The Nature of Subjective Experience: An Interview with Brian McLaughlin

THE NATURE OF SUBJECTIVE EXPERIENCE

By Brian P. McLaughlin and Tony Sobrado

***

The Montréal Review, June 2026

Tony Sobrado: The 'hard problem of consciousness' can be thought of in two ways that essentially overlap - why is it that a physical brain gives rise to subjective first-person qualitative experiences, or why is it that some physical things, like brains, are conscious and some physical things, like rocks, are not conscious. The issue is experience.

Some think that this philosophical question isn't actually answerable akin to asking ‘where the laws of physics come from?’ Others think it is answerable and that over time we may find a reductionist approach to how consciousness ‘arises’ from a physical brain in a formulation that mimics how H2O = water, and so in the same vein we can have a reductionist chemical computation that states that neural properties = conscious experience. As with any philosophical topic, plenty rests on definition and interpretation but the above example of H2O and water is one way of answering the question and is the kind of answer that David Chalmers himself is looking for.

Others say this is a nonsensical question and the wrong way of looking at it. Illusionists such as Daniel Dennett and Keith Frankish deny the actual premise in the first place. Dennett likened it to vitalism in biology whilst Keith Frankish argues that we systematically misrepresent our experiences as having phenomenal properties.

Then there is the noted Frank Jackson who once was an ardent qualia advocate but these days proposes representational knowledge. That is that there is no direct acquaintance with experience and our experience simply represents the external world to us; and therefore there's no formal qualia. For representationalists, the hard problem of consciousness and the explanatory gap - coined by Joseph Levine, simply dissolves.

We have even more aggressive approaches, such as Michael Graziano who flat out denies the existence of actual consciousness itself. A similar proposition is advocated by Susan Blackmore who states that the ‘consciousness meter’ has never found the neural correlates of consciousness because consciousness doesn't exist and therefore asking how it ‘arises’ from a physical brain renders the question intractable. Consequently, ‘what it is like’ to undergo any kind of experience doesn't exist in a formal philosophical sense because it's better understood by means of the predictive modelling machine of the brain and therefore ‘what it is like’ is generally what that model of the neuroscientific brain says ‘it is like to be’. So as an example the difference between Tony’s and Brian's ‘what it is like to be’ depends on their model based on their neuroscientific brain as humans - compared to bats (in this respect challenging the famous paper from Thomas Nagel). This is because the bat’s sense of ‘what it is like to be a bat’ is based on their model, which in turn is based on their neurology as a bat.

Others however are not so dismissive of the hard problem of consciousness. This includes leading philosophers of physics such as Tim Maudlin and Barry Loewer who think there is an issue with how subjectivity can be computed by an objective scientific neuron. Other perspectives say the problem of experience is perpetually there and no matter how it is repackaged by illusionists, representationalists and functionalists, the problem of why we have a subjective experience at all by definition is the essence of the hard problem of consciousness and that it will not dissipate.

Now as one of the world’s leading experts in the area of consciousness and the editor of Oxford University Press’ Contemporary Debates in Philosophy of Mind, I want to start by asking you two questions:

What do you understand by the term ‘consciousness’ and how has this concept changed and evolved in the field over history from your perspective?
What do you understand the hard problem of consciousness to be and how has this concept changed and evolved in the field over history from your perspective?

Brian McLaughlin: When you ask what I understand by the term “consciousness,” I will address this in the context of the kind of consciousness that presents “the hard problem.” As you say, it is subjective experience. Subjective experience presents the hard problem of consciousness. The hard problem of consciousness is the problem of how subjective experiences relate to brain states and events. More generally, it’s the problem of how subjective experiences fit into the natural world. A subjective experience is an experience that is like something for the subject having the experience. The ‘what-it’s-like’ aspect of the experience is its phenomenological character. Subjective experiences are thus often called states and events of phenomenal consciousness. They include sensory experiences such as visual experiences, auditory experiences, and the like; they include having bodily sensation states such as aches, pains, itches, tickles, hunger pangs, headaches, and the like; they include states of having images, such as visual or auditory images; they include occurrent emotional feelings, such as feeling fear, feeling anger, and feelings of love; and they include mood feelings such as feeling joy, feeling elated, and feeling bored. (This list of subjective experiences is of course not exhaustive.)

In terms of its history, I can make a few pertinent historical remarks. The notion of subjective experience can be found in René Descartes’ work and in John Locke’s work. Descartes wrote of what we are conscious of as operating within us. Locke stated that consciousness is the perception of what passes in one’s mind. There is a debate about whether Aristotle employed a conception of consciousness. Victor Caston, in his excellent “Aristotle on Consciousness” (2002), argues that it is at least clear that Aristotle wrote about phenomenal awareness in perception.

But what is relatively new is the use of the locution “what it is like” to refer to the phenomenal characters of subjective experiences. To the best of my knowledge, the first such use was in B.A. Farrell’s 1950 article “Experience.” The “what it is like” locution was then used by Iris Murdoch in her 1951 article “Nostalgia for the Particular” and by Timothy Sprigge in his 1971 article “Final Causes.” The article that resulted in its widespread use in the philosophy of mind, though, was Thomas Nagel’s ground-breaking 1974 article “What is it Like to be a Bat?”

With phenomenal consciousness in mind, Nagel opened that 1974 article with the remark: “Consciousness is what makes the mind-body problem really intractable.” Colin McGinn, in his “Can We Solve the Mind-Body Problem?” (1989), called consciousness “the hard nut of the mind-body problem,” and asked “How is it possible for conscious states to depend on brain states? How can technicolour phenomenology arise from soggy grey matter?” In “Mental Reality” (1994), Galen Strawson stated that “the existence of experience is the only hard part of the mind-body problem for materialism,” and went on to say: “It is the heart of the difficulty; the rest is easy.” David Chalmers introduced the label “the hard problem of consciousness” in his 1995 article “Facing up to the Problem of Consciousness,” in which he distinguished various “easy” problems of consciousness (e.g., What is it for an organism to be awake?) from the hard problem of explaining how subjective experiences are related to physical states of the brain. That article and his 1995 Scientific American article “The Puzzle of Consciousness” had the distinction of calling the problem of subjective experience to the attention of some neuroscientists working on consciousness. Chalmers followed these articles with his impressive book “The Conscious Mind” (1996), in which he argued that no materialist or physicalist theory of phenomenal consciousness could be correct. The problem itself was not new. There was much discussion of subjectivity and the mind-body problem (or better “mind-brain problem”) in the 19th Century. In 1866, T.H. Huxley famously remarked: “How it is that anything so remarkable as a state of consciousness comes about as a result of irritating nervous tissue, is just as unaccountable as the appearance of the Djinn, when Aladdin rubbed his lamp.”

