Type B physicalism is a view in philosophy of mind, and “powerful qualities” (PQ) theory is a view in the metaphysics of properties. They share an important similarity: they both combine conceptual dualism with ontic monism. Type B physicalists hold that phenomenal concepts (e.g. concepts of reddish experience) are not analytically definable in terms of physical concepts, yet can co-refer (“pain is C-fiber firing” being a simplified example), and that every property is a physical property. PQ theorists claim that there are both qualitative concepts (referring to qualities such as the redness of a red object) and dispositional concepts (referring to tendencies such as the disposition to reflect ~700nm light), and that every property is both really qualitative and really dispositional; hence, qualitative concepts co-refer with dispositional concepts.

I suggest that type B physicalism combines well with powerful qualities theory. First, generalizing phenomenal concepts to qualitative concepts makes phenomenal concept theory less ad hoc. Second, considering “phenomenally conscious” as a secondary qualitative concept, and considering un-conscious qualities to exist, yields a more comprehensible theory. Third, philosophical debates about the two views are similar, and type B physicalists find themselves in a similar dialectical place to PQ theorists.

Background

I take type B physicalism to be the conjunction of three theses:

• Physicalism: There are no non-physical mental properties. Here, a property is physical if it is specified by a physical predicate, and a physical predicate is a predicate definable in terms of the predicates of fundamental physics, or in other words, a predicate logically supervenient on those of fundamental physics. Such predicates include Fodor’s “wildly disjunctive” functional predicates and ordinary scientific predicates. I take it that two predicates can refer to the same property, the way two nouns can refer to the same thing (“Hespherus is Phosphorous”).
• Non-analyzability: There are concepts of phenomenal experience (“phenomenal concepts”) which have no analytic definitions in terms of physical predicates. In other words, phenomenal concepts form predicates that are not logically supervenient on physical predicates. In particular, it is ideally negatively conceivable that there could be beings physically the same as humans but with different phenomenal properties, e.g. P-zombies, or people whose color qualia are spectrum-inverted.
• Phenomenal realism: Some phenomenal concepts are positively satisfied. In particular, some humans are phenomenally conscious.

Non-analyzability rules out analytic functionalism; phenomenal realism rules out strong illusionism. I take property dualism and Russellian monism to be paradigm non-physicalist views.

Powerful qualities theory, in strong form, is John Heil’s identity view:

If is an intrinsic property of a concrete object, is simultaneously dispositional and qualitative; ’s dispositionality and qualitativity are not aspects or properties of ; ’s dispositionality, , is ’s qualitativity, , and each of these is : .

As an example, perhaps an object’s qualitative redness is a light reflectance property, and perhaps an object’s sphericity is its spherical dispositions (e.g. rolling down slopes). Dispositional properties are more straightforwardly measurable by physical devices, e.g. an object’s disposition to exert forces or reflect light can be measured by standard instruments. The physics notion of “observable” includes dispositional properties that are only measurable in ideal imagination, not in practice.

Quoting Philip Goff on sensory qualities (Consciousness and Fundamental Reality):

Before Galileo, philosophers took the world to be full of sensory qualities: colors, smells, tastes, sounds. And intuitively one cannot capture the redness of a tomato, the spicy taste of paprika, or the sweet smell of flowers in the austere, abstract language of mathematics. Galileo got around this problem by stripping the world of such qualities and locating them in the soul.

And quoting SEP on primary and secondary qualities:

Many philosophers maintain there is a significant difference between primary and secondary qualities but disagree about its foundation. It may be plausible that we perceive things as having a small number of basic qualities which are determinates or degrees of the following: size, figure, extension, duration, motion, position, color, taste, odor, sound, heat, coldness, and tactual qualities such as hardness, softness, roughness and smoothness. The first six (to which solidity and number are sometimes added) are called “primary”; roughly speaking, they are said to be real objective properties of objects and to be distinctly known. The remaining, called “secondary”, are said to be in some way—metaphysically, epistemically, linguistically—derivative, less than fully real, or otherwise metaphysically feeble; or misleading, subjective, ambiguous, or otherwise not perspicuous.

Physics has more to say on primary qualities than secondary qualities. Qualia are generally considered to have secondary qualities even if objects don’t have them, e.g. the redness of an experience of red light. For the purposes of this post, I will consider secondary qualities to be ones without accepted conceptual reductions to physics. In this sense, I don’t consider “heat” a secondary quality, except as qualia.

Since PQ theorists hold that every dispositional property is a qualitative property, they believe that secondary qualities exist both in objects and in the mind. PQ is contrasted with a “pure powers” view, under which only dispositional and not qualitative properties are positively instantiated, and a “pure qualities” view, under which only qualitative and not dispositional properties are positively instantiated. Roughly, the objection to “pure powers” is that dispositional properties face a regress problem, never grounding in any disposition for a variable to take on a value; and the objection to “pure qualities” is that non-dispositional properties are physically and epistemically idle.

A natural “conceptual dualist” approach PQ theorists can take, analogous to that of type B physicalists, is to say that concepts and predicates can be dispositional-only or quality-only, but that properties are all simultaneously dispositional and qualitative. This approach helps explain why people can believe that PQ is false without running into analytic contradiction. It is not supposed to be obvious that dispositional properties are all qualitative properties and vice versa; it could perhaps be the case that no knowledge of dispositional predicates suffices to know which qualitative predicates are satisfied. This non-analyzability could include the philosophy of mind non-analyzability of “red qualia” into physical or functional concepts.

