Research Comment on "Grounding, Physicalism, and the Explanatory Gap"

Comment on “Grounding, Physicalism, and the Explanatory Gap”

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This paper this post comments on can be found here.

By Janet Levin

Zach Blaesi’s goal in this paper is to challenge the claim, advanced by many physicalists, that appeal to the notion of grounding can help to explain how the mental—in particular, the phenomenal—can be “nothing over and above” the physical, even if phenomenal states and properties are not type-identical with, or analyzable in terms of, physical states and properties.

Just to remind ourselves, Blaesi characterizes grounding (in general) as a relation between facts (in different domains) that is transitive, asymmetric, irreflexive, necessitating, and also explanatory—in that facts about grounds can provide a “metaphysical explanation” of the facts that they ground, or show how the latter can be true “in virtue of” the former.  More specifically, Blaesi characterizes Grounding Physicalism as the thesis that

The facts about consciousness are fully grounded in the physical facts,

where “fully grounded” means “that there is some chain of ground leading up from the physical facts to the facts about consciousness such that there is no fuller account of why the facts about consciousness obtain”.

Now, as Blaesi points out, defenders of Grounding Physicalism argue that the thesis is superior not only to reductive physicalist accounts of the phenomenal such as the identity theory or analytic functionalism, but also to what he calls Supervenience-Based Non-reductive Physicalism, the view that for any phenomenal fact M, if M obtains, then there is a fact of physical type P that obtains—and in every world in which P obtains, M obtains as well.  One advantage of Grounding Physicalism is that mere supervenience (unlike “full groundedness”) would not guarantee that the phenomenal is nothing over and above the physical, since phenomenal facts could include facts about fundamental non-physical properties as long as they are necessitated, in the way just specified, by the physical facts.  Indeed, this is just what occurs in classic cases of emergence.  Moreover, the necessitation afforded by the supervenience relation doesn’t provide a “metaphysical explanation” of why, or how, the physical necessitates the phenomenal, and thus the modal relations between phenomenal and physical facts must be regarded as “brute”.

So, has Grounding Physicalism provided an intuitively plausible non-reductive physicalist theory of phenomenal (conscious mental) states?  Blaesi, as we know, has serious questions about the adequacy of the view.

His primary worry (which also arises for other attempts to defend physicalism) is that appeal to grounding cannot close the explanatory gap between the phenomenal and the physical—that is, that it seems that no matter how much we know about the physical properties of our brains, bodies, and the world around us, it remains mysterious or unintelligible that phenomenal states such as pain and the experience of red could be nothing over and above any combination of those physical properties.  And if this is so, Blaesi argues, the Grounding Physicalist has a dilemma:  “either leave an explanatory gap or abandon the considerations that motivated Grounding Physicalism in the first place” —which (presumably) were to provide an intuitively satisfying, a posteriori, non-reductive physicalistic theory of phenomenal states.

Now I agree completely that grounding cannot close the explanatory gap between the phenomenal and physical, even if grounding can provide what its advocates call a “metaphysical explanation” of the phenomenal in terms of the physical.   But Blaesi and I disagree, I think, about where the explanatory gap arises, what produces it, why Grounding Physicalism is unlikely to close it, and ultimately what this means for the prospects of physicalism.  So I’ll focus on these questions here.

Blaesi, you’ll recall, develops his argument by discussing some standing general questions about grounding.  One is whether facts about what grounds what (e.g. that the fact that A’s being in pain is grounded in the fact that A’s C-fibers are firing) have to be grounded themselves—and if so, what could do this job (without inviting regress).  Some have suggested that—at some level that counts as basic—if the fact that p is grounded in the fact that q, then the fact that [the fact that p is grounded in the fact that q] is also grounded in the fact that q—and so on.

However, Blaesi argues that this is not an intuitively satisfying answer, and many agree.  But some maintain that this explanation could be enhanced by adding to it “essentialist truths” about the nature of some constituent of that grounding fact—either the grounds or what is grounded.  And, after considering a number of alternatives, Blaesi suggests (in agreement with Kit Fine) that the best bet for such an “enhancement” is to appeal to the nature of the item that is grounded.  As he notes, this option seems correct for a number of important cases, for example, sets and their members and determinable and determinate shades of colors.  Indeed, he adds, “it is hard to find examples in which the essence of a genuinely grounded fact doesn’t point to its grounds”.

If this is indeed the best option, then by analogy, the grounding of facts about conscious mental states (phenomenal states) in facts about physical properties must be explained by appeal to the nature of consciousness.  But it’s here, Blaesi argues, that we confront the Explanatory Gap, since “there just doesn’t seem to be anything about the nature of consciousness that could explain the grounding phenomena involving it”—or, in particular, anything about the nature of pain that could explain why the firing of C-fibers gives rise to that distinctive feeling, rather than to another, such as pleasure.

