The topic of this book is phenomenal consciousness. Its thesis is that phenomenal consciousness can be explained by appeal to the modal structure of our neurophysiology. This provides a solution to the so-called hard problem of consciousness.Footnote ¹ This chapter is an introduction to that problem and to the solution proposed.

1

Consciousness seems to many a great and evident mystery, something that may even require of its possessors a special metaphysical status as dualist or spiritual beings, outside the natural order otherwise well described by the physical sciences. To Aristotle, there seemed a great divide between the living and the nonliving. But to many today, there seems a great divide between living plants and sentient, conscious animals.

One reason for this historical difference is that Aristotle believed we live in a much more familiar and cozy world than we do. He thought that things out in the world were very much as we experience them to be, for instance that there are irreducibly green trees and irreducibly red apples. Color on his view was a fundamental feature of reality, not constituted by anything else. Any omniscient god would see pretty much the colors we see; any creator must have spangled color intentionally throughout the world. This is not to say that Aristotle thought our experience was always veridical. As a lemon recedes from us, it in some sense looks smaller. But this distortion in our experience was supposed to be due to the nature of the omission and reception of sensible species of colors that fly off the lemon and somehow converge on the eye, or alternatively was supposed, as Plato thought, to be due to differences in fanciful extramissive rays that emerge from the eye. But the color on the objects and the color we perceive were supposed to be much the same. If bats or the color blind have a different experience of the color of the receding lemon,Footnote ² that is only, it was thought, because their perception misses or distorts things in the world that ordinary humans can see. If in the dark the lemon looks black, that is only because the sensible species cannot make it through the air unless the air is energized by light, so that the true color is blocked from us by darkness. Although some complications like these were recognized, according to Aristotle there is basically no gap between the way we experience the world and the way it is.

But we know better. We inherit a sophisticated science predicated in part on Galileo’s thought that colors are mere names, or at least on the recognition that the colors we experience are not simple irreducible aspects of reality. There are other ways than Galileo’s inflammatory way to think of this. Descartes thought that our perception of colors rather involved a kind of confusion of what was really there. Other near contemporaries, like Locke, thought instead that objective colors of lemons should be conceived as powers in objects to cause experiences in us. In any case, there is experience on one hand and there is the world on the other, and aspects of colors we most immediately experience, of which we are most immediately aware, of what we might call “phenomenal colors,” are held to be merely in experience and not in the world itself. They are analogous in some respects to perceptual illusions. Some features of our sensory experience are, on this conception, misleading about the world itself.

We now generally think there may well be a gap between, on one hand, any objective features of reality that correspond to experienced colors and, on the other hand, the so-called qualia such color experiences involve, relevant to differences in what it is like for us to experience red, green, and yellow. But creatures for whom it is like something to experience things are creatures with consciousness. Hence we have more trouble with consciousness than Aristotle recognized. The problems of consciousness and of qualia are in this way closely entwined.

There are several reasons why we need an explanation of our experience that is not so commonsensical as Aristotle’s, several reasons to think many of the properties and relations that concrete objects seem to present in our experience are, at least in large respects, not out there in reality. First, there are dreamers and hallucinating madmen and deluded perceivers, who see things that aren’t there. Second, the world that our physics reveals is radically different from that our experience seems to present to us. In a strange world of curved space-time and quantum mechanical amplitudes, this problem is even more dramatic for us than it was for Galileo. But third, and most important from our perspective, there are very many detailed ways in which our sensory experience is not plausibly veridical even under the best circumstances, even when we are awake and sane and the light is good and microphysics is not in question. We will be accumulating many cases of this third sort as we proceed. But, for purposes of initial orientation, consider one cluster involving color.Footnote ³

There are those who still say with Aristotle that the phenomenal colors we experience, the red of some umbrella and ball we seem to see, are in fact present in reality. And such objects do have in reality certain physical properties, certain spectral reflectances, which is to say certain tendencies to reflect various wavelengths of light in various proportions, that correspond reasonably well to specific perceived surface colors. When an object is perceived to have a certain hue when in white light by normal humans, then it is within a certain limited range of spectral reflectances in reality, a specific range of fully objective physical properties. So perhaps we might identify the colors we see with surface spectral reflectances of a certain range.Footnote ⁴But this cannot suffice to deliver all the features of the kinds of colors we seem to experience, all the structure of similarities and differences among experienced colors. Even contemporary physicalists about color, who identify colors out in the world with surface spectral reflectance ranges, do not characteristically attempt to defend the implausible view that the entire structure of the color properties that we seem to see, the full nature of phenomenal colors, is present in objective surface spectral reflectances.

There are many relevant examples. Lights are seen as colored but involve no surface spectral reflectance. The sky is blue and has no surface. There are differences in spectral reflectance that are not visible to normal humans. Perhaps we might say that some of these are imperceptible differences in color, which is strange enough. Even so, there are metamers, which involve very different surface spectral reflectances, but yet present the same colors to those with normal human color vision under normal conditions of illumination, while yet they can be seen to be different in odd conditions of illumination. What’s more, bluish purples have quite different physical bases than some reds, but seem to be quite similar colors. And there is the structure of unique hues in color experience – the specific red that is neither orangish nor purplish but rather pure red, and also analogous unique yellows, blues, and greens. These are privileged phenomenal colors that correspond to no objective privilege in reality. Furthermore, because infrared and ultraviolet radiation exist but are invisible to humans, there is nothing about surface spectral reflectances that explains why there are just the colors that we see.Footnote ⁵

Phenomenal color – the color with all the structure that we see – is not in fact out there in reality. No plausible account of the color we experience can have the general form favored by Aristotle and untutored common sense. So one aspect of the hard problem of consciousness is how to deliver our color qualia, the specific what it’s like of our color experience, in our at least mostly physical world. The peculiarities of humans plausibly matter to this. The specific way it is like for us to experience some flying colorful bug is plausibly quite different from the very foreign way it is for some bat to experience the bug through its sonar.

I will attempt to show here that our human neurophysiology of color vision accounts for our human color qualia when that neurophysiology is understood in the particular way I develop, which I call the modal structural way. There are of course other senses, and there is also intuitively much more to the hard problem of consciousness than just the problem of sensory qualia. There is a second key difficulty about consciousness to which we should attend, and which requires other aspects of my proposal. Even if some mechanical device could in some way represent a bug in just the way our qualia, or the different qualia of a bat, suggest, it wouldn’t follow immediately that it was conscious, that it was like something to be that device.

And on this issue, I think that Aristotle, with his focus on animal life as the arena in which consciousness arises, has something still to teach us.Footnote ⁶ Animals sense the world and act on the basis of what they sense, and their perception and action is mediated by their neurophysiology. It is specifically in such a locus of animal life that I believe that our neurophysiology of vision constitutes our experience of phenomenal color. Whether or not animal life with a neurophysiology is strictly necessary for phenomenal consciousness of any sort, still such life includes all the obvious cases, and it plausibly constrains at least our human form of it. Modal structure, as we will see, is also involved in this aspect of our phenomenal consciousness.

That’s the very short version. Before I elaborate the solution I propose to the hard problem of consciousness, explain modal structure, and sketch the plan of the book, it will be useful to further refine our topic and problem, and introduce some standard terminology in which it is now customarily posed.

2

Humans have some relatively unique capacities, and what it is like to be us is in some respects inflected by these capacities. I will be concerned here with what explains what it is like to have our human experience. But I will be specifically concerned with our perceptual or sensory experiences in particular, which is the sort of thing that other animals also plausibly possess. I will not be concerned for instance with how we experience our own thoughts and emotions and desires, which may require something fancier. Only human sensory experience is our target.

I will of course be yet more specifically concerned with conscious sensory experience in particular, and not for instance any unconscious analogue. And still more exactly, I will be concerned with the sort of phenomenal consciousness involved in conscious sensory experience. And while we will attempt to understand the qualia involved in our sensory experience, that is only in one sense of that ambiguous term, which is closely linked with phenomenal consciousness in particular. So let me now explain better what this jargon means.

