rationality, (ii) cases where sensory experience is paired with cognitive phenomenology in ways that respect norms of epistemic rationality, and (iii) cases where cognitive phenomenology is paired with behavior in ways that respect norms of instrumental rationality, among others.
We also discuss another kind of psychophysical harmony, semantic harmony, which occurs when experiences are linked to physical states in a manner that induces semantic correspondence. For example, a certain brain state disposes us to make structural claims about our experience, such as “I experience a smooth black expanse immediately next to a sharply contrasting smooth white expanse.” The psychophysical laws pair this brain state with an experience of a smooth black expanse next to a sharply contrasting white expanse. The report you are disposed to make is thereby true. But if the psychophysical laws had instead paired your brain state with TV-static phenomenology, or buzzing phenomenology, or uniform gray phenomenology, or almost anything else, your structural report would have been untrue.
Given epiphenomenalist dualism, an especially striking form of semantic harmony has to do with our metaphysical statements about consciousness. (This is closely related to what Chalmers calls the “meta-problem of consciousness.”) We have a brain state that disposes us to make metaphysical claims about consciousness, like “I currently possess a property (consciousness) that is (e.g.) irreducible, non-physical, fundamental, modally independent of the physical, etc.” The psychophysical laws associate this physical state with a state that is irreducible, non-physical, fundamental, and modally independent of the physical. Thus, the metaphysical statements we are disposed to make are true, despite the fact that what makes them true (consciousness) is epiphenomenal. Neither the presence of consciousness nor the fact that consciousness is irreducible (etc.) play any causal role in generating our reports about the presence and metaphysical nature of consciousness. No mechanism in the brain is triggered by the presence of an irreducible (etc.) phenomenal state. If we had lived in a nomologically simpler world without psychophysical laws, a materialist zombie world with only our physical laws, these reports would have been untrue. Likewise if the psychophysical laws had only assigned consciousness to non-verbal physical systems.
Psychophysical Harmony is Surprising on Naturalism
All these forms of psychophysical harmony seem like lucky coincidences, at least from the standpoint of naturalist atheism. It seems that most conceivable sets of psychophysical laws— most ways of pairing physical states with experiences—would have failed to generate anything approaching the degree of psychophysical harmony we find in our world. One might respond that, even if most psychophysical mappings would be disharmonious, the simplest mappings are harmonious. In that case, given an a priori bias toward simpler theories, psychophysical harmony may not be especially surprising given naturalistic atheism. But on reflection, it’s not very plausible that the simplest mappings would be harmonious. The psychophysical laws would be simpler if they mapped all physical states onto the same experience of buzzing noise, or if they mapped each physical object onto a grayscale sensation, with phenomenal brightness proportional to the object’s mass, or if they only assigned experiences to subatomic particles, perhaps with a limited palate of simple phenomenal qualities corresponding to basic physical properties like charge or spin. None of these mappings would induce the level of psychophysical harmony we find in our world. Relatedly, it’s striking that the psychophysical laws, unlike other fundamental laws, appear to operate on relatively macroscopic physical states, such as neural firing patterns or high-level information structures in the brain. As J.J.C. Smart remarked, it is this feature of the dualist’s ultimate laws that give them an odd “smell,” unlike anything else known to science. We might have expected the psychophysical laws to instead be directly sensitive to microphysical phenomena, with our conscious experiences somehow mirroring the microphysical structure of our brains. But that would result in a chaotic and disharmonious mess.
So it seems like psychophysical harmony was very improbable on naturalism. Now, this fact by itself is no reason to doubt naturalism. (The exact arrangement of papers on my desk was also very improbable on naturalism.) However, the naturalist should be worried if there is some other hypothesis H incompatible with naturalism such that (i) psychophysical harmony is not extraordinarily improbable on H, and (ii) the prior probability of H is not extremely low. We argue in the paper that theism is such a hypothesis, though I won’t argue for this here. If theism is such a hypothesis, then a fortiori, so is the disjunction of theism with a certain other non-naturalistic views, such as axiarchism (John Leslie, Derek Parfit), value-involving laws of nature (Thomas Nagel, Brad Saad), and some non-theistic designer hypotheses like Paul Draper’s “aesthetic deism.” Psychophysical harmony seems relatively unsurprising on each of these hypotheses, and we don’t argue that psychophysical harmony favors theism over these theism-adjacent views. But we do think that psychophysical harmony provides very strong evidence against naturalistic atheism.
The Causal Closure and Dualist Assumptions are Unnecessary
Dropping causal closure in favor of interactionist dualism doesn’t avoid the problem. On interactionist dualism, pain plays a certain nomological role involving both “bottom-up” causation (e.g., c-fiber firing → pain) and “top-down” causation (e.g., pain → avoidance behavior). But if the psychophysical laws had slotted other experiences into this nomological role (e.g., pleasure, a neutral gray sensation, or just about anything else), there would have been disharmony. The appearance of psychophysical luck remains.
We also argue that the problem remains even if we drop the assumption of dualism and start with a substantial prior probability for physicalism. As long as there is at least an epistemic gap between the physical and the phenomenal (as there is according to the most popular form of physicalism, so-called “type-B” or “a posteriori” physicalism), the Bayesian reasoning in our argument goes through just fine. We need only be careful to distinguish epistemic possibilities from metaphysical possibilities and remember that epistemic probabilities are distributed over epistemic possibilities. (For the details of this argument, see section 3.2 of the paper.)
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