That is, as he says a bit later, “the essence of consciousness does not make the grounding phenomena involving consciousness intelligible”[—as made clear by the conceivability of zombies and the fact that we’re not in an epistemic position to know that we are having C-fiber stimulation when we’re experiencing pain—] “and thus Grounding Physicalism fails to explain those phenomena—that’s what I mean when I say that Grounding Physicalism leaves an explanatory gap”.

Once again, I agree.  But this raises some questions that have implications for the prospects of Grounding Physicalism—and which I hope can also shed light on the role of the Explanatory Gap in arguments about the plausibility of various versions of physicalism.  The first question is whether the appeal to the “nature” or “essence” of what gets grounded can explain—in the sense of “make intelligible”—the grounding facts in other domains, and if so, how.  The second is whether non-reductive physicalism is any more threatened by the Explanatory Gap than reductive views, in particular, the Type-Identity theory.

To pursue the first question, let’s compare ‘x’s being in pain is grounded in x’s undergoing C-fiber stimulation’ with an analogous claim about the grounding of other sorts of higher-level properties in lower-level properties—for example, ‘x’s being fragile is grounded in x’s having some particular physical structure y’.  Here, it seems, we may think of the nature or essence of an object’s being fragile as its disposition (caeteris paribus) to break when struck, and thus if having structure y necessitates x’s having that disposition, we have reason to affirm that it grounds x’s being fragile. Alternatively, we may understand the nature or essence of an object’s being fragile non-dispositionally, perhaps as its having parts that are compounded in certain ways.  But here too it would not seem mysterious why x’s being fragile is grounded in structure y if x’s having y is necessitated by x’s having parts compounded in those ways.

In contrast, the nature or essence of pain does not seem to be captured by any sort of functional (dispositional) characterization.  Nor, it seems, can it be captured by any sort of compositional, causal, or structural characterization that is not itself phenomenal.  And this seems true for any type of conscious experience; this is what the conceivability of zombies, etc. tells us.  Thus it seems clear why there is an asymmetry between phenomenal-physical grounding claims and the others; namely, that—unlike for the other cases—there is no a priori (or partially a priori, or quasi a priori) characterization of the nature of conscious experience that is functional, compositional, or anything other than phenomenal (i.e. hurting, or feeling like that (pointing in)).  Because of this, the initial “mystery” attaching to phenomenal-physical grounding claims cannot be dispelled by the acquisition of more knowledge about the functional, dispositional, microphysical, or causal structure of the world—and thus that Grounding Physicalism cannot close the Explanatory Gap.

Blaesi, however, suggests that Identity Theorists have more resources than Grounding Physicalist to do so.  As he notes, some physicalists (e.g. Papineau, Block and Stalnaker) contend that identities don’t need explanation; to think that they do is to succumb to a “cognitive illusion” that can be dispelled by careful reflection on what it is for x to be identical with y.  In short, phenomenal-physical identity claims may seem brute—but as Blaesi quotes from Papineau:  “once you really accept that pain, say, really is some material M, then you will see that this requires no more explanation than does Mark Twain = Samuel Clemens. Identities need no explaining.”  In contrast, Blaesi continues, this sort of response is not available to Grounding Physicalists: “Grounding phenomena, unlike identities, are apt to be explained. Therefore, if Grounding Physicalism is true, it leaves a genuinely explanatory gap, not a mere cognitive illusion.”

Once again, I agree that the only way to be an a posteriori non-reductive physicalist is to accept the explanatory gap.  But are statements such as ‘pain = C-fiber stimulation’ really no more problematic than statements such as ‘Mark Twain = Samuel Clemens’ or—to stick with property identities—‘Water = H2O’?  I’d say ‘no’:  there is just as much of an explanatory gap for phenomenal-physical identity statements as for statements about phenomenal-physical grounding—and the gap exists for the same reasons.  Think about ‘pain = C-fiber stimulation’.  It still, I submit, seems mysterious, and more mysterious than ‘Water = H2O’—even when you’re looking at a brain scan of your own C-fiber stimulation while at the same time feeling pain.  You may still wonder:   How could that neural activity be identical with (or “fully ground”) this feeling (pointing in)?  So—or so it seems—phenomenal-physical identity statements also call out for explanation in a way that other identity statements do not.

In my view the best explanation of why there is an explanatory gap for all phenomenal-physical grounding and identity claims—and why it occurs nowhere else—is that phenomenal concepts are special and unique.  In particular, they are recognitional-type-demonstrative concepts derived via introspection.  Therefore they, and only they, have no conceptual connections to any physical or functional (or physical-functional) descriptions; they are—as many put it—radically conceptually isolated.  This is why the Explanatory Gap arises both for identity (or grounding) statements in which one term expresses a phenomenal concept.

