Gaze dualism and omnisubjectivity

I have toyed with a pair of theories.

The first is what I call gaze-dualism. On gaze-dualism, our sensory conscious experiences are constituted by a non-physical object—the soul—“gazing” at certain brain states. When the sensory data changes—say, when a sound goes from middle A to middle C—the subjective experience changes. But this change need not involve an intrinsic change in the soul. The change in experience is grounded in a change in the gazed-at brain state, a brain state that reflects the sensory data, rather than by a change in the gazing soul. (This is perhaps very close to Aquinas’ view of sensory consciousness, except that for Aquinas the gazed-at states are states of sense organs rather than of the brain.)

The second is an application of this to God’s knowledge of contingent reality. God knows contingent reality by gazing at it the way that our soul gazes at the brain states that reflect sensory data. God does not intrinsically change when contingent reality changes—the change is all on the side of the gazed-at contingent reality.

I just realized that this story makes a bit of progress on what Linda Zagzebski calls “omnisubjectivity”—God’s knowledge of all subjective states. My experience of hearing a middle C comes from my gazing at a brain state B_C of my auditory center produced by nerve impulses caused by my tympanic membrane vibrating at 256 Hz. My gaze is limited to certain aspects of my auditory center—my gaze tracks whatever features of my auditory center are relevant to the sound, features denoted by B_C, but does not track features of my auditory center that are not relevant to the sound (e.g., the temperature of my neurons). God’s gaze is not so limited—God gazes at every aspect of my auditory center. But in doing so, he also gazes at B_C. This does not mean that God has the same experience as I do. My experience is partly constituted by my soul’s gaze at B_C. God’s experience is partly constituted by God’s gaze at B_C. Since my soul is very different from God, it is not surprising that the experiences are different. However, God has full knowledge of the constituents of my experience: myself, my gaze, and B_C, and God’s knowledge of these is basically experiential—it is constituted by God’s gazing at me, my gaze, and B_C. And God also gazes at their totality. This is, I think, all we need to be able to say that God knows my sensory consciousness states.

My non-sensory experiences may also be constituted by my soul’s gazing at a state of my brain, but they may also be constituted by the soul’s gazing at a state of the soul. And God gazes at the constituents and whole again.

Dualism, humans and galaxies

Here is a mildly interesting thing I just noticed: given dualism, we cannot say that we are a part of the Milky Way galaxy. For galaxies, if they exist at all, are material objects that do not have souls as parts.

Brains, bodies and souls

There are four main families of views of who we are:

1. Bodies (or organisms)

2. Brains (or at least cerebra)

3. Body-soul composites

4. Souls.

For the sake of filling out logical space, and maybe getting some insight, it’s worth thinking a bit about what other options there might be. Here is one that occurred to me:

5. Brain-soul (or cerebrum-soul) composites.

I suppose the reason this is not much (if at all) talked about is that if one believes in a soul, the body-soul composite or soul-only views seem more natural. Why might one accept a brain-soul composite view? (For simplicity, I won’t worry about the brain-cerebrum distinction.)

Here is one line of thought. Suppose we accept some of the standard arguments for dualism, such as that matter can’t be conscious or that matter cannot think abstract thoughts. This leads us to think the mind cannot be entirely material. But at the same time, there is some reason to think the mind is at least partly material: the brain’s activity sure seems like an integral part of our discoursive thought. Thus, the dualist might have reason to say that the mind is a brain-soul composite. At the same time, there is a Cartesian line of thought that we should be identified with the minimal entity hosting our thoughts, namely the mind. Putting all these lines of thought together, we conclude that we are minds, and hence brain-soul composites.

Now I don’t endorse (5). The main ethical arguments against (2) and (4), namely that they don’t do justice to the deep ethical significance of the human body, apply against (5) as well. But if one is not impressed by these arguments, there really is some reason to accept (5).

Furthermore, exploring new options, like the brain-soul composite option, sometimes may give new insights into old options. I am now pretty much convinced that the mind is something like the brain plus soul (or maybe cerebrum plus intellectual part of soul or some other similar combination). Since it is extremely plausible that all of my mind is a part of me, this gives me a new reason to reject (4), the view that I am just a soul. At the same time, I do not think it is necessary to hold that I am just a mind, so I can continue to accept view (3).

The view that the mind is the brain plus soul has an interesting consequence for the interim state, the state of the human being between death and the resurrection of the body. I previously thought that the human being in the interim state is in an unfortunately amputated state, having lost all of the body. But if we see the brain as a part of the mind, the amputated nature of the human being in the interim state is even more vivid: a part of the human mind is missing in the interim state. This gives a better explanation of why Paul was right to insist on the importance of the physical resurrection—we cannot be fully in our mind without at least some of our physical components.

More fun with monochrome Mary

Here’s a fun variant of the black-and-white Mary thought experiment. Mary has been brought up in a black-and-white environment, but knows all the microphysics of the universe from a big book. One day she sees a flash of green light. She gains the phenomenal concept α that applies to the specific look of that flash. But does Mary know what green light looks like?

