Mental causation is not load-bearing

In philosophy of mind, “mental causation” means mental entities have causal effects, especially physical ones. If physicalism is true, then physical effects are explainable in terms of physical causes (or at least, fundamental physical laws), needing no recourse to causation by anything that is not in fundamental physics. This is the “causal exclusion principle” explicated by Jaegwon Kim (and recently cited in “The Abstraction Fallacy…”), which suggests that, if physicalism is true, then mental entities cannot causally affect anything physical, except insofar as they are already physical entities.

Substance dualists believe in mental causation rather straightforwardly: they believe that the soul has physical effects. Of course, substance dualism contradicts standard physics and physicalism. Type-identity physicalists believe that mental kinds reduce to physical kinds, and that as such, mental causation is a form of physical causation. Mental causation is contrasted with epiphenomenalism, a view under which physical causes can have mental effects but not vice versa.

Epiphenomenalism (e.g. in property dualist form) faces a number of epistemic problems:

Why did evolution create consciousness if consciousness has no physical effects?

If our conscious experience has no physical effects, why would our reports about our experience correlate with our experience?

Why are the physical-mental correlations the way they are, isn’t this unparsimonious?

Mental causation can help answer these questions. Mental causation can explain why minds have evolutionary utility, why mental facts correlate with reports about them, and why a unified explanation of physical and mental entities could be parsimonious.

However, I suggest that mental causation is not essential to addressing these problems, and that intelligible supervenience of the mental on the physical matters more. By “intelligible supervenience”, I mean that it is not mysterious why the physical facts imply the mental ones. For example, the state of a VM in a computer intelligibly supervenes on the hardware state; it is not hard to understand VM states using hardware specifications and operational semantics. Meanwhile, many philosophers of mind believe that the concept “red qualia” does not intelligibly supervene on neurological states, as it’s mysterious how any neurological state could lead to the experienced redness of red.

More specifically, by intelligible supervenience, I mean that higher-level facts can be explained in terms of grounding low-level facts, by unpacking both the high-level and low-level concepts involved. The explanation may require empirical discovery and need not be available a priori. But an intelligible explanation does not involve brute, opaque bridge laws connecting the higher-level facts to the lower-level facts. Once the realization relation is understood, the correlation ceases to appear arbitrary. Chalmers’ “logical supervenience” (a priori conceptual entailment) is somewhat stronger; I mean intelligible supervenience to be a better match for the way in which scientific subject matter supervenes on physics, which involves empirical study, not just conceptual analysis.

I suggest that intelligible supervenience addresses the epistemic problems of epiphenomenalism, and that mental causation fails to address these problems when it does not go along with intelligible supervenience. I will contrast two views, epiphenomenalist functionalism and Russellian monism, to demonstrate the point.

Epiphenomenalist functionalism

Functionalism is the view that existent mental states are functional, psychological states. For example, functionalism says that memory is a cognitive process which stores and retrieves information, including sensory information and the outputs of object recognition processes. This process may or may not be localizable in the brain; memory could be a distributed function realized by multiple brain regions, rather than being in one place.

Functionalists can be physicalists, and can “bite the bullet” on the causal exclusion principle. Perhaps human memories do not have causal effects, because memory is a distributed function, and it is the fundamental entities in the human brain (e.g. particles) that have causal powers, not distributed functionality.

Functionalists need not believe that mental states have causal effects. We can associate a mental state with its physical macrostate (the set of physical microstates compatible with the mental state), but it is not entirely clear how to attribute causal powers to physical macrostates. Maybe causation only exists at the microscopic level, not the macroscopic level. Thus, functionalist physicalists may be epiphenomenalists.

By analogy, imagine a child playing a game of Minecraft. The child believes that entities in the game, such as creepers, are having causal effects, such as blowing up buildings.

A physicalist could say that causation is really at the hardware level: fundamental particles have causal effects, which explains how the hardware works, and the hardware’s dynamics explain why the Minecraft software works. This explanation does not need to attribute causal powers to Minecraft entities such as creepers. And the supervenience relationship is intelligible: it is not hard to see how a hardware state would specify the positions of different creepers.

The physicalist’s epiphenomenalist account explains why Minecraft players could develop the belief that creepers have causal effects, even though creepers don’t “really” have causal effects. There are no remaining hard questions like “why does the building blow up if the creeper isn’t causing it to blow up?”.

