Abstract
Russellian physicalism is a view on the nature of consciousness which promises to satisfy the demands of both traditional physicalists and non-physicalists. It does so by identifying subjective experience with physically acceptable categorical properties underlying structural and dispositional properties described by science. Though promising, the view faces at least two serious challenges: (i) it has been argued that science deals in both categorical and non-categorical properties, which would undercut the motivation behind Russellian physicalism, and (ii) it has been argued that only nonphysicalist Russellian views—like panpsychism—are useful when it comes to explaining consciousness. I address these criticisms, arguing that there is no viable reason for maintaining that science deals in categorical properties of the sort which a Russellian physicalist is interested in, and that features of fully-physical categorical properties can be described which provide useful explanations for various essential features of subjective experience. These projects are connected: it turns out that when the explanatory relevance of Russellian physicalism is explained in detail, constraints are put the sort of categorical properties that Russellian physicalists can say are left out of science. Specifically, Russellian physicalists are forced to subscribe to the view that science leaves out any categorical properties whatsoever, as opposed to the view that some scientifically scrutable properties are categorical, but not the ones which Russellian physicalists are interested in. I hope that by addressing these criticisms of Russellian physicalism, and drawing logical connections between the responses, further appeal is added to a promising, but so far relatively unexplored, view.
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Notes
One might think that some of these arguments straightforwardly contradict physicalism, rather than supporting inscrutability. For instance, the conceivability argument (Chalmers 1996) typically concludes that physicalism is false. However, as Chalmers (2015) acknowledges, this argument tacitly assumes that physical properties are scientifically scrutable properties, and the argument fails to rule out physicalism if a broader view of physical properties is assumed.
This definition of ‘physical’ is consistent with via negativa physicalism (Smith 1993; Papineau and Spurrett 1999; Levine 2001; Montero 2005; Montero and Papineau 2005; Worley 2006), which says the essence of a physical property is that it is not identical to nor dependent upon anything which is fundamentally mental, but not theory-based physicalism (Hellman and Thompson 1975; Smart 1978; Hellman 1985; Poland 1994; Melnyk 1997, 2002; Stoljar 2001), which says that ‘physical’ means ‘a posit of physics, or entirely dependent upon posits of physics’. For present purposes it suffices to take the via negativa understanding of physical as a sufficient-for-false condition on physicalism, such that the existence of fundamentally mental properties would make physicalism false. Nearly everyone accepts this sufficient-for-false condition, even if they think a full understanding of the physical requires something else in addition (e.g. Wilson 2006).
Whether fundamental properties must be properties of fundamental objects is a metaphysical issue that Russellian physicalists can remain neutral on. As an alternative to a substance-based metaphysics, bundle theory says that there are only properties which are bundled together, and no additional substances or non-property-objects which the properties are attached to.
By “protomental” I mean a property which is especially suited to generating mentality. These properties are unlike e.g. the subatomic properties as discussed by particle physicists, which may be capable of generating higher-level mentality, but are not especially suited to this purpose. A counterfactual test devised by Morris (2016) can determine whether a property is protomental in a physically problematic way: if it is possible for some world’s protomental properties to be swapped with non-protomental properties, and there would be no other change save a difference in mentality, then the protomental properties of that world are physically unacceptable. When I speak of protomental properties, I am only thinking of physically unacceptable protomental properties. Further arguments that protomental properties of this sort are unacceptable under physicalism can be found in Howell (2009) and Brown (2017).
These are not the only criticisms of Russellian physicalism, but I believe other criticisms have been sufficiently dealt with elsewhere. For instance, it has been argued that Russellian physicalism is a disguised version of non-physicalist panprotopsychism (Morris 2016); that it leads to epiphenomenalism (Howell 2015); and that it cannot solve the combination problem of generating human consciousness from non-human-conscious properties (Chalmers 2016). I appeal to the respective solutions to these criticisms from myself (Brown 2017), Alter and Coleman (2019, forthcoming), and McClelland (2013), though versions of these issues will come up as I progress.