You might think she knows because her microphysics book will inform her that on such-and-such a day, there was a flash of green light in her room, and so she now knows that a flash of green light has appearance α. But that is not quite right. A microphysics book will not tell Mary that there was a flash of green light in her room. It will tell her that there was a flash of green light in a room with such-and-such physical properties. Whether she can deduce from these properties and her observations that this was her room depends on what the rest of the universe is like. If the universe contains Twin Mary who lives in a room with exactly the same monochromatically observable properties as Mary’s room, but where at the analogous time there is a flash of blue light, then Mary will have no way to resolve the question of whether she is the woman in the room with the green flash or in the room with the blue flash. And so, even though Mary knows all the microphysical facts about the world, Mary doesn’t know whether it is a green flash or a blue flash that has appearance α.

This version of the Mary thought experiment seems to show that there is something very clear, specific and even verbalizable (since Mary can stipulate a term in her language to express the concept α, though if Wittgenstein is right about the private language argument, we might require a community of people living in Mary’s predicament) that can remain unknown even when one knows all the microphysical facts and has all the relevant concepts and has had the relevant experiences: Whether it is green or blue light that has appearance α?

This seems to do quite a bit of damage to physicalism, by showing that the correlation between phenomenal appearances and physical facts is a fact about the world going beyond microphysics.

But now suppose Joan lives on Earth in a universe which contains both Earth and Twin Earth. The denizens of both planets are prescientific, and at their prescientific level of observation, everything is exactly alike between Earth and Twin Earth. Finer-grained observation, however, would reveal that Earth’s predominant surface liquid is H₂O while Twin Earth’s is XYZ, but currently there is no difference. Now, Joan reads a book that tells her in full detail all the microphysical structure of the universe.

Having read the book, Joan wonders: Is water H₂O or is it XYZ? Just by reading the book, she can’t know! The reason she doesn’t know it is because her prescientific observations combined with the contents of the book are insufficient to inform her whether she lives on Earth or on Twin Earth, whether she is Joan or Twin Joan, and hence are insufficient to inform her whether the liquid she refers to as “water” is H₂O or XYZ.

But surely this shouldn’t make us abandon physicalism about water!

Now Joan and Twin Joan both have concepts that they verbalize as “water”. The difference between these concepts is entirely external to Joan and Twin Joan—the difference comes entirely from the identity of the liquid interaction with which gave rise to the respective concepts. The concepts are essentially ostensive in their differences. In other words, Joan’s ignorance of whether water is H₂O or XYZ is basically an ignorance of self-locating fact: is she in the vicinity of H₂O or in the vicinity of XYZ.

Is this true for Mary and Twin Mary? Can we say that Mary’s ignorance of whether it is a green or a blue flash that has appearance α is essentially an ignorance of self-locating facts? Can we say that the difference between Mary’s phenomenal concept formed from the green flash and Twin Mary’s phenomenal concept formed from the blue flash is an external difference?

Intuitively, the answer to both questions is negative. But the point is not all that clear to me. It could turn out that both Mary and Twin Mary have a purely comparative recognitive concept of “the same phenomenal appearance as that flash”, together with an ability to recognize that similarity, and with the two concepts being internally exactly alike. If so, then the argument is unconvincing as an argument against physicalism.

The epistemic gap and causal closure

In the philosophical literature, the main objection to physicalism about consciousness is the epistemic gap: the alleged fact that full knowledge of the physical does not yield full knowledge of the mental. And one of the main objections to nonphysicalism about consciousness is causal closure: the alleged fact that physical events, like our actions, have causes that are entirely physical.

There is a simple way to craft a theory that avoids both objections. Simply suppose that mental states have two parts: a physical and a non-physical part. The physical part of the mental state is responsible for the mental state’s causal influence on physical reality. The non-physical part explains the epistemic gap: full knowledge of the physical world yields full knowledge of the physical part of the mental state, but not full knowledge of the mental state.

Something Mary doesn't know

Here is something our old friend Mary, raised in a black and white world, cannot know simply by knowing all of physics:

1. What are the necessary and sufficient physical conditions for two individuals to be in exactly the same phenomenal state?

Of course, her being raised in a black and white world is a red herring. I think nobody can know the answer to (2) simply by knowing all of physics.

Some remarks:

• Knowledge of the answer to (1) is clearly factual descriptive knowledge. So responses to the standard knowledge argument for dualism that distinguish kinds of knowledge have no effect here.

• The answer to (1) could presumably be formulated entirely in the language of physics.

• Question (1) has a presupposition, namely that there are necessary and sufficient physical conditions, but the physicalist can’t deny that.

• A sufficient conditions is easy given physicalism: the individuals have the exact same physical state.

• Dennettian RoboMary-style simulation does not solve the question. One might hope that if you rewrite your software, you can check if you have the same qualia before and after the rewrite. But the problem is that you can only really do exact comparisons of qualia that you see in a unified way, and there is insufficient unification of your state across the software rewrite.