There is impressive ongoing neuro-scientific work aimed at finding the neural correlates of states and events of phenomenal consciousness, work that I take to be directly relevant to understanding the place of phenomenal consciousness in nature. But even if we found strict (i.e. exceptionless) neuro-scientific correlates of states (and events) of phenomenal consciousness, the hard problem of consciousness would remain. Their discovery would just make the problem more sharply focused. Consider the kinds of subjective experiences we humans can have. Suppose that we found that for any such kind of subjective experiential state E, there is a kind of neuro-scientific state N such that an individual is in E if and only if the individual is in state N. The problem would remain: What explains those correlations? It could turn out that the answer is that nothing explains them, in which case the correlations would be fundamental laws of nature. I myself regard that answer as enormously implausible. Be that as it may, were we to find such psychophysical correlations, the hard problem would be “What, if anything, explains the psychophysical correlations?”

You used the expression “the brain gives rise to first-person subjective experiences” in your characterization of the hard problem. That’s a typical way of characterizing it. Let me explain why I didn’t formulate the problem using “gives rise to” or any expression like that. Suppose that we found that there is a kind of neuro-scientific state N such that someone is in experiential state E if and only if they are in state N. The hard problem that remains is typically taken to be: Why does N give rise to (or result in) E, rather than some other type of experiential state E*, or no experience state at all? Notice that this question, unlike the question of what, if anything, explains the correlation, presupposes that N gives rise to, or results in E. I didn’t formulate the question in that typical way, since that presupposition could well be false, even though the correlation holds. It could be the case that N doesn’t give rise to, or result in, or bring it about that, or produce, or generate E. It could be the case that there is no mechanism that explains why an individual is in experiential state E if and only if the individual is in N. Yet there could still be an explanation. The explanation could be that N is E. There is one kind of state that we conceptualize in two very different ways, two ways that bear no a priori connection to each other.

I’m in the camp that thinks that if such psychophysical correlations were found, we would be in a position to justify the claim that the experiences are identical with their strict neuro-scientific correlates by inference to the best explanation of the correlations. This position faces a host of truly formidable challenges. (What theory of consciousness doesn’t?) For the most part, addressing them involves answering questions that training in neuroscience doesn’t prepare one to answer, questions such as, for instance, whether coherent conceivability entails possibility, and how concepts are related to kinds and properties. The challenges to this identity view are formidable, but I think they can be answered. I think the identity view would be the most reasonable view, all things considered, were we to find such correlations.

Tony Sobrado: I think many philosophers of mind would generally agree with the framework of your answers. The one thing I immediately note is your use and application of phenomenal consciousness. Phenomenal consciousness is a difficult topic to define and understand. You have said ‘what-it’s-like aspect of the experience is its phenomenological character’ – so basically any accompanying subjective experience is tantamount to phenomenal character. Phenomenal consciousness, what it is and its role is therefore partly responsible for the hard problem of consciousness; and so there are many that deny the very existence of phenomenal consciousness. For example, illusionism argues that we misrepresent our experiences as having a phenomenal character. This is further articulated by Frank Jackson. For example, when we look at qualia there's subjective sensations, the ‘likes’ and ‘feels’ of ‘what it is like’ to have an experience but there is no formal qualia inherent to itself. There is nothing above and beyond the direct experience itself; nothing that outruns the experience itself in some kind of autonomously intrinsic way. For Jackson and others, all experience and thus ‘what it is like’ is just representational knowledge. There is no qualia, there is no phenomenal consciousness and thus no hard problem.

Now of course depending on how you use the term phenomenal consciousness, you may deny it but what's still going to be there, as you know and what I agree with, is the issue of experience de facto. Or, the experience of experience as Frank Jackson said to me and this is also how David Chalmers fundamentally frames the problem. For the sake of overall clarity and alignment I describe it as ‘sensational realism’.

More importantly, perhaps, is that you make a very interesting point: In what capacity is the hard problem actually answerable? And I think this is an extremely valid position. The hard problem lies on a manifold of two pillars. One pillar is the scientific reductionist approach - how a physical brain via neurological states gives rise to phenomenal consciousness so to speak or qualia, or a subjective experience, or sensational realism. Here we could have a chemical compound law or a logical equation where neurological inputs X&Y = consciousness. This would be a scientific reductionist approach explaining how the physical brain via its neurological frameworks and pathways create, cause or give rise to subjective experience and in this respect it may be akin to how H2O = water. And here some attempts have been made by Karl Friston of UCL via the Free Energy Principle and Earl Miller of MIT in which consciousness lies in the elements of electromagnetism.

This in a sense may answer the explanatory gap by Joseph Levine but it may also culminate in identicalism and if so it then begs the question, paradoxically, of where is the issue of subjective conscious experience in the first place if it literally just is a brain state which then simply dissolves an ontological gap between physicalism and consciousness. This is all to say that this form of identicalism that may result from a chemical compound law = consciousness might just be identicalism and paradoxically dissolve consciousness in one broad stroke.

Now the second pillar of the hard problem of consciousness is a metaphysical one. Why is there consciousness at all? And this may not be answerable. So for example in the scientific reductionist approach stated above, that may explain the explanatory gap but then some would also say it doesn't explain the explanatory gap because you still have to state why neural state X is conscious even if it’s identical. But right now let's assume that it does answer the explanatory gap by Joseph Levine via a chemical compound law found in neurological substrates but then you can push the question back metaphysically in terms of why is this the case? And this harks back to the hard problem being a metaphysically unanswerable question akin to asking where the laws of physics come from? As you rightly stated about the use, meaning and role of laws in general.

Now Chalmers in the actual paper “Facing up to the Problem of Consciousness” asserts that the hard problem is not scientifically answerable which means it delves into the metaphysical realm - making consciousness something more fundamental in existence. This has obviously spurned and reinvigorated elements of panpsychism. Now of course this still has a combination problem because if consciousness is fundamental it reverses the hard problem of consciousness in one respect because if we're talking about the hard problem being how a physical brain produces conscious experience but then posit that consciousness is fundamental you still have to explain how physicalism comes out of fundamental consciousness? So again, you have a combination issue: physicalism with consciousness and hence why many in the fundamental consciousness camp want to eliminate physicalism and many in the fundamental physicalist camp want to eliminate consciousness.

Laws of Nature

Earlier you said:

What explains those correlations? It could turn out that the answer is that nothing explains them, in which case the correlations would be fundamental laws of nature

It is interesting the way you framed it there, that if we are requiring a law or find a fundamental law - like the fundamental laws of physics - then it doesn't need any further explanation. For me this highlights the metaphysical baggage with the hard problem because you can always keep asking why - via an infinite regress. Having spoken to the world's leading physicists such as Paul Davies, Sean Carroll and Carlo Rovelli many are actually intrigued by the laws of physics themselves and why fundamental laws are the way they are. Many theologians debate the same things in terms of metaphysics, which when pushed to their logical extremity might be just about necessity and brute facts i.e. the universe, existence and laws have to be the way they are because another way is impossible.