An alternative and less popular way of articulating Russellian physicalism says that science may invoke categorical properties of some sort, but that there are more fundamental pure categorical (or “super-categorical”) properties underlying the posits of science. I will address both of these routes to Russellian physicalism.
It is worth mentioning the “powerful qualities” view, championed by Martin (1997) and Heil (2005). Under this view, properties are simultaneously categorical and dispositional, and neither aspect is prioritized over the other. I must admit that I have some difficulty understanding this position—since “categorical” means “non-dispositional”, and it seems somewhat odd that one and the same property can be both dispositional and non-dispositional—but let me nonetheless try to describe the relationship between this view and Russellian physicalism. If all properties can be correctly referred to via a description or concept which invokes only dispositions, then all properties are scientifically scrutable, even if science only employs disposition-invoking descriptions. As far as I can tell, this would render the Russellian physicalist position on the hard problem nonviable, which means that Russellian physicalism and the powerful qualities view are not consistent with each other.
Since I am using the term ‘feature’ to refer to any property of a property, it will turn out that non-categorical properties will have features which mention their categorical role-fillers; e.g. non-categorical property N has the feature of depending upon categorical property C. This is not an issue for Russellian monism so long as categorical-mentioning features of non-categorical properties are omitted from science. Similarly, super-categorical properties will have non-categorical properties, e.g. C has the property of forming part of the dependence base for N. This is not an issue for super-categorical Russellian monism so long as these non-categorical features are not essential to super-categorical properties.
This account assumes that dispositional properties depend on spacetime relations between categorical relata, and that any fundamental categorical relata suffice to generate spacetime-dependent dispositions. However, one might wonder why property swaps among fundamental categorical properties are less absurd than property swaps among non-fundamental categorical properties—perhaps the intuition that swaps of the former sort are less absurd than swaps of the latter sort comes from a bias concerning the ontological specialness of middle-level objects like ourselves and the objects we are directly acquainted with in perception. Though this may be, it does not significantly affect my overall argument, since (i) this sort of Humean mosaic account of reality is quite popular, and (ii) I will end up defending super-dispositional Russellian physicalism rather than super-categorical Russellian physicalism.
One might worry that these commitments of super-categorical Russellian monism collectively entail that fundamental categorical properties are protomental in a way which precludes them from being physically acceptable, similar to a problem discussed by Morris (2016) and myself (Brown 2017) for Russellian physicalism generally. This is because it seems that categorical properties make no difference to the properties of physics, since the properties of physics are non-categorical and swapping fundamental super-categorical properties has been stipulated to make a difference to only higher-level categorical properties. If all non-fundamental categorical properties are phenomenal properties, then it seems that super-categorical properties are mentality-specific. A super-categorical Russellian physicalist has a way out of this problem, which follows my (Brown 2017) lead: if there are non-fundamental categorical properties which are non-mental, then swapping fundamental super-categorical properties will affect these non-mental properties as well. Assuming that the notion of a non-mental, non-fundamental categorical property is coherent, this allows super-categorical Russellian monists to endorse physicalism.
Of course, other primitive sensory or sensory-like properties can be posited, such that there is primitive color, and primitive sound, and primitive smell, and so on for all the sensory modalities. In my eyes, this further illustrates how ridiculous the primitive color proposal is: there would have to be as many types of fundamental categorical properties as there are sense modalities (and likely more—one for every kind of color, sound, smell, etc.), and somehow they would have to be employed in the brain in a way that selectively instantiates appropriate sensations in appropriate physical contexts. I find such a view both ugly and implausible.
My goal at this point in the paper is to show that Russellian physicalism is consistent with some basic requirements for mental causation. Toward the end of the paper, I will sketch out some more specific Russellian physicalist accounts of causation.