Analogously, functional psychological states can seem to have causal effects, even if some physicalist views deny them causal powers. We can answer the epistemic questions from before. Evolution produces functional psychology, because functional psychology correlates with fitness-increasing behaviors via brain states. Functional psychology correlates with reports about our consciousness, because functional psychology intelligibly correlates with brain states that make such reports (as brain states without such functional psychology would not tend to cause such reports). And because the supervenience is intelligible, there is not a severe problem of parsimony. If we can explain the physical brain states, there are few or no needed extra assumptions to understand why the brain would have the functional properties it does; it’s primarily a matter of unpacking the functional concepts and noticing the realization match.

Epiphenomenalist functionalism, therefore, may avoid epistemic problems associated with epiphenomenalism, despite in principle denying mental causation. The basic epistemic objections to epiphenomenalism have responses. For prior work on pattern realism and physicalism, see Daniel Dennett’s “Real Patterns” and David Wallace’s “Decoherence and Ontology, or: How I Learned To Stop Worrying And Love FAPP”.

Russellian monism

Russellian monism combines three theses:

Structuralism about physics

Realism about quiddities

Quidditism about consciousness

Bertrand Russell claimed physics is structural, in that it specifies lawful relationships between quantities, but does not specify the intrinsic nature of its fundamental entities:

All that physics gives us is certain equations giving abstract properties of their changes.

But as to what it is that changes, and what it changes from and to—as to this, physics is silent.

In particular, gauge-invariant quantities (such as mass) are straightforwardly physical, while gauge-dependent ones (such as absolute positions of particles, if they have any) are not. “Quiddities” are posited intrinsic essences of the entities in fundamental physics. They have intrinsic properties that physics does not specify. According to Russellian monism, quiddities are real, and their structure is (or includes as sub-structure) the structures of physics, e.g. quantum field theory may correctly specify a subset of relationships between quiddities.

Russellian monism further posits that these quiddities are relevant to consciousness. In particular, in reductive form, it claims that consciousness does not logically supervene on physics, but does logically supervene on the full reality, which includes quiddities; see Philip Goff’s “Against Constitutive Russellian Monism” for details.

There are panpsychist variants of Russellian monism, which claim that quiddities have experiential qualitative properties (as many philosophers suppose human “red qualia” do), and panprotopsychist variants, which claim that quiddities have some non-experiential properties (perhaps qualitative) which give rise to human experiences, and help explain the phenomenal qualities present in human experience.

As a cartoon version of panpsychist Russellian monism, imagine that a ghost is excellent at mental visualization, and visualizes a great number of small shapes (some colored, others not), which change (perhaps due to the ghost’s intentions, or perhaps “on their own” in awareness) in such a way that they realize the structure of our physical universe, e.g. perhaps they evolve according to cellular automaton rules that underlie physics. One can imagine variants, such as multiple ghosts passing visual shapes to each other telepathically.

Panpsychist Russellian monism endorses mental causation, in that quiddity-level experiences have causal effects on physics. The ghost’s qualia could causally affect the properties of fundamental particles, and higher-level physics. If the ghost’s visualization broke the usual laws of physics, the disturbance could propagate to observable violations of these laws. Thus, panpsychist Russellian monism is not epiphenomenalist.

However, Russellian monism denies intelligible supervenience of the mental on the physical, so mental properties cannot be inferred from physical properties. Imagine a “P-colorblind” human, who is physically identical to a normal human, and yet has no color qualia. Perhaps the ghost visualizes colored shapes when “implementing” the physics of normal humans, yet visualizes grayscale shapes when implementing the physics of P-colorblind humans. Russellian monists would consider this scenario conceivable, for similar reasons as with P-zombies.

This scenario raises epistemic problems, since P-colorblind humans report colored qualia just like normal humans. It is not apparent why human reports of colored qualia would correlate with these humans being made of colored quiddities, how humans could know they are not P-colorblind, how they could know their past selves or other people around them are not P-colorblind, why evolution would not create P-colorblind humans, and so on.

As such, Russellian monism faces similar epistemic problems as epiphenomenalist property dualism does. Even though Russellian monism (at least panpsychist forms) has a place for the mind in fundamental causality, it does not explain why such fundamental mental properties would correlate with human reports about their mental properties. The core reason for this is that it denies intelligible supervenience of the mental on the physical.

For prior work on epistemic problems with Russellian monism and panpsychism, see David Lewis’s “Ramseyan Humility” and Keith Frankish’s “Panpsychism and the Depsychologization of Consciousness”.

Type-identity physicalism

A physicalist view endorsing mental causation is type-identity physicalism. According to this view, mental kinds (e.g. “pain”) are physical kinds (e.g. “C-fiber stimulation”, or some similar neuroscientific kind). If pain is C-fiber stimulation, then pain can have causal powers inherited from C-fiber stimulation. This makes it understandable why people might report pain when their C-fibers fire, as the C-fibers cause downstream mental effects (themselves identical with physical effects).