Things are said to be conscious in several different ways. We say that animals are conscious or aware of their environment in a way that rocks and plants are not. We say that animals who are asleep or knocked out are not at the time conscious, in a perhaps more demanding sense. So there is at least one sense in which any awake animal who has sensations or perceptions of an environment is conscious.

But we pursue here a kind of consciousness that is more specific and seems more demanding than merely that. We are interested in the conscious sensations of these awake animals, of which they are in some sense aware. The horrible sensation felt by a squirrel when a limb is ripped or bitten off is something of which they are plausibly aware in this way, whereas they might even while awake have an unconscious perception of some subtle conspecific pheromone of which they are not aware in this vivid way.Footnote ⁷

On the other hand, there are related kinds of consciousness that are more demanding still, at least on the surface, than what we pursue here. Sometimes we are quite explicitly conscious or aware of our own mental states in a very articulate way, when we report them to ourselves, in words we say out loud or to ourselves. Sometimes we also seem to enjoy a special kind of introspective access to their nature, and sometimes we are even explicitly aware of ourselves as thinking and seeing selves, with these particular mental states. But these are kinds of consciousness or self-consciousness that are fancier, at least on the surface, than our focus. They are plausibly beyond the capacity of the squirrel.

Since Freud and the development of cognitive science, we generally believe that we have states of awareness of things in the world of which we are not and cannot be aware in any explicit and introspective way.Footnote ⁸ But even some of which we are aware of in a way relevant to our focus, we are not aware of in the fancy ways noted in the last paragraph. Think again of the pains of an unsophisticated animal, say some robin or cardinal. It seems aware of them in some relevant sense, even though it cannot reflect and introspect in any very fancy way upon them, even though it cannot talk about what it feels or ruminate about the fact that it feels them. That is the kind of thing we are after.

It is like something to be the pained bird or squirrel. That is the kind of consciousness that we seek to understand. Pain of course may seem a sensation very unlike the sensation of color. But my point is that we are interested in a kind of human conscious experience of color and other sensory properties that has the same rough character as a bird’s or squirrel’s conscious experience of its pain.

There may be philosophical arguments linking consciousness in one of the less demanding or more demanding senses noted to consciousness of the sort we are centrally concerned with. But on the surface, what we seek is in between. There is something it is like for an animal to have sensory experiences of certain sorts, for instance to have certain views of bright yellow objects. That is our focus.Footnote ⁹ It is possible that there are unconscious perceptions of environmental features by awake animals that lack this vivid sort of consciousness. And, on the other hand, it seems that creatures can have the intermediate sort of consciousness we seek, say creatures in pain or sensing yellow things, even though they do not possess, and indeed are incapable of, explicit introspective awareness of their own mental states as such, or of themselves as thinking and seeing selves, and even though they can’t talk.

This in-between sort of consciousness on which we are focused, enjoyed by awake animals when it is like something for them to feel a pain or see a yellow thing, is called “phenomenal consciousness.”Footnote ¹⁰ Differences in what it’s like, differences in phenomenal consciousness, are called differences in “qualia,” in the sense of that term I will use.Footnote ¹¹ As I use the term “qualia,” there is no implication that qualia are properties of sense data, that they are nonrepresentational properties of experience, that they are nonphysical, or even that they are nonveridical aspects of experience although I have already argued that in some respects they are. And the term is sometimes taken to imply those things. But I deploy a sense of the term that does not imply presumptions on these issues, that is focused on the details of what it’s like however it is in fact constituted.

So now I can put our topic in this more exact way: We are trying to account for the qualia involved in our sensory experience, for that type of human phenomenal consciousness, particularly in a world that is, as we will see, very unlike the one we seem to experience.

But to focus and situate our topic still more closely, it will be useful to introduce a little more standard terminology.

Today, many of us think Galileo was basically right about the world. Nevertheless, quite a few philosophers still favor the sort of commonsense conception of perception and the world that Aristotle fostered. It is natural to wonder whether this is a coherent set of views, whether Galileo really fits with Aristotle in this way. But in any case, we inherit the complex problem of fitting this together and working it out. And in the current climate of opinion, some distinctions must be kept in mind.

There is an apparent division between, on one hand, the phenomenal consciousness or qualia involved in sensory experience, for instance color qualia, and what is called the “representational content” of sensory experience, on the other hand. There is this apparent division even when we are restricting our concern to the phenomenally conscious sensory experiences of awake animals. The representational contents of these experiences are what they are about out in reality, and are relevant to whether they are veridical or not. In a Galilean world, that is unlikely to be Aristotelian colors. But we are interested here in the qualia, in the what-it’s-like, in the relevant sorts of phenomenal consciousness, in the sort of Aristotelian color that we at least naively seem to experience. The general idea behind the distinction at hand is that it is like something for a human to experience a bright green car in good light, but that that what it’s like, those qualia, that phenomenal consciousness, may well not be exhausted or fixed or even affected by the way that experience represents the green car in the world to be, by the representational content of that experience. Something like this distinction is required if we are to insist that our sensory experience represents the world more or less accurately, and that the way qualia are present to us in consciousness can lead us to mistake the true Galilean world for a fanciful Aristotelian world.

Such a distinction between qualia and representational content in sensory systems is not uncontroversial. In fact, I myself believe that the what-it’s-like and the representational content of a sensory experience are closely related, in the sense that the qualia fix the representational content. And a much larger number of philosophers believe that there is a dependency that runs the other way, that the qualia are fixed by what our senses truly represent, and so the distinction collapses in the other direction, despite the difficulties for such a view I have already noted. Still, the relevant point for now is that neither of these views can be presumed in our current philosophical context. If anything, a distinction between qualia and representational sensory content is currently presumed. So while I stress that my use of the word “qualia” will itself make no presumptions on this issue at all, that it is focused on the what it’s like of sensory experience, whether or not that should be distinguished from sensory content, still, nevertheless, there are many well-known cases that are supposed to support the now popular distinction between qualia and sensory content, cases that we will need to bear in mind as proceed. The cases can be divided loosely into the fanciful and the real.

Many hold that there might be so-called color inverts, those who have the same sort of qualia and conscious sensory experience when they see, for instance, red things that color normal people have when they see green things, with corresponding inversions throughout color experience. And it is also often held that color inverts still have sensory experiences with the same veridicality conditions, with the same representational contents, as the color normal. The inverts only differ from the color normal in qualia, in the what-it’s-like, not in sensory content, on such views. Beyond color inverts, there might be those on Inverted Earth, who are presumed to be individuals who generally have the same qualia but different sensory contents.Footnote ¹² And philosophical zombies are alleged to be physical duplicates of us who lack any what it’s like, whatever they say, and so experience sensory representational contents but no what it’s like. There are also analogous stories about fading or dancing qualia that do not affect sensory contents.Footnote ¹³

Maybe these fanciful stories are relevant in some indirect way to what is actual. But in any case, there are also real cases where there is a gap between qualia and the world, and so between qualia and at least any veridical sensory content. First, and most important from our perspective, there are numerous phenomena involving human sensory experience that are analogous to those relevant to color experience that I have already mentioned, for instance the unique hues. We will consider many such cases as we proceed. Second, some people who are color-blind must have a different what-it’s-like in at least certain cases from the color normal. It is not plausible that those who are wholly red-green color-blind could miss such a vivid difference in their qualia if it was really there for them. But if we are prepared to call their perceptions veridical, then the what-it’s-like must be distinct from their sensory content. Even if we aren’t prepared to call their experiences veridical, color experience provides other analogous cases. Even different color normal people disagree somewhat about which objects in the world have unique hues. We will return to such cases as well.

Third, there are mundane cases like this: Even if a tree doesn’t really look smaller as it recedes from you, there is some difference in what it’s like to see a distant or close-up tree of the same objective size.Footnote ¹⁴

To repeat, we are interested here specifically in the what-it’s-like of sensory experience, in sensory qualia and phenomenal consciousness, which, for purposes of discussion, we are granting may be distinct from sensory content, although we are not presuming that. Still, we will consider views that collapse representational sensory content and the what-it’s-like. Moreover, as I said, I myself think one idiosyncratic version of the collapse view is correct. I think that the world is very unlike the way we experience it to be, because I think the way we experience it to be is closely tied up with our qualia, while our qualia and the real world are not in close alignment. But I will not presume that idiosyncratic conception here, though we will be gathering some grounds to believe it.