The role of causation in the hard problem of consciousness

You said:

Suppose that we found that there is a kind of neuro-scientific state N such that someone is in experiential state E if and only if they are in state N. The hard problem that remains is typically taken to be: Why does N give rise to (or result in) E, rather than some other type of experiential state E*, or no experience state at all?

This is a twofold approach. The second part where you say:

Why does N give rise to (or result in) E, rather than some other type of experiential state E*, or no experience state at all?

So this might encompass a metaphysical element, an infinite regress of questions but it also taps into the explanatory gap of why N results in Experience E?
However this also delves into the issues of causation in general that plague neuroscience and its overlap with philosophy of mind. Let me flesh this out further. When you say:

Why does N give rise to (or result in) E, rather than some other type of experiential state E*

This entails the methodological and statistical issue regarding whether all variables have been controlled for in the model? Thus we may be able to apply an interventionist account of causation from the philosopher James Woodward here. Moreover when you say:

There is a kind of neuro-scientific state N such that someone is in experiential state E if and only if they are in state N.

Some would argue that this sentence using ‘if and only’ entails causation by necessity. Therefore under interventionist and manipulability theories of causation if conscious experience E occurs ONLY when in Neuro state X then Neuro state X must be causing it under the frameworks of interventionist and manipulability theories of causation. In fact the neurological field of optogenetics is loaded with causation and how neurological states cause certain experiences - and medication is the most obvious example here.

But other neuroscientists are more cautious, wanting to stick to correlations as opposed to formal causation. But what is clear is that when one talks of the hard problem of consciousness, and the practice of two disciplines - neuroscience and philosophy of mind, it’s not just that the physical brain and consciousness is important to consider and define but so too is the role of causation. This directly connects with phenomenal consciousness, physicalism and causation. So please tell me your thoughts on causation and its role in the hard problem of consciousness and phenomenal consciousness.

Brian McLaughlin: You’ve raised a lot of important issues so I think it is appropriate to discuss these generally before addressing specific questions.

Phenomenal consciousness and its conceptual role in the hard problem of consciousness

As we have discussed, the hard problem of consciousnesses is a problem concerning subjective experiences. First of all, then, what is a subjective experience? Physicists tell us that rocks experience acceleration, and the like. They experience acceleration, but it doesn’t feel like anything to a rock when it experiences acceleration. Nothing feels like anything to a rock. Rocks don’t have subjective experiences. Subjective experiences are experiences such that it is like something subjectively, from a first-person point of view, to have the experience. As I noted, the what-it’s-like for the subject aspect of an experience is called its “phenomenological character,” or, for short, its phenomenal character, hence the term “phenomenal consciousness.” States and events of phenomenal consciousness are subjective experiences.

What, then, is the hard problem? Chalmers introduced the term “the hard problem” for a problem that would remain even if neuro-scientists were to discover the neural substrates of our subjective experiences, something that’s compatible with all contemporary realist views of subjective experience. The problem can be posed as follows. Suppose neuro-scientists discover a system of strict correlations between certain neuro-scientific states and the types of subjective experiences we humans have, a system that entails, for a certain neuro-scientific state N and a certain type of subjective experience E, that a human being has a E if and only if the human being is in N. The question would remain: Why are instances of N accompanied by instances of E, rather than some other type of subjective experience E*, or with no type of subjective experience at all? The would-be answers include:

(1) Because instances of N are necessary and sufficient causes of instances of E -at least in humans.
(2) Because N constitutes E.
(3) Because N realizes E -perhaps relative to an environment.
(4) Because E ontologically emerges from N.
(5) Because N is related to E as determinant to determinable.
(6) Because is identical with E.

The list isn’t exhaustive, but I haven’t been terribly neglectful. These would-be answers are pairwise incompatible: No two of them can be correct. Each faces formidable challenges.

As I indicated earlier, “the hard problem” now gets used in a broader sense for the more general question of how subjective experience, phenomenal consciousness, fits into the natural world.

Philosophers who pursue it hope to provide the most reasonable answer, all things considered. One key issue is whether phenomenal consciousness has an ontologically fundamental place in the natural world.

Illusionism as a theory of consciousness

You mentioned illusionism. I’ve never written anything about it, but I’ll take this opportunity to say a few things. Illusionism is a view held by Daniel Dennett and Keith Frankish, among others. There are a variety of illusionist claims in the illusionist literature, some much stronger than others. The strongest illusionist thesis one finds in at least some of the literature is that there is no phenomenal consciousness, no subjective experiences, no experiences such that it is like something for the subject of the experience to have them. Proponents of this strong illusionist thesis acknowledge that it seems to us that we have experiences such that it is like something for us to have them, experiences with phenomenal characters. But they maintain that, in fact, we don’t have such experiences. It only seems to us that we do. We’re only under the illusion that we do. They don’t think the seeming is an experiential seeming; an experiential seeming would be a subjective experience. The illusion is supposed to be a cognitive illusion, a brain-induced cognitive illusion.

If the strongest illusionist thesis is correct –that is, if there is no phenomenal consciousness, no subjective experiences, since there are no experiences such that it is like something for the subject to have them—then of course there is no hard problem of consciousness. Those of us who think there is such a problem are mistaken. Neuro-scientists will never find neural substrates of subjective experiences, since there are no subjective experiences. They’ll find only neural bases of our dispositions to be under the cognitive illusions in question. It’s a mistake to think we need a theory about the place of phenomenal consciousness in nature, since there’s in fact no such thing as phenomenal consciousness. (Compare the claim that we don’t need a theory of the place of ghosts in nature, since there are no ghosts.) Those of us who think there are subjective experience don’t need a theory of their place in nature. We need a cognitive therapist to set our skewed thinking straight. The message for people encountering the hard problem seems to be: Move on, there’s nothing to see here.

I’m a realist about phenomenal consciousness. I’ve seen no reason whatsoever to deny there are subjective experiences. I’ve felt pain. It’s like something to feel pain. That’s what it is for the feeling of pain to be a subjective experience. People who have Congenital Insensitivity to Pain (CIP) don’t know what it’s like to feel pain; but I’m sure readers who have felt pain know what it’s like to feel it. If there’s indeed something it is like to feel pain, that by itself suffices for there to be phenomenal consciousness. But it’s also the case that there is something it’s like have an experience of a loud sound, or an experience of red, or a feeling of thirst, or of anger, or of elation, or of pleasure, or of fear, or of loneliness.

