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 or as the noted Frank Jackson said to me ‘the experience of experience’ so to speak.

Now there are some ways to initially address the hard problem of consciousness:

• It's simply a philosophical conundrum, a problem once again conjured up by pesky philosophers that is ultimately metaphysically unanswerable - akin to asking ‘where do the laws of physics come from?’

• No, it is a problem, and the problem is the metaphysical assumptions behind the universe and total ontological existence itself i.e. physicalism. Physicalism is incomplete or isn't true at all. Hence the problems that arise when one tries to marry consciousness (the mental experience) with the brain (physicalism).This harks back to the days of Descartes’ and the traditional mind-body problem which itself has evolved over history and today manifests itself in panpsychism and also in the conscious realism of Donald Hoffman.

• The opposite of number two. No, this isn't a problem. Physicalism is true. Physicalism is the only metaphysical truth and the only ontological realm that exists and therefore the conscious/mental has to be repackaged and re-conceptualised into a framework that accommodates physicalism. Here we see frameworks such as Illusionism, representational knowledge and functionalism. So here there is no phenomenal consciousness, there is no formal qualia - nothing that intrinsically outruns our direct experience, nothing above and beyond experience itself. Our experiences are essentially representational knowledge. As a consequence, elements of ‘what it is like’ simply being representational knowledge is partially supported by research from neuroscience that says ‘what it is like to undergo a conscious experience’ for any type of species is basically what their neurological model and thus neurological states dictate it is. ‘Consciousness’ is simply a model used by the physical brain to understand itself and navigate the world and its ‘experience’ is not phenomenologically real. It’s merely an illusion and working function of a physical brain.

• The hard problem of consciousness is quite a reasonable assertion. The mental and consciousness does exist and so does the brain and physicalism. The issue is how you marry the two and in what capacity you do it. So property dualism would say that the mind and brain are two different properties but ultimately one substance - physicalism - and therefore an explanation is required. This explanation could be addressing the explanatory gap or we could have a causal model, a causal chain model or a casual theory that states how consciousness arises from physical matter; or a fully 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.

And it is with the latter in mind that I turn to you - as a leading expert in the world in second order realizability and realizability in general. How it is that consciousness and other ontological entities in the world might be realized in, or even somehow reduced to, physical properties is one of your specialisms that ties into elements of consciousness. Moreover it impacts conceptual frameworks such as emergence, either strong or weak, i.e. how things such as the mind can emerge from physical properties and whether elements of realization are ultimately elements of identicalism disguised as ‘token identicalism’; or whether realization itself requires some kind of causal chain regarding how you get to elements such as consciousness being realized in physical properties and being ‘caused’ by physical properties.

Hopefully we can get to some of these issues that address the deeper and more mysterious elements about existence in general and what's going on with physicalism and what's going on with the mind?

But before we both dive straight into the deep end, let's take a step back and firstly tell me how you think of the hard problem of consciousness, does it exist at all for you?

Consciousness, phenomenal consciousness and representational knowledge

Andrew Melnyk: Let’s start with how we use the word “conscious” and its cognates in daily life, not because we should be doing a priori conceptual analysis of these words (we shouldn’t!) but simply because (i) it’s a reasonable working hypothesis that in daily life we often state truths when we use such words, and (ii) it will help to keep the discussion grounded. Then the first thing we should notice is that, at least very frequently, “consciousness” is just a synonym for “knowledge” or indeed  “awareness,” - another word that gets people very excited. I can be conscious, or aware, that my business plan involves risks, or of its riskiness. I can be conscious, or aware, that the dishwasher is on, or of the dishwasher itself and so on. I assume that it is in this sense that a rock is not conscious but a mouse is: the rock forms no knowledge-constituting representations of its environment, but the mouse does. Similarly, when I am asleep I am (mostly) not forming knowledge-constituting representations of  my environment (I say mostly, because I can be woken up by a loud noise).

Consciousness in this first sense of the word is simply the property of being conscious of something - a property possessed by organisms and more generally by complex systems. And to be conscious of something, or that something is the case, is for an organism to be in a certain kind of presumably knowledge-constituting internal state. To be in such a state is to be in a mental state. And it’s controversial whether any mental state could just be a physical state (e.g., a neural state of the brain) and dualists deny this. So I don’t want to make it sound as if there’s no problem of consciousness in this sense of the word; but it’s not the problem that philosophers of mind have been most troubled by or that fascinates some non-philosophers like neuroscientists.

Now when people speak of consciousness in connection with philosophy of mind, they often have in mind what they call ‘self-consciousness’. To be self-conscious is simply to be conscious of one’s own current mental states. Therefore to be self-conscious is simply to form knowledge-constituting representations of one’s being in certain mental states rather than of one’s environment, though obviously one can be conscious of both. But presumably not all organisms that are conscious of features of their environment are also conscious of their own mental states. For example one assumes that mice are not and it’s possible that humans are unique in this respect but I have no view on this question.

Now self-consciousness, in this sense, is just a special case of consciousness  - a synonym of “knowledge” or “awareness.” In being self-conscious, I have knowledge-constituting beliefs to the effect that I am thinking about philosophy, or that I have a mild pain in my foot etc.

This is introspection. What distinguishes such beliefs is that they don’t appear to arise from my use of any of the traditional five senses. For example, I don’t see or hear or smell my pains. How such beliefs do arise is an important empirical question, and it may be, as I suspect, that knowledge-constituting beliefs about one’s current beliefs and desires arise in a different way than do knowledge-constituting beliefs about one’s current sensations such as one’s physical pains.
So far perhaps so good. But a few decades ago philosophers commandeered the ordinary word “conscious,” and started to use it as an abbreviation of phenomenally conscious  to describe not organisms but mental states in a certain class, namely, sensations (such as pains, itches, afterimages, and waves of nausea), emotions (such as fear or anger), and moods (such as elation). And they often explained their usage by saying that a mental state, say, a pain, is phenomenally conscious if, and only if, there is something it’s like, for the person having the pain, to have the pain. Examples of such properties are the “orangeness” of an orange.

These properties are phenomenal properties or qualia. When philosophers of mind say ‘consciousness’, this is what they’re most likely to be talking about. Physicalists (or materialists) of one stripe or another think that phenomenal properties just are certain physical properties.

So do I think the hard problem of consciousness exists? Yes I do, it exists, and it concerns phenomenal properties. But we need to say exactly why phenomenal properties constitute a problem if we think that they do. We can’t just point at them, strike a deferential pose, and say, awestruck, “Those properties—they’re a problem.” And they constitute a problem because, on the one hand, there’s evidence that they are just physical properties of certain neural events in our brains - therefore neural properties, perhaps, or neurally - realized representational properties. The most important such evidence, in my view, is evidence for the systematic neural dependence of phenomenal properties on neural properties. For example, experiments have been performed in which volunteers who have been trained to describe the phenomenal character of their pains comment on pains that are deliberately inflicted on them while their brains are scanned. No sort of introspectible change over time in pains, or variation among pains at a time, has been discovered to which there fails to correspond some sort of simultaneous change in, or variation among, neural states, even though discovering such failures of correspondence lies within our current observational abilities. The neural dependence of phenomenal properties on neural properties is logically consistent with dualism; but it’s more economically explained by physicalism. That’s why it’s evidence – albeit defeasible, less than conclusive evidence, to be sure - for physicalism.

But on the other hand, however, certain plausible philosophical arguments conclude that phenomenal properties couldn’t be physical properties. Kripke’s conceivability argument at the end of his classic book Naming and Necessity, Frank Jackson’s knowledge argument, Joe Levine’s “explanatory gap” argument and David Chalmers’s zombie argument (and others). It’s easy, especially for scientists, to dismiss such arguments because the arguments don’t seem to provide empirical evidence against physicalism. But they can be formulated with theoretically considerable precision that makes them valid.