The main point for the moment is that, despite these various differences, more or less everyone in the current climate can agree that the qualia of conscious sensory experience require some explanation that it isn’t easy to provide. The old Aristotelian story doesn’t work, at least in that respect. That much should be reasonably uncontroversial. So that will be our organizing focus despite what I admit is my desire to eventually deploy such qualia in other and more ambitious ways, to explain the representational content of sensory experience, and despite the fact that we will have to attend somewhat to the popular views of those who think the dependency runs in the opposite direction. We will be trying to solve this crucial portion, relevant to sensation, of the hard problem of consciousness.

There is another restriction on our focus of concern worth noting up front. There are debates about the richness of sensory content and hence about relevant associated qualia. On one traditional conception, the contents of sensory perception are limited to the traditional characteristic objects of the senses, for instance, in the case of vision, to shapes and sizes and colors and motions, and to smells and tastes and sounds and tactile feels in the case of other senses. But a competitor view is that fancier properties such as being an oak tree, or even a written word of English that means tree, might be present in the most immediate way in the perceptual experience of someone who is trained in the requisite way, in a way that affects their relevant phenomenology.Footnote ¹⁵ As will eventually be evident, I have considerable sympathy with this more expansive second view, and think that the general model we will develop here might be extended profitably to cover its favorite cases. Indeed, it is arguable that the ultimate viability of my proposal may depend on that extension. But without presuming to resolve this dispute, we will focus here principally on the traditional sensory properties.

3

So that is our problem. Now consider possible solutions. While our major focus will be on building a positive plausible account of human sensory phenomenal consciousness, it is worth mentioning for purposes of orientation who I think is wrong about it. Among philosophers, I think almost everyone is. While I can’t aspire to disprove all standing accounts in any brief space, it is worth mentioning obvious difficulties of the major standing views for which there are no obvious solutions, by way of motivating another sort of attempt. If you don’t feel the need for such motivation, which of necessity will get down into the weeds a little, you can skip to Section 4.

There are two clusters of solutions that have some contemporary currency. Some deploy naturalistic accounts of representation, and others resort to dualism or analogs like panpsychism. Begin with the first cluster.

Talk of representation and information is ubiquitous in contemporary biology and psychology, and also in contemporary discussions of sensory qualia and sensory content.Footnote ¹⁶ There are thought to be mental representations, neural analogs of words, which represent certain things because they carry information about those things, paradigmatically because they are caused by those things in such a way as to assure covariation.Footnote ¹⁷ That’s the basic idea, but there are necessary refinements. Representation plausibly requires something slightly more complicated than actual causal covariation, because of the following worries: When something is caused, it generally has more than one cause, in a chain. What’s more, false representations and nonveridical experiences are not usually caused by what they are about. The standard reply to these standard worries specifies that the relevant cause, the one that constitutes for instance the sensory content of a sensory representation, is the “normal” cause of that mental representation. When false, or when it has many causes, a mental representation is caused by other than its normal causes, but it is only the normal cause that counts as what is represented, as its “content,” about which the mental representation is said to carry information. Then we face the question of what a normal cause is. And there are various standing accounts of normal causes. There are teleological accounts, which focus on what causes something should have, in some sense of “should” allegedly delivered by evolutionary or learning history.Footnote ¹⁸ Or perhaps a normal cause is a statistically normal cause.Footnote ¹⁹ Or perhaps it is specified by asymmetric dependence so that the normal cause is the cause on which all the other causes depend while it depends on no other.Footnote ²⁰

I argue at length elsewhere that none of these proposals can deliver mental content of any sort,Footnote ²¹ and I can’t repeat all that here. So I will grant here for purposes of argument what I do not believe, that the currently dominant informational accounts of representation can be made viable, in the sense that they can provide some plausible account of normal causes that undercuts standard objections. And I will make no objection to their use in biology or psychology. And I will even grant that they might deliver sensory content of some sort.

Nevertheless, focus closely on whether, even granting all this, they can help much with sensory qualia and phenomenal consciousness. There is certainly reason to be initially doubtful. As we have already noted, many features of sensory qualia do not correspond to objective features of external objects out there in reality, so cannot be normal causes. We see objects as unique red, and as having purples similar to reds, but that sort of structure is absent in any physical correlate of color out there on the objects. The tree looks in some sense larger when it is merely closer, but it isn’t. In fact, cases like these are bound up in the very notion of what sensory qualia are. And we will be gradually collecting many cases of this sort. A blunt way to put this criticism is that qualia are nonveridical, whereas informationally based representation must be dominantly veridical. There are no things in the world corresponding to many qualia for mental words to informationally represent.

Nevertheless, information-based accounts of sensory qualia have a variety of ingenious resources to deploy towards defusing these initial worries. For instance, so-called representationalist views maintain that, despite the surface cases we have considered that suggest a distinction between the qualia associated with sensory states and their sensory contents, still in fact sensory contents constituted by causally based information do fix the relevant qualia. So despite the initial difficulties of representationalist accounts of phenomenal color and other sensory qualia, you may want to consider some of these resourceful details.

There are two rough forms such a representationalist reply may assume. The first focuses on more objective properties of external objects, and the second on more subjective properties of objects, that involve their relations to the perceiver.

Tye’s account is a well-developed objective version. We might distinguish two periods of Tye’s work on color: Tye A and Tye B. Tye A, in 1995, deployed a physicalist account of color experience apparently modeled on suggestions of Hilbert about color.Footnote ²² There are cone cells in the retina that are maximally responsive to short, medium, and long wavelengths of visible light. And our perception of color depends on light being reflected from objects. So “the color of a surface is an ordered triple of the reflectances of the surface with respect to light in these three wavelength bands …, where the reflectance of a surface at a given wavelength is its disposition to reflect a certain percentage of light at that wavelength.”Footnote ²³ But the problem is that there are standard objections to this as an account of our experience of phenomenal color, of color qualia. Metamers, you will recall, have different spectral reflectances but look the same in normal light. Tye A thought that this worry can be handled by specifying relevantly wide bandwidths.Footnote ²⁴ Though this is overly optimistic, let it pass. More importantly, there are relations of similarity between colors that color objectivism of this sort seems to miss. The standard hues form a similarity circle, but light frequencies do not. Tye A says, in response, that we are to think of color space as three dimensional, with each dimension corresponding to the surface reflectances at one of the three wavelength bands, and to think of the relevant triples of reflectances as coordinates in this space, with the hues marking out a closed circular loop in color space.Footnote ²⁵ But this is fanciful. It is true that any test light can be matched by three primary color lights whose intensities scale a three-dimensional space in which ordinary hues mark something like a circle. But this is not a color appearance space that captures similarity of phenomenal colors.Footnote ²⁶ Another standard worry about such an account of color qualia is that there is a phenomenological distinction between unique hues like pure red, blue, yellow, and green, and binary hues like orange, which seems yellowish and reddish. Tye A says this: “As for the binary-unitary distinction, it can be preserved as a basic truth about color mixing. Orange, for example, is the color you get when you mix red and yellow pigments; but red is not the color you get when you mix purple and yellow pigments.”Footnote ²⁷ But green can be got by mixing yellow and blue and still there is unique green, so this story doesn’t work.

Tye has moved on.Footnote ²⁸ “Opponent processing” is a feature of our neurophysiology of vision to which we will return. According to Tye B in 2000, an object is pure red if it has a surface spectral reflectance that normally produces opponent-processing that is distinctive of the experience of pure red.Footnote ²⁹ And an orange object generates forms of opponent-processing characteristic of being seen as yellowish and also forms characteristic of being seen as reddish.Footnote ³⁰ On such a view, color qualia present us with these subjective features of human visual processing. This account is much less objective than that of Tye A, and faces characteristic difficulties for subjective accounts to which we will shortly turn. There is no explicit account of the color similarity circle in Tye B, but it is presumably supposed to be connected to this proposal, and hence similarly subjective. And there remains a general problem for even such a very limitedly objective account of color qualia. The apparent colors of objects shift somewhat as the light changes. “The colors of objects typically do not change when they are moved from outdoors to a setting illuminated by incandescent lights, for example,” according to Tye.Footnote ³¹ But of course there is some difference in our phenomenal experience introduced by this shift. Tye has no account of this.