If materialism is true, we can't die in constant pain

Here is an unfortunate fact:

1. The last minute of your life can consist of constant conscious pain.

Of course, I think all pain is conscious, but I might as well spell it out. The modality of the “can” in this post will be something fairly ordinary, like some sort of nomic possibility.

Now say that a reference frame is “ordinary for you” provided that it is a reference frame corresponding to something moving no more than 100 miles per hour relative to your center of mass.

Next, note that switching between reference frames should not turn pain into non-pain: consciousness is not reference-frame relative. Thus:

2. If the last minute of your life consists of constant conscious pain, then in every reference frame that is ordinary for you, in the last half-minute of your life you are in constant conscious pain.

Relativistic time-dilation effects of differences between “ordinary” frames will very slightly affect how long your final pre-death segment of pain is, but will not shorten that segment by even one second, and certainly not by 30 seconds.

Next add:

3. If materialism is true, then you cannot have a conscious state when you are the size of a handful of atoms.

Such a small piece of the human body is not enough for consciousness.

But now (1)–(3) yield an argument against materialism. I have shown here that, given the simplifying assumption of special relativity, in almost every reference frame, and in particular in some ordinary frames, your life will end with you being the size of a handful of atoms. If materialism is true, in those frames towards the very end of your life you will have to exist without consciousness by (3), and in particular you won’t be able to have constant conscious pain (or any other conscious state) for your last half-minute.

Unconscious aliens

Lately I’ve been starting my philosophy of mind course with Carolyn Gilman’s short story about unconscious but highly intelligent aliens.

We can imagine such aliens having thoughts, beliefs, concepts, representational and motivational states. After all, we have beliefs even when totally unconscious, and we have subconscious thoughts, concepts, as well as representational and motivational states.

I’ve wondered what unconscious aliens would think about our philosophical arguments about physicalism and consciousness. They might not have the concept of consciousness or of an experiential state, but they could have the concept of “that special mode of representing reality that humans have and we don’t”. And so now I ask myself: Would these aliens have any reason to think that consciousness-based arguments for dualism have any force? Would they have any reason to think that “special mode” is a non-physical mode?

Of course, the aliens might be convinced of dualism on the basis of intentionality arguments. But would something about humans give them additional evidence of dualism about humans?

The aliens shouldn’t be surprised to discover that humans when awake have some ways of processing inputs that they themselves don’t, nor should that give any evidence for dualism. Neither should the presence of some special “phenomenological” vocabulary in humans for describing such processing.

But I think what should give the aliens some evidence is the conviction that many humans have that their “experiences” lack physical properties, that they are categorically different from physical properties and things. If someone describes an object of sensory perception as lacking color, that gives one reason to think the object indeed lacks color. If someone describes the object of introspective perception as lacking charge or mass, that gives one reason to think the object indeed lacks charge or mass.

The aliens would need to then consider the fact that some people have the conviction and others do not, and try to figure out which ones are doing a better job learning from their introspection.

The fundamentality of souls

Some dualists say that the soul is a fundamental entity.

I think we’re not in a position to think that. Compare this. We have no reason to think electrons are not elementary particles. They certainly aren’t made of any of the other particles we know of, so they are, we might say, “relatively elementary” with respect to the particles we know. But we would not be very surprised if electrons turned out to be made of other particles.

Similarly, we have good reason to think the soul is not grounded in any of the other things we know of (matter, accidents, etc.) But we should not be really surprised if a finer-grained analysis would reveal the soul to have a grounding structure beyond our current knowledge. We should be cautious and say the soul is “relatively fundamental” with respect to the entities we know.

Ways out of the closure argument for physicalism

One of the main arguments for physicalism is based on the closure principle:

1. Any physical event that has a cause has a physical cause.

It is widely thought that it follows from (1) that:

2. If a physical event has a nonphysical cause, the event is overdetermined.

And hence in the absence of systematic overdetermination, mental causes must be physical.

But (2) doesn’t follow from (1). There are at least three ways for an event E to have two sufficient causes A and B:

• overdetermination

• chaining: A causes B which causes E or B causes A which causes E

• parthood: A causes E by having B as a part which causes E, or B causes E by having a part A which causes E.

Let’s think a bit about how the chaining and parthood options might avoid physicalism in the case of mental causation and yet allow for closure.

Option I: Nonphysical-physical-physical chaining: A nonphysical event M causes a physical event P which causes a physical event E. This can’t be the whole story for how we respect closure. For by closure, P will need a physical cause P₂, and so it is looking like P is going to be overdetermined, by M and P₂. But that does not follow without further assumptions. For we could have the following scenario:

• E is caused by an infinite chain of physical causes which chain is causally preceded by M, namely: P ← P₂ ← P₃ ← ... ← M, with infinitely many physical events in the “…”.

