The Spectrum

Where do you fit on attitudes to the Explanatory Gap?

This is not a real post… Just a brief teaser, for those already down in the weeds of this issue, and possibly a bunch of meaningless babble for those who are new to it.

I’ve made adjustments as I’ve received feedback, and will continue to do so.

I’ve been thinking about where people might fit in a spectrum of how impressed they are with the so-called Explanatory Gap for qualia, and this represents my current best attempt to place the spread of opinions on that spectrum, marking key landmarks with labels that identify recognisable positions.

In it’s broadest sense, the Gap is the lack of any satisfying explanation for how the brain generates qualia (the raw feels of subjective experience like redness, pain and so on). The term can also be used in a much narrower sense, too: as a synonym for what might be called the non-derivability of qualia, which is the lack of any analytical process that starts with brain circuitry and ends with qualitative subjective properties like redness. (On this substack, the capitalised version “the Gap” will refer to the narrow version by default).

The narrow and broad senses of the “explanatory gap'“ are often run together under the assumption that, if we can’t derive the nature of qualia from the physical substrate that supposedly underlies them, we can’t meaningfully claim that we understand them. This assumption can be expressed in many ways, but the core logic is this: a theory that leaves out redness can’t really pass muster as a theory of redness. Superficially, this just seems obvious.

(I think this assumption is wrong, but I concede that it seems plausible.)

The narrow and broad senses of the Gap do not have to be collapsed into a single idea, and part of the purpose of this post is to tease them apart.

It is possible to believe that we face a barrier in the deductive derivation of qualia, but also believe that we can understand qualia anyway — perhaps not as well as we would have liked. We can have a theory of redness that a blind person could read, for instance, and that theory could be as correct as any scientific theory could possibly be, but the blind person might still not know what redness looks like. I think that’s fine. We don’t expect them to see just because they understand what sight consists of, either. We might nonetheless think that the theory is acceptable, and the fact that it had “left out redness” need not be considered a fatal flaw. In fact, this is where I think neuroscience will eventually land, and I know many other physicalists feel the same way, but the distinction between the narrow and broad senses of the Gap are not often drawn. (To see how this sort of explanation might be feasible, check out Rhonda the Retinal Researcher, and stay tuned for a more detailed assessment of the Gap in future posts.)

The sort of understanding of redness a brilliant blind scientist might achieve and the sort of understanding achieved by a child with sight are fundamentally different at the cognitive level, and they involve different parts of the brain.

Existing discussions in this field often fail to distinguish between these two different types of understanding, and the available vocabulary does not readily distinguish between them.

In my experience, the people who are most impressed by the inability of science to derive qualia are also the folk who blur these different aspects of the puzzle together. It is just obvious to them that neurons cannot produce redness, and the source of that obviousness is not questioned. We can’t explain how physical brain tissue produce qualia because qualia are non-physical, they say, and with that the argument’s over.

The Gap is also often treated as synonymous with the Hard Problem.

Future post will tease these apart in more detail, but that’s not the purpose of this current post. I accept that the Gap and the Problem are closely related, but I will be arguing that there is conceptual space between them; it is possible to think that we face a Gap while also holding that the Hard Problem is ill-posed. For instance, there could be cognitive features that make it impossible to derive qualia, and those features might make zombies seem plausible, but they don’t actually make zombies possible. In that case, the essential challenge of the Hard Problem, explaining why we are not zombies, would end up as an ill-posed problem inspired by the Gap, but not synonymous with the Gap.

Again, drawing a distinction between these positions seems much less common among those who are most impressed by the Gap.

Chalmers usually links the Gap and the Hard Problem quite explicitly, with his landmark Hard Problem paper citing the Gap as evidence of a non-functional extra:

“There is an explanatory gap (a term due to Levine, 1983) between the functions and experience, and we need an explanatory bridge to cross it. A mere account of the functions stays on one side of the gap, so the materials for the bridge must be found elsewhere.” (Chalmers, 1995)

In his follow-up book, he also also leans on a series of anti-physicalist arguments that essentially fall back on various versions of the Gap, or rely on the cognitive features that are the natural sequelae of the non-derivability of qualia.

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Before presenting what I think is a useful way of placing people on a spectrum of opinions on the Gap, I will need to define the narrowest possible conception of the Gap, via the concept of Jacksonian derivation.

Jacksonian derivation is that thing Mary couldn’t do.

Mary is a brilliant scientist who is, for whatever reason, forced to investigate the world from a black and white room via a black and white television monitor. She specializes in the neurophysiology of vision and acquires, let us suppose, all the physical information there is to obtain about what goes on when we see ripe tomatoes, or the sky, and use terms like “red”, “blue”, and so on. She discovers, for example, just which wavelength combinations from the sky stimulate the retina, and exactly how this produces via the central nervous system the contraction of the vocal cords and expulsion of air from the lungs that results in the uttering of the sentence “The sky is blue”. [...] What will happen when Mary is released from her black and white room or is given a color television monitor? Will she learn anything or not? It seems just obvious that she will learn something about the world and our visual experience of it. But then it is inescapable that her previous knowledge was incomplete. But she had all the physical information. Ergo there is more to have than that, and Physicalism is false. (Jackson, 1982)

To perform a Jacksonian derivation of a quale, one must start off not knowing it, sit in a room with access to all the relevant discursive facts, think about them very hard, and then acquire the cognitive state that we usually think of as knowing what that quale is like.