It is not a surprise that a developed representationalism tends in a subjectivist direction, since qualia are frequently nonveridical artifacts of perception. A more uniformly subjectivist representationalism is developed by Hill. He identifies qualia with properties of external objects that are more subjective than most of those that Tye deploys. He calls the properties in question “appearance properties” or “A-properties.” Qualia, on his view, are A-properties.Footnote ³² But which properties in particular are A-properties?Footnote ³³ Color physicalists often identify objective colors of solid objects with certain surface spectral reflectances. But since color appearances change with the light, this is too objective for A-properties. Perhaps, then, we should say that when an object presents a red appearance to you, the proper focus is what is going on in your retina, that the “object is projecting a retinal image that involves appreciably more activity in long wavelength cones than in middle wavelength cones, and about the same amount of activity in short wavelength cones as in long wavelength cones and middle wavelength cones combined,”Footnote ³⁴ that they have a “red projection property” of this sort. But this neglects the effects of color constancy in our visual processing. It is too subjective. So Hill believes that we should say instead “an object counts as A-red if (i) it has a red projection property, (ii) appropriate constancy transformations have been applied to this property, (iii) the output of the transformation falls within a certain range.”Footnote ³⁵

But the problems for such a subjectivism, in the context of a representationalist, information-based account of qualia, are manifest and debilitating. These fancy complicated A-properties seriously misrepresent the relatively simple and straightforward qualitative content of our sensory experience. Color properties seem to objectively qualify external objects themselves; experience of such properties does not seem to be about our own cones even in part. What’s more, it is hard to believe that information-based accounts of representation can deliver such complicated and recherché contents.Footnote ³⁶

Hill has a resource in response to at least the first of these worries. He distinguishes between visual qualia as represented and visual qualia as they are in themselves.Footnote ³⁷ Visual qualia are appearances, but appearances that appear to one in a somewhat misleading way.Footnote ³⁸ But if it is the appearance of an appearance that really matters to intuitive visual phenomenology, we have in fact moved into the next class of views we need to consider.

On these other views, it is the representation of mental states, for instance states of sensory experience, that is supposed to deliver phenomenal consciousness. According to these higher-order representational accounts of consciousness, an experience is conscious when it is represented by a higher-order mental state, a mental state about a mental state. To avoid a regress, the higher-order state need not itself be conscious. There are different forms of this view. In the opinion of Armstrong and Lycan, what is involved is a kind of higher-order perception.Footnote ³⁹ In the opinion of Rosenthal, it is higher-order thought.Footnote ⁴⁰ It might also be that phenomenal consciousness merely requires of a state the capacity to be accessed in one of these higher-order ways rather than actual access of that sort.Footnote ⁴¹ That would be a dispositionalist higher-order account.

There are significant worries about both higher-order thought and perception, or about dispositions to them, as resources necessary for phenomenal consciousness, since young children and animals intuitively have phenomenal consciousness without such apparently fancy mental states. But focus on the main issue for us, whether they can plausibly deliver sensory qualia. It is striking that no higher-order view has so far provided a reasonably well-developed account of the different natures of different first-order sensory qualia, which is our central concern.Footnote ⁴² How might higher-order representation conceivably help to deliver first-order qualia that differ from the representational contents of first-order perception? On the surface, sensory qualia seem to involve features of the world itself, and it is not obvious how representation of our mental states of experiencing can deliver this aspect of the qualia without presuming that those mental states of experiencing themselves already involve the very qualia in question. But there seem to be roughly three possibilities. First, what is represented at the higher level might be the content of the lower-level state. It might seem that this possibility would not allow the higher-order representation to do any work beyond representationalism itself in determining the relevant sensory qualia, although perhaps a kind of partial or misrepresentation of first-order sensory qualia might sometimes be a useful resource. Second, what is represented at the higher level might not be the content but the intrinsic nature of the first-order representational state. Or third, what is represented might be the representation by that first-order state of its first-order content. The first model might help with metamers, where there is a difference in what is represented out in the world but not in phenomenal consciousness. It is, however, hard to see how it can deliver the structure of unique hues, or adjust our sense of the content of sensation as much for instance as Hill generally requires, because orthodox information-based accounts of representation are not suited to deliver significant and normal misperceptions or analogous errors in representational states. They can abstract in representation from what is there, but have serious difficulty in adding to it in any general way. But it might seem that in that type of case, our second model might help. It might be that there are intrinsic differences among the mental states that are representations of unique hues as opposed to other hues. But it is still a puzzle how representations of internal mental states can be as of the world itself, how one could see, for instance, differences in neural processing as differences in worldly colors. And our experience of colors seems to mix together two different sorts of factors that the first two models handle differently, without there being any obvious way to understand how in our color qualia they might be conjoined. And most significant, such a focus on the intrinsic properties of the first-order representing states suggests that that is really the key to qualia differences, not how they are represented at a higher-order. But perhaps the third and itself mixed model of what higher-order representation represents can evade this worry, and also explain how the factors characteristic of the first and second model might be mixed. Perhaps what is represented at the higher level is the representing by the first-order state of its first-order content. But it is very difficult to see how a causal-covariation story about representation could deliver such a complex and modally complicated content to the higher-order state in question.

Our first two attempts to deploy information-based representation to deliver sensory qualia seem to face insuperable difficulties. Third attempt: Some views of consciousness with current defenders hold that it involves mental self-representation. The idea is that conscious states of sensory experience involve self-representing states. But it is hard to see how this would help with the particular worries about representation and qualia that engage us. And in Kriegel’s relatively well-developed version, self-representation is not supposed to determine the differing natures of specific sensory qualia, which are instead given a representationalist account.Footnote ⁴³

We have been focused on accounts by philosophers in which representation and information play crucial roles. But there are also neuroscientific accounts to which such notions are crucial. Still, these somewhat analogous proposals about the nature of phenomenal consciousness also don’t seem very well positioned to tell us what constitutes the differences among sensory qualia. For instance, the global workspace theory is that there is a kind of central clearinghouse into which information from various neural subsystems is gathered, in which it is subject to unified processing and from which it may be broadcast throughout the nervous system, and holds that being accessed by that central neural clearinghouse is what constitutes consciousness.Footnote ⁴⁴ The integrated information theory holds that it is a kind of integration of informational representation that constitutes consciousness.Footnote ⁴⁵ I think we should be cautious about what it means for the relevant sort of information to be gathered, broadcast, or integrated in these ways. But, suspending complications regarding normal causes, it would be possible to transmit causally based representation down any chain of representers that is locked together in suitable covariation, and so such causal influences might be gathered and broadcast in a way that makes some sense of these ideas. So, maybe, such a proposal can help isolate consciousness of some sort. But still, it is hard to see how such locked covariation could help make any special sense of qualia differences and similarities, how it provides sufficient help for us in that crucial role. These neuroscientific accounts inherit the difficulties for information-based views we have already discussed.

We have been focusing on the difficulties for representation-based views of phenomenal consciousness in delivering human sensory qualia. But another relevant objection is that at least the philosophical versions fail to explain why only animals are intuitively phenomenally conscious, since representation is ubiquitous and consciousness intuitively is not. Even evolutionary teleology encompasses plants. So let’s move on to our second cluster of familiar views, which in some forms have at least a crude, brute-force answer to this worry.

This cluster deploys ghostly, spiritual, dualist stuff, which is not constituted by the neurophysiological or even by the physical, at least according to standard understandings of those things. So it might be thought that phenomenal consciousness in general is, or at least requires, such a general type of dualist stuff, and it might be thought that different qualia are constituted by different forms of it. When dualist stuff is proposed, it is customarily proposed to fill both of these roles. There are two basic forms of dualism relevant to phenomenal consciousness, although some partisans of the first do not accept the dualist label. And at least the second form might plausibly allow that only animals enjoy phenomenal consciousness.