The concordance between type B physicalism and powerful qualities has been noted in the literature (H. Taylor 2017, H. Taylor 2024).

Is the red in the head?

We more easily bridge the gap between type B physicalism and powerful qualities by imagining a world w’ of direct realists, following Byrne 2006. In this world, people believe that the secondary quality of color is a property of objects. They don’t believe in qualia; they believe there are really colors on the objects out there, and that they directly perceive these colors. Moreover, they do not believe object colors are analytically reducible to physical properties. Their debates mirror the qualia debates of our own (predominately indirect-realist) world.

These w’ inhabitants consider a physical property which is reliably correlated with objective redness (crudely, ~700nm light emission, but better specified than that). Philosophers of w’ argue for an epistemic gap between and redness. One could just as well conceive of going along with blueness and (a refinement of “~450nm light emission”) going along with redness.

As such, inhabitants of w’ face a hard problem of color. There are at least 3 general approaches:

• Dualism: Color properties are non-physical properties. Redness is not or any other physical property. Psycho-physical bridging laws and/or interactions explain why they correlate.
• Eliminativism: No color predicates are positively satisfied. Color qualities do not exist.
• Identity: Redness is , that’s why they correlate. This identity is either a priori (if color swaps are not really ideally conceivable) or a posteriori (if color swaps are ideally conceivable).

The arguments against dualism need not be rehearsed. Inhabitants of w’ are strongly disposed to reject color eliminativism. And they usually reject a priori conceptual links on the basis of conceivability arguments and related intuitions. As such, a posteriori identity theory is well worth considering, though it faces conceptual obstacles.

The identity theory equates a qualitative property (redness) with a dispositional property (, a disposition to emit a light spectrum in some range). So it posits a powerful quality, though it need not generalize PQ to all properties.

If this identity (“redness is ”) is correct in w’, then perhaps a related identity is correct in our world. Perhaps some neural-representational physical property is identical with the property of “having red qualia”, for example. If “having red qualia” is a qualitative predicate, and the neural property has a dispositional predicate (e.g. tendency to respond positively to an ideal measurement of the neural cluster), then these predicates would naturally refer to the same dispositional and qualitative property.

Phenomenal concepts as qualitative concepts

An important element of type B physicalism is the phenomenal concept strategy (PCS). The objective is to explain the conceivability gap between physical and phenomenal predicates (e.g. why P-zombies are conceivable), in a way compatible with physicalism and phenomenal realism. In particular, PCS should explain why there are no analytic definitions of phenomenal concepts in terms of physical and functional ones.

The general idea is that, when people have experiences, they form phenomenal concepts of those experiences. When Mary of Mary’s Room sees red the first time (say, by seeing a tomato), she forms a direct phenomenal concept (call it R) on this basis. This allows her to form a justified true belief she lacked before: “Tomatoes look like <R> to me”, in her “mentalese” private language. Here, “<R>” indicates a use, not a mention, of the phenomenal concept R.

To preserve compatibility with physicalism, this new knowledge must be about a physical property. In particular, there is some predicate P, which can in principle be stated in physical language, which is true of Mary if and only if “Tomatoes look like <R> to me” is true of her (in her mental language), picking out the same (physical) property. Mary could in principle have known P without leaving her room, even though it refers to the same property that “Tomatoes look like <R> to me” does. Again, this is conceptual dualism combined with ontic monism.

One criticism of PCS is that it is ad hoc. Phenomenal concepts are described as “special”, and in particular “direct demonstrative” and/or “quotational” (Foerster 2019). These features are posited to explain non-analyzability while preserving reference to phenomenal features, which could plausibly be physical features in the real world, but could conceivably come apart (such as in the P-zombie hypothetical). Moreover, some PCS theorists hold that phenomenal concepts cannot entirely be explained in physical terms, since phenomenal concepts must be used, not just mentioned, in a full explanation of themselves (Balog 2012).

Powerful qualities can fit into PCS in that the explanatory gap between physical and phenomenal concepts contains an explanatory gap between dispositional and qualitative concepts. Physics in general deals with dispositional concepts and primary qualitative concepts (e.g. position). Inhabitants of w’ find that they cannot explain the secondary quality of color in physical terms. This dispositional-to-qualitative inference does not get easier when we consider color quality to be in the mind (as “qualia”). It isn’t any easier to explain why the brain has red qualia than to explain why objects emitting ~700nm light have red color quality.

Quoting Henry Taylor (2017) on the matter:

Recall that the adherent of the PCS has to explain how scientific and phenomenal concepts could both correctly and substantively characterise the same experience, without claiming that they do so by describing different properties or parts of the experience. If the advocate of the PCS adopts the powerful qualities view, she can solve this problem. On such a view, an experience has properties, which are powerful qualities. A scientific concept has a mode of presentation that characterises an experience’s properties in a particular way (a dispositional way), whilst a phenomenal concept has a mode of presentation that characterises the very same properties of the experience in another way (a purely qualitative way). Importantly, on this view both phenomenal and scientific concepts substantively and correctly characterise the experiences they refer to.

Phenomenal concepts theories are less ad hoc if they can show that phenomenal concepts are not sui generis. Since concepts of secondary qualities are generally considered to be non-physical concepts (at least, not clearly physical concepts), phenomenal concepts can be considered as a special case of qualitative concepts. Once this step is taken, the powerful qualities view helps make sense of how phenomenal concepts can co-refer with physical concepts, as “redness” plausibly co-refers with in w’.