Illusionists, strong illusionists who deny there are subjective experiences, will be unconvinced by what I just said. They readily acknowledge that people report having subjective experiences, and do so because they take themselves to be having them. But they are mistaken: They’re under a cognitive illusion. Removing the cataracts, for instance, will enable the individual to see, but also result in neural states that induce the cognitive illusion of having a subjective experience, just as your stepping on my toe will result in a neural state that induces in me the cognitive illusion of a feel of pain. Strong illusionists readily acknowledge that the cognitive illusions and the verbal behavior and non-verbal behavior they led to require explanation. (For readers more nuanced in the know, I think here of Dennett’s hetero phenomenology). But they hold those reports and the beliefs they express are false, since there is no subjective experience that is being reported. It’ll have to suffice for me to repeat that I’ve seen no reason whatsoever to believe the strong illusionist claim. I thus respond to it with an incredulous stare (to borrow a David Lewis expression).

I should mention that my impression is that a number of self-professed illusionists would reject the claim that there are no subjective experiences, no experiences that are like something for the experiencer. They would acknowledge that we have subjective experiences, experiences that are like something for us. They’d take me to be attacking a straw man illusionism. If, however, there are such experiences, then there’s a hard problem.

There are much weaker illusionist claims. Some of them even Cartesian property dualists, who take phenomenal consciousness to be ontologically fundamental, would accept. (Most contemporary Cartesian property dualists are not Cartesian substance dualists; they don’t posit an immaterial mind.) Daniel Dennett has used the following example to illustrate what he takes to be an illusion: It seems to people that when they see, they’re normally presented with a detailed environmental scene but that’s in fact not the case. (I don’t know whether it seems that way to people, but certainly some philosophers have written as if it seems that way to them.) The angular size of the area we can see is only 2 degrees of arc, which is about the angular size of your thumb nail at arm’s length. If your reading this text on a computer science, put the screen a tad longer than arm’s length away with a font large enough that you can easily read the text from that distance. Then, extend one of your arms very close to the screen with your hand in a fist and your thumb up. Next focus your visual attention on your thumb nail. You’ll find you won’t be able to make out any of the words on the screen; even the ones near your thumb nail but not occluded by it will be too out of focus. No empirically informed Cartesian property dualist would dispute that. The relevant moral to draw from the example is not that there is no visual phenomenology, and so nothing that it is like to have a visual experience, but rather that people who think visual experiences normally present detailed environmental scenes haven’t paid careful enough attention to visual phenomenology. You can get people to see they are mistaken in their belief by having them pay careful attention to their visual phenomenology. I don’t want to pick a fight about the word “illusion,” but I wouldn’t call the mistaken belief an illusion. People don’t pay much attention to visual phenomenology; they have more important things to do. I wonder, for instance, how many people notice foreshortening all on their own (without being informed by others), or that the horizon is always at eye level, whether one is standing, sitting, or lying down.

Qualia and its role in the hard problem of consciousness

You used the term “qualia”. Let me provide some background for the readers on qualia. The phenomenal character of a subjective experience is a qualitative character. It is fairly widely claimed that the qualitative character of an experience consists of qualia. But what are qualia? The term “qualia” was introduced by Charles Saunders Pierce in the late Nineteenth century, a period in which there was a lot of discussion of the subjectivity of experiences. C.I. Lewis used the term “qualia” in his 1929 book “Mind and the World Order”, and placed great emphasis on the subjectivity of experiences in his 1930 book “Pragmatism in Current Thought”. The term was also used by Lewis’s famous student, Nelson Goodman, in his 1951 book “The Structure of Appearance”. On this use of the term, qualia are essentially private and ineffable. Cartesian property dualists maintain that there are qualia in that sense. The meritorious illusionist claim I alluded to is that there are no essentially private, ineffable qualities and so no qualia. Virtually all realists about phenomenal consciousness who count their view as physicalism friendly (myself included) agree that there are no qualia in that sense.

I mentioned earlier that it is fairly widely claimed that the qualitative character of an experience consists of qualia. But that agreement is paper thin. The term “qualia” is a term of art that is used in a few non-equivalent ways in the contemporary literature. If there are indeed no qualia in C.I. Lewis’s sense, it patently doesn’t follow that subjective experiences lack phenomenal or qualitative characters. You mentioned representationalist theories of phenomenal consciousness. Leading representationalists such as Fred Dretske, Michael Tye, and Christopher Hill, are all realists about phenomenal consciousness. Moreover, they all use the term “qualia”. They take subjective experiences to be experiences with phenomenal characters and take phenomenal characters to consist of qualia. But they reject the thesis that qualia are private and ineffable. They maintain that qualia are physical properties, and that in the case of sense experiences they are environmental physical properties that the experiences represent. For example, they hold that visual qualia include colors, and that each surface color (redness, blueness, and so on) is a spectral reflectance property of some kind. Spectral reflectance properties are neither private nor ineffable. Ned Block, a robust realist about phenomenal consciousness, takes qualia to be non-representational, and maintains that they will likely turn out to be neuro-scientific properties of some sort yet to be determined. No neuro-scientific property is either private or ineffable.

Accusing opponents of being under a cognitive illusion is no way to make friends and influence people. (At least it wouldn’t be in a better world.) Those of us who deny that the phenomenal characters of subjective experiences are either private or ineffable incur a dialectical obligation: to explain why it can seem that the phenomenal characters of a subjective experiences (or qualia) are private and ineffable. It’s important, first of all, to acknowledge the grains of truth in the claim that the phenomenal characters of subjective experiences (or qualia) are private and ineffable. As concerns privacy, there is no question (no serious question at any rate) that I can come to know that I’m feeling pain, for instance, in a way that others couldn’t come to know that I’m feeling pain. As concerns ineffability, nothing those of us who’ve felt pain could say to a person with CIP could enable them to have anything like the understanding we have of what it’s like to feel pain. Similarly, nothing those of us who are sighted could say to people completely blind from birth could enable them to have anything like the understanding we have of what it’s like to have a visual experience. There are no such words. That much is right. It is, however, a different matter whether any properties (or states or events) are essentially private or ineffable. Many realists about phenomenal consciousness (myself included) deny that subjective experiences involve essentially private or ineffable properties.

Panpsychism as a theory of consciousness

Panpsychism traces back to antiquity. I said that rocks don’t have subjective experiences. Traditional panpsychists disagree. They hold everything, or at least every object in space-time, has subjective experiences. Traditional panpsychism entails a corresponding pan-subjectivism: Every object is a subject of experience. If traditional panpsychism is true, then we face a hard problem of consciousness not only for rocks, but all the way up and all the way down the micro-macro scale. To look down the scale, suppose that electrons have a certain subjective experience E. Then, a hard problem arises: Why do electrons have E, rather than some other subjective experience E*, or no subjective experiences at all? Panpsychists acknowledge that if electrons indeed have subjective experiences, there is no reason to think they have any of the kinds of subjective experiences we have. We’d thus never be able to formulate the question that would arise, since we could have no conception of what it is like to be an electron, or to be a rock. Still, that itself is no reason to deny that there is something it’s like to be an electron or to be a rock. There’s no reason to think every subjective experience is such that we humans can have a conception of it. To use an example due to Nagel, bats may have a subjective experience whenever they engage in echo-location, even if we can have no conception of what that experience is like. That seems to me a plausible claim about bats. But is there really any reason to think rocks or electrons have subjective experiences?