The first form is panpsychism. It is the view that everything has a phenomenal character, down to the smallest bits of matter, and that the phenomenal aspects of the bits of matter that make up your physical aspect, or some of it, somehow sum up to constitute your phenomenal consciousness.Footnote ⁴⁶ Everything is phenomenally conscious on such a view. That last point is an intuitive objection to the view. But such a view still might provide an interesting story about qualia differences.

Still, there are serious problems with panpsychism in its crucial role as an account of qualia similarities and differences. Since we know our physical aspect is constituted out of a limited number of types of molecules with a fairly limited chemical basis, and also that atoms are constituted by protons, neutrons, and electrons, it would seem that the phenomenal aspects of protons, neutrons, and electrons would, by necessity, play at least a relatively basic role in such a story about our qualia differences. Or perhaps we should proceed on down to quarks. But there are debilitating difficulties regarding how the relevant summation of phenomenal aspects of such parts into those of relevant wholes would work. This is called “the combination problem.”Footnote ⁴⁷ Simple addition seems obviously inadequate, and there are no obvious coherent and metaphysically unproblematic alternatives.Footnote ⁴⁸ Goff has distinguished various aspects of this problem:Footnote ⁴⁹ The “subject-summing problem” is how little subjects like electrons and quarks can sum up to specific big subjects like you and me. The “structural-mismatch problem” is how and why the structure of our phenomenal consciousness matches the structure of our psychology in particular and not our more detailed physical structure. And the “palette problem” is how the variegated differences and similarities among sensory qualia can be introduced by any sort of summation of basic phenomenal aspects, when experiences of such different qualia are constituted by the same limited sorts of microphysical particles with the same limited types of phenomenal character. That relatively fundamental phenomenal character would be so ubiquitous as to be apparently irrelevant to intuitive qualia differences of sensory qualia. The palette problem is especially damning in our context. As far as I can see, there is no remotely plausible solution available.

So a second type of dualist story about phenomenal consciousness, a more traditional form, may seem preferable to the first. Such a view says that there is an irreducible dualist phenomenal aspect for only certain sorts of physical structures, which of course might be only animals. And a traditional dualist is able to posit exactly the dualist aspect that delivers the details of our qualia.

But this view still faces severe difficulties. Why think that in all the vast universe some extra fundamental metaphysics is required to account merely, at least for all we know, for one psychological feature of a small portion of the biomass that exists on a very thin layer around the third planet of a mediocre star on the edge of a mediocre galaxy? We aren’t that important. Nor are all the earthly animals. And why does it have just the structure it has, which is correlated with our neurophysiology in just the detailed way that it is, so we can talk accurately about our phenomenal consciousness and it matches our behavior in the various ways that it does, when our talk and behavior seems obviously directly explained by our neurophysiology. There are no other fundamental correlational laws in the world as we understand it that have the same kind of inelegant complexity as the correlational laws required to explain this.

There are motivations for dualism beyond metaphysical pride and theological commitments. There are dualist arguments that physicalist resources such as I will deploy here can be seen to be incapable of providing an adequate account of phenomenal consciousness. We will return to these arguments at the end of the book, when my positive proposal is available for scrutiny. And it may be that the various surface difficulties I have reviewed in this section for standing accounts of phenomenal consciousness are merely that, that they can be suitably answered by fans of dualism or naturalist representation as accounts of phenomenal consciousness. But these difficulties suffice at least to provide motivation to look for something else, a physicalist account of phenomenal consciousness that deploys a mechanism other than information-based representation. That is my goal.

4

My positive account of phenomenal consciousness in human sensation has three key features. Its first two features can be indicated quite briefly, although their proper development and explanation will require Chapters 2 and 3. We will begin here with these. Its third feature is perhaps most unfamiliar and characteristic, and will require a bit more initial explanation.

While our central focus is the phenomenal consciousness involved in human sensory experience, still one good intuitive test for something being a thing that it is like something to be, a being with phenomenal consciousness, is that it feels pains or itches, even if those aren’t always considered, like vision and hearing, cases of sensation. It is certainly like something to feel a pain or itch. And it is quite natural to think that, in the actual living creatures who are the entities we are most intuitively certain feel pains or itches, it is the way that their nervous systems actively mediate between stimulations of certain sorts and actions that somehow constitutes such experiences. We don’t intuitively expect such sentience in a tree stump or a rock, although they may register information in analogous ways and might even conceivably have dualist substance attached.

And a part of my proposal about our sensory phenomenal consciousness, in fact two of its three main parts, rests on considerations like that, on a certain understanding of the sort of living neurophysiology that mediates in us between stimulation and action, an understanding that focuses on what I will call the modal structure and dynamics of all that, and also on an analogous understanding of the phenomenal consciousness that it plausibly constitutes. We will develop first a certain modally inflected understanding of our nature as living beings with unified nervous systems, and, second, a certain modally inflected understanding of our phenomenal consciousness as a whole, and see, pushing at once up from below and the neural facts and down from above and the phenomenological facts, or, if you prefer, in from the third-person facts and out from the first-person facts, how the two sides fit together, how we should expect such a live human animal to possess a human phenomenological consciousness.

Those are the first two key features of my proposal. But you may well wonder what I mean by a modally inflected understanding of these things. And perhaps the best way to provide an initial, rough understanding of that, as well as of my overall positive proposal, is to focus in a more extended way on its third key aspect, my modal structural proposal about sensory qualia details and differences. Briefly put, but a little less briefly than before, the account of phenomenal consciousness to be developed here is that the modal structure of our sensory neurophysiology explains our conscious sensory qualia, largely because the actual modal structure of that neurophysiology explains the apparent modal structure of those qualia. Those details and differences of sensory neurophysiology and of sensory qualia match.

So let me sketch these ideas. Begin with the central notion of this book, the idea of modal structure.

Modality involves what is possible and necessary, what might be, and what must be. I mean something very general and inclusive by “modal structure.” I count any modal aspect of anything as one kind of modal structure. Different things involve very different sorts of modal structure, but are rarely without some modal aspect that is significant to what they are. Some tree house might be painted in a variety of colors. Perhaps through some special technology or magic, it might even fly or shrink. But it could not be a red corpuscle or Notre Dame de Paris. It could not survive certain alterations, but it could survive others, and that modal nature is part of what such a thing is. I also count any dispute about the nature of what makes modal claims true as a dispute about modal structure.

Consider this case: A blood cell is some vivid red, or, if such tiny things aren’t really red, a cherry or child’s ball is so. Presume for the moment such a color is just as Aristotle assumed. It is then a fundamental ontological entity, which yet has essential relations and differences to other colors, colors the ball might sequentially exhibit. I also count such essential similarities and differences of that color, similarities and differences it must have to be the color it is, as relevant to its modal structure. They are part of what I mean by “structure” in that phrase.

That general characterization of modal structure may well remain opaque, and crucial aspects of the notion will gradually unfold throughout the book. But perhaps the best way to convey the flavor of what I mean by this notion in a helpful preliminary way is to focus on some examples of shared modal structure.

Presume a perfectly scaled desktop model of some town, deployed in some world’s fair or war game, or a hugely enlarged model of some living human animal. Each model bears a very special sort of isomorphism with its original. It is not just that to each element in the model there corresponds some element of the original, with properties and relations except spatial distances in fact strictly duplicated, but that even essential similarities between properties and relations are duplicated. One building in the desktop model is just as similar in color to another building in the model as the original of the first is to the original of the second. And the heart of the body facsimile also consists of chambers arranged in the same way but on a smaller scale.

But there is an important aspect of shared modal structure not captured by this sort of isomorphism. A static model submarine with a frozen propeller or rudder lacks something other than size that its original has, and not merely a certain trajectory of change over time. Even an appropriately moving and developing model town or submarine, which tracks the history of its original, lacks something important and relevant to shared modal structure. It would be better if the rudder could move in other characteristic ways even at each moment of its history, so that there were alternative possible states of the model submarine at each moment that corresponded to alternative possible states of its original at the relevant moment, preserving patterns of similarity as well. Shared modal structure requires not just an isomorphism between the actual and the actual, but among the merely possible and the merely possible. And notice that any merely possible color variation in a red barn in the model town matches a corresponding possible color variation in its original. There are even appropriate relations of similarity among possible variations in the respective lengths of the relevant barn doors, though the model has in reality a much smaller door than the original.

