Jaegwon Kim has developed an argument that interactionist dualists cannot account for the causal relations between minds and brains. This paper develops a closely related argument that focuses instead on the causal relations between minds and neurons. While there are several promising responses to Kim’s argument, their plausibility relies on a relatively simple understanding of mind–brain relations. Once we shift our focus to neurons, these responses lose their appeal. The problem is that even if mind–brain causal pairing can be explained at no great theoretical cost, the complex interactions non-physical minds would need to have with neurons cannot.
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Kim attributes his worry originally to Foster (1968).
Kim spends little space elaborating on this requirement, and so he might not accept my formulation of the relevant principle. It differs slightly from what other commentators have provided. Audi (2011) uses "if two things interact causally, they instantiate a pairing relation" (p. 4). Bailey et al. (2011) use "for all x and all y, if x causes y, then there is a relation or relations… such that their holding makes it the case that x causes y" (p. 350). Saad (2017) uses "necessarily, objects differ causally only if they differ non-causally" (p. 725).
One notable difference between my formulation and these others is that mine concerns causal powers rather than causal relations. A causal power encapsulates an object's (probabilistic) potential to produce causal effects in specific situations. There is a sense in which a 'causal power' is a property in its own right, but this is not the intended sense. Rather, a 'causal power' here is intended merely as a description of an object's tendency to cause changes. Causal powers in this sense cannot explain causal relations. Instead, they summarize them. The advantage of formulating the principle in terms of causal powers is that it allows for unaccountable differences in the chancy instantiation of causal relations. Saad (2018) develops a related idea.
It has been taken for granted in this debate that such differential pairing between indistinguishable minds and brains is possible. There is no empirical evidence for this. While it is intuitive, we must be deeply skeptical about the reliability of our intuitions with respect to natural laws. Nevertheless, the possibility of indistinguishable brains under the control of indistinguishable minds illustrates a larger issue: the intrinsic properties of minds do not appear to be the right kind of properties to determining pairing, even if they should turn out to actually vary in countless subtle ways between individuals.
Kim is sympathetic with the view that spatial properties are characteristic of the physical, and hence if we ascribe minds spatial relations, we thereby concede to physicalism.
There are currently billions of human minds, trillions of vertebrate minds, and untold numbers of alien minds. There were many more minds in the past (that presumably would have controlled only their individual bodies had they managed to survive to the present) and no limit to the number of possible future minds.
While these minds may be phenomenally and intentionally distinct, it is unlikely that intrinsically distinct minds differ in their causal powers entirely in virtue of their non-causal differences so long as intrinsically identical minds also differ in their causal powers.
This is not to say that neurons are identical. On the contrary, neurons can be distinguished from each other in a variety of ways: size, arborization, mylination, and neurochemistry. However, these distinctions don't correspond with the sorts of distinctions that would be needed to guide neural discernment. It is possible that there are elusive neurons whose distinctiveness could ease discernment, but interactionists should not rest their hopes on the oversights of neuroscience. Even if some neurons were distinguished by the structure, they would most likely be composed of the same parts as other neurons. The problem would arise again at a lower level as the ion channel discernment problem.
According to a dominant view in the neuroscience of cognitive representations:
Active representations in the mind are thought to correspond to the patterns of activation generated over a set of units… This representational scheme is held to apply to essentially all kinds of cognitive content: Words, letters, phonemes, grammatical structures; visual features, colors, structural descriptions of objects; semantic, conceptual, and schema representations; contents of working memory and contextual information affecting processing of current inputs; speech plans, motor plans, and more abstract action plans — all are thought to take the form of distributed patterns of activation over large neural populations. (Rogers and McClelland 2014, p. 1038)
Even among the minority of cognitive scientists sympathetic with the existence of grandmother neurons, the possibility that complex concepts or propositions are represented by single neurons is not taken seriously. Bowers (2009), for instance, mounts an intriguing defense of the claim that grandmother neurons may play a role in face or word recognition, but does not go so far as to suggest that they are responsible for the representation of whole scenarios or complex action plans.