Unconscious qualities

Unlike in w’, philosophers in our world are disposed to locate red quality in the mind, not in red objects. This “re-location” strategy can be pragmatic, in allowing science to proceed without explaining secondary qualities. However, re-location raises the problem of explaining qualia (as mental versions of qualities) down the line.

Re-location is especially problematic for the concept “phenomenal consciousness”. Most philosophers of mind believe there is a fact of the matter about whether any particular bat is phenomenally conscious. If a bat is phenomenally conscious, then the consciousness of the bat is supposed to be an intrinsic feature of that bat. If such bat consciousness cannot be analytically reduced to physical or functional predicates (as Nagel claimed in his original essay), then the “re-location” strategy for secondary qualities suggests re-locating “the bat’s phenomenal consciousness” into the minds of humans. But this raises regress issues, and presses towards illusionism; compare with Hofstader’s “the self is an hallucination hallucinated by an hallucination”.

When discussing “phenomenal consciousness”, philosophers of our predominately indirect-realist world sound like the direct-realist w’ philosophers discussing “redness”. A natural PQ view, here, is that “phenomenal consciousness” is a qualitative concept, and co-refers with some dispositional (and likely physical) concept, perhaps a variant of Ned Block’s “access consciousness” (Block 1995). Again, considering “phenomenal consciousness” to be a secondary qualitative concept is less ad hoc than considering it to be a special kind of non-physical concept.

If “phenomenal consciousness” is a qualitative concept, a natural next question is whether “<R> qualia” is a qualitative concept; here, suppose R is your phenomenal concept associated with🔴. Supposing that color qualia inverts are ideally conceivable, “<R> qualia” cannot be a physical concept. The natural inference is that “<R> qualia” is a qualitative concept, and so are phenomenal concepts more generally.

Consider the simplified psycho-physical identity, “pain is C-fiber firing”. “Pain” is, presumably, a secondary qualitative concept. “C-fiber firing” could be interpreted as dispositional (in terms of being physically measurable), or perhaps also including primary qualities such as shape. Plausibly, C-fiber firing can occur with or without phenomenal consciousness. In general, neural clusters can spike with no associated access consciousness. Similar considerations apply to “functional pain”, i.e. “when people suffer bodily damage, psychological distress, etc., they often enter states that tend to generate avoidant or fighting behavior” (Kammerer 2022); in principle, functional pain could occur unconsciously.

The rough suggestion here is that it is possible to have “unconscious pain”, “unconscious <R> perception”, and so on. The visual cortex can have firing patterns as if seeing red, but with no access consciousness or phenomenal consciousness. Imagine a Venn diagram of “<R> perception” and “phenomenally conscious”, with “<R> qualia” being at the intersection. If “<R> qualia” and “phenomenally conscious” are both qualitative concepts, this strongly suggests that “<R> perception” is, likewise, a qualitative concept.

Type B physicalists, in accepting identity theory, will therefore gain theoretical virtue in also positing unconscious secondary qualities. The general form is that there are brain states that, if one were conscious of them, would have qualia; what separates these states from qualia is absence of phenomenal consciousness.

Of course, this raises the question of where to draw the line. PQ theory in its strong form says “nowhere”: all properties are qualitative in addition to being dispositional. The natural way to restrict only some physical properties to be qualitative is through restricting secondary qualities to only apply to qualia. However, both the idea of “phenomenally conscious” as a qualitative concept, and unconscious qualities in type B identity theory, suggest this is not the right place to draw the line.

Moreover, in principle, if animals can sense dispositional properties (e.g. light reflectance) qualitatively, then so can a large range of other beings, including aliens, cyborgs, and AIs; these “xenoqualia” hypotheticals suggest that a large range of dispositional properties could, in principle, have corresponding secondary qualities.

These considerations suggest that PQ theory is a reasonable default in the absence of a principled line between physical properties which are qualitative, and physical properties which are not qualitative. We can see perception as signal transduction, e.g. from light to optic nerve firing patterns to visual cortex firing patterns and so on; if later stages have secondary qualities (due to having qualia), why not earlier stages?

Contrasting with other views

A unifying thread between type B physicalism and PQ theory is “conceptual dualism, ontic monism”. Quoting John Taylor (2012) on PQ:

The second point I would like to emphasise is that, in stating the powerful qualities view, there is a temptation to think of the qualitative/categorical and the dispositional as ‘parts’ or ‘aspects’ of the single underlying property, but this is a mistake. When we think of a property under a qualitative/categorical concept, we are not thinking of a part or an aspect of the property, but we are thinking of the whole property in a certain way. Equally, to think of the property under a dispositional concept is not to think of only an ‘aspect’ of the property but again is to consider the whole property in a certain different way.

Compare with Janet Levin (2018) on type B physicalism:

These [phenomenal] concepts, Type B physicalists maintain, have special features that explain how they can denote physical-functional properties of the brain even though they are not connected a priori to any physical-functional concepts—and therefore an epistemic gap between the phenomenal and the physical provides no evidence that they are (metaphysically) distinct. Moreover, Type B physicalists suggest, it is this lack of connection between these concepts that explains why phenomenal-physical identity statements may seem uniquely mysterious or unintelligible (and also why it’s rational to question phenomenal-physical identity statements, no matter how much we know about the world). In short—as many put it—Type B physicalists embrace conceptual dualism while explaining why this does not entail metaphysical dualism.