There isn’t much variation between the exact models and originals in these cases. As far as it can be managed, just proportional variation in size is involved. But modal structure can also be shared in much more latitudinarian ways. Imagine a creature with experience that is inverted on many axes relative to our human experience, although they look at the same world as we do. For instance, what seems on the left to us seems on the right to them, and not because they are facing us. Their experience is as ours in a mirror wherever they look. They intend to act into such a mirror-inverted world, we would say in error, but things come out alright on the outside, because of the systematicity of their mental inversions of left and right. They seem to themselves to live in a world that is mirror-inverted relative to what we see, but they never encounter conflicts of perception or belief that reveal that, and their actions suffer what we take to be a similar inversion relative to their expectations and intentions, so that everything works out fine. This mirror inversion is not the only inversion in their experience. Their color experience is also inverted relative to ours, with red exchanged with green, yellow with blue, and black with white, and with corresponding changes all over the similarity space of phenomenal colors, such that similarity relations in their experience of the colors of things preserve the similarity relations that are present in our experience.Footnote ⁵⁰ There are also corresponding inversions in their other forms of sensory experience, in tastes and smells and the like.

Though many philosophers disagree about this, I think that a part of what you and I mean when we say “red” has much to do with our own experience of phenomenal red. If these inverted creatures call “red” the things out there in the world that we call “red,” they will apparently mean something different by that. They will arguably mean what we mean by “green.” But regardless of my idiosyncrasies on this topic, there is clearly a very high degree of shared structure between what we think and say and experience and what they think and say and experience.

Now imagine something more, that they are dead right, that the world is just how they experience it to be, and that we are wrong, that our experience is inverted relative to reality in all these ways. Aristotle thought that ordinary human experience of green captured something out there in reality. But imagine instead that these creatures get it right in that way, and we get it wrong. Consider our experience and thoughts under such a condition. I think in one strict sense our experiences and related thoughts are pretty clearly false. We are wrong about what things in the world are like. We think things are green when they are red. But it is also oversimple to say just that, even if you accept my unpopular view of the meaning of color terms. There is a very serious isomorphism between what we think on one hand and what the other creatures think and also reality on the other.

This is an important kind of shared modal structure. It is not merely that there is a pairing between any of our given claims about reality and some one of the other creatures’ true claims, with for instance red of some shade in our experience paired with green of some shade in theirs. There is more structure of reality than that which even we capture accurately. The ball is a certain red and we think it is a certain green, but more, the ball might have been, or might become, a slightly more orangey red, and we think in a corresponding way it might have been, or might become, a slightly more blueish green. It might be further to the left, but we think it might be further to the right. It is not merely that to any true claim they make there corresponds a somewhat different thought we would have under the same circumstances that bears a recognizable isomorphism to theirs. Rather, beyond that, various possible claims we might make about things preserve a kind of actual modal structure possessed by reality and by the fully veridical claims of the other creatures as well. Our own various possible claims are related to other possible claims we might make in what is in fact, despite our inversions relative to reality, a veridical way. The whole structure of alternative possibilities that the other creatures recognize corresponds as a body in structure to ours. A slight deviation in color in their experience maps to a similarly small deviation according to us, and to every change in color that something might undergo in our experience, there is a corresponding change it might undergo in theirs. Possibilities within each system have equivalent similarities amongst themselves.

This is another example of what I mean by a shared modal structure. But notice that here, unlike the case of the toy submarine, it is the content of our thought and its apparent modal structure that matches the true modal structure of reality. So now consider a further step. Maybe sometimes the apparent modal structure of someone’s experience fails to meet the true modal structure of reality. Just as you might hallucinate a dragon when there is no dragon in reality, you might see something with such modal structure and it may not really be present in reality. Reality and the content of experience might not share modal structure. I think we have already seen reason to think this happens in the case of phenomenal color, although why this is so will require further explanation.

There might be even more radical differences that yet preserve modal structure. Shared modal structure may not require that lengths go to lengths, though perhaps of different extent or in different directions, or colors to different colors. We might switch lengths with colors, as long as similarity relations among different lengths in the first system correspond to similarity relations among corresponding colors in the other, and preserve the relevant sort of modal structure. But let’s continue to focus on the case of color.

5

Such a notion as modal structure may seem too general to be useful. But what matters here are certain specific sorts of modal structure. Consider the way in which some yellow lemon is presented in our experience, and pretend for the moment that that experience is entirely veridical, that we live in an Aristotelian world. That particular lemon, its nature as a lemon, and its shape and color are presented in experience as having certain modal characters, I believe, which underwrite some characteristically Aristotelian claims about them. For instance, that color might be found on some other object, say, an umbrella, and the lemon might survive turning brown, while that piece of fruit arguably would not survive loss of the property of being a lemon, and its color arguably could not exist unless had by something. That is part of the modal structure of that object and that color, at least as they appear in our experience, I claim.Footnote ⁵¹ Now focus specifically on the essential nature of the exact yellow hue of one bit of the lemon’s surface, as it appears in our experience. In other words, focus on that phenomenal color. Its nature involves, I believe, essential relations of similarity and difference to other exact phenomenal colors, other exact colors that may not color anything even in an Aristotelian world and so are in that sense merely possible. For instance, it is part of what that yellow is that it has a certain relation of similarity to unique yellow, and other similarity relations to various specific greens and oranges. The yellow of the lemon assures, if it really exists, that unique yellow is possible, and its being is entwined with that possibility.

Of course, it may well be that this complex modal nature of the phenomenal yellow in question is not really out there on the relevant bit of any real-world lemon. Indeed, perhaps, that is just one more reason to think that such aspects of our experience are not veridical, but are mere qualia. However, my basic idea about color qualia is to explain the apparent modal structure of such nonveridical phenomenal color qualia by appeal to the real modal structure of our neurophysiology of color vision that underlies, that indeed constitutes, that experience.

Focus on both sides of this equation, the qualia as experienced and its neural basis. And begin with the first, continuing to presume for expository purposes that Aristotle was right, that things out in the world really have the phenomenal colors that our experience seems naively to exhibit to us.

Some chair is a certain phenomenal red, a certain scarlet. But it isn’t unique red, the red that is neither orangish nor purplish. Nothing in even Aristotelian reality, we will presume, is unique red, which is analogous in that way to Hume’s missing shade of blue. Yet that scarlet red of the chair has essential relations of similarity to unique red. How can that be if nothing is unique red, if unique red lacks that familiar sort of existence? There two ways to make the metaphysics work, I believe, two ways to make sense of the unique red in question. There might be a Platonic transcendental universal of unique red, which exists even though nothing has it, to which our instanced red bears some essential relation. Or it might be that there is somehow a subsisting but not existing unique red, which is entwined in being with the instanced, existing red, yet itself merely subsists without existing. Plato or Meinong:Footnote ⁵² take your pick. You may well object to both sorts of fancy and questionable metaphysics. But remember we are just talking now about the metaphysics of things that appear in our experience, and experience is not necessarily veridical. We are just talking about the putative metaphysics of what appears as it appears. I argue at length in Experience and Possibility that the second model of entwined subsistence and existence is more coherent and better fits the phenomenology of color,Footnote ⁵³ but either model can work for our purposes. What matters most is that the experienced phenomenal color is, if it exists in reality as Aristotle presumed, entwined in being with colors that things might but don’t have, with the merely possible colors of things.

Let me elaborate my own preferred model of how this would work in a bit more detail, partly because it is unfamiliar and yet I think phenomenologically more accurate, but mostly because it provides a better guide to analogous claims about our visual neurophysiology that will be important to us here. In a world of Aristotelian color, I claim: (i) the actual and the merely possible are deeply entwined and inseparable in being in certain ways, and (ii) the merely possible subsists without existing, has a different and more shadowy type of being than what is actual.