One example of this comes from grasping studies:
Whether [people] grasp objects with one orientation or another depends on how they plan to orient the objects. Where along the lengths of objects they grasp the objects depends on the height to which they plan to carry the objects… Plans can take into account a multiplicity of factors, including bio-mechanical efficiency and comfort, the relative importance of different kinds of costs such as the symmetry or asymmetry of bimanual movements, and considerations of other needs. (Rosenbaum et al. 2012, p. 26).
These studies indicate that our behavior is sensitive to unconscious computations of considerations relevant to consciously set goals. We often do not realize the utility of our grasping choices until they are pointed out to us.
There might be no clean separation between perceptual representation, outcome valuation, and goal description in the brain (Anderson 2014). This would relieve interactionists of having to explain how a mind might produce a representation of a goal within the brain, but it doesn't solve their fundamental challenge. Minds would still need to influence the factors that go into producing action. Instilling a goal representation simplifies the process. The task of influencing actions through altering neural representations of outcome evaluation, the perception of affordances, fine motor representations, or something intermediate between these would be at least as complex.
I will leave Alvin Plantinga's theistic intervention response out of the following, though I take it to be perfectly adequate for those with the right prior commitments. Plantinga (2007) observed that pairing might be achieved by divine concurrence. God only concurs with some of the possible causal outcomes of our mental states. In the context of the present proposal, while our intentions may be sufficient to trigger every neuron in our brains (or every neuron everywhere), God only concurs with a causal effect on a very specific subset of neurons.
Omnipotence can overcome many philosophical problems. The chief drawback of this proposal, aside from its theistic assumption, is that it demands quite a lot more divine intervention than metaphysicians have lately been tempted to accept. If our minds are incapable of discerning the neurons that and are not to be activated, then God must be responsible for deciding and producing the behavioral products of all of our intentions.
Kim was explicitly concerned with substance dualism rather than property dualism, but the issues facing the latter view are similar. Property dualists, by attributing mental properties to physical objects, may secure some connection between physical and mental properties by virtue of co-inherence. The appeal of this route and its problems mirror those of pairing by spatial co-location discussed in this section, or pairing by union relations discussed in the next.
Kim's argument takes the form of a series of difficult questions for interactionists: Where are minds located? Why don't minds count as material objects? How do minds have enough structure to produce complex effects on the brain? (2005, pp. 88–90).
A difficult question is not an argument, but rather an appeal to intuitive implausibility. Our intuitions about such things are often malleable, and are subject to overturning as the field of conceivable theories expands. The last of these difficult questions is the most serious, since it carries a hint of the neural discernment problem.
This complements Chalmers' response to the purported advantages of interactionism over epiphenomenalism:
Even on [interactionism], there is a sense in which the phenomenal is irrelevant. We can always subtract the phenomenal component from the explanatory account, yielding a purely causal component… Some might argue that psychons (or ectoplasm, or whatever) are entirely constituted by their phenomenal properties. Even so, there is a sense in which their phenomenal properties are irrelevant to the explanation of behavior; it is only their relational properties that matter in the story about causal dynamics. (1996, pp. 157–58)
Foster (1968) proposes that we need a primitive notion of 'ownership' to make sense of mind-brain pairing. Whether or not it is a proper instance of the present proposal, it bears a sufficient resemblance to share its problems.
Jehle (2006) makes a similar point.
Bailey et al. (2011) briefly consider a version of this hypothesis. They attribute the persistence of a mind's causal powers to its historical properties: the fact that the mind was created by the brain is sufficient to explain why the mind continues to hold sway over that brain. It is more plausible that a brain might produce a mind with the standing properties necessary to subsequently influence it, because purely historical properties are not known to play roles in causation.
Kim introduces the pairing problem in the context of a discussion of reductive theories of causation. The viability of brute causation will depend in part on the viability of reductive theories: Humean approaches to causation cannot make sense of brute causation. If reduction about causation is required to motivate the pairing problem, then the argument will be dialectically ineffective, because dualism correlates with opposition to such theories.
There is a difference between brute causality, in which there is no explanation of the causal relation, and haecceitistic causation, where causation is explained by haecceitistic differences. This distinction is important in part because haecceities may persist through time and thereby explain diachronic patterns of interaction. Haecceitistic causation falls under the third proposal.
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Shiller, D. Interactionism for the discerning mind?. Philos Stud 177, 931–946 (2020). https://doi.org/10.1007/s11098-018-1213-5
- Pairing problem
- Mental causation