Panpsychism of this traditional sort is a giddy idea. Still I don’t think that it is a priori false. Panpsychists acknowledge that it faces a battery of truly formidable problem. For example, the combination problem, which you mentioned. The problems are fun to think about, but I see no reason to pursue them in trying to understand the place of phenomenal consciousness in nature since I see no reason whatsoever to believe panpsychism. I’m phenomenally conscious. I also think I’m a wholly material being: I’m made up of cells, which are made up of molecules, which are made of atoms, which are made up of electrons, protons and (save hydrogen) neutrons and protons are made up of quarks. A wholly material being can be phenomenally conscious. In that sense then there is conscious matter. Still I see no reason whatsoever to think all matter is conscious.

Physicalism and the hard problem of consciousness

Physicalism is supposed to be a general doctrine about reality. Unfortunately, there is no received view about what, exactly, the doctrine is. Moreover, every attempt in the literature to define “physicalism” has met with apparent counterexamples. Thankfully, a proper treatment of the hard problem doesn’t require an adequate formulation of the general doctrine of physicalism.

The dominant basic idea of physicalism nowadays is that it is the thesis that the natural world is fundamentally physical, where the notion of physicality is to be explicated by appeal to physics. Subtleties aside (and they are many and varied), as concerns phenomenal consciousness, the main dispute between physicalists and non-physicalists is this: Physicalists who are realists about phenomenal consciousness (which includes the vast majority of physicalists) want to explain how it fits into our fundamentally physical world. Philosophers I earlier called Cartesian property dualists maintain that our world is not fundamentally physical, since subjective experiences are ontologically fundamental yet not physical. Panprotopyschists deny that our world is fundamentally physical since they speculate that there are yet to be discovered proto-mental properties, which are fundamental yet not physical. But they deny that subjective experiences are fundamental, since they are reducible to complexes of physical and proto-mental properties.

Appealing to physics to explicate the notion of physicality faces a well-known dilemma posed by Carl Hempel in 1969. Consider the thesis that something is physical if and only if it is posited by physics. Hempel pointed out that if by “physical” one means what is posited by current physics, then the proposal faces the problem that current physics is incomplete; we don’t have the final, completed physics. If instead by “physical” one means what would be posited by the physics that is in fact true of our world (a physics we don’t yet have and, for all we know, may never have), then we don’t know what such a physics would posit. A leading response to Hempel’s dilemma is to say that physicalism is an empirical thesis that presupposes that the physics that is in fact true of our world will be a recognizable descendent (to use a phrase due to Frank Jackson) of current physics. “Recognizable descendent” is, of course, quite vague and doing a lot of heavy lifting here. Nagel had in mind an idea like that, and thought that proto-mental properties would make the physics in fact true of our world unrecognizable as a descendant of current physics. The relationship between current physics and the completed physics might turn out to be as remote as the relationship between air, earth, fire, and water theory and quantum chemistry. Some physicalist simply say that, like current physics, the physics in fact true of our world will not posit subjective experiences (at least as such). That claim, though, is compatible with panprotophycism, which is incompatible with physicalism.

I have no crystal ball, but as for predicting future physics, I’m prepared to go as far as the physicist Sean Carrol: Quantum field theory (like the rest of current physical science) has no need of the hypothesis that there are subjective experiences, and there is nothing we know or will come to know about subjective experiences that will give us reason to reject quantum field theory. We may someday have reason to reject quantum field theory, but if so, the reason won’t have anything to do with the fact that there are subjective experiences. There’s of course a ton to say about all this, but let’s work with a rough and ready idea of what a physics-based notion of physicality is and move on to fundamentality.

Unfortunately, I’ll have to get into the weeds here. In his 1998 book From Metaphysics to Ethics: An Essay in Conceptual Analysis, Frank Jackson formulated physicalism as follows (there are other closely related formulations in the literature): It is the thesis that any possible world that is a minimal physical duplicate of our world is a duplicate simpliciter of our world. (That’s called a supervenience thesis, more specially a global supervenience thesis. I should mention The Stanford Online Encyclopedia of Philosophy is an excellent source for technical philosophical terms.) Possible worlds are total ways the world might be. A possible world is a physical duplicate of our world if and only if it is exactly like our world in every physical respect, in respect of physical laws, the distribution of physical objects, the distribution of physical properties, and so on, and so forth. A minimal physical duplicate of our world is a world that includes only whatever is metaphysically necessary for it to be a physical duplicate of our world. A possible world is a duplicate simplicter of our world if and only if it is exactly like our world in every respect whatsoever. One reason Jackson hasn’t provided a sufficient condition for physicalism is that his supervenience thesis, as he himself points out, is compatible with their being a necessary God (one who exists in every possible world), and the existence of a God is surely incompatible with any doctrine deserving of the name “physicalism”. But the supervenience thesis is plausibly a necessary condition for physicalism. It should be obvious that whether this necessary condition is met turns on far more than just the place of phenomenal consciousness in nature. But it is fairly widely held in philosophy that the existence of phenomenal consciousness poses the most difficult challenge to the claim that the condition is met.

We can appeal to that necessary condition for physicalism to mark a key difference between physicalists and non-physicalists realist views of phenomenal consciousness. Physicalists who are realists about subjective experiences maintain they don’t violate the condition. Cartesian property dualists maintain that subjective experiences violate it, and so that physicalism is false. Indeed, they hold that there is a possible world that is a minimal physical duplicate of our world yet, unlike our world, is entirely devoid of subjective experiences. Employing a use of the term “zombie” introduced by Robert Kirk in his 1974 paper “Zombies v. Materialists,” Chalmers, in The Conscious Mind, calls such a world a zombie world; in it, our physical duplicates are entirely devoid of phenomenal consciousness, and so are in that sense zombies. Given that there are subjective experiences in our world (something the strongest illusionist claim denies), if there is a possible world that is a zombie world, then physicalism is false: Not every minimal physical duplicate of our world is a duplicate simpliciter of our world, since the zombie world is a minimal physical duplicate of our world, yet not a duplicate simpliciter of our world. It’s not a duplicate simpliciter of our world, since, unlike our world, it’s entirely devoid of subjective experiences.

Many physicalists, myself included, acknowledge that it is coherently conceivable that there is a zombie world: No contradiction can be a priori extracted from the thesis that there is a zombie world. But we deny that a zombie world is possible: There is no possible world that is a minimal physical duplicate our world yet devoid of phenomenal consciousness. We reject the Cartesian view that coherent (or clear and distinct) conceivability entails possibility, regarding coherent conceivability as instead providing a prima facie reason for thinking that something is possible, but a reason that can be defeated by other considerations. In this case, we argue that it will be defeated.