There are less and more complicated ways to elaborate such a structure, but focus on one relatively simple modal structure of this type that I will call “the superworld,” which can serve our purposes here. Please remember that I am not going to ask you to believe in such a metaphysical monster. Rather, I claim that our experience involves the appearance of such a structure and that this mere appearance is an important clue to what actual neurophysiology constitutes us to have such experience, and how it does that.

The superworld has two key features. First, the merely possible is neither actual nor existent. It has rather a different type or mode of being, which I am calling “subsistence.” There is a true metaphysical difference between the merely possible and the actual, but it is not a mere locational difference captured by some indexical term, nor captured by the difference between the abstract and the concrete, and it does not involve a special property of actuality had only by some existent things, something superadded on to existence, as some philosophers have proposed. On this conception, in such a superworld, what exists is actual and what is actual exists. But the merely possible involves a different sort or lesser degree of being than what is existent and actual.Footnote ⁵⁴

There is also a second key aspect of a superworld. The so-called possible worlds are various alternative ways that the universe might be as a whole and in detail. One way to put this second aspect is that possible worlds are not distinct individuals, as is traditionally claimed. Another is that facts about possibility are more local than traditional possible worlds models suggest, in a way that implies we cannot easily disentwine modal facts into distinct worlds. Though this a nonstandard view, it is natural and intuitive, at least when we consider certain cases. It really is not very intuitive to think that many of the modal features of my bike, for instance that it might be green though it is actually purple, involve a whole different universe, a different possible world out there somewhere which happens to have in it that bike being a different color. All that is intuitively relevant seems located right here with the actual bicycle. If the bike has a disposition, say to squeak when the peddles turn, or a power, say to refract light in certain ways even though now the light is off, then the bike itself and its actual properties, things here in actuality, seem to extend into what is merely possible, not only in something like the way that particulars extend on traditional conceptions from the present back into the past, or even in which scarlet might exist in more than one possible world, but in an even deeper way. The very being here in actuality of some properties and particulars, it seems, extends out into various alternative ways things might be. And this happens in such a manner that various alternative ways the world might possibly be, including the actual way it is, are not really wholly distinct from one another in the way that traditional conceptions of possible worlds presume. At least some of the very properties and particulars that make up some possible worlds, including our fancifully actual Aristotelian world, cannot be disentwined from other possibilities that obtain only in other worlds. The actual cannot be as easily separated from the merely possible as the standard conception of distinct possible worlds suggests. The actual and the merely possible are entwined, and in a very local way, particular by particular and property by property. Here’s a case that even a physicalist may accept: This electron here in reality has a charge of a nature that will necessitate various effects under various merely possible background circumstances. The charge is itself at least partly modal in nature, not just because it involves necessitation but because what it is cannot be isolated within a single possible world, the actual one, that is wholly distinct from other possible circumstances; yet it is a basic element of the actual world. The charge must be a part of the actual world itself, but it is by its very nature something that involves other mere possibilities also. In an existing charge, the actual and the merely possible are essentially entwined, and in a highly localized way. This second characteristic feature of the type of modal structure found in the superworld is that the actual and the merely possible are entwined in a local way. What we might call the “truth grounds” of certain modal claims are local, yet not merely actual.

As I noted, there are more and less complicated ways to develop this general type of modal structure, with locally entwined actuality and subsistence. Some for instance involve different varieties of subsistence. But what will be most relevant for our purposes will be the relatively simple form of this type of structure found in the superworld. In such a superworld, there is only one type of mere subsistence, which underwrites what we might call “real possibility.”

What is actual and what merely subsists are often deeply entwined and interdependent in this conception, and the entwining is local, linking specific parts of actuality with specific mere possibilities with which their being is enmeshed. So notice that on this conception, the actual retains a kind of priority in fixing the kinds of possibilities that are relevantly real. Those are merely subsisting things, but they must be entwined in being with parts of actuality. There are no merely subsisting things without that actual root. Because possibility and actuality are locally entwined, distinct possible worlds do not root this sort of modality. But still there might be a vast system of intertwined real possibilities and actualities, locally rooted in the actual, and including all of what is said to exist “in the actual world,” but also including merely possible elements with the other mode of being, with which those actualities are locally entwined. This whole structure is the superworld. It is focused on its actual root, and includes all of what is actual, the entire actual world if I can put it that way, but it also includes not fully existing but merely subsisting parts, so to speak, surrounding or sticking out of relevant actual parts with which their being is entwined, which are real possibilities in the relevant sense.

For instance, assume that here in actuality is something with a basic property that is a phenomenal color. That actual basic property may have by its essence relations of similarity to merely possible properties that merely subsist, yet that are intertwined in being with the actual property by those similarity relations. Those various subsisting properties are parts of the superworld, locally entwined with the actual property in the ways noted. If this conception were realistic, then there would be only one superworld, because it is rooted in the actual world. The superworld does not contain all the merely possible worlds per se, even if we restrict ourselves to possible worlds containing only real possibilities of the sort with which we will be concerned. The mere possibilities the superworld contains are very local; they are alternatives bound to this particular or that property, alternatives that are entwined with the actual being of those things. How they might be recombined into whole alternative worlds is another question.

Am I really going to ask you to believe in a superworld with such extravagant metaphysics? As I said, no. Absolutely not.

I think it merely provides a good model of what the content of our experience would require if that experience were fully veridical. In fact, I think, such experience isn’t fully veridical. I think the superworld is one kind of illusion of our experience. But such a superworld provides an important clue to what in fact constitutes our phenomenal consciousness. That is why this quite baroque metaphysics is worth our attention in a discussion of phenomenal consciousness.

Focus once more on the case of phenomenal color.

If we presume that very specific phenomenal colors, very determinate hues such as a specific scarlet, are among the basic properties of things present in reality, that our experience is veridical in that way, and if we also presume, as some claim, that they are actual entities fully independent in being of other actual properties, then various puzzles arise: If something has a specific scarlet shade, yet that necessitates that it be red. Red is a so-called determinable color, which can be filled out in different ways to yield a specific hue, yet it also seems a quite fundamental fact about the Aristotelian world that some things are blue and some are red, that they have certain determinable colors as well as very specific and determinate hues. That relation between properties is a part of the essence of a specific scarlet. It is by its nature an instance of red. But then those two properties cannot be fully independent entities, as fundamental properties are often conceived to be. What’s more, as we noted before, that specific hue, and for that matter also that determinable color, has of necessity various relations of similarity and difference to other colors, colors that, if not instanced in actuality, are still possible. The scarlet of some ball is very similar to some other red hue that nothing in reality has, even nothing in the reality suggested by our experience, yet that relation seems a part of its nature. Further, a special similarity to unique red seems an essential feature of that color. The scarlet seems to be in some sense an independent entity, yet dependent on and entwined in being with other colors, some of which may not even be instanced in the world, and so may not exist.

I think the resolution of these puzzles, if our experience were veridical, would require that we embrace the general type of modal structure characteristic of the superworld, and give up one sort of independence of metaphysically basic properties, by recognizing a characteristic kind of modal structure. If we presume that specific colors, very determinate hues such as a specific shade of red, are among the basic properties that are instanced in reality, then there will be modal structure of this sort: If something is a specific red, that necessitates that it also be red, and if something is red, that necessitates that it be some specific red among the full range of possibilities. That relation between those instanced properties is a part of their essence, part of their characteristic modal structure, and that specific hue, and also that general color, have of necessity various relations of similarity and difference to other colors that, if not instanced in actuality, are still possible, and on the view we are developing subsist. One detailed way this might work is if the instantiation of each specific color would necessitate the instantiation of a more general color of which it is a specific form, which in turn would require at least the subsistence of all the different more specific forms which that general color might take, and hence the obtaining of the various relations of similarity and difference among them. And perhaps above the so-called determinable colors, for instance red and green, there is also the yet more general determinable of being colored. On this conception, the actuality of a specific red requires the actuality of the property red in general and even color in general, and that in turn assures the mere possibility of all the colors, colors bound by essential similarity relations to each other. At least the mere possibility of all these variously related colors, their subsistence, is a part of what an actual specific color is, but they are also all rooted in it. The actual and merely possible are in this way locally entwined in the hue of some object.