These two passages are saying almost the same thing. “Physical” does not mean exactly the same thing as “dispositional”, but is close. “Functional” can mean “dispositional”; function is often thought of in terms of input/output processes. Phenomenal concepts generally present their referents (e.g. “this reddish experience right now”) as having qualities, not in terms of their dispositions (e.g. disposition to psychologically react as if to red light).

Let us contrast both these views with Russellian monism. According to Russellian monism, physics gives only structural and relational properties, leaving open the intrinsic nature of its elements, “quiddities”, which are in some way relevant to consciousness. Russellian panqualityism, in particular, claims that quiddities are qualities.

Russellian monism disagrees with type B physicalism, in that according to Russellian monism, quiddity properties are real and relevant to the mind, and are not physical properties, since physical properties are all structural and relational. Russellian panqualityism disagrees with the powerful qualities view, in that it considers qualities fundamental, not equating them with any dispositional properties. Other forms of Russellian monism, such as Russellian panpsychism, are in a similar boat, in that they consider qualia and/or consciousness fundamental and qualitative, and do not equate them with dispositions.

Let us consider a case of reddish experience, or “red qualia”, when seeing a tomato. Russellian monists such as Philip Goff will tend to think that such experiences reveal the essence of the property (phenomenal redness), and that this phenomenality (or a proto-phenomenal precursor) is fundamental to the universe, unequal to any structural or relational property. Type B physicalists will tend to think that such experiences reveal some neural and/or functional property (call it NeuralR, some red-correlated neural firing pattern in the visual cortex) under a phenomenal mode of presentation, which does not reveal the neural basis. The disagreement is about how fundamental a property is being revealed. “Powerful qualities” adds that the property revealed by having reddish experiences can be genuinely secondarily-qualitative, while still physical.

Russellian monism does, however, align with the powerful qualities view, in saying that “relations without relata” would face regress. There is, conversely, alignment between a “pure powers” metaphysical view, ontic structural realism (“structure is all there is”), and illusionism in philosophy of mind: the basic idea is to eliminate secondary qualities (and perhaps qualities in general), and not equate them with anything physical. (See Keith Frankish’s “Galileo’s Real Error” for an illusionist perspective on qualities.)

Property dualism, in positing an ontic difference between physical and phenomenal properties, mirrors alternatives to PQ which consider qualitative properties to be distinct from dispositional properties. The basic intuition, in both cases, is that two kinds of property exist, and that they cannot be identical.

Analytic functionalists tend to think that everything in experience has analytic definitions in terms of physics, and in particular, in terms of the dispositional/functional implications of physics. This applies to phenomenal consciousness and concepts of qualia more generally. Analytic functionalism, if successful, challenges the “conceptual dualism” of both type B physicalism and the powerful qualities view: the two concepts may be analytically equivalent in a non-obvious way. At the same time, analytic functionalism affirms psycho-physical identity and quality-disposition identity, in common with type B physicalism and PQ.

Conclusion

Type B physicalism is notable in combining conceptual dualism with ontic monism. This is a significant philosophical commitment, contra the conceivability-possibilty link and Chalmers’ modal rationalism. The powerful qualities view, likewise, holds that qualitative and dispositional concepts are distinct, but can refer to the same property anyway. These views go well together, in taking on similar commitments and having overlapping implications.

In particular, PQ shows how the phenomenal / physical conceptual divide contains the quality / disposition conceptual divide, so that phenomenal concepts belong in a larger category of qualitative concepts, rather than being sui generis. There are good reasons for type B physicalists to consider “phenomenal consciousness” to be a qualitative concept, and to believe in unconscious qualities; such broadening of the meta-concept “qualitative concept” tends towards PQ unless a line can be drawn, and “phenomenal consciousness” is an unlikely boundary.

The powerful qualities view implies that the universe is full of qualities, few of which are ever experienced. There are more colors than the eye can see, more sounds than the ear can hear. This sounds like panqualityism, but disagrees rather specifically with Russellian panqualityism on whether qualities equal dispositions.

I have focused in this essay on explaining type B physicalism, and arguing for PQ conditionally, rather than on evaluating the different views in philosophy of mind. To my mind, the most important views are the five: analytic functionalism, type B physicalism, strong illusionism, property dualism, and Russellian monism. Comparing these views is hard in part because understanding what it would mean for any of these views to be true is difficult. Nagel wrote in 1974, “physicalism is a position we cannot understand because we do not at present have any conception of how it might be true”. Hopefully, relating type B physicalism to powerful qualities helps to develop a positive conception of what it would mean for physicalism to be true, one that can be reasonably understood by humans using the concepts we tend to use.

I will examine the concept of chirality (the difference between a right hand and a left hand, generalized) and its relevance to philosophy of mind. Philosophy of mind often deals with colors: colors of worldly objects and of mental representations of them. Chirality, like color, can be experienced: it feels different to look at a left hand compared with looking at a right hand. Physics treats chirality more directly than it treats color.

Parity symmetry is a feature of some physical universes, but not our own. A parity symmetric universe (assuming it is, like ours, 3D in spatial coordinates) has the property that a universal parity inversion (which negates x, y, z coordinates of everything) makes no physically detectable difference. Parity symmetry is broken in our universe; this was shown in 1957. As a science fiction exercise, I imagine a universe much like ours, but with parity symmetry.