Tony Sobrado: Very interesting let's just take a step back and unpack some of these concepts and frameworks. Firstly, I think it's interesting that you mentioned representational knowledge and the comparative example between a human mind and a mouse’s consciousness in terms of representative knowledge of an external environment and how that stimuli is presented to the organisms in question. Obviously we can't to a certain extent say whether a mouse has self-awareness and self-consciousness like a human does - it's pretty safe to assume that they don't - but obviously you can’t completely know and in homage to Thomas Nagel’s ‘what's it like to be a bat’ paper no one can really know ‘what it's like to be a mouse’ which has parlayed into the zombie argument by David Chalmers. 

But it's interesting that you mentioned representational knowledge, phenomenal consciousness, qualia and the knowledge argument which I find fascinating by Frank Jackson. So firstly in terms of representational knowledge there are many that would say that there is no formal qualia, no phenomenal consciousness and in fact this is what illusionists say: that our sense that it is like something to undergo conscious experiences is due to the fact that we systematically misrepresent them as having phenomenal properties.  

Now you've also alluded to the fact that we are self-conscious, that we are aware that we have awareness - through introspection - and illusionists would say again this is just another working function of the human mind and so ‘what is it like’ in memory recall or introspection is just the working function of the mind because in real time there is nothing ‘what it is like to be’ in that moment - nothing that directly outruns the experience itself you just have that experience, you don't think ‘what it's like’ to have that experience whilst actually having the experience. I spoke to Frank Jackson for this series and Jackson has actually since his knowledge argument become a latter day physicalist so to speak and in fact Frank himself was espousing the wonders of representational knowledge to me and how there is no actual formal qualia. So between a once qualia freak, Jackson, who's now all in on representational knowledge in terms of functionalism and then also illusionism stating that there is no phenomenal consciousness that doesn't leave consciousness in a very good state currently. 

So I would like to get your thoughts on what you think of illusionism in general and whether that solves any issues regarding formal qualia and phenomenal consciousness. You see David Chalmers is going to say that the issue of experience is still there or as I like to say sensational realism is still there - you still have sensations and this can't be just simply dissolved or conceptually repackaged. Yes you may not have ‘what it is likeness’ in real time only in introspection or reflection but the emotions of fear and adulation are very pronounced and noticeable even in real time. This is the issue of experience or at least ‘the experience of experience’. So I’d like to get your thoughts on illusionism, representational knowledge and even functionalism and whether they can dissolve the hard problem of consciousness and meta-experience so to speak.

Additionally I like your conceptual understanding of the hard problem of consciousness but I'd like to discuss its actual answerability. So answering why subjectivity, experience and sensations can come out of a physical brain may be answerable either by necessity or sufficiency. For example in the case of necessity, even functionalism might do it but then you left with ‘why does functionalism itself give rise to consciousness?’ If you require a causal mechanistic explanation then, to a certain extent and depending on your interpretation of the metaphysics of causation, one could already argue that interventionist theories of causation already demonstrate that neurons cause ‘conscious’ experience but then you are left with ‘why do neurons cause conscious experience’ i.e. Joseph Levine’s explanatory gap and so asking more than that might be an unanswerable philosophical question.

I think there are certain questions that probably hark back to some elements of necessity or brute facts, things just are the way they are so if you ask me why sentience comes out of a physical brain I suppose physicists can't really tell you why the laws of physics are the way they are and not some other way! So is the hard problem of consciousness actually answerable?

More on phenomenal consciousness, the actual answerability of the hard problem and illusionist rebuttals

Andrew Melnyk: Let me start with a clarification. I explained that by phenomenal properties I mean those properties of our sensations that we’re aware of in introspection from the inside when we pay introspective attention to our sensations (e.g., to our pains).

Thus, for example, I may think, introspectively, that there is something orange about my sensation when I have an orange afterimage (hence my calling it “orange”); but it isn’t orange in the sense in which a piece of citrus fruit or a child’s toy can be orange. So in some sense orange is a phenomenal property of my visual afterimage, though it remains to be determined what this sense is.

I also wouldn’t characterize introspective awareness of the phenomenal properties of my sensations as “meta experience” or as “experience of experience.” I do think that my sensations are representations - episodes of my sensing or experiencing, which is a kind of representing; we’ll get to this eventually. But introspective awareness, in my view, is a kind of believing, believing that one’s sensations (or experiences) have phenomenal properties, and hence also a kind of representing, but not the same kind of representing. To put it crudely, an orange afterimage represents sensorily that something before me is orange, while my introspective belief that my afterimage is orange represents conceptually that my afterimage is orange (in the sense in which afterimages can be orange); and these are different modes of representing. Spelling out the differences fully would take empirical work, I think; but that there are differences is plausible.

I try to avoid using the word “qualia,” because it’s used in several different ways in contemporary philosophy of mind. But if I do use it, I use it simply to refer to the phenomenal properties of sensations in a theoretically non-committal way, which leaves certain controversial questions about these properties open save, of course, for whether they exist! For example, it leaves open whether or not these properties are immaterial (as opposed to physical), or intrinsic (as opposed to relational), or representational (i.e., whether they represent that so and so).

Now is the hard problem of consciousness actually answerable? I always worry when people doing philosophy use shorthand; it tends to create the impression that we all agree on something when we may well not. So if people are going to speak of ‘the hard problem’ of consciousness, then I think they must spell out exactly what they take the problem to be. If they just say, “Phenomenal properties are the hard problem,” without saying what makes phenomenal properties problematic, then the goalposts can always be moved and nothing will ever be accepted as a solution. That’s why earlier I offered a characterization of the hard problem as our having prima facie reason to believe incompatible things - both that phenomenal properties are physical properties of brain states and that they’re not. The former reason coming from our discovery of the neural dependence of phenomenal properties and the latter reason coming from certain well-known philosophical arguments concluding that phenomenal properties aren’t physical in any interesting sense.

I think that the hard problem, when it is characterized in this way, is not only soluble but has actually been solved! Every one of the well-known philosophical arguments concluding that phenomenal properties aren’t physical in any interesting sense is open to serious objection; and these objections can be found in books by such philosophers as Christopher Hill, Bill Lycan, Michael Tye, and David Papineau. These objections are controversial, of course; philosophy of mind has not achieved consensus.

Given my characterization of the hard problem, if the philosophical arguments for property dualism all fail then the problem has been solved. But you’re probably expecting more - a positive account of what phenomenal properties are. A positive account is not required to solve the hard problem as I have characterized it but still. The positive account that strikes me as most plausible is that phenomenal properties are—are one and the same thing as—representational properties (of a certain kind) of sensations—by which I mean something a little different from what is meant by most other philosophers who have endorsed representationalism (e.g., Tye, Lycan, and Fred Dretske). I am inclined to think that the orangeness of an orange afterimage is—is one and the same thing as—the afterimage’s property of representing (in a certain sensory way) that something before one is orange; and that the burningness of a burning pain is—is one and the same thing as—the pain’s representing that some part of one’s body is burning.

A natural reaction to my positive account of phenomenal properties is to protest that it doesn’t solve the hard problem. But this just takes us back to the question of what the hard problem is. If the hard problem is what I said it is, then of course my unorthodox representationalist account doesn’t solve the hard problem: it’s irrelevant to the hard problem, which has already been solved by the refutation of all the philosophical arguments for property dualism (Phenomenal Properties and the Intuition of Distinctness: The View from the Inside, Oxford University Press, 2025).

What I call, following David Papineau, ‘the intuition of distinctness’ is its seeming to us, when we pay introspective attention to, say, the phenomenal orangeness of an afterimage, that phenomenal orangeness couldn’t literally be a physical or functional, say, representational property. Like Papineau, I think the intuition of distinctness is widespread, including among physicalists. I suggest that, when people react to my unorthodox representationalist account of phenomenal orangeness by dismissing it as just not touching the hard problem, they are undergoing the intuition of distinctness, which tells them that the account just couldn’t be true.

If my suggestion is correct, then perhaps the hard problem is not, or at least not only, what I said it was; perhaps it is, or is fundamentally, the clash between (i) our discovery of the neural dependence of phenomenal properties and (ii) our having of the intuition of distinctness. (The intuition of distinctness might be thought psychologically to underlie the philosophical arguments for property dualism.)