Whether coherent conceivability entails possibility is an issue in modal epistemology. It must be addressed if one wants to engage in the debate over the solution to the hard problem. You won’t find any discussion of this sort issue in the neuroscience literature in which theories of consciousness are proposed; scientists (qua scientists) don’t engage in modal epistemology. Nor would one expect them to. I look to neuroscience in the hope of finding strict lawful correlates of types of subjective experiences. The hard problem would remain even if they are found.

So, then, physicalists who are realists about subjective experiences deny that any possible world is a zombie world. Cartesian property dualists maintain there a possible world that is a zombie world, though the world is nomologically impossible; that is, it would have to differ in its laws of nature from our world, since its laws of nature won’t include the relevant psychophysical laws that hold in our world. Why, though, are philosophers concerned about possible worlds, especially ones that may even be nomologically impossible? Don’t we have enough to worry about in understanding our own world?

Here’s one reason why. Physicalists typically maintain that types of subjective experiences are identical with types of physical states or physical-functional states (functional states realized by physical states) of some sort. In his seminal 1971 paper “Identity and Necessity,” Saul Kripke gave a compelling a priori argument that there is no contingent identity: If A is identical with B, then necessarily A is identical with B; it’s literally impossible for A to fail to be identical with B. If A is identical with B, then that’s so in every possible world. Kripke appealed to two premises in his argument for that necessity of identity thesis. The first is that everything is necessarily identical with itself. (How could anything fail to be identical with itself?) The second is Leibniz’s law of the indiscernibility of identicals: If A is identical with B, then something is true of A if and only if it is true of B. (If A is identical with B, how could something be true of A yet not true of B?) Here, then, is the argument for his necessity of identity thesis. Suppose A is identical with B. From the first principle it follows that B is necessarily identical with B. From the assumption that A is identical with B and the second principle, it follows that A is necessarily identical with B. So, by conditional proof, if A is identical with B, then necessarily A is identical with B. There is no contingent identity. He didn’t maintain, though, that all statements of identity are non-contingent (either necessarily true or necessarily false). The statement “Benjamin Franklin is the inventor of bifocals” is a true, yet contingent statement of identity. Benjamin Franklin is the inventor of bifocals, but he might not have been. Someone else, Newton say, might have invented bifocals. But Kripke maintained that any statement of identity in which the “is” of identity is flanked by rigid designators is non-contingent. A rigid designator is a term that picks out the same thing in any world in which it picks out anything. Kripke maintained that proper names and kind terms are rigid designators, but that descriptions like “the inventor of bifocals” are not. Most physicalists, myself included, accept the necessity of identity thesis and Kripke’s notion of a rigid designator and so do leading contemporary Cartesian property dualists.

Kripke’s “Identity and Necessity” is thus must-reading for anyone who wants to understand the hard problem of consciousness. So is Kripke’s 1972 masterpiece Naming and Necessity, in which he pointed out a striking disanalogy between a posterior yet non-contingent identity claims like “Water is H20” and a posterior yet non-contingent identity claims like “Pain is N,” where N is a kind term of neuroscience. Chalmers appeals to the disanalogy as part of his case against physicalism in The Conscious Mind. Any neuroscientist who wants to critically engage Chalmers on the hard problem, rather than opting out of addressing it and just focusing on finding the neural correlates of subjective experiences, needs to be familiar with this Kripkean background otherwise, as I have directly seen, they will simply end up talking past Chalmers. There is, I think, an adequate physicalist response but it requires addressing the issue I noted in modal epistemology and the relationship between conceivability and possibility.

You mentioned Joseph Levine’s “explanatory gap” thesis, which he first proposed in his 1983 paper “Materialism and Qualia: the Explanatory Gap.” He argued that qualia (his term for the qualitative characters of subjective experiences) cannot be reductively explained by physical or physico-functional states and events. He was spot on. The reason for such an explanatory gap is that there are virtually no a priori connections between our concepts of subjective experiences (concepts such as the concept of the feel of pain, the concept of a visual experience of red, and so on) and our physical and physico-functional concepts. That’s why analytical behaviorist and analytical functionalist theories of subjective experience are false.

If there is a way to get across a conceptual gap then it’s by constructing a conceptual bridge. Nagel sees no hope of a bridge constructed of concepts that would count as physical concepts, but hopes that we’ll someday form concepts of proto-mental properties that will figure in the construction of a bridge that enables us to reductively explain subjective experiences. Colin McGinn holds that there is a conceptual bridge, but that we are cognitively closed to the concepts that form it (just as rabbits, say, given their furry little minds, are cognitively closed to the concept of a quantum field), and so we humans will never be able to construct it (though beings that are our cognitive betters might). The hard problem, he thinks, isn’t a tractable problem for us - it’s a mystery because no human could ever solve it. (Owen Flanagan labelled this view “mysterianism.” Think here of Huxley’s the Djinn analogy, which I cited earlier.) I’m deeply sceptical that here lies any conceptual bridge. But concepts are one thing and properties another. Properties are ways things might be, concepts are ways of thinking of things as being. It’s my position that there is an unbridgeable conceptual gap and so there is a reductive explanatory gap. The conceptual gap in question, however, doesn’t entail an ontological gap. Two very different concepts can apply in virtue of the same property. We can, I think, explain how by appeal to certain facts about the structure of our sub-personal level cognitive architecture, but that’s a long story.

Turning now specifically to causation. How does the concept of causation underpin the hard problem of consciousness? Well the concept of causation doesn’t underpin the hard problem of consciousness but it underpins the strongest physicalist objection to any Cartesian property dualist solution to the hard problem. The most formidable objection that the Cartesian property dualist view faces is to explain how subjective experiences could figure as causes in the web of causal relations.

It’s part of commonsense psychology that subjective experiences have causal effects. My feeling of pain makes me wince, my visual experience of the clear blue sky makes me smile, my feeling of terror makes me shake in my boots, and so on, and so forth. Physicalists appeal to the claim that subjective experiences have physical causal effects in arguing against non-physicalist views of phenomenal consciousness. If, for instance, my feeling pain makes me wince, it is a cause of my cheeks moving, which involves the movement of atoms. Physics, however, which seeks a comprehensive theory of motion, has no need of the hypothesis that there are feelings of pain. Of course hurricanes, mudslides, billiard balls, bullets, and beating hearts also affect motion, including the motions of atoms and more fundamental physical particles, yet physics doesn’t posit them (at least as such). They do so, though, by means of underlying micro-physical causal processes—ultimately, if quantum field theory can be trusted (and there has never been a physical theory more trustworthy), by means of a series of basic local interactions at points in fields, and so indirectly. Physicalists about phenomenal consciousness claim that the same is true when subjective experiences have causal effects. If, however, subjective experiences are ontologically fundamental, then they’d have to have a direct causal influence on physical events to have any causal influence at all on them; in which case, physics, given its aims, would have to posit them. Dualists sometimes claim that result can be avoided since subjective experiences in our world always only causally overdetermine their physical effects; physics needn’t posit them, since they’re causally redundant. Physicalists respond that the kind of overdetermination in question would be very different from the familiar kind of overdetermination one finds in cases in which, say, two fatal shootings cause the same death. Had one of the shots not occurred, the victim would have died, but not at exactly the same time or in exactly the same manner. If, however, subjective experiences overdetermine a physical event, the physical event would have occurred at precisely the same time and in precisely the same manner had the subjective experience not occurred. The subjective experiences would thus make no difference to the course of physical events.