This scenario requires the possibility of an infinite sequence of causal means, contrary to causal finitism, and hence is unacceptable to me. But those who are less worried about infinite chains of causes should take this option seriously. Note that this option is reminiscent of Kant’s view on which our noumenal selves collectively cause the physical universe as a whole.

Option II: Physical-nonphysical-physical chaining: Here, the physical event P causes E by having a mental event as an intermediate cause. This option exploits a loophole in the closure principle as it is normally formulated: nothing in the closure principle says that the physical cause can’t operate by means of a nonphysical intermediary. Granted, that’s not how we normally think of physical causes as operating. But there is nothing incoherent about the story.

Option III: Physical parts of larger events: A physical event E is caused by a physical event P, and the physical event P is itself a part of a larger event M which is only partly physical. One might object that in this case it’s only P and not the larger event that counts as the cause. But that’s not right. If someone dies in the battle of Borodino, then at least three causes of death can be given: a shot being fired, the battle of Borodino, and the War of 1812. The shot is a part of the battle, and the battle is a part of the war. One particular way to have Option III is this: a quale Q is constituted by two components, a brain state B (say, a state of the visual cortex) and a soul state S of paying attention to the brain system that exhibits B, with B being the causally efficacious part of the Q. So a physical event—say, an agent’s making an exclamation at what they saw—counts as caused by the physical event B and the event Q which is not physical, or at least not completely physical.

One might object, however, that by “nonphysical”, one means entirely nonphysical, so Q’s having a nonphysical part S does not make Q nonphysical. If so, then we have one last option.

Option IV: Some or all physical causes cause their effects by having a nonphysical part that causes the event. That nonphysical part could, for instance, be an Aristotelian accidental or substantial form. Thus, here a physical event E is caused by a physical event by means of its nonphysical part M.

What if one objects that “physical” and “nonphysical” denote things that are purely physical and nonphysical, and neither can have a part that is the other? In that case, we have two difficulties. First, the closure principle is now stronger: it requires that a physical event that has a cause always has a purely physical cause. And we have a serious gap at the end of the argument. From closure at most we can conclude that a physical event doesn’t have a purely nonphysical cause. But what if it has a partly physical and partly nonphysical cause? That would be enough to contradict physicalism.

Physicalism and the progress of science

People sometimes use the progress of science to argue for physicalism about the mind. But it seems to me that Dostoevskii made more progress in understanding the human mind by existential reflection than anybody has by studying the brain directly. More generally, if we want to understand human minds, we should turn to literature and the spiritual masters rather than to neuroscience.

Thus, any argument for physicalism about the mind from the progress of science is seriously flawed. And perhaps we even have some evidence against physicalism. For it is a surprising fact that we learn more about the mind by the methods of the humanities than by study of the brain if the mind is the brain.

Animalist functionalism

The only really plausible hope for a materialist theory of mind is functionalism. But the best theory of our identity, materialist or not, is animalism—we are animals.

Can we fit these two theories together? On its face, I think so. The thing we need to do is to make the functions defining mental life be functions of the animal, not of the brain as such. Here are three approaches:

1. Adopt a van Inwagen style ontology on which organisms exist but brains do not. If brains don’t exist, they don’t have functions.

2. Insist that some of the functions defining mental life are such that they are had by the animal as a whole and not by the brain. Probably the best bet here are the external inputs (senses) and outputs (muscles).

3. Modify functionalism by saying that mental properties are properties of an organism with such-and-such functional roles.

I think option 2 has some special difficulties, in that it is going to be difficult to define “external” in such a way that the brain’s connections to the rest of the body don’t count as external inputs and outputs and yet we allow enough multiple realizability to make very alien intelligent life possible. One way to fix these difficulties with option 2 is to move it closer to option 3 by specifying that the external inputs and outputs must be inputs and outputs of an organism.

Options 1 and 3, as well as option 2 if the above fix is used, have the consequence that strong AI is only possible if it is embedded in a synthetic organism.

All that said, animalist functionalism is in tension with an intuition I have about an odd thought experiment. Imagine that after I got too many x-rays, my kidney mutated to allow me exhibit the kinds of functions that are involved in consciousness through the kidney (if organism-external inputs and outputs are required, we can suppose that the kidney gets some external senses, such as a temperature sense, and some external outputs, maybe by producing radio waves, which help me in some way) in addition to the usual way through the brain, and without any significant interaction with the brain’s computation. So I am now doing sophisticated computation in my kidney of a sort that should yield consciousness. On animalist functionalism, I should now have two streams of consciousness: one because of how I function via the brain and another because of how I function via the mutant kidney. But my intuition is that in fact I would not be conscious via the kidney. If there were two streams of consciousness in this situation (which I am not confident of), only one would be mine. And that doesn’t fit with animalist functionalism (though it fits fine with non-animalist functionalism, as well as with animalist dualism, since the dualist can say that the kidney’s functioning is zombie-like).

Given that functionalism is the only really good hope we have right now for a materialist theory of mind, if my intuition about the mutant kidney is correct, this suggests that animalism provides evidence against materialism.