And if this further suggestion is correct, then the crucial question becomes whether the intuition of distinctness gives us any good reason to believe that, say, phenomenal orangeness is distinct from (i.e., not one and the same thing as) any physical or functional (including representational) property. My new book argues (amongst other things) that it doesn’t, because there is no plausible story of how it arises in us that would explain how it provides such good reason. If this conclusion is correct, then we may in good conscience disregard the intuition of distinctness, and therefore the newly conceived hard problem is also solved (or dissolved). There’s no reason to expect the intuition to go away, but we needn’t listen to it.

All this, of course, like pretty much everything in the philosophy of mind, is enormously controversial, and you’re well within your rights not to believe a word of it!

Tony Sobrado: It is very interesting when you talk about the importance of definitions. I had a conversation with the editor of Philosophy Now, Grant Bartley, on whether the mental is simply physical and we couldn't quite agree on the definition of the mental. Physicalism itself is even more problematic, defining physicalism is difficult. Some have tried by stating the rather simple proposition that it's the metaphysical assumption that all that exists and all that can exist is composed of physical properties but what are these physical properties? some would say they're objective independent properties outside of the human mind, some state the physical ontology of mass, spin and forces etc. Others still have struggled with defining physicalism even more so - some have tried by stating that physicalism is comprised of laws i.e. the  laws of physics. But that then itself becomes problematic, the distinguished philosopher of physics Nancy Cartwright actually denies the existence of any laws whatsoever and instead posits a universe where causation occurs but there are no laws and is yet a physicalist. 

In a similar vein I had a conversation with George Ellis, the Stephen Hawking co-author, on emergence and he was describing that there are properties that emerge from a physical world but cannot be reduced to a physical world and have downward causation. I therefore asked him whether he believed in physicalism and was a physicalist? And he said that all things such as algorithms and the mental are realized in the physical so yes he was but after that he had trouble ascertaining whether these apparent emergent things were caused by, were identical to or reduced to the physical. Sean Carroll, the noted physicist flat out denies emergence.

So yes semantics and definitions are very important in philosophy and so here comes another one that’s quite a difficult concept to define - phenomenal consciousness. Illusionists reject the that there's something distinct about your experience and sensations. There is nothing ‘that it is like something’ to have a sensation in real time. You might have it post fact but that's just the function of working memory. So when you say the following: 

By “phenomenal properties” I mean those properties of our sensations that we’re aware of, in introspection, from the inside, when we pay introspective attention to our sensations (e.g., to our pains).  

Most Illusionists would flat out deny this. For them, and the noted Michael Graziano at Princeton, introspection is just the hardware, the brain modeling itself, Frank Jackson says there's nothing above and beyond the direct experience itself and thus there's nothing intrinsic about qualia. So when you say:

As I inspect the lemons at the supermarket I have a visual sensation that’s yellow, but if my attention is on the lemons, as it will usually be, rather than on the phenomenal character of my visual sensations, then I will not be thinking, introspectively, that my current visual sensation is yellow. 

Most illusionists won't grant you this distinction. If your attention is on the lemon it won’t simultaneously be on introspection about that sensation of yellow or as you term it ‘the phenomenal character of my visual sensations’ - hence how the brain processes many different bits of information simultaneously. Daniel Dennett called it Fame in the Brain: at the same time you are aware, consciously and unconsciously, of many stimuli and phenomena but only one at a time are you only consciously of any of these sensations. For example the color yellow, when you see it in a supermarket  there is no distinction between the color yellow of the lemon and you being aware and focused on it and then switching to what you term as the phenomenal character of your sensations. There is no phenomenal character to your sensations, for illusionists, your sensations are just that it's a yellow lemon in the moment that's the direct experience - no more no less. Then, introspectively you might be thinking ‘oh I've just seen yellow, I am aware that I just saw yellow’ but that's not phenomenal consciousness for illusionists that is the shifting of awareness, and this is Attention Schema Theory by Michael Graziano at Princeton. The way you term phenomenal consciousness here is quite frankly what the illusionists deny. And so when you say:

Now if I pay attention to a current orange afterimage, then I will form the introspective belief that my afterimage is orange (in the sense, whatever it is, in which afterimages can be orange). If illusionists are saying that I am mistaken in so believing, not just occasionally or under special circumstances but always, then I reject their claim. 

I believe that from the illusionist perspective, you're claiming that there is some sort of experience and there is some sort of sensation + self awareness and introspection but introspection is another model of the brain’s awareness and reflection post fact in mere memory recall. For illusionists, introspection is just another facet of functionalism under  a different Attention Schema to your visual perception and sensation of seeing the yellow of the lemon in real time. So your sensation, your introspective belief is a function of the brain and so it's not phenomenal consciousness.

I think the illusionist would also claim that you do not form the belief that the orange is yellow because there's nothing about experience that outruns experience itself so you do not consciously form the belief of the color yellow, you see the color yellow it is recognized by ‘you’ and then later when you introspect on that you think to yourself  ‘Oh I was seeing the color yellow back then and I am aware that I saw the color yellow back then’. Again that's not phenomenal consciousness, it’s just different stages of conscious awareness and at no point are any of these sensations or experiences anything more than that - sensations and experience - whether in real time, memory or introspection.  As Dennett famously said ‘they wonder where the color went’ the color went nowhere you are aware of it when you see it but that’s not the same, for illusionists at least, as phenomenal consciousness. And so when you say: 

That’s why earlier I offered a characterization of the hard problem as our having prima facie reason to believe incompatible things—both that phenomenal properties are physical properties of brain states. 

An illusionist would deny you the proposition regarding the sequence of ‘phenomenal properties of physical properties of brain states’ because that causes the misnomer of the hard problem of consciousness for illusionists. ‘Mental’ properties are physical properties. Illusionists are forced almost into an identicalist position or in the case of the Churchlands they just eliminate consciousness and the mental hence why I put ‘Mental’ in abbreviated commers. Illusionists may find the distinction between an experience de facto and the introspective belief of phenomenal consciousness of that experience untenable as a distinct framework.

That’s why earlier I offered a characterization of the hard problem as our having prima facie reason to believe incompatible things—both that phenomenal properties are physical properties of brain states

 I would agree with that premise but illusionists and certain representationalists and functionalists  could deny phenomenal properties and just say it's all representational and that there's no addition, no add on to the experience. The experience just is the brain property. 

Now I'm not an illusionist. I actually happen to agree with your general claim that there is consciousness - and then your general assertion of the hard problem being how does consciousness somehow latch onto, interact or depend on physical properties? 

I'm just making the illusionist argument for them that there is no need for a distinction between consciousness and brain states by way of going down ‘phenomenal consciousness’. Phenomenal consciousness doesn't formally exist for illusionists and that's why I, like you, also don't like the term ‘qualia’ I also happen not to like the term ‘consciousness’ or ‘phenomenal consciousness’.  I like the more simplistic and widely applicable term of ‘sensation’ or just brute experience or awareness and I like the way David Chalmers characterizes it as ‘experience’.

At the end of the day rocks do not have a sensational experience, sentient creatures do. And yes we can play this analytic game by saying that there is no qualia or nothing that outruns the direct experience and it's just representational and functional knowledge and that's all that representationally exists; and it's just a schema of the brain and therefore there is no hard problem, there's no real consciousness or at least no phenomenal consciousness and so on. But that still doesn't really explain the fundamental principle for me of the hard problem of consciousness which is ‘sensations being experienced by a sentient creature’ coming out of what appears to be a physical brain. 

Illusionists are often forced to be identicalists and therefore ultimately dispatch of any kind of phenomenal consciousness or the mental in general or just eliminate it like eliminative materialism but I am of the opinion that the mental and the physical both largely exists and you can have a wider definition of the mental and boil it down simplistically to sensations so in many respects I am a type of property dualist.  So tell me about your perspective on property dualism  how you understand the term and whether you are one and how does this relates to realization in general and phenomenal consciousness being realized in physical properties?