Huxley held that we are conscious automata, by which he meant biological machines that are conscious. He also held that although consciousness has causes, it itself is causally inert, causally impotent, devoid of any causal effects. It makes no causal difference to what happens in the brain, and so no causal difference in what happens elsewhere as a result of what happens in the brain. On this view, states and events of consciousness are epiphenomena (to use a term introduced by William James). Frank Jackson, in his 1982 paper “Epiphenomenal Qualia,” acknowledged that the kind of qualia he maintained we have (C.I. Lewisian qualia) are epiphenomena, devoid of any causal effects. (Later, he became a physicalist representationalist.) In The Conscious Mind, one of the positions Chalmers maintained remains a serious option for acceptance, given what he took to be the failure of physicalism, is the view that qualia are epiphenomena. He held it could turn out that we may have to accept what he calls “the Paradox of Phenomenal Judgment,” which entails that there are no causal connections between subjective experiences and our beliefs or judgments that we are having them. You’re feeling pain and you believe you are in pain, but the feeling of pain isn’t a cause of the belief.

It should be apparent that that’s quite a bullet to bite. The claim that subjective experiences are epiphenomena seems to me absurd, which is not to say that it’s a priori false that they are. In any case, the apparent causal efficacy of subjective experiences raises the most formidable challenge to Cartesian property dualism. Some dualists are resigned to epiphenomenalism. Attempts to avoid epiphenomenalism by those who aren’t so resigned have included maintaining that physicists will eventually find (if there’s enough time, money, etc.) that they have to posit subjective experiences after all. Another response is that we should embrace what looks to me to be a kind of idealism, according to which all of fundamental reality is entirely experiential, experiential states providing the categorical bases for the dispositions proponents of the response maintain are the proper business of science.

I think the solution to the hard problem will have no consequences for physics. Moreover, on the view I favor, there’s no problem of how subjective experiences have causal effects. If types of subjective experiences are identical with types of neuroscientific states, then it trivially follows that they have whatever effects the neuroscientific states have. There’s just one type of state that we conceptualize in two very different ways, ways with virtually no a priori links to each other. Explanations, whether reductive or instead causal, employ concepts. But a state’s having the causes and effects it has doesn’t depend on how we conceptualize it. Still, to be sure, the view I favor faces a host of challenges, in addition to the one posed by what I take to be the deepest puzzle concerning objectivity and subjectivity. I haven’t even mentioned most of them. Some of them arise for any physicalist view; some are specific to views like mine that depend on certain empirical results being forthcoming from neuroscience. I keep an eye on relevant neuroscientific work and continue to address the challenges. Philosophy and science go on and, hopefully, they’ll survive budget cuts and continue to go on long after I pass on and make my final contribution to entropy.

Is Identity Theory an ontological contradiction?

Tony Sobrado: Throughout this discussion, you’ve posited the existence of the mental and the conscious. You're not an illusionist or an eliminativist but you do espouse identity theory. With that being the case, how can the physical brain and physicalism be one thing and consciousness be another thing—and yet simultaneously consciousness is identical to physical brain states? Isn’t that an ontological contradiction? How can consciousness be identical to physical brain states yet also be distinct from it?

Brian McLaughlin: If a type (or kind) of subjective experience E is identical with a neuroscientific state type (or kind) N, then it logically follows that E and N are not distinct. E and N are identical and so numerically one and the same—and nothing can be distinct from itself.

What are distinct, even if this identity theory is correct, are our concepts of subjective experiences and neuroscientific concepts. Our concepts of subjective experiences (for example, our concept of the feel of pain) are concepts that, once mastered, we can reliably apply to our own experiences on the basis of attending to them. Neuroscientific concepts, on the other hand, are highly theoretical concepts. These differing sets of concepts have very different roles in our cognitive architecture. The conceptual roles are so different that there are virtually no a priori connections between our concepts of subjective experiences and neuroscientific concepts, not only our current neuroscientific concepts, but also any concepts that would be invoked by any future neuroscientific theory that is a recognizable descendent of current neuroscience. There is, in that sense, an unbridgeable gap between these two sorts of concepts. However, I deny that there is an ontological gap because two concepts with no a priori links between them can refer to the same state type.

Tony Sobrado: Your articulation of the existence of a conceptual gap, because of two distinct conceptual frameworks regarding neuroscience and subjective experience, yet no accompanying ontological gap is enlightening. But if identity theory presents no ontological gap nor contradiction between physicalism and consciousness then can it be said that there’s no hard problem of consciousness at all? We don't need a reductionist approach, we don't need a causal theoretical role or a causal model explaining how consciousness derives from a neurological state because mental states simply ARE a type of physical state (a neurological state in this case). If you believe there is no ontological contradiction with the mental being identical to a brain state then the hard problem debate is unfounded. The same applies to subjective experience and its role in the hard problem of consciousness because it then follows that experience and subjectivity must also be identical to brain states. Alternatively, is there still an explanatory gap, along with a conceptual gap, when employing identity theory as an explanation of consciousness?

Brian McLaughlin: The hard problem is sometimes formulated in such a way that it presupposes that the kind of identity view in question is false. Here is such a formulation: We are first asked to suppose that neuroscientists discover strict neuroscientific correlates of our subjective experiences, so that for any type (or kind) of subjective experience E, there is a type of neuroscientific state N, such that someone would be in state E if and only if they were in state N. The hard problem is then posed this way: Why does N give rise to E (say, a feeling of pain), rather than to some other type of subjective experience (e.g., a visual experience of blue), or to no type of subjective experience at all? Since nothing “gives rise to” itself, that question presupposes that N is distinct from E, and so not identical with E. Thus, if the kind of identity theory in question is correct, that question is wrong-headed since its presupposition is false. But notice that that’s a conditional claim. The question is wrong-headed if the identity theory is true. But is it true? As I’ve said, the identity theory faces formidable challenges. The hard problem, moreover, can be formulated instead in this way: For each such E and N, why it is that we would be in state E if and only if we were in state N? That question doesn’t presuppose that the identity theory is false. Moreover, it cries out for an answer. According to proponents of the kind of identity theory I favor, the answer is that E is identical with N, but that answer faces a number of well-known challenges that involve the issues that anti-physicalists maintain make the problem “hard.” The issues are metaphysical and epistemological. I think that they can all be adequately addressed. I thus think that there is indeed a hard problem, one that no advances in neuroscience alone will make disappear (since a conceptual gap will remain), but that the problem admits of a physicalist solution.