Physicalism, persons, fission and eliminativism

People are philosophically unhappy about nonlocality in quantum mechanics. It is interesting to me that there is an eerily similar nonlocality on standard psychological theories of personal identity. For on those theories:

1. You survive if your memories survive in one living person.

2. You perish if your memories fission between more than one living person.

Now imagine that your brain is frozen, the data from it is destructively read, and then sent to two different stations, A and B, located in opposite directions five light minutes away from your original brain. At each station, a coin is simultaneously flipped (say, in the rest frame of your original brain). If it’s heads (!), the data is put into a freshly cloned brain in a vat, and if it’s tails, the data is deleted.

On a psychological theory, if both coins land heads you perish by (2). But if exactly one coin lands heads, you survive at that station. So whether you exist at one station depends on what happens simultaneously (according to one frame) at a station ten light minutes away.

Note, however, that this is not explicable via quantum nonlocality, because quantum nonlocality depends on entanglement, and there is no relevant entanglement in this thought experiment. It would be a nonlocality beyond physics.

I think one lesson here is that ostensibly physicalist or physicalist-friendly theories of persons or minds can end up sounding oddly dualist. For if dualism were true, it wouldn’t be utterly surprising if facts about where your soul reappears could have a faster-than-light dependence on far away events, since souls aren’t governed by the laws of physics. Similarly, on functionalism plus psychological theories of personal identity, you could move between radically different physical embodiments or even between a physical embodiment and a nonphysical realization. That, too, sounds rather like what you would expect dualism to say.

If I were a physicalist, I would perhaps be inclined to be drawn by these observations towards eliminativism about persons. For these observations suggest that even physicalist pictures of the person may be too deeply influenced by the dualist roots of philosophical and theological reflection on personhood. If these roots are seen as intellectually corrupt by the physicalist, then it should be somewhat attractive to deny the existence of persons.

Distancing oneself from one's brain

It can be quite useful for someone suffering from a variety of brain conditions, such as obsessive compulsive disorder, to deliberately distance themselves from their brain’s unfortunate doings, by saying to themselves things like: “That’s not me, just my brain.”

If physicalism is true, then brains are either identical with us or at least are the core of who we are. But “That’s not me, just me” is a contradiction while “That’s not me, just the core of my being” isn’t much of a distancing. A similar issue arises in second and third person contexts: if physicalism is true, one must admit brain problems to be grounded in that which is at the core of the other’s being.

The dualist, on the other hand, can pull off the distancing much more easily: “That’s not my soul, just my brain” makes perfect sense. An impairment in the brain is just an impairment of a body part, albeit one of the most important ones.

Of course, that something is a helpful way of thinking does not prove that it’s true. But it is an insight from the beginnings of Western philosophy that truth is generally better for us than falsehood, and so that something is a helpful way of thinking is some evidence that it is true. We may, thus, have some evidence for dualism here.

Fading knowledge of qualia

I am one of those people who do not have vivid memories of pains.

Suppose I stub my toe. While the toe is hurting, I know what the toe’s hurting feels like. After it stops hurting, for a while I still know what that felt like. But I know it less and less well as my memory fades, until eventually I know very little how it felt like. The whole process might take only a few minutes.

Thus, that mysterious “knowing what it’s like” involving qualia is something that comes with a parameter that varies as to how well you know it.

This should worry physicalists. Thin physicalists should worry because it doesn’t seem that the fading corresponds to any knowledge of the underlying physical reality. Thick physicalists who think that Mary just acquires a new recognitional concept when she sees red should worry, because it does not seem that there is any gradual loss of a concept. I continue to have the same “that experience” concept (the demonstrative “that” points to the same past experience, and does so in a first-personal way) and the recognitional abilities it enables (I can tell if another pain is like that one or not), even as my knowledge of what “that experience” is like fades.

It’s also not completely clear what a dualist should say about the fading of the knowledge. Normally, when knowledge fades, what happens is either that we lose details (as when I forget much of what I once learned in school about the Metis uprising), or we find the dispositional knowledge harder to make occurrent. But the fading is neither of these. Maybe what is happening is that our present knowledge becomes a less good representation of what it is the knowledge of.

God's vision of reality

Consider the simple theory of visual sensation on which for me to have a visual sensation as of y is for x to stand in a “vision relation” to y, with the relation being external to x so that x is no different intrinsically when x has a visual sensation as of a red cube and when x does not.

We know that this simple theory is false of us for the obvious reason that we suffer from visual hallucinations or illusions: there are cases where we have a visual sensation as of a red cube in the absence of a red cube. Our best explanation of visual misperception is that visual sensation is mediated by an internal state of ours that can occur in the absence of the apparently visually sensed object. Thus, we have internal modifications—accidents—of visual perception.

But now consider what I think of as the biggest objection to the doctrine of divine simplicity: God’s knowledge of contingent facts. This objection holds that God must be internally different in worlds where what he knows is different, or at least sufficiently different. This objection is based on the intuition that knowledge is written into the knower, that it is an intrinsic qualification of the knower.