The mental, the physical and property dualism

Andrew Melnyk: I don’t know enough about the illusionist views you mention to be able to comment usefully, so I’ll remain silent. But I will comment on one thing you said. You spoke of the hard problem of consciousness which is ‘sensations being experienced by a sentient creature’ coming out of what appears to be a physical brain.

This is fine as a characterization of the phenomenon that gives rise to the hard problem - the phenomenon that (I agree) turns out to be hard-problematic so to speak. But it tells us nothing at all about what makes it hard-problematic. (Perhaps you don’t disagree?) It is not a priori that there is anything unphysical about either sensations or experience or sentience - just as it is not a priori that there is anything unphysical about biological phenomena such as an organism’s development or digestion. The crucial philosophical notion here is that of a posteriori identity statements - statements, to the effect that X is the very same thing as Y, whose truth can only be determined by appeal to empirical evidence, because whatever descriptive information is associated with the words “X” and “Y” does not allow one to deduce either that X is, or that it is not, the same thing as Y. Just as we discovered empirically that digestion is a physical process, we may discover, and perhaps already have discovered, that sensations are physical states and sentience a physical capacity for representing the organism’s body and environment.

Let me turn to your question about property dualism. For our present purpose, discussion of the mind-body problem - let us stipulate that a physical property is a property expressed or expressible in the technical language of a standard neurophysiology textbook. As I have already explained, my view is that what I call “phenomenal properties” are one and the same things as certain representational properties - certain properties of representing, in a certain way, that such and such is the case. For example, on this view, a visual sensation of red is red in the sense that it represents, in a certain way, that something before one is red.

Is my view a property dualist view? I am happy to allow that the representational properties I have in mind are not physical properties in the sense I have stipulated (i.e., that they’re not neurophysiological properties). So if property dualism is simply the view that some mental properties are not physical properties, in this sense of “physical,” then my view is a property dualist view. Some philosophers of mind, a minority, I would say, use “property dualism” in this sense.

But there is a wrinkle. I insist that the representational properties in question (that all mental properties, actually) are, though not themselves physical, still physically realized, as philosophers of mind put it. Intuitively, physically-realized properties are made real by, or owe their reality to, physical properties (and no others). My property right now of digesting a meal is realized, in this sense, by all sorts of purely physiological processes going on in my digestive system right now. My property of digesting a meal is therefore nothing over and above my undergoing those physiological processes. But digesting a meal isn’t the very same property as undergoing these physiological processes, since an animal of a different species could be digesting its (very different) meal and yet not be undergoing the very same kinds of physiological process that I undergo as I digest my meal.

Now I think of physicalism as the view that all mental properties are either physical or physically realized. But I insist that all mental properties are physically realized. So I count myself as a physicalist on the mind-body problem. (I am oversimplifying by ignoring the role of an organism’s environment is determining the intentional content of its mental states; but that’s another huge topic in its own right.) But it is common in philosophy of mind to construe property dualism not (as above) as the view that some mental properties are not physical properties but as a non-physicalist view, as the view, in effect, that some mental properties are not just non physical properties but also not even physically-realized properties. Since I insist that phenomenal properties are representational properties that are physically realized, I don’t count as a property dualist on this common understanding of “property dualism.”

In my writings, I have spelled out precisely what I take the physical realization of a property to be. But it’s complicated, so I’ll try just to give the flavor here. Consider a non-mental example, the property of being poisonous. Chemically very different substances can be poisonous, for example, cyanide and strychnine, so it won’t work to try to identify the property of being poisonous with some single chemical property (i.e., to claim that being poisonous is the very same property as some single chemical property). But being poisonous is still physically realized (in every case we know of). How so? Because, according to me, being poisonous can be identified with a certain higher-order property (as I put it), namely, the property of having some property that causes illness in anything that ingests it. And cyanide and strychnine both have this higher-order property (of having some property that causes illness etc.). They both have some property (but not the same property) that causes illness in anything that ingests them; they both have some or other chemical property that causes illness in anything that ingests the substances. The chemical property of cyanide that causes illness in anything that ingests it realizes the property of being poisonous in cyanide; and the chemical property of strychnine that causes illness in anything that ingests it likewise realizes the property of being poisonous in strychnine.

Now I’m not committed to thinking, and I don’t think, that every property that is physically realized is like the property of being poisonous in being a causal role property. There are also other kinds of higher-order property—for example, properties of having the teleo-function of doing so and so. And teleo-function is the key, I believe (following Ruth Millikan), to understanding representation, including mental representation in general and in particular the representational properties that, I hold, are one and the same as phenomenal properties. But rather than try to spell out how Millikan’s theory could be applied to sensations, let me zoom out for a moment. On my view, we can give an account of phenomenal properties by identifying them with certain representational properties; whether we can then say that phenomenal properties are physically realized depends on whether representational properties can be physically realized. I am optimistic that they can be. There is a standard battery of arguments for denying that phenomenal properties are physical or physically realized; but there is no such battery of arguments for denying that representational properties are physical or physically realized

Tony Sobrado: In response to my comment on the hard problem of consciousness as the following ‘sensations being experienced by a sentient creature coming out of what appears to be a physical brain’. You said the following:  

This is fine as a characterization of the phenomenon that gives rise to the hard problem—the phenomenon that (I agree) turns out to be hard-problematic, so to speak. But it tells us nothing at all about what makes it hard-problematic. (Perhaps you don’t disagree?).

No I generally wouldn't disagree with that in fact your summary captures a lot of the balanced nuance and thinking that we have already discussed. So the hard problem of consciousness as ‘sensations being experienced by a sentient creature coming out of what appears to be a physical brain’ - on the one hand I feel that it does explicate the conceptual and theoretical issues behind the hard problem of consciousness but I do generally agree with the premise in your statement – i.e. that it doesn't explain necessarily why this is a problem which obviously reaches further out into the discourse and frameworks of metaphysics, ontology, reductionism, causation, identicalism, realization and explanatory power.  

So I agree with you that on the one hand that it doesn't say why it's a problem but on the other hand someone like David Charmers will say the very essence of the hard problem is minimally captured right there: the issue of experience and sensations coming out of a physical brain. But generally, nonetheless, from my perspective you are right and I agree with you that it doesn't capture why and how is this a problem? - When we think specifically about what are sensations, experience, representational knowledge and representational experience for example so I agree with you there. 

I also agree with your statement: 

It is not a priori that there is anything unphysical about either sensations or experience or sentience.

So you are preaching to the choir here but again to play devil's advocate I suspect there'd be some philosophers of mind and some philosophers of physics that may push back on that and again this goes back to the idea that experience itself and sensations themselves can't be built into the paradigm physicalism - on simple a priori grounds alone. This is not the case for me so I will not push that further here as I agree with you here as well. 

As for your position on property dualism and its meanings: 

Let us stipulate that a physical property is a property expressed or expressible in the technical language of a standard neurophysiology textbook.......As I have already explained, my view is that what I call “phenomenal properties” are one and the same things as certain representational properties—certain properties of representing, in a certain way, that such and such is the case. For example, on this view, a visual sensation of red is red in the sense that it represents, in a certain way, that something before one is red. Is my view a property dualist view? I am happy to allow that the representational properties I have in mind are not physical properties in the sense I have stipulated....... So if property dualism is simply the view that some mental properties are not physical properties, in this sense of “physical,” then my view is a property dualist view. Some philosophers of mind, a minority, I would say, use “property dualism” in this sense we got in your aspect of property.  

I would actually be in this minority camp. I think others that say that the mental exists but isn't reducible or realizable in the physical wouldn't necessarily be advancing property dualism because when pushed they would be, from my perspective, ultimately espousing substance dualism because if the mental is not at all physical then what is it and how does it relate to a physical brain? Which then has consequences on the combination issue of how we get the brain interacting with the mind? Because clearly they coexist. This is why many neuroscientists and philosophers of mind today are attracted to illusionism and elements of eliminative materialism in terms of culling the realm of ‘consciousness’ all together but this is outside the scope here. 

I want to turn now to your great work on realization. This is why I wanted to speak to you because I generally agree with this framework. I think that using your loose interpretation and  definition of property dualism can work: 

So if property dualism is simply the view that some mental properties are not physical properties, in this sense of “physical,” then my view is a property dualist view. 