In another universe…

In this parity-symmetric universe, physicists fail to detect any parity violation, concluding that parity symmetry really does hold. They conclude that a possible cosmic state of affairs, and its parity inversion, are physically equal. There is no physical difference between them, only a change in coordinates. The universe needs no absolute chirality, any more than it needs absolute spatial coordinates: chirality is not an intrinsic physical feature of objects.

Philosophical attitudes differ. Physicalists believe the physicists’ parity-invariant ontology is correct: absolute chirality exists neither in objects, nor in mental perceptions. This ontology is counter-intuitive, because the experience of looking at a normal clock seems different from the experience of looking at a backwards clock.

Chiral materialists believe that physicists have left something out of their description of the universe. They believe that objects really do have absolute chiral properties: a forwards clock is intrinsically different from a backwards clock. Chiral materialists hold that, while chirality is not strictly speaking a physical property, it is a material property of objects, and not an intrinsically mental one. Chiral materialists are attracted to a Newtonian or 3D cellular-automaton picture of the universe, in which chirality really exists at the fundamental level, even if physicists cannot detect it.

Chiral materialists disagree about how human perception of chirality works. Direct realists say that humans directly perceive the material chirality of objects they look at, at least in the good case of veridical perception. Indirect realists say that humans create internal mental replicas of objects, and then directly perceive the (material) chirality of these replicas.

In cases of veridical chirality perception, there is not a good way to tell the difference: any internal replica of the object would have the same chirality as the object itself. But hallucination is, in principle, possible. A human could look at a normal clock, and by physical miracle, receive a retinal image as if looking at a left/right flip of that clock. Indirect realists reason that the human’s internal replica of the clock now has reversed chirality, and the human perceives this replica, which is why they see the clock as backwards. Direct realists say this is a case of false perceptual belief, and should not be taken too seriously as ontology.

Direct and indirect realist chiral materialists agree that, if there is a planet out there that is an exact chiral inverse of Earth, then reverse-chiral humans are having chirality-reversed experiences. Both the material objects they look at, and any internal replicas (if those exist), have reverse chirality. The reverse-chiral humans’ veridical perception of what they would consider a normal clock is, according to humans, a backwards clock.

Chiral dualists point out an “epistemic gap” for chiral materialism. Even granting that material objects (and any internal replicas of them) have intrinsic chiral features, why must phenomenal experiences of them take on the chirality of the objects or the replicas of them in the brain? Chiral dualists argue that a “phenomenal chiral invert” is conceivable: someone could be physically (and material-chirally) identical with a normal human, yet have a consistent left/right mirroring in their entire experience (visual, auditory, tactile, and so on). Their visual experience of seeing a normal clock is like a typical person’s visual experience of seeing a left/right inverted clock; they’re just used to it, so they act normal about it.

Chiral materialism gives no easy way of ruling out this scenario; it’s really a guess that experiences track the material chirality of external or internal objects. Chiral dualists infer, from the conceivability of chiral inverts, that there must be a non-material feature which fixes chirality. Perhaps humans have souls, which contain Euclidean world models, and these models generally agree with the physical aspects of their perception.

Chiral idealists argue that chiral dualists’ picture is inelegant. While people feel like they are separate from each other, it is possible to consider that “group minds” might exist, spanning multiple humans, and that this group mind could experience chirality. And a region of the human brain could be its own subject experiencing chirality. Chiral dualists need to believe in strong subject boundaries so that phenomenal chirality can flip on a per-subject basis. Instead, chiral idealists suppose, like chiral materialists, that objects have intrinsic chiral properties, but unlike chiral materialists, they consider the object to be entirely an idea in the mind of God, who dissociates into multiple apparent subjects (like human subjects). When chiral idealists imagine a “chiral invert”, they most easily imagine that this invert lives in an entirely chirally-inverted universe, not that only their soul is chirally inverted.

Chiral Russellian monists present a middle path between chiral materialism and chiral idealism. They believe that physics gives the chirally-invariant structure and dynamics of the universe, but leaves out the intrinsic nature of objects. That intrinsic nature, they say, includes chirality, neutral between mental and physical, and un-detectable by physics. Chiral Russellian monists agree with indirect realists that phenomenal consciousness is influenced by intrinsic chiral features of the brain, but attribute mental or proto-mental aspects to such features instead of purely material ones.

Chiral physicalists believe that physics (which quotients over parity) gives the complete fundamental ontology, and attempt to reconcile this ontology with chiral experience in one way or another. Chiral reductionists believe that chiral concepts can be analyzed into physical concepts (which are non-chiral), contra chiral dualists’ claim that chirality inversion is conceivable. However, they run into trouble giving a convincing reductive definition.

Advocates of the chiral concept strategy (CCS) take a sophisticated approach. They divide concepts into chirally-invariant concepts (such as those of algebra) and chirally-variant ones (such as those of constructive geometry). They claim, contra chiral reductionists, that chirally-variant concepts cannot be defined in terms of chirally-invariant concepts, because chiral inversions change chiral-variant properties but not chiral-invariant ones. However, CCS theorists disagree with chiral dualists: they believe this failure of conceptual reduction implies no ontological gap. CCS theorists believe that chiral-variant concepts can still co-refer with physical concepts, even if physicalism is true. This co-reference must be a posteriori, as no decisive logical inference from the chirally-invariant concepts of fundamental physics to chiral-variant concepts is possible.