I think that modal structure like that is part of the superworld suggested by our experience whenever we see some scarlet thing. I also think that similar things might be said of other sensory properties and even forms of particularity. I think that the general structure of the superworld applies to all our sensory qualia. I also think, as you may also, that this is an implausibly rich metaphysical conception, too rich for reality. Nevertheless, it provides an important clue as to how we actually have such experience, even though that experience is not fully veridical.

How does such a richly modal understanding of the content of our experience help explain how we have such experience? Because our neurophysiology has an actual modal structure that corresponds quite well to this fanciful superworld structure that we experience.

It is very unlikely that phenomenal color, color just as we experience it, reflects only veridical and objective aspects of the world. For instance, we have noted that color as we experience it involves the unique hues and a circle of similarities that is captured by a child’s color wheel, and specific determinable colors like red, and these structures do not plausibly correspond to any objective features of reality. But these structures in our experience are plausibly due to our human neurophysiology of color vision, and in particular to its modal structure.

I will argue in detail in Chapter 4 that your neurophysiology of vision is such that your actual state of experiencing a determinate red implies the real possibility of the experience of other colors and necessitates the actual experience of determinable red. For instance, when you are in state of experiencing something as red, that involves a certain specific pattern of neural activation in the context of a background structure that, if activated in some alternative way, would constitute the experience of green. No metaphysical hocus-pocus is required. There are two layers of structure in the aspect of your nervous system responsible for your color vision. One stable background layer is shared by more specific states of actually seeing green and actually seeing red. And it assures even when you are actually seeing red that there is the real possibility of your seeing green. This in turn explains why the actuality of the red you experience would be locally entwined in being with the mere subsistence of green in the manner of the superworld, if only that red were actual. More generally, your neurophysiology of vision is such that your actual state of experiencing a determinate red implies the real possibility of your experience of other colors with which it bears essential relations of similarity, including a special relation to the real possibility of your experience of unique red, and necessitates your actual experience of determinable red, and this aspect of the modal structure of your neurophysiology of vision explains the modal structure characteristic of the phenomenal colors you experience, in which the instantiation of some determinate red would necessitate that the object in question also be determinable red and in which that determinate red would have essential relations of similarity even to colors not instanced in reality.

That is the general idea behind the theory of sensory qualia propounded here, the third key aspect of my proposal about phenomenal consciousness. We will consult the apparent essences of apparent sensory properties to discover the forms of entwined subsistence and actuality they would require to be real, and then look to see how experience of things with that implausible modal structure is rooted in the plausible modal structure of our human neurophysiology, a neurophysiology which, I argue, constitutes that experience. This has also been a brief introduction to the general idea of modal structure, which will also play important roles in the other two key aspects of my proposal.

6

Now we are in position so that I can properly summarize the whole thesis of this book and sketch its plan. As noted, there are three main positive features of the general account of sensory phenomenal consciousness to be developed here.

The first involves a modal structural understanding of our physical, animal nature, which is the crucial general basis of our phenomenal consciousness. Animals are the most intuitive locus of phenomenal consciousness, and this core idea involves a certain understanding of their nature. It itself has three components. The first of these components reflects the fact that our phenomenal consciousness is crucially that of agents, who have an abstract modal structure which is the linking of a range of possible stimulations and a range of possible actions in various possible ways. Second, our phenomenal consciousness is crucially that of a living thing of the familiar sort found on earth. We are constituted out of living cells of familiar types, and which crucially involve both metabolism and replication. Metabolism and replication both involve modal structure in certain ways we will soon consider. Third, our phenomenal consciousness involves the very complex dynamics of our neurophysiology, which is what mediates between stimulation and action in us, and which has, I will argue, a relevant sort of modal structural complexity. One example that has already been noted is that it sometimes matters that actual neural firing occurs in a context in which other sorts of firing are really possible given that relatively fixed background state of our neurophysiology. This first main feature of my positive view is the topic of Chapter 2. This chapter also includes an introduction to the necessary rudiments of neurophysiology, which underwrite this model.

The second main positive feature of my proposal is a conception of the neurophysiological basis of our experience of qualia in particular, of phenomenal consciousness. Chapter 3 will develop this idea. It does not involve information or representation, but rather identifies what constitutes phenomenal consciousness with the much more complex modal structure of the neurophysiology that intervenes between sensation and action. I call this “the whole nervous system model.” This requires an allied account of phenomenal consciousness as involving what I call “hyperexperience.” This is richer in certain ways than traditional conceptions of that consciousness. Some examples of mere hyperexperience, which has a kind of lesser presence in our phenomenal consciousness, include our awareness of the immediate past of seen objects and of some of their spatially occluded aspects. Another important related aspect of my proposal is the claim that there are different forms and degrees of phenomenal consciousness, even beyond the complexities found in hyperexperience. But, putting such complexities for the moment aside, the basic idea of this second main feature of my view, put very bluntly, is that what constitutes our phenomenal consciousness is the entirety of our nervous system that intervenes between sensory stimulation and motor action. The apparent modal structure of our phenomenal consciousness in general is mirrored, predicted, and explained, by the actual modal structure of more or less our entire neurophysiology.

What is phenomenal consciousness, at least in a sentient human animal? It is a modal structure that links sensory stimulation to action. What is the neurophysiology of that sentient human? A complex thing that has a modal structure, perhaps at a certain level of abstraction that ignores fine details, and links sensory stimulation with action. And those two modal structures are the same thing. This is a natural but unconventional idea, and this conception faces a number of obvious objections. So much of Chapter 3 is devoted to answering pressing worries. Some are rooted in commonsense phenomena like intuitively unconscious aspects of beliefs and desires, while others are rooted in such things as the unconscious representations deployed in cognitive science and surprising psychological phenomena like blindsight.

The third main feature of my view is an account of particular sorts of sensory qualia, which depends on a match between the specific apparent modal structures of various qualia and the specific actual modal structures of various sorts of relevant sensory neurophysiology. I argue that our neurophysiology suffices in detailed ways to constitute our phenomenal consciousness in the case of sensory qualia. This component is initially developed in Chapter 4 through further attention to the relatively well-studied case of color experience. It is a way in which details of our sensory qualia reflect details of our neurophysiology, through a kind of shared modal structure. As I’ve indicated, the full range of possible phenomenal colors seems to be rooted in any actual instance of any phenomenal color, and such colors involve a complicated structure of essential similarities and differences. That is part of the modal structure of the color properties we experience. And I will argue in Chapter 4 that this reflects in various detailed ways the actual modal structure of our neurophysiology of color vision.

While the notion of modal structure is very general and abstract, various specific sorts of modal structure are relevant in these ways to the understanding of all three main facets of the view I propose. My proposal involves pressing on both sides of the key equation at once, pressing up from below, in its first facet, on our understanding of our neurophysiology, and in its second facet, pressing down from above on our understanding of our phenomenology, in both cases in a way attentive to modal structures of various sorts. And the details of the realization of our experience of particular sensory qualia will involve matching modal details below and above. So the general theory of the phenomenal consciousness associated with human sensory experience proposed here might be called the MOdalized Up and Down and in Details account, the MOUDD theory, if you like that sort of nomenclature.

The remaining chapters will apply that general account to a series of different cases, and in that way develop it. Chapter 5 considers some other senses. Chapter 6 distinguishes various sorts of spatial structure and particularity that are sometimes present together in our visual experience, in a kind of palimpsest. For instance, glimpsing the red of a barn outside through a window with a yellow frame, you can see it at once on the distant barn and yet as characterizing a visual field in which it is very close to the occluding yellow edge of the window. This chapter develops a modal structural understanding of the neurophysiology that roots core features of these sorts of experience. Chapter 7 applies a modal structural understanding of our neurophysiology, and the allied notion of hyperexperience, to our conscious experience of time, and to what I argue is a kind of causal experience. It does this on the way to an account of our conscious experience of the robust particularity of ordinary concrete objects present in our visual experience. One novelty of this discussion is that I argue that the proper modal structuralist understanding of our neurophysiology can help explain the complex structure of temporal consciousness explored by Husserl.

Once the MOUDD theory is on the table, Chapter 8 reviews it and considers a standing dualist objection to any physicalist account.