I believe that your elements of phenomenal consciousness relating to representational knowledge can also work. I know some philosophers would push back on that by saying that representational knowledge by definition can't be phenomenal consciousness. I think someone like Keith Frankish would say that and I think someone like a Frank Jackson would say that as well but I'm not going to get into that because we've already discussed that and because I think how we're depicting and defining consciousness here is sufficient and operable.

I, like you, believe that there's something to be said about how we have this ‘mental world’ - however loosely conceived - and how it relates to the physical brain so let's turn to realization. 

Physical Realization

You have just said this: 

Now I think of physicalism as the view that all mental properties are either physical or physically realized. But I insist that all mental properties are physically realized. So I count myself as a physicalist 

And I agree. 

And in your paper REALIZATION AND THE FORMULATION OF PHYSICALISM you say this: 

Three negative features of the realization physicalist’s account of realization bear emphasis. First, whether a functional token (e.g., my present headache) is identical with the physical token that realizes it (e.g., the event in my brain) is, on this account, a question left open by the fact that the former is realized by the latter; identity between realizer and realized is neither required nor forbidden by the account. Secondly, the account is not restricted in its applicability to cases of same-subject realization. So if the instantiation of a certain physical property realizes the instantiation of a distinct mental property, then, according to the account, the two properties may be instantiated in the same object, but they needn’t be. Thirdly, nothing in the realization physicalist’s account of realization – and nothing in realization physicalism more generally – requires that the functional nature of any non-physical type be discoverable a priori. In particular, realization physicalism isn’t a semantic thesis; it neither asserts nor re[1]quires the existence of any functional concepts or predicates. 

So now we get to the crux of the matter - relating the sequential steps from physical properties to mental properties and experience. Do we need causation? As in a causal theoretical role explaining why these neurological states cause and explain conscious sensations when we think about them being realized in the physical? Or is it sufficient just to have interventionist and manipulation theories of causation which some neuroscientists think is sufficient but some do not. How important is causation for physical realization at the end of the day? 

If something is realized in the physical how's is it realized? What does it mean to be realized? Is it by causal chains? Is it just by emergence or is it simply at the end of the day identical to its physical properties and so is realization ultimately the same as identicalism? If not why not? Or is realization just supervenience? If not why not? 

Andrew Melnyk: I’ll answer your questions in reverse order, but let me continue with my earlier non-mental example, which will illustrate my points about the metaphysics of inter-level relations without the distraction of the mental. Imagine we have some powder that’s poisonous. What is this property of being poisonous? How does it relate to the physico-chemical properties that the powder has? How do the powder’s physico-chemical properties give rise to the powder’s being poisonous? My view is that the powder’s being poisonous isn’t identical with—isn’t the very same property as—any physico-chemical property of the powder (e.g., its property of containing cyanide); if being poisonous were identical with containing cyanide, then substances that don’t contain cyanide couldn’t be poisonous, but they can be (e.g., antifreeze is poisonous). At the same time, if a second powder had exactly the same physico-chemical properties as the first powder, then it too would be poisonous. Indeed, any two powders that had exactly the same physico-chemical properties would have to be either both poisonous (like rat poison) or both not poisonous (like baking soda).

That last claim is a claim of supervenience: it says that any two things exactly alike in one respect must (in some sense of “must”) be exactly alike in a second respect. Now I accept that (with the right sense of “must”) a powder’s being poisonous supervenes on the powder’s physico-chemical properties. But to make this claim of supervenience is just to say that there’s a certain modal correlation between two families of properties: the property of being poisonous and physico-chemical properties don’t just always go together but must go together in a certain way—certain physico-chemical properties are such that, if a substance has these properties, then the substance must be poisonous. But to say that this modal correlation holds is not yet to explain why it holds. And there are different possible explanations of why it holds. It could conceivably hold because a certain set of causal laws hold, including the causal law that containing cyanide simultaneously causes any substance that contains cyanide to have the entirely distinct property of being poisonous and the causal law that containing strychnine simultaneously causes any substance that contains strychnine to have the entirely distinct property of being poisonous.

But I favor a different explanation of why certain physico-chemical properties are such that, if a substance has these properties, then the substance must be poisonous. This explanation is that being poisonous is always realized by some or other physico-chemical property, though not the same physico-chemical property in the case of every poisonous substance. Talk of realization can sound like a magical incantation, or causation by a new name, but it’s neither. The physico-chemical realization of being poisonous is just the holding of two unremarkable truths: that being poisonous just is - i.e., is the very same property as - the (higher-order) property of having some or other property that causes illness in animals that eat the substance, and that the “some or other property” is always, as a matter of fact, a physico-chemical property, though not always the same physico-chemical property. The realizing property, e.g., containing cyanide, realizes the property of being poisonous by causing illness in animals that eat the substance that contains cyanide—an effect it presumably produces through some biochemical mechanism known to pharmacology. But the realizing property doesn’t cause the property of being poisonous. For one thing, the realizing and realized properties are contemporaries; the latter doesn’t follow the former. For another, we would say that a powder’s being poisonous is in some sense nothing over and above its containing cyanide, whereas we would never say that an effect (e.g., a pot’s boiling) is nothing over above its cause (e.g., its being heated). So realization and causation (in its commonest sense) are different relations.

Let me now tackle your questions more specifically.

As regards supervenience, realization entails supervenience: if mental properties are always realized by physical properties, then mental properties supervene on physical properties—two possible worlds exactly alike physically (with nothing “extra”) are exactly alike mentally. But supervenience doesn’t entail realization. We can, I think, make sense of mental properties’ supervening on physical properties without their being realized by physical properties: the physical way the world would brutely necessitate the mental way it is, “brutely” meaning “without being explained in terms of the identity of mental properties either with physical properties or with higher-order properties.”

As regards claims of property identity, for it to be true that being poisonous is always realized by physico-chemical properties it must be that being poisonous is identical with some kind of higher-order property, which can be true even though being poisonous can’t be identified with (claimed to be the same thing as) any particular physico-chemical property. Similarly, the view that mental properties are always realized by physical properties does require that every mental property turn out to be one and the same thing as some (multiply realizable) higher-order property; but it doesn’t require that every (or even any) mental property turn out to be one and the same thing as some physical property. So physicalism requires claims of property identity, in my view, but not claims that mental properties are (are the same things as) certain physical properties.

As regards emergence, the word “emergence” is used in different ways in the metaphysics of mind and kindred fields. But in one useful and common philosophical sense of the word, to say that mental properties emerge from, or are emergent relative to, physical properties is to say that there are certain fundamental laws of nature whereby, if a system exhibits the sort of complex physical characteristics typical of a human being, then the system (the human) also exhibits the mental properties typical of a human being, but these mental properties are not the same things as the system’s physical properties or even its higher-order properties. And these emergent mental properties may endow the system with causal powers different from the causal powers it would possess if it merely had its physical properties and there were no fundamental laws of physical-mental emergence. This kind of emergentist view is incompatible with my view that mental properties are higher-order properties that are always realized by physical properties.

Finally, let me comment on the role of causation in my view. I’ve suggested that being poisonous is a certain higher-order property: the property of having some or other property that causes illness in animals that eat the substance that has the property. If the suggestion is correct, then obviously causation is an essential constituent of what it is to be poisonous. I’ve also said that there can be other kinds of higher-order property, whose nature can be spelled out without making explicit reference to causation. Perhaps being in pain is the property of containing some device whose activation has the teleo-function of preventing bodily damage. But even though causation is not explicitly mentioned in that characterization, it may still be presupposed if a device’s having a teleo-function requires that ancestors of the device sometimes actually performed the function and hence produced some effect.

But I doubt that, in order to say the sorts of things I think are true about the relationship between mental and physical properties, I am committed to any particular view about the nature of causation. In my first book, I lightly sketched a regularity theory of causation, but a counterfactual or manipulationist theory would be fine by me too. I think I could even accept, as David Papineau suggests, that there is no causation at all at the fundamental physical level—that causation is a non-fundamental phenomenon.