CCS theorists point to research of “neural correlates of chirality” (NCCs). When human subjects see normal clocks, they have different neural firing patterns than when they see left-right inverted clocks. Notably, these firing patterns are not chiral inverses of each other: they differ physically, not just chirally. This suggests empirical evidence in favor of an posteriori identity: maybe normal-clock neural firing patterns are experiences of normal clocks, even though this connection is non-analytic.

CCS proponents disagree with chiral materialists. First, CCS proponents believe physicalism is likely, implying that nothing has absolute chirality. Second, CCS proponents believe that reverse-chiral humans would have the same experiences, because their neural correlates of chirality (NCC) are the same, up to a parity inversion (which, they emphasize, makes no physical difference).

Critics, especially chiral dualists and idealists, argue that CCS mis-characterizes chiral concepts. Since NCCs are characterized in chiral-invariant neuroscientific language, it is highly counterintuitive, if not contradictory, to claim an identity with experiential chirality, even an a posteriori one. This identity would require a lack of conceptual transparency in chiral-variant concepts (such as those of constructive geometry, and mental Euclidean imagination): that users of these concepts fail to grasp the nature of the properties the concepts refer to. But Euclidean geometry, with all its chiral-variance, is as intuitive as can be: why expect concept users to be ignorant as to the nature of the properties referred to by these concepts?

Chiral illusionists agree with CCS proponents that chiral concepts cannot be analyzed into chiral-invariant concepts, and agree with non-physicalist critics that chiral concepts are really supposed to be referring to something chirally variant, not anything physical (therefore chirally-invariant). Chiral illusionists hold that physicalism is nonetheless true, and that accordingly, chiral-variant concepts do not refer. Chiral illusionists believe that chirality, both the chirality of external objects and of internal experiences, is an illusion, which can be “debunked” by explaining the appearance of chirality using chirally-invariant language. As long as the illusionist can predict people’s chirally-invariant reports about their so-called “chiral experiences”, they believe they have an adequate model, and positing “true chirality” is unnecessary.

This idea seems crazy and incoherent to many. Isn’t it obvious that experiences have chiral properties? That right hands have a way they look, and left hands have a different way they look? If the chirality is, as physicists say, not in the object itself, it has to be in the mind: where else could it be? CCS advocates say that chiral illusionism goes too far, and that physicalism can be reconciled with the reality of chiral experience.

Chiral reductionists point out that CCS theorists could be over-estimating the epistemic gap between physical and chiral concepts. In particular, to the degree reference is physical, physics is enough to decode the meanings chiral concepts; and the empirical evidence of NCCs and the plausibility of a posteriori identities suggests, on many accounts of meaning, that such connections exist, and could be unpacked by Laplace’s demon, if not by actual humans.

Comparison with color quality

Philosophers of mind discuss color much more than they discuss chirality. Some of the lessons translate, though there are notable differences. In the parity-symmetric universe, chirality is close to a real fundamental physical feature of objects, but doesn’t quite make it. Color is further from being a fundamental physical feature. In particular, “color materialism” as an analogue of “chiral materialism” would be implausible as a physical theory: objects are not really painted with colors that are further facts on top of their quantitative physical features like reflectance patterns.

Direct realism about color says that objects really have color qualities, as perception presents them as having. Indirect realism about color says that color is “in the mind”: mental pictures of the external world have color quality, or “qualia”. The brain itself is not correspondingly colored like these apparent mental pictures (it’s dark inside, and looks pink when illuminated), so it’s not obvious how to locate color qualia.

The “inverted qualia” thought experiment is famous: many philosophers believe that it is conceivable that someone could behave identically to a normal person (and even be physically identical) while having a red/blue inversion in their color qualia. This conceivability claim is deployed in favor of non-physicalism about color (e.g. property dualism). The “inverted chirality” thought experiment is similar; I don’t see a good reason why the conceivability of color inverts would differ from the conceivability of chiral inverts.

With both chirality and color, dualism has problems with subject boundaries: if two humans start sending neural messages to each other (through some medically-innovative neural connection between their brains), and one human is a color invert, do the color qualia invert when traveling across the boundary? Similar questions arise for “group minds” and sub-personal minds. Idealism presents a more color-coordinated image of the universe, where color qualia really exist and are in principle comparable between different humans, e.g. because all qualia are in the mind of God. Russellian monism (especially panpsychism) has some resonance with idealism, but scales back the theology towards a “physicalism + intrinsic natures” ontology. It retains the idea that the qualities of color qualia are fundamental to the universe.

Instead of reverse-chiral life, idealists and Russellian monists can imagine a universal color quality inversion (say, red/blue). Russellian monists imagine this by imagining quiddities swapping with each other, while preserving all structural-physical features; idealists might imagine a color swap in the mind of God. Either way, there is some theoretically possible implementation of a color quality swap that makes no physical difference, and is physically undetectable.

Color reductionists (e.g. analytic functionalists) believe that, in principle, terms like “red qualia” have physical definitions, which would be conceptually clear on ideal reflection. However, most philosophers of mind disagree with them: they think a physical definition would miss the mark of the actual “red qualia” concept, deflating it into something weaker.

Type B physicalism generally involves the “phenomenal concept strategy” (PCS, like CCS above), and claims that there are a posteriori co-references between phenomenal concepts (including “red qualia”) and physical concepts. In the chirality case, it is easy to see, at the mathematical level, why the chiral-variant language of constructive geometry is irreducible to the chiral-invariant language of algebra. PCS claims, analogously, that color qualia concepts are irreducible to physical and functional concepts; that qualities cannot have reductive definitions in the quantitative, mathematical language of fundamental physics. Compare the “language” of visual art to the “language” of theoretical physics. Nevertheless, a posteriori identities are plausible.