I use pain as an example of a phenomenal property which has an obvious behavioral requirement. Some may find my selection problematic on the grounds that some phenomenal properties do not seem to have a specific behavioral requirement—e.g. seeing the red of an apple seems not to necessitate any particular behavior. I nonetheless feel that at least some phenomenal properties should necessitate some behavioral dispositions, which is why I focus on pain in this paper. It also seems reasonable that clusters of phenomenal properties should necessitate behavioral dispositions, such as the phenomenology of seeing an apple eliciting the disposition to make the appropriate hand behavior to grasp the apple (if the apple is desired).
Some Russellian monists hold that there are possible worlds which have not just different categorical properties from our world, but no categorical properties at all (see Morris 2016). They also hold that such worlds could be alike in all non-categorical respects to our world. This is disanalogous to the mousetrap metaphor, since it seems inconceivable that a part of a mousetrap could instantiate the property of being bait without some lower-order role-filler. However, in my eyes, Russellian monists lose nothing by giving up the view that non-categorical-only worlds are possible, since the Russellian answer to the conceivability argument can be secured without this commitment. Further, denying the possibility of such worlds strengthens the motivation for Russellian monism, since it would be metaphysically impossible for a world to only instantiate the structural and dispositional properties described by science without there also being categorical role-fillers.
If absolute intrinsicness is only inherited by non-fundamental properties which are constituted by fundamental categorical properties, then non-fundamental properties which depend on fundamental categorical properties without being constituted by them cannot have absolute intrinsicness. This seems to rule out functional role properties from being identical to phenomenal properties under Russellian physicalism, since functional role properties are generally recognized to depend on their lower-order realizers without being constituted by them. A Russellian physicalist might still endorse realizer functionalism, and say that the actual-world realizers of appropriate functional role descriptions are identical to phenomenal properties. What exactly ‘constitution’ means remains open—my hope is that this openness allows Russellian physicalism to be consistent with a range of views on the nature of non-fundamental categorical properties. See the discussion at the end of the next section for some options.
One might wonder whether we can acquire knowledge of the phenomenal properties of non-humans through instantiation of qualitatively identical phenomenal properties, e.g. by somehow generating bat-like experiences in a human. I am unsure whether this should count as knowledge, and perhaps it depends on whether those bat experiences were generated through chance (as in a dream), or through a more deliberate and reliable process, like neurosurgery. Even if knowledge of bat phenomenology can be acquired through neurosurgery (or something similar), the ineffability of phenomenology is still secure, since a person still only knows about the phenomenology of a bat by having the experiences of a bat.
It may be hard to see why categorical properties should be partially defined relative to laws which necessitate non-categorical properties, since it seems that categorical properties themselves are distinct from laws and from necessitated properties. While I admit that this may be an issue for laws-based accounts of necessitation, it is not a special problem for Russellian physicalism.
Thanks to an anonymous Erkenntnis referee for pushing me on this.
Upon investigation, it may turn out that one or more of these solutions to the Russellian-monism-specific exclusion problem are barred to a Russellian physicalist. Unfortunately, such an investigation is beyond the scope of the present paper, and it suffices for present purposes that each of these solutions is at least prima facie available to a Russelian physicalist.
One might object that the reductionist route eliminates non-fundamental categorical properties, since there seems to be nothing more in this ontology than fundamental categoricals and their relations. However, I think reduction of this sort is not elimination: a non-fundamental categorical property N might be identical to the set (F1, F2, RF1,F2), which is the conjunction of two fundamental properties and a relation between them. This set is not identical to any individual fundamental property—so non-fundamental categorical properties are not eliminated under this view, if one is a realist about these sets.
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Much thanks to Torin Alter and to anonymous Erkenntnis referees for useful feedback on prior drafts.
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Brown, C.D. Consciousness and Categorical Properties. Erkenn 88, 365–387 (2023). https://doi.org/10.1007/s10670-020-00359-5
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DOI: https://doi.org/10.1007/s10670-020-00359-5