Now some philosophers (e.g., Jessica Wilson) who share my enthusiasm for realization give a different account of realization. Very roughly, they think of properties as bundles of causal powers, and hold that a physical property P realizes a mental property M if the causal powers constitutive of M form a proper subset of the causal powers constitutive of P. I don’t claim to understand this view fully, but it seems possible to me that it does require a particular and controversial view of causation.

Tony Sobrado: OK so let's start off with causation first because I think this is very important. So I like your high-level property being realized in a physical property and the outcome of the high-level property being identical to the higher level property itself i.e. in the case of poison the high-level property being poison, poison itself is identical to the high-level property and it is realized in some physical-chemical property at the lower level like cyanide. So essentially at the top level, the high-level property is being realized in something physical (so poison is realized in cyanide).  

So the mental is realized in the physical. And at the that top level that property (the mental) is identical to the higher-level property itself so being ‘poisonous’ or being the ‘mental’ is identical to the high-level property; but it doesn't have to be identical to the physical property at the lower level - it is just realized in the physical property at the lower level. So the high-level property and its relation to being realized in the physical property at a lower level does not require identicalism. Nor at the top level of the property itself does it require causation, because ‘poison’ or the ‘mental’ is identical to the high-level property itself.

My issue is how you get from the physical property at the lower level, the realizer, to the higher-level property, the realized. For you the mental is realized in a physical property which is the realizer, this high-level property which is realized in a lower-level property of the physical is itself identical to the high-level property but not necessarily identical to the lower-level physical property, the realizer, nor is it necessarily caused by this lower-level physical property, the realizer, either. So how you get from the physical low-level property to the high-level property (from the physical brain - the realizer - to the high-level property which is the mental - the realized) is where the detail lies. 

I agree with you that interventionist theories of causation and manipulative theories of causation will probably be sufficient. In fact I was working on an essay for this very series for the Montreal Review addressing how the hard problem itself could be a misnomer. This is because when we talk about the generative or productive elements behind consciousness and the mental and its co-aligning with a physical brain, substantial evidence from neuroscience suggests using interventionist theories of causation; and so conscious states can be seen as being caused by physical brain states - the field of optogenetics in neuroscience demonstrates this by widely using causal models.  

Now why causation is so important here is because for you there's nothing above and beyond the property itself at the higher-level, between the mental itself and the high-level property itself. This identicalism at this top tier, the high-level property, as you say requires no causation as there is nothing above beyond this. But again it's getting from the physical property, the realizer (the brain) to the high-level property, the realized (the mental), without it being identical to each other. This could instead entail causation whether interventionist or manipulative, where the ‘mental’ is above and beyond the complete identity of the physical property and so is caused by it and therefore is a subset of it. Ergo, the physical brain causes the mental and the mental is a subset of the physical. And so here Jessica Wilson’s work might be highly viable if properties are bundles of causal powers, and physical property P realizes a mental property M if the causal powers constitutive of M form a proper subset of the causal powers constitutive of P.

This is why I think causation is very important because realization entails supervenience but not causation or identicalism when relating the realizer to the realized - hence supervenience. But the crux is how they are related? If it’s just by supervenience this may not particularly add much to the discourse because supervenience itself can be ambiguous even though realization does elaborate on supervenience further via its employment of the higher-level property. But here supervenience and realization alone (without causation or identicalism to the lower-level physical property) may not add a lot to the discourse of the hard problem because that's already what neuroscientists at a minimum would say - that the mental supervenes on physical brain states as evidenced by neuroscience, regardless of whether they're illusionists, causal eliminativists or some variant of property dualists. In fact these three camps can employ realization (without causation or identicalism) to justify their views.

Moreover it may actually be compatible with elements of emergence itself depending on how one thinks about emergence because emergence is a complex issue. So you've stated that the high-level property is identical to the mental (in our case) and there's nothing above and beyond that - it's identical to it - and doesn't in this context lend itself to certain types of emergence. However this depends on what kind of emergence we're talking about. So you say it's nothing above and beyond that high-level property but it's still realized in the physical. This is fine.  

But in fact this is also what George Ellis, the renowned cosmologist, Stephen Hawking co-author and leading expert in emergence, would basically also say yet within this he still endorses emergence because of  causal top-down properties. Now you may not assert causal top-down properties because as you say:

And these emergent mental properties may endow the system with causal powers different from the causal powers it would possess if it merely had its physical properties........ This kind of emergentist view is incompatible with my view that mental properties are higher-order properties that are always realized by physical properties.

But the issues here regarding the distinctions of emergence is not about physical realization per se but about the ontological status of the high-level properties and whether they ontologically exist in their own right. So George Ellis would ascribe to realization, even as you endorse it but with the caveat of causal powers and an additional ontological status at the top level regarding the high-level property itself that is possibly distinct from the low-level physical property. I endorse the causal elementary requirement but not the distinct ontological status of the high-level property (the mental) itself because it is ultimately realized in the physical at the lower level (ultimately the base is always just physicalism).

And so this is where interventionist theories of causation and manipulative theories are fundamental because it’s how we get from the low-level physical property to the high-level realized property whilst all being encompassed by, and thus entailing, physicalism. So in a certain respect, the high-level property need not be ontologically distinct but can be caused by the low level physical property as a merely ‘realized function’ of it and in so doing be interpreted as weak form of emergence as noted by Wilson (1999). Whereby this functionalist approach is that any token power associated with a weak emergent feature will be identical to a token power of its realizer rendering emergence compatible with the physicalist thesis of physical causal closure. And so we are back to the intricacies of causation and identicalism and at what stage in the order they occur and thus how this may be deemed as some form of weak emergence.

So a specific form of realization as you depict it does leave the possibility for those that endorse both the physical and the mental, just with the mental being a higher-level of a physical property that is realized. As you are not necessarily committed to either causation or identicalism do you believe the mental exists in any capacity? And if so is it just as a phenomenal property that is representational? Moreover how does realization illuminate the problem of ‘consciousness’ and its relation to the physical in a novel way that has consequences for how we think about the hard problem of consciousness? 

What is your perspective on ‘mental’ causation? Is top-down causation possible in physically realized systems as you describe them? Can the high-level property, the mental, cause anything in the lower-level physical property? I very much doubt one could claim that poison causes cyanide. 

Andrew Melnyk: Before I address your official concluding questions, let me comment on something you said earlier: “My issue,” you said, “is how you get from the physical property at the lower level, the realizer, to the higher-level property, the realized”. This is a crucial question, which deserves a clear answer. Indeed, my explicit aim in appealing to realization is to make the “getting from the physical to the mental” transparent and, in fact, prosaic—just a matter of (i) deductive logic and (ii) metaphysical necessity, itself a consequence of the nature of realized properties. The idea is that, given the realizing physical property and relevant laws of physics (perhaps plus certain physical circumstances), it follows logically that the physical property meets a certain condition C (perhaps this condition is the playing of a specified causal role), and therefore that the bearer of the physical property is the bearer of a property that meets condition C; that’s step one. But it’s also the case that the mental property that the physical property realizes is identical with, hence (given the necessity of identity) is necessarily identical with, a certain functional or higher-order property, namely, the property of having some or other property—any property—that meets condition C. So, and this is step two, given that the bearer of the physical property is the bearer of a property that meets condition C, it must, as a matter of metaphysical necessity, also be the bearer of the mental property—because all it takes to have the mental property is to have some property that meets condition C, and it does have some property that meets condition C. To have the mental property just is to have some or other—any—property that meets condition C; but to have the physical property (given the physical laws and circumstances) is to have a property that meets C; so an object can’t—can’t metaphysically—have the physical property without having the mental property.