Let’s, however, think what a perfect knower’s knowledge would be like. My knowledge divides into the dispositional and the occurrent: I dispositionally know my multiplication table, but at most one fact from that table is occurrent at any given time. It is clear that having merely dispositional knowledge is not the perfection of knowledge. A perfect knower would know all reality occurrently at once. Moreover, my knowledge varies in vividness. Some things, like perhaps the fundamental theorem of algebra, I know “theoretically” (in the modern sense of the word, not the etymological one) and “discursively”, and some facts—such as my visual knowledge of the screen in front of me—are vividly present to my mind. The vivid knowledge is more perfect, so we would expect a perfect knower to know all reality occurrently at once in the liveliest and most vivid way, more like in a vision of reality than in a discursive mental representation.

Let’s go back to the simple theory of visual sensation. Our reason for rejecting that theory in our own case was that it did not accord with the fact that humans are subject to visual misperception. But suppose that we never misperceived. Then we could easily believe the simple theory, at least until we learned a bit more about the contingent causal processes behind our visual processing.

Thus, the reason for rejecting the simple theory in our case was our imperfection. But this leaves open the possibility that something like the simple theory could hold for the vision-like knowledge of reality that a perfect knower would have. Such a knower might not have any internal state “mirroring” reality, but might simply have reality related to it in a relation of being-known which is external on the knower’s side. In the case of a perfect knower, we have no need to account for a possibility of misperception. Thus, the perfect knower may know me simply by having me be related to it by a relation of being-known, a relation external to the knower.

Objection 1: How do we account for God’s knowledge of absences, such as his knowledge that there are no unicorns? This cannot be accounted for by a relation between God and the absence of unicorns, since there is no such thing as the absence of unicorns.

Response: In the case of an imperfect knower, absence of knowledge is not knowledge of absence, since there is always the possibility of mere ignorance. But perhaps in the case of a perfect knower, knowledge of absence is constituted by absence of knowledge.

Objection 2: This account makes the perfect knower’s “knowledge” too different from ours for us to use the same word “knowledge” for both.

Response 1: We have good reason to think that all words applied to us and the perfect being to be applied merely analogously. A perfect being would be radically different from us.

Response 2: While the simple theory is false of us, given dualism we may have a somewhat more complex theory that is not so different from what I said about God. We have significant empirical reason to think that the brain is modified by our visual experiences, and that our visual experience is in some way determined by an internal state of the brain. However, if we are dualists, we will not think that the internal state of the brain is sufficient to produce a visual experience. There could be zombies with brains in the same state that we are in when we are seeing a red cube, but who do not see.

We can now give two different dualist theories about how I come to see a red cube. Both theories suppose an internal red-cube-mirroring state r_b of my brain. On the causal theory, the state r_b then causes an internal state r_s of the soul (=mind) which mirrors the relevant features of r_b, and I have a red-cube experience precisely in virtue of my soul hosting r_s. But the causal theory is not the only option for the dualist. There is also a relational theory, on which my red-cube experience is constituted by my soul’s standing in an external relation to the brain state r_b.

The two theories yield different predictions as to possibilities. On the causal theory, it is possible for me to have a red-cube experience in a world where God and my soul (and my soul’s states and me-constituted-by-my-soul) are all that exists—all that’s needed is for God to miraculously cause r_s in my soul in the absence of r_b. On the relational theory, on the other hand, I can only have a red-cube experience when my soul stands in a certain external relation to a brain state, and in that God-and-my-soul world, there are no brain states.

The causal theory of our visual perception is indeed very different from the external-relation theory of divine knowledge. The relational theory, however, is more analogous. The main difference is that our visual experiences come not from our mind’s direct relation to the external world, but from our mind’s (=soul’s) direct relation to a representing brain state. And that is very much a difference we would expect given our imperfection and God’s perfection: we would expect a perfect knower’s knowledge to be unmediated.

We have reason independent of divine simplicity not to opt for the causal theory in the case of God. First, on the causal theory, we seem to have great power over God: every movement of ours causes an effect in God. That seems to violate divine aseity. Second, the causal theory in the case of God seems to lead to a nasty infinite causal chain: if God’s vision-like knowledge of y is caused by y, then we would expect that God’s knowledge of his knowledge of y is caused by his knowledge of y, which leads to an infinite causal chain. Moreover, God would know every item in this infinite sequence, which leads to a second causal chain (God’s knowledge of God’s knowledge of … the first chain). This would violate causal finitism, besides seeming simply wrong.

Do we have independent reason to opt for the causal over the relational theory in our case, or perhaps the other way around? I don’t know. Until today, I assumed the causal theory to be correct. But the relational theory makes for a more intimate connection between the soul and brain, and this is somehow appealing.

A weird escape from the Knowledge Argument?

Take Jackson’s story about Mary who grows up in a black-and-white room, but learns all the science there is, including the physics and neuroscience of color perception. One day she sees a red tomato. The point of the story is that in seeing the red tomato, she has learned something, even though she already knew all the science, so the science is not all the truth there is, and hence physicalism is false.