To comply with the spirit of Jackson’s thought experiment, one must not use some cheating method that relies on meditation, dreaming, inducing migraines or seizures; we cannot see red via optical illusions that achieve glimpses of colour by having fine gratings of black and white at different spatial frequencies.

The process must be a derivation that is essentially analytical in nature.

Jacksonian derivation is a deductive process capable of reaching a good, natural sense of the property of redness, or the taste of cinnamon, or the feel of pain, without ever having had the experience — just by studying the physical substrate of those experiences.

If Jacksonian derivation is possible, then it is not necessary to have the relevant trained networks on-hand to reach the desired cognitive state; it is enough to read about those networks and then apply logic.

If pure Jacksonian derivation is possible, and perceptual concepts can be reached through logic alone, that implies that the same successful analytical process could be shared with others who have not had the sensory deprivation. Folks like you and me. If Mary can derive redness while still in her black-and-white room, then she can show her technique to someone else who already knows what red looks like. They can follow her methods and acquire the cognitive state by a new, deductive route that does not rely on reactivating their innate, naturally acquired concept of redness. At that point, they can probably announce that they have an illuminating understanding of the quale in question.

This process of derivation without prior deprivation would also constitute a form of Jacksonian derivation, but the analytical process being shared in such a scenario still needs to be notionally defined though a Mary-like process of deprivation. In this second context, the person following the deductive process already has the relevant trained perceptual networks, and their concept of redness can be triggered with a mere word (“RED!”). The capacity for this non-analytical ostensive route to the sought-after concept would make it harder to know if the analytical process had truly reached its target independently, which is what would be needed to satisfy the usual hardist challenge to prove that neural circuits give rise to the redness quale.

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With that context in place, we can take different positions on the prospects for Jacksonian derivation, and on our interpretation of a failure of such derivation. Only a couple of the resulting positions are truly at odds with physicalism.

Where do you think you lie?

This is a work in progress, so please let me know if any of it makes sense.

Note that this list does not itself carry any connotation that Jacksonian derivation is necessary for understanding, or something we should be trying to do. Instead, I am suggesting that we should explicitly dissociate the narrow question of whether we can derive qualia from the broader issues of whether we can understand qualia and whether we need to modify ontology to accommodate qualia.

If you think Mary’s story misses the point, then I agree, and this very opinion lies on the spectrum below.

Also, it is important to note that the list does not cover uncertainty or agnosticism about what the science will eventually suggest. You might not yet have an opinion on whether Jacksonian derivation is impossible, or whether the barriers to such a derivation are themselves likely to be explicable. That’s fine: your agnosticism can be captured by the range of the positions you are prepared to consider as plausible.

Some groups of positions are worth noting: #0 and #1 are Chalmer’s “Type A Physicalism”; #2 and #3 are roughly equivalent to “Type B Physicalism”; #2-#4 are Gap Compatibilism; everything <#5 is Anti-hardism; #5 and #6 are hardism, with the classic Hard Problem centred on #6.

The EG Spectrum

#0. Gap Super-denialism. There is no gap at all. People can read black-and-white text and, from those inputs alone, never having seen colour, they can achieve a brain-state compatible with a standard layperson’s sense of knowing what red looks like. A colour-blind vision scientist does not just understand the place of redness in the world, but can also engage with that concept in a natural way, picturing red objects in their mind. Jackson’s core intuition was completely wrong.

#1. Gap denialism. The EG is temporary and Jacksonian derivation will eventually be possible.

#2. Gap deflationism. The EG is permanent, but it is partial and explicable. The only substantial epistemic barrier we face is the one to Jacksonian derivation, which prevents us from engaging in a misguided attempt to produce an example from a description. There are other, more appropriate forms of explanation.

#3. Weak mysterianism. The EG is permanent, and it is itself explicable, but it is complete. Phenomenal and physical properties cannot be reconciled in any way that we can understand. Jacksonian derivation was the only potential route to understanding. We can trace out the cognitive barriers to understanding, so we can understand why we are mystified at the mechanistic level, but we must nonetheless remain mystified.

#4. Strong mysterianism. The EG is permanent, complete, and inexplicable, but it is only epistemic; the blame for explanatory failure is likely to lie with our cognitive ability to understand the mind-body relation, but that same failure prevents us from understanding why we are mystified.

#5. Weak hardism. The EG is permanent, complete, and inexplicable, and merely epistemic, but the blame – or credit – lies with the nature of consciousness. We are mystified, and we are destined to remain so, but our cognitive ability is unlikely to be the limiting factor. The nature of consciousness itself is such that it resists reductive explanation, albeit within what is likely to be a physical ontology. Our mystification does not, by itself, have genuine ontological implications – but it might as well, because the only ontology accessible to us will have to take consciousness as an unexplained fundamental element.

#6. Strong hardism. The EG is permanent, complete, inexplicable, and not merely epistemic: it points to an ontological rift between the physical world and mental properties. We need materials for a bridge, or some other radical revision to our ontological world view (such as panpsychism, idealism, strong emergentism, mysterious non-functional biological processes, and so on).

So, that’s the range of opinions. I ask again, where do you think you lie?