Now the only fundamental laws of nature that this “can’t” reflects are laws of physics: laws that connect physical conditions with other physical conditions. No appeal is made to fundamental laws of nature that connect physical conditions with mental conditions. That’s why I resist the suggestion that the realizing property (synchronically) causes—in something like the sense of Aristotelean efficient causation—the realized property. But I accept that efficient causation may not be the only kind of causation there is. Our everyday talk of causation sometimes concerns other kinds of explanation, including, notably, reductive explanation. So I’m happy to say that the system in question has the mental property it has because it has the physical property it has; but all I mean is that there is a reductive explanation, along the lines I have sketched, of its having the mental property in terms of its having the physical property (plus physical laws and circumstances). And of course I accept that we can induce visual sensations in a neurosurgical patient by directly stimulating his visual cortex—which is, indeed, an implication of my view. But if an interventionist account of causation has the consequence that the physical property induced by direct stimulation is a cause of the mental property in the same way in which my hand’s being burnt by the hot pan handle  is a cause of my searing pain, then I say the account of causation needs further refinement; the two cases strike me as significantly different. But let me turn to your explicit questions.

Question: A specific form of realization as you depict it does leave the possibility for those that endorse both the physical and the mental, just with the mental being a higher-level of a physical property that is realized. As you are not necessarily committed to either causation or identicalism do you believe the mental exists in any capacity? And if so is it just as a phenomenal property that is representational?

I think the mental is every bit as real as the biological or the geological. Predators (e.g., lions) are real, even though they’re always realized by unimaginably large and complex systems of fundamental physical particles. Erosion is a real (geological) process, even though it’s realized by physical changes in unimaginably large and complex systems of fundamental physical particles. The mental and the biological and the geological are all in the same boat in not being fundamental, in my view; but being non-fundamental doesn’t entail not existing. There’s a further question, perhaps, if you believe in degrees of reality, whether all these non-fundamental things are as real as the fundamental physical. I’m inclined to say that they are: I like to say that a dry-stone wall is every bit as real as the stones that make it up.

Not all mental properties are phenomenal properties. The propositional attitudes (e.g., my thinking that it’s now 2025) aren’t. (Yes, some philosophers believe in cognitive phenomenology, but I don’t.) But I think that believing and desiring are also states with intentionality (=directedness toward states of affairs). So I think that for an organism to have a mind is for the organism to have the capacity to host all sorts of causally interacting representations whose ultimate function is to guide the organism’s behavior in its environment. Some of these representations represent the organism’s internal states, while others represent the organism’s environment.

Question: From your perspective how does realization illuminate the problem of ‘consciousness’ and its relation to the physical in a novel way that has consequences for how we think about the hard problem?

I don’t think it does, actually. Realization (understood in my proprietary way) is a relation that I posit in order to give an account of the relation between any of the so-called special sciences, on the one hand, and physics (or some proper part of physics), on the other. So naturally I claim that the mental, including the phenomenal, is realized by the fundamental physical. But I don’t think that the appeal to realization makes it easier to defend a physicalist view of the phenomenal. It does indeed allow for the multiple realization of the phenomenal (though people are least persuaded that the phenomenal is multiply realized!). But the standard anti-physicalist arguments that I’ve mentioned before (conceivability arguments as advanced by Kripke and Chalmers, Jackson’s (now repudiated) knowledge argument, and Levine’s explanatory gap) are no easier to refute if phenomenal properties are realized by physical properties than they are if phenomenal properties just are physical properties. It has sometimes seemed otherwise: Kripke’s main argument at the end of Naming and Necessity is targeted at mental-physical identity claims, and you might think that the argument would have no force against weaker claims of realization. But that would be a confusion, in my view. Claims of realization don’t get you out of claims of identity. True, you don’t have to claim that mental properties are identical with physical properties; but you do have to claim that mental properties are identical with functional (in my very liberal sense) properties, and if Kripke’s argument is any good, it counts against mental-functional identity claims as much as against mental-physical ones.

Question: What is your perspective on ‘mental’ causation? Is top-down causation possible in physically realized systems as you describe them? Can the high-level property, the mental, cause anything in the lower-level physical property? I very much doubt one could claim that poison causes cyanide.

I certainly wouldn’t want to claim that poison causes cyanide, i.e., that a substance’s now being poisonous causes it now to contain cyanide, even if the substance’s being poisonous is realized by its containing cyanide. But the substance’s being poisonous can surely be a cause of my throwing up (if I eat the substance), even if my falling ill is realized by vast systems of fundamental physical particles—those that realize my digestive system—undergoing enormously complex physical changes. And in my view mental properties are in the same boat as the property of being poisonous: my sensation’s being a pain, and in particular a toothache, can cause me to pick up my phone and call the dentist.  Now some philosophers, as you know, argue that in all these cases “all the causal work” is really being done at the fundamental physical “level,” which leaves no causal work to be done at any higher “level,” e.g., the mental or biological. My reply is that causation is ultimately a matter of regularities or patterns of counterfactual dependence or something like that, and that the relevant regularities or patterns of counterfactual dependence can hold at different “levels” at the same time. In the poisoning case, certain regularities or patterns of counterfactual dependence mean that my eating a substance that is poisonous causes me to throw up; at the same time, other regularities or patterns of counterfactual dependence mean that systems of physical particles that realize molecules of cyanide in the poison I eat cause enormously complex physical changes in the vast systems of fundamental physical particles that realize my digestive system. The situation might then seem to involve causal overdetermination, but it doesn’t, I claim, because the two sets of regularities or patterns of counterfactual dependence aren’t independent of one another: roughly, the first set is realized by the second set. This, by the way, is why talk of levels is so misleading: it suggests layers, like layers of paint of different colors that have built up over decades on the interior walls of an old building. That’s not my physicalist view. My view, to put it a little loosely, is that mental phenomena, like biological and geological phenomena, are (just) patterns in the fundamental physical world. But the fundamental physical world really does exhibit these patterns, so the mental, and biological and geological, are real, and can perfectly well be causes and effects.

You also asked about top-down causation. We have top-down causation if, for example, my eating of a teaspoonful of a poison (a “higher level” phenomenon) causes a biochemical change inside some epithelial cell in the lining of my stomach (a “lower level” phenomenon), or if my toothache (a “higher level” phenomenon) causes muscle cells in my right forearm to contract (a “lower level” phenomenon). But we need to distinguish between two very different things that might be going on in such cases, which we can call top-down causation in a weak sense and top-down causation in a strong sense. Top-down causation in the weak sense, which I take to be a pervasive feature of the world, just requires the holding of the right regularities or patterns of counterfactual dependence between “higher level” and “lower-level” phenomena; but these regularities or patterns hold because the “higher level” phenomena are realized by “lower level” physical phenomena. So there are always physical mechanisms by which the “higher level” phenomena cause the “lower level” phenomena, and as a result “lower level” physical phenomena that are the effects of “higher level” phenomena are always produced in accordance with the laws of fundamental physics. Top-down causation in the strong sense occurs if “lower level” phenomena that are the effects of “higher level” phenomena are not produced in accordance with the laws of fundamental physics—if different “lower level” effects are produced than what you would predict solely on the basis of the laws of fundamental physics plus prior fundamental physical circumstances. If physicalism is true, then there is no such thing  as top-down causation in the strong sense.

Tony Sobrado:

The idea is that, given the realizing physical property and relevant laws of physics (perhaps plus certain physical circumstances), it follows logically that the physical property meets a certain condition C (perhaps this condition is the playing of a specified causal role), and therefore that the bearer of the physical property is the bearer of a property that meets condition C; that’s step one.  But it’s also the case that the mental property that the physical property realizes is identical with, hence (given the necessity of identity) is necessarily identical with, a certain functional or higher-order property, namely, the property of having some or other property—any property—that meets condition C.

So basically the low level physical structure, the realizer by some kind of metaphysical necessity that meets condition M, condition M being for example an evolutionary functional need - for example the ability to observe and distinguish between different kinds of red apples for consumption, means that ‘experience’ in this sense would start to be realized in the physical low-level structure itself and this ‘experience’ itself - the high-level property - is identical to the function of condition M.

Have I got this essentially correct in the simplest of terms? Please clarify or address. 