Many people have advanced some version of this view (the so-called “Phenomenal Concepts Strategy”) and there are many objections to it—which I will not discuss here.  My interest, instead, it to show how it can answer certain perplexing questions about Grounding Physicalism and the Identity Theory—and thus avoid the conclusion that Blaesi suggests is attractive to “some philosophers”, namely, that (p. 16) they “might give up the claim that consciousness is metaphysically grounded in the physical and instead defend the weaker claim that it is naturally [that is, nomically] grounded in the physical”.  However, as he continues, “these philosophers will find in turn that they have arrived at a version of dualism.”

On the view of phenomenal concepts sketched above, however, physicalists can avoid this conclusion.  First, it explains why zombies are conceivable, namely, that there is no a priori connection between concepts such as [feels like] that and any physical or functional concepts.  Second, as detailed above, it explains the asymmetry between phenomenal-physical grounding claims and the others in which appeal to grounds provides a “metaphysical explanation”.

Indeed, Blaesi observes that there is a difference between the paradigm cases of grounding and non-reductive physicalistic claims about phenomenal states.  ”In the former] cases”, he suggests, “we have an a priori basis for positing essentialist truths…[but] … even if it is essential to pain that for any x, if x’s c-fibers are firing, then the fact that x’s c-fibers are firing grounds the fact that x is in pain, that does not seem to be the sort of thing we are in a position to know a priori.”  Maybe so, but (in my view) there are good reasons why this is the case that do not suggest that there is any ontological gap between the physical and the phenomenal.

In a final footnote to his paper, Blaesi acknowledges that “it might be objected that the alleged explanatory gap is to be expected given the distinctive character of phenomenal concepts. Pain, for example, has a hidden nature, but we fail to recognize this because we only know about pain under a phenomenal concept”.  However, he continues, “if phenomenal concepts are a bar to our ever knowing the full essence of consciousness, then Grounding Physicalism turns out to be a version of “mysterianism” according to which the explanatory gap is uncloseable”.

As I’ve suggested, however, physicalists can acknowledge that the Explanatory Gap will never be closed without embracing mysterianism if they can explain why this is so and why it is exclusive to phenomenal type-demonstratives—and the Phenomenal Concepts Strategy provides a way to do just that.  And if physicalists don’t have to worry about closing the gap, then they can appeal to other criteria to decide between reductive views such as the Identity Theory and non-reductive views such as Grounding Physicalism.

More generally, the explanation of why the inability to close the Explanatory Gap leads neither to reductive theories nor dualism can be seen as good for grounding theories, in that it explains why, in some cases, the “metaphysical explanation” provided by grounding does not seem to be sufficiently explanatory, even though it can provide just as good an asymmetric, necessitating, etc. connection between physical and phenomenal facts as between facts in other domains.  There may be something weird and special about phenomenal-physical grounding (or identity) statements, but that should be no concern to grounding theorists who want to clarify what metaphysical explanation requires.  The upside of Cartesian Dualism at the time of Descartes, some have argued, was that it made the rest of the world safe for mechanistic explanation.  Even better, the upside of conceptual dualism—the view that I’ve been characterizing here—is that it makes even phenomenal states safe for metaphysical explanation, while preventing worries about Grounding Physicalism from spreading to other grounding views.

Granted, this is good for physicalists only if we can be assured that conceptual dualism does not entail Cartesian (or any other sort of metaphysical) dualism, but that’s the point of this theory.  So let’s embrace safety wherever we can find it.


Janet Levin is a professor of philosophy at USC.   She works primarily on topics in the philosophy of mind and theory of knowledge, and has recently published papers on consciousness, phenomenal concepts, and philosophical method.


  1. First Question: Would I be making a grounding theory if I said that what’s called ‘consciousness’ is simply a bio-magnetic effect of the synchronous firing of neurons in the central nervous system, which creates a bio-magnetic field around the organism that allows for the transmission of information more-or-less instantaneously throughout the consciousness field, and that therefore explains for the astonishing fact that the billions and billions of cells in the ‘physical body’ are able to function together to sustain the life of a biological organism?

    Second Question: Would this dilemma (the good old mind/body split, rephrased in different terms) be less difficult to solve if it were acknowledged that what is called ‘physical,’ put in terms of contemporary astrophysics, is no longer simply a bedrock materialist phenomena (i.e., is not reducible to a physical ‘body’ or a material particle), but is also a gravitational-electromagnetic field phenomena which simply manifests to our thinking as a physical cosmos and a physical body, thereby obviating the gap between ‘consciousness’ and ‘the physical body’?

    And, with apologies for my bluntness, does all this terminological jargon really help to answer the question of what relationship exists between ‘consciousness’ and ‘the physical body’ (also terms in need of definition?) or does it simply make the argument difficult to follow, even by sympathetic questioners like myself?

    And please feel free to correct me if I do not follow the argument…


  2. The technical jargon is necessary to create authority, to separate the professional philosopher from the rest of us, to justify the salary which pays the mortgage which keeps the spouse happy and so on.

    Without the technical jargon which makes arguments hard to follow, the authors on this site would be people on the Internet with opinions.

    There is a logic to it. They are getting paid for this. And we are not.


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