This story is generally told in the context of the philosophy of mind, and the conclusion drawn is that physicalism about the mind is false. But that does not actually follow without further assumptions. As far as the argument goes, perhaps Mary didn’t learn anything about herself that she didn’t already know, but has learned something about tomatoes, and so we should conclude that physicalism about tomatoes is false.

Let’s explore that possibility and see if this hole in the argument can be filled. I will assume (though I am suspicious of it) that indeed the kind of knowledge gap that Jackson identifies would imply an ontological gap. Thus, I will accept that Mary has learned what it is like to see the red of a tomato, and that the knowledge of what it is like to see the red of a tomato is not a knowledge of physical fact.

Can one say this and yet accept physicalism about the mind? The one story I can think of that would allow that is a version of Dretske’s qualia externalism: just as most of us think that the content of our thoughts is partly constituted by external facts, so too the qualitative character of our perceptions is partly constituted by external facts. But in fact for the story to work as a way of blocking the inference to non-physicalism about the mind, the qualia (understood as that in the experience that cannot be known by Mary by mere book-learning) would need to be entirely constituted by extra-mental facts.

I think this kind of qualia externalism is not all that crazy. Divine simplicity requires that all of God’s knowledge of contingent fact be partly constituted by states of affairs outside God. But it is plausible that God has something like contingent qualia: that were God to contemplate a world with unicorns, it would “look” different to God than our world. On divine simplicity, we would need to have externalism about these qualia.

That said, the above affords no escape from literal anti-physicalism about the mind. If physicalism about the mind is true, then minds are brains. But if we accept that colored things have a nonphysical component that partly constitutes the perceiver’s qualia, then brains have a nonphysical component, since brains are colored things, namely pinkish (here is a description of their color in vivo, though I cannot vouch for its accuracy).

Maybe, though, this misses the point in the debate. The typical dualist thinks that there is something different about minds and other physical things. If it turns out that minds are just brains, but that they are not physical simply because their pinkness is not entirely a physical property, that’s really not what the dualist was after. The dualist’s intuition is that there is something radically different in the human brain, something not found in a pink sunset cloud (unless it turns out that panpsychism is true!).

Maybe this works to save a more robust dualist conclusion: Plausibly, one doesn’t need a tomato to make Mary have a red sensation. All one needs is to do is to induce in her brain’s visual centers the same electrical activity as normally would result from her seeing a red tomato. And the equipment inducing that electrical activity need not be red at all.

Aquinas and Descartes on substance dualism

Roughly, Aquinas thinks of a substance as something that:

1. is existentially independent of other things, and

2. is complete in its nature.

There is a fair amount of work needed to spell out the details of 1 and 2, and that goes beyond my exegetical capacities. But my interest is in structural points. Things that satisfy (1), Aquinas calls “subsistent beings”. Thus, all substances are subsistent beings, but the converse is not true, because Aquinas thinks the rational soul is a subsistent being and not a substance.

Descartes, on the other hand, understands substance solely in terms of (1).

Now, historically, it seems to be Descartes and not Thomas who set the agenda for discussions of the view called “substance dualism”. Thus, it seems more accurate to think of substance dualists as holding to a duality of substance in Descartes’ sense of substance than in Aquinas’.

But if we translate this to Thomistic vocabulary, then it seems we get:

3. A “substance dualist” in the modern sense of the term is someone who thinks there are two subsistent beings in the human being.

And now it looks like Aquinas himself is a substance dualist in this sense. For Aquinas thinks that there are two subsistent beings in Socrates: one of them is Socrates (who is a substance in the Thomistic sense of the word) and the other is Socrates’ soul (which is a merely subsistent being). To make it sound even more like substance dualism, note that Thomas thinks that Socrates is an animal and animals are bodies (as I have learned from Christopher Tomaszewski, there are two senses of body: one is for the material substance as a whole and the other is for the matter; it is body in the sense of the material substance that Socrates is, not body in the sense of matter). Thus, one of these subsistent beings or substances-in-the-Cartesian-sense is a body and the other is a soul, just as on standard Cartesian substance dualism.

But of course there are glaring difference between Aquinas’ dualism and typical modern substance dualisms. First, and most glaringly, one of the two subsistent beings or Cartesian substances on Aquinas’s view is a part of the other: the soul is a part of the human substance. On all the modern substance dualisms I know of, neither substance is a part of the other. Second, of the two subsistent beings or Cartesian substances, it is the body (i.e., the material substance) that Aquinas identifies Socrates with. Aquinas is explicit that we are not souls. Third, for Aquinas the body depends for its existence on the soul—when the soul departs from the body, the body (as body, though perhaps not as matter) perishes (while on the other hand, the soul depends on the matter for its identity).