Andrew Melnyk: This isn’t quite right. It’s a tiny bit misleading to say that the realizer meets condition M (where meeting M is responding differentially to red and to non-red objects) by metaphysical necessity (i.e., truth in all possible worlds). It’s certainly true that the realizer responds differentially to red and to non-red objects in all possible worlds in which (i) the actual neurophysiological laws hold, (ii) the realizer has its actual neurophysiological nature, and (iii) the realizer is in the same physical circumstances that it’s actually in. But the realizer’s responding differentially to red and to non-red objects could in principle be deduced from premises about the actual neurophysiological laws, the realizer’s neurophysiological nature, and its actual physical circumstances. So there’s nothing mysterious about the metaphysical necessity here; it’s just logical deducibility, like the metaphysical necessity of my being mortal given that I’m human and that all humans are mortal.

A more serious problem concerns the nature of the red experience. I wouldn’t call it “the function of conditions M.” My idea is this sort of thing: a person’s having a red experience is (that is, is identical with) the person’s being in a state that responds differentially to red and to non-red objects; that is, it’s being in any state (it could be a brain state or in principle a silicon chip state or even some immaterial ectoplasmic state) that responds differentially to red and to non-red objects. Now if X is identical with Y, then X and Y can’t come apart in any possible world, no matter how much the laws of nature in the possible world may differ from the actual laws of nature. So if someone is in any state that responds differentially to red and to non-red objects, then the person must be having a red experience. Similarly, if my soup contains sodium chloride, it must contain salt (given that salt is sodium chloride).

So suppose that the realizer is in my head. Then I’m in a state (as it happens, a neurophysiological state) that responds differentially to red and to non-red objects. But (we’re assuming) being in a state—any state—that responds differentially to red and to non-red objects is one and the same thing as having a red experience. So (given the realizer in my head) I must be having a red experience. To start at the top and go down: I’m having a red experience; so I must be in some state that responds differentially to red and to non-red objects; and, as it happens, I’m in a particular neurophysiological state that responds differentially to red and to non-red objects. To start at the bottom and go up: I’m in a particular neurophysiological state that (given its physical nature, its physical circumstances, and the physical laws) does, and must, respond differentially to red and to non-red objects; but being in a state—any old state—that responds differentially to red and to non-red objects just is to have a red experience; so I’m having, and indeed must be having, a red experience.

Tony Sobrado: So if I am in a neurophysiological state that responds differentially to red and to non-red objects and given the realizer in my head, the physical structure of my brain, I must be having a red experience. Basically if I’m having a red experience I must therefore be in some physical state that responds differentially to red and to non-red objects. Conversely if  I’m in a particular neurophysiological state that does, and must, respond differentially to red and to non-red objects I must be having a red experience. 

I can see now how this is a complete physicalist project in which phenomenal consciousness and the mental, as you depict it through introspection, is ultimately physically realizable hence your detraction from elements of emergence. I can also see how it gives an explanatory account of what the mental is (loosely and not via necessary scientific explanation) and how the mental ‘arises’ (as loose depiction of its relation to the physical - ultimately) and it is a reasonably good theory of consciousness and the mental. Whether it solves the hard problem of consciousness - probably not for the reasons we’ve both alluded to - but then again it begs the question of whether the hard problem is actually solvable and a viable question in the first place. 

But perhaps it also doesn't address the hard problem of consciousness for other more detailed reasons. First of all one could say it's very circular - mental states must be grounded and realized in physical states because physical states realize mental states. 

Moreover I don't think it escapes identicalism, it merely delays it.

So if someone is in any state that responds differentially to red and to non-red objects, then the person must be having a red experience. So ultimately the perceptual experience of seeing red is the physical state and so it only delays identicalism by staggering it in stages. And I appreciate that multiple realizability does not entail identicalism to the lower-level physical structure only the higher-level functioning property, but that property is still ultimately the physical structure as referenced in perceptual red being a physical brain state - the mental is the physical state when realized. And there are different forms of poison but ultimately all poison is the physical structure, whether cyanide or arsenic because both are just their physical chemicals. Multiple realizability does not solve the issue that all properties (even higher level ones) are essentially just their physical properties - the difference is in description not ontology or metaphysics.

Perhaps even more importantly is how one untangles the metaphysics of physicalism from neurophysiological laws. So I appreciate the metaphysics involved when discussed in all possible worlds but when you say: 

This isn’t quite right, I’m afraid. It’s a tiny bit misleading to say that the realizer meets condition M (where meeting M is responding differentially to red and to non-red objects) by metaphysical necessity... But the realizer’s responding differentially to red and to non-red objects could in principle be deduced from premises about the actual neurophysiological laws, the realizer’s neurophysiological nature, and its actual physical circumstances

What is the criterion for demarcation between the metaphysics and the neurophysiological states? How do you untangle the metaphysics specifically from neurophysiological laws? Because if neurophysiological laws must result in mental states by logical necessity then this is a metaphysical claim i.e. is that the mental must be reducible to the physical, ergo all that exists is physical. Is this not a metaphysical claim?

Finally on interventionist theories of causation in neuroscience. I do appreciate there is something to be said about Colin McGinn’s argument about the broad spectrum of the mental not being amenable to full capture in scientific causal models but I also take the sentiment from Keith Frankish: to model and put a computer in pain is to execute the inputs of pain for the computer and so now the computer is in pain. So what more is required to explain pain then? And in the same neuroscientific spirit, the medial spinoreticulothalamic pathway responds to stimuli from deep somatic and visceral structures. The signal is then sent to the thalamus and higher cortical regions and the brain then detects the signal as pain. What more is needed to explain pain here? Are the medial spinoreticulothalamic pathways not causing pain?

Andrew Melnyk: I’m not willing to cop to the charge of circularity! You paraphrase my view as saying that “mental states must be grounded and realized in physical states because physical states realise mental states.” But I don’t argue in this way. My evidence for thinking that mental states are physically realized is the observed dependence, de facto, of mental states on neural states, the best explanation of which, I say, is that mental states are functional states that happen always to be realized by physical states. I do claim that my current headache is realized by my being in brain state B if, and only if, my being in brain state B necessitates (in a certain way) my being in pain; but that claim is just  my stipulative definition of “realized.”  The left-hand side and the right-hand side are meant to say the same thing.

I’m not sure what identicalism is or why it might be thought to be bad. I do assert the identity of every type of mental state with some or other type of functional state, but I deny that my being in pain right now is identical with my being in brain state B right now. True, I insist that my being in pain right now is my being in brain state B right now, if “is” can mean “is realized or constituted by”; but I take it that there are two relations that suffice for being nothing over and above: identity and realization.

Regarding metaphysical necessity, what I’m against is the suggestion that brute, i.e., unexplained, necessity is the relation that holds between the physical and the mental: that the physical metaphysically necessitates the phenomenal—and there’s an end on’t (as Samuel Johnson might have said). The physical does metaphysically necessitate the phenomenal, in my view, but not brutely; I insist that this necessitation can be explained. To explain it, the physical must be taken to include the holding of physical laws, not just the existence of physical states of affairs, and appeal must also be made to the metaphysically necessary (and a posteriori) identity of phenomenal properties with functional (specifically, representational) properties.

Finally, on explaining pain, I agree that the computer and the human may both be in pain, but if we turn up the magnification of our microscopes and look at the systems’ respective innards, what we find in each case is very different. If they are both in pain, they must have something in common, but what, exactly, is it? Now all the options familiar from textbooks in the philosophy mind present themselves. For example, pain is a kind of immaterial state of a suitably complex system that the system can be caused to be in by undergoing physical changes; pain is a total behavioral disposition of a system, no matter how the disposition is explained by occurrent internal causes; or perhaps pain is a kind of state of representing that certain events are occurring in the system.

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Andrew Melnyk is a Professor of Philosophy at the University of Missouri, Columbia, specializing in the philosophy of mind, metaphysics, and the philosophy of science. His work focuses extensively on defining and defending physicalism, the view that everything in the world is fundamentally physical. He is the author of A Physicalist Manifesto: Thoroughly Modern Materialism and actively engages in debates surrounding the nature of consciousness. *** Tony Sobrado is a social scientist and freelance writer focusing on philosophy, science, atheism and current affairs.

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