While color qualities per se are not really out there painted on objects, it is possible to maintain that external color is a certain light reflectance pattern (say, ~700nm wavelength for red), and that this identity is a posteriori, like “water is H2O”. Brain-internal a posteriori identities might be plausible based on investigating neural correlates of consciousness, and in particular, neural correlates of color experience. Identity would explain why red qualia appear whenever their neural correlates occur. This may lead to some a posteriori identity of the classic “pain = C-fiber firing” sort for color qualia, perhaps in terms of the neurology of the visual cortex.

As with chirality, the neural correlates approach disagrees with idealists and Russellian monists about “universal color inversion”. Idealists and Russellian monists hold that universal color quality inversion (e.g. by a quiddity swap) would make a difference to human color qualia, yet no neural correlate would change (as nothing would physically change). Type B physicalists would disagree, holding that even if fundamental qualities exist, quality swaps that make no physical difference do not change humans’ color qualia. This is in line with the type B conclusion that reverse-chiral life has identical experiences (in a parity-symmetric universe).

Non-physicalists object to type B physicalism and PCS on various bases. Philip Goff’s “transparency” and “revelation” critiques are popular, which claim that PCS’s a posteriori identities are incompatible with the commonly-held intuitions that phenomenal concepts (e.g. that of “red qualia”) reveal the nature of what properties they refer to, are easily mastered by their users, and are not opaque. This is analogous to the intuitive mastery of Euclidean geometry and its implied chirality (Kant claimed that Euclidean geometry is synthetic a priori). Type B physicalists hold that the “red qualia” concept fails to disclose the a posteriori identity with a neural structure, contra transparency and revelation.

Illusionism about color qualia states, simply, that color qualities exist neither out in the world nor in the head, nor in any non-physical “phenomenal realm”. The basic idea is that there is a common improper reification in the idea of “color qualia”, and that the concept actively misrepresents the situation (by attributing primitive qualities that do not really exist), rather than just being opaque, as the type B physicalist claims.

Conclusion

As for my own views, I believe that in a parity-symmetric universe, reversal-chiral life does not feel any different. This claim is suggested by the neural correlates approach, and it remains likely even if chirality is a real material property, as it would be an undetectable material property. Type B physicalism about chirality therefore seems more likely than dualism, idealism, or Russellian monism about chirality.

I think the color case is reasonably analogous. Even if there are fundamental qualities to the universe (“quiddities”), it seems more reasonable to identify color experiences with neural correlates or functional states than with anything quiddity-level. This is analogous to an a posteriori identity between the colors of external objects and the objects’ wavelength reflectance patterns. Advanced neuroscience would predictably find neural correlates of color experience, making the empirical case for identity clearer.

With chirality, it is easy to make a case for the non-analyzability of chiral-variant concepts into chiral-invariant concepts. With color, the case for non-analyzability is less straightforward. Perhaps certain structural asymmetries about color hold as a consequence of the asymmetry in the human color space, and these asymmetries will yield structural conceptual analyses of color. Such analyses would vindicate analytic functionalism about color qualia. On the other hand, if such structural analysis fails, type B physicalism and illusionism are more plausible forms of physicalism. (The disagreement between type B physicalism and illusionism is mostly about how phenomenal concepts characterize their supposed referents; positive mis-characterization would suggest illusionism, while opacity would suggest type B physicalism.)

My overall view is that there is no “hard problem of color”: scientific understanding of human color perception and color-related phenomenal concepts will yield hard-problem dissolution as a side effect. I am less sure about non-color phenomenal concepts, such as “phenomenal consciousness” (the property that, supposedly, humans have and P-zombies lack). If there are “consciousness qualia” which inform people that they are conscious, they seem significantly more abstract than “red qualia”, so it’s less clear how to model them. In any case, better understanding of sensory qualia concepts is an important step towards understanding of more abstract consciousness-related concepts.

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:

1. Why did evolution create consciousness if consciousness has no physical effects?
2. If our conscious experience has no physical effects, why would our reports about our experience correlate with our experience?
3. 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:

1. Structuralism about physics
2. Realism about quiddities
3. 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).

Type-identity physicalists usually deny logical supervenience of the mental on the physical; they endorse “type B physicalism” and appeal to necessary a posteriori Kripkean identities (though, Kripke himself criticized “pain is C-fiber stimulation” in “Naming and Necessity”). Such denial is not strictly necessary, in that perhaps physical omniscience would allow unpacking the identities; see “How to be a type-C physicalist”. The details of type B physicalism involve rather confusing philosophical dialectic around “2D semantics” and “phenomenal concept strategy”; I’ll omit the details.

Importantly, type-identity physicalism makes significant empirical claims, at least insofar as it claims to ground subjective experience. Since identities like “pain = C-fiber stimulation” would be a posteriori, there is not a strong a priori reason to believe that there is such a grounding for mental concepts in general. Some concepts, like “elan vital”, fall out of favor in science, rather than being identified with anything. What seem to be experienced mental kinds may be realized by a distributed function, perhaps of a rather general neurological learning system; a given neural cluster may assist in multiple object recognitions and/or concepts, blocking straightforward type identities. For an overview, see SEP’s “Multiple Realizability”.