You ask if there is an explanatory gap if this sort of identity theory is true. There is a kind of explanatory gap that remains even if this sort of identity theory is true. It is impossible to give what Chalmers calls a ‘reductive explanation’ via a functional analysis of subjective experiences as such because that kind of explanation requires that there be certain a priori connections between our concepts of subjective experiences and neuroscientific concepts... and there are no such a priori connections! This means there is an explanatory gap, in the sense that this kind of reductive explanation is impossible. The reason for this explanatory gap, however, is because there is a conceptual gap, but still the conceptual gap is compatible with subjective experiences being identical with neuroscientific states. Moreover, as Ned Block and Robert Stalnaker have spelled out, the psychophysical identity claims in question would transmit explanations and, in that way, enable us to explain subjective experiences as such.

The role of necessity in consciousness

Tony Sobrado: If you believe there is no ontological contradiction between the mental and the physical in identity theory and that the presence of a conceptual gap does not entail an ontological gap then what does this mean for necessity and laws? Earlier you said the following regarding the possibility of physical brain states causing consciousness by some necessary law de facto:

What explains those correlations? It could turn out that the answer is that nothing explains them, in which case the correlations would be fundamental laws of nature. I myself regard that answer as enormously implausible.

If consciousness just is a physical brain state, however, isn’t this a form of necessity in itself? And if so, then no additional explanation is required?

Brian McLaughlin: If a type of subjective experience is identical with a type of neuroscientific state, then that’s necessarily the case: There is no contingent identity. (There can be contingent statements of identity, but in the psychophysical identity claims that the identity view is committed to, the identity sign will be flanked by rigid designators, and so the claims will be non-contingent: They’ll either be necessarily true or necessarily false.) The psychophysical identity claims in question won’t themselves have explanations, but they require justification. To repeat: They could be justified, I maintain, by inference to the best explanation of the system of correlations. I find implausible the contrary view that the correlations are fundamental laws of nature, and so admit of no explanation. My skepticism is specifically targeted. I’m not at all skeptical about there being unexplainable laws. I think that there are fundamental laws of nature, and fundamental laws of nature are not explainable in terms of other laws and conditions. I’m skeptical that the psychophysical laws in question (laws linking types of subjective experiences and types of neuroscientific states) are fundamental, and so unexplainable. I don’t think that view is a priori false. It can’t be ruled out on a priori grounds. But I find it enormously implausible. I’ll mention some reasons why when I answer your question below about emergence, since the view that the psychophysical laws are fundamental is a kind of emergentist view.

Tony Sobrado: Ultimately, why do you prefer identity theory over emergence or physical realization when it comes to explaining consciousness?

Brian McLaughlin: There are a number of different notions of emergence, both within philosophy and within the sciences. In the sense of “emergence” used in solid-state physics, it may very well be the case that the kinds of neuroscientific states that are subjective experiences are emergent states, and so, trivially, given identity, that subjective experiences are emergent states. That’s compatible with my view. But “emergence” is used differently in the philosophy of mind. Solid-state physicists take emergent phenomena to be ontologically reducible, and so not ontologically fundamental; but as “emergence” is used in the philosophy of mind, emergent phenomena are supposed to be ontologically irreducible, and so ontologically fundamental. I focus on the notion of emergence used in the philosophy of mind. If types of subjective experiences emerge from their neuroscientific correlates, then the correlational laws linking them would be fundamental, metaphysically contingent laws of nature. (They’d be what C.D. Broad, in The Mind and Its Place in Nature (1925), called “trans-ordinal laws.”) If that’s so, then either the physics in fact true of our world will include the psychophysical laws in question among its fundamental laws, and so will posit subjective experiences as such, or else particular instances of types of subjective experiences, while having physical causes, will be devoid of physical effects, and so be epiphenomena. (There is a long story to tell here, but for a tiny bit more detail, see my earlier remarks about quantum field theory and about epiphenomenalism.) Neither alternative is a priori false, but I think both alternatives are wildly implausible.

You ask about physical realization. “Realization,” in the relevant sense, is a philosophical term of art. I myself briefly mentioned realization earlier. So, what, then, do philosophers tell us realization is? They don’t answer in one voice. Various non-equivalent uses of the term “realization” have been stipulated in the philosophical literature. They’re to be judged by their philosophical fruits. Some are more fruitful than others. I’ll be brief and focus on, arguably, the most commonly used notion of realization in philosophy: the role-functionalist notion. A functional state is a higher-order state, a state of being in some lower-order state or other that occupies a certain causal role, a certain role as cause and effect. A lower-order state that occupies the causal role in question realizes the functional state, and so is a realizer of the functional state. The lower-order state is a physical realizer if and only if it is a physical state. If the functional state has more than one realizer, it’s multiply realizable. Various dispositions such as water-solubility, water-absorbency, and fragility are, arguably, functional states. Subtleties aside, the state of water-solubility, for instance, is the state of being in some state or other that causes its bearers to dissolve when immersed in water. It’s multiply realizable. One of its realizers is being composed of sodium chloride; all of its realizers are physical. A role-functionalist theory of subjective experiences is a kind of identity theory: Subjective experiences are identical with certain functional states. This role-functionalist identity theory is compatible with physicalism for subjective experiences if the functional states are realized (in the actual world and in nomically possible worlds) only by physical states. Most, though not all, of the anti-physicalist challenges to the kind of identity theory I hold could be addressed in the same way I address them by a proponent of this role-functional identity theory. I myself think many kinds of mental states, including beliefs, desires, and intentions are functional states that are realized in us by neuroscientific states. But I don’t think that subjective experiences are functional states. We type-individuate subjective experiences by their phenomenal characters, and their phenomenal characters are not higher-order properties of having some property or other with a certain causal role. Beliefs, intentions, and desires (though not feelings of desire, they’re subjective experiences) are kinds of very complex dispositional states. Subjective experiences can activate dispositions, manifest dispositions, and induce dispositions, but they aren’t themselves dispositions—they are occurrences.

Brian P. McLaughlin is a Distinguished Professor of Philosophy and Cognitive Science at Rutgers University. A leading scholar in the philosophy of mind, physicalism, and consciousness, he is the co-editor of The Oxford Handbook of Philosophy of Mind and the co-author of Terrestrial Logic: Bringing Formal Semantics Down to Earth (Oxford University Press, forthcoming 2006). His extensive research focuses on the mind-body problem, color perception, and the history of emergentism.

***

Tony Sobrado is a social scientist and freelance writer focusing on philosophy, science, atheism and current affairs.

***

MORE CONVERSATIONS