Because of uncertainty about type-identifications or multiple realizability of a specific experienced mental kind, type-identity physicalism has trouble grounding introspective certainty about experience. A given experienced kind may or may not correspond to a natural physical or neurological kind; it’s an open empirical question. The part of “pain = C-fiber stimulation” that could be intelligible is the functional aspect: C-fiber stimulation could intelligibly fill the functional role of pain, e.g. responding to bodily damage and motivating avoidance behaviors. It is much easier to gain introspective confidence about functional role aspects of experience than about neurological implementation details.

Type-identity physicalism partially addresses the problems with epiphenomenalism. Evolution may create pain, because pain is C-fiber stimulation, and C-fiber stimulation implements the functional role of motivating avoidance of bodily damage, which is evolutionarily useful. Reported beliefs such as “I experience pain” may be justified by scientific confidence that a matching physical type will be found, even if it hasn’t been found yet. And pain correlates with C-fiber stimulation because of the identity. However, these answers are only partially explanatory, because of the unintelligible, a posteriori nature of the mind-brain identity.

Structural realism and causation

Let’s revisit the causal exclusion principle. We have a reason to dis-believe in mental causation: physical events have sufficient physical causes, except perhaps in cases of stochastic under-determination, and such stochasticity doesn’t accommodate mental causation either. Hence, perhaps functionalists should bite the bullet on epiphenomenalism. But it is worth considering criticisms of the causal exclusion principle.

Bertrand Russell, in “On the Notion of Cause, with Applications to the Free-Will Problem”, noted:

All philosophers, of every school, imagine that causation is one of the fundamental axioms or postulates of science, yet, oddly enough, in advanced science such as gravitational astronomy, the word “cause” never occurs.

While this is an overstatement, it is by no means obvious how to derive causal claims from fundamental physical theories such as quantum field theory; the theories are more naturally stated as laws over spacetime, laws over a wave-functional configuration space, or in operator-algebraic terms. (See “Quantum common causes and quantum causal models” for existing work in quantum causation.)

Structural realism is a view in philosophy of science, which agrees with Russellian monism’s “structuralism about physics”, denies any epistemic access to non-structural properties, and in “ontic” form, denies non-structural properties altogether. A central structural realist book, “Every Thing Must Go” (ETMG), criticizes Kim’s causal exclusion argument on physical grounds:

Kim’s argument [for causal exclusion], however, depends on non-trivial assumptions about how the physical world is structured. One example is the definition of a ‘micro-based based property’ which involves the bearer ‘being completely decomposable into nonoverlapping proper parts’ (1998, 84). This assumption does much work in Kim’s argument—being used, inter alia, to help provide a criterion for what is physical, and driving parts of his response to the charge, an attempted reductio, that his ‘causal exclusion’ argument against functionalism generalizes to all non-fundamental science.

ETMG, in common with Russell, expresses skepticism about causation in fundamental physics:

Causation, we claim, is, like cohesion, a notional-world concept. It is a useful device, at least for us, for locating some real patterns, and fundamental physics might play a role in explaining why it is.

I find this view of causation in fundamental physics highly plausible. Perhaps “causation” does not function well as a heavyweight metaphysical or fundamental physics concept, but has a useful explanatory role in science and in everyday life. This view of causation would, of course, demote the causal exclusion principle in philosophy of mind, and make it easier to formulate functionalism without epiphenomenalism. However, as I’ve argued, the metaphysics of causation are not load-bearing for epistemology about mental properties; instead, intelligible supervenience does the work.

Conclusion

In explaining how consciousness correlates with reported beliefs about consciousness, it is prima facie desirable to appeal to mental causation: if consciousness is causing the reports, this causation could explain the correlation. But mental causation is hard to reconcile with physicalism and the causal exclusion principle. As such, it makes sense to consider alternative ways that consciousness could correlate with reports. Intelligible supervenience (and its stronger counterpart, logical supervenience) can explain correlations without recourse to heavyweight causal claims. Moreover, causation might not exist in fundamental physics, adding extra incentive to find non-causal explanations of mental-physical correlations. As such, I believe intelligible supervenience provides better explanations of introspective accuracy than does mental causation.

A residual worry is that there are remaining qualitative, subjective facts that cannot be characterized functionally or structurally. On an exhaustively structuralist or materialist account of physics, such qualities cannot be characterized physically either. Features attributed to qualia (subjectivity, privacy, ineffability) undermine any attempt to fit them into a physicalist and/or functionalist theory of mind. This poor fit is not just a metaphysical problem, but also an epistemic problem; it makes it hard to explain why beliefs about qualia would correlate with the qualia themselves. For criticisms of qualia realism, see Daniel Dennett’s “Quining Qualia” and Keith Frankish’s “Consciousness is not what it seems”; perhaps it is more correct to debunk qualia (explaining why people would believe in them, even if they are not real) than to ground them in physics.

While there is ongoing philosophical debate in the metaphysics of causation, I have argued that it is mostly irrelevant to the epistemology of mental properties, because epistemology is much more dependent on correlations (especially intelligible ones) than on causation. Causation can explain correlations and lawful constraints, but the correlations and laws ground the base of epistemology: how judgments correlate with reality. As such, epistemic arguments against epiphenomenalism in philosophy of mind are more properly formulated as epistemic arguments against views lacking intelligible mental/physical correlations, especially intelligible supervenience.