Now, let’s move to Descartes. Descartes’ substance dualism is widely criticized by Thomists. But when Thomists criticize Descartes for holding to a duality of substances, there is a danger that they are understanding substance in the Thomistic sense. For, as we saw, if we understand substance in the Cartesian sense, then Aquinas himself believes in a duality of substances (but with important structural differences). Does Descartes think there is a duality of substances in the Thomistic sense? That is not clear to me, and may depend on fine details of exactly how the completeness in nature (condition (2) above) is understood. It seems at least in principle open to Descartes to think that the soul is incomplete in its nature without the body or that the body is incomplete in its nature without the soul (the pineal gland absent the soul sure sounds incomplete) or that each is incomplete without the other.

So, here is where we are at this point: When discussing Aquinas, Descartes and substance dualism we need to be very careful whether we understand substance in the Thomistic or the Cartesian sense. If we take the Cartesian sense, both thinkers are substance dualists. If we take the Thomistic sense, Aquinas clearly is not, but it is also not clear that Descartes is. There are really important and obvious structural differences between Thomas and Descartes here, but they should not be seen as differences in the number of substances.

And here is a final exegetical remark about Aquinas. Aquinas’ account of the human soul seems carefully engineered to make the soul be the sort of thing—namely, a subsistent being—that can non-miraculously survive in the absence of the substance—the human being—that it is normally a part of. This makes it exegetically probable that Aquinas believed that the soul does in fact survive in the absence of the human being after death. And thus we have some indirect evidence that, in contemporary terminology, Aquinas is a corruptionist: that he thinks we do not survive death though our souls do (but we come back into existence at the resurrection). For if he weren’t a corruptionist, his ontology of the soul would be needlessly complex, since the soul would not need to survive without a human being if the human being survived death.

And indeed, I think Aquinas’s ontology is needlessly complex. It is simpler to have the soul not be a subsistent being. This makes the soul incapable of surviving death in the absence of the human being. And that makes for a better view of the afterlife—the human being survives the loss of the matter, and the soul survives but only as part of the human being.

Substance dualism and relativity theory

Here is an interesting argument against substance dualism:

1. Something only exists simultaneously with my body when it exists in space.

2. My mind now exists simultaneously with my body.

3. So, my mind now exists in space.

4. Anything in space is material.

5. So, my mind is material.

If this argument is right, then there is at least one important respect in which property dualism and physicalism are better off than substance dualism.

The reasoning behind (1) is Relativity Theory: the temporal sequence that bodies are in cannot be separated from space, forming an indissoluble unity with it, namely spacetime.

One way out of the argument is to deny (4). Perhaps the mind is immaterial but in space in a way derivative from the body’s being in space and the mind’s intimate connection with the body. On this view, the mind’s being in time would seem to have to be derivative from the body’s being in time. This does not seem appealing to me: the mind’s spatiality could be derivative from the spatiality of something connected with the mind, but that the mind’s temporality would be derivative from the temporality of something connected with the mind seems implausible. Temporality seems too much a fundamental feature of our minds.

However, there is a way to resolve this difficulty, by saying that the mind has two temporalities. It has a fundamental temporality of its own—what I have elsewhere called “internal time”—and it has a derivative temporality from its connection with spatiotemporal entities, including the body. When I say that my mind is fundamentally temporal, that refers to the mind’s internal time. When we say that my mind is derivatively temporal, that refers to my mind’s external time.

If this is right, then we have yet another reason for substance dualists to adopt an internal/external time distinction. If this were the only reason, then the need for the distinction would be evidence against substance dualism. But I think the distinction can do a lot of other work for us.

Nomic functionalism

Functionalism says that of metaphysical necessity, whenever x has the same functional state as a system y with internal mental state M, then x has M as well.

What exactly counts as an internal mental state is not clear, but it excludes states like thinking about water for which plausibly semantic externalism is true and it includes conscious states like having a pain or seeing blue. I will assume that functional states are so understood that if a system x has functional state S, then a sufficiently good computer simulation of x has S as well.

A weaker view is nomic functionalism according to which for every internal mental state M (at least of a sort that humans have), there is a law of nature that says that everything that has functional state S has internal mental state M.

A typical nomic functionalist admits that it is metaphysically possible to have S without M, but thinks that the laws of nature necessitate M given S.

I am a dualist. As a result, I think functionalism is false. But I still wonder about nomic functionalism, often in connection with this intuition:

1. Computers can be conscious if and only if functionalism or nomic functionalism is true.

Here’s the quick argument: If functionalism or nomic functionalism is true, then a computer simulation of a conscious thing would be conscious, so computers can be conscious. Conversely, if both computers and humans can be conscious, then the best explanation of this possibility would be given by functionalism or nomic functionalism.

I now think that nomic functionalism is not all that plausible. The reason for this is the intuition that a computer simulation of a cause normally only produces a computer simulation of the effect rather than the effect itself. Let me try to be more rigorous, though.

First, let’s continue from (1):

2. Dualism is true.

3. If dualism is true, functionalism is fale.

4. Nomic functionalism is false.

5. Therefore, neither functionalism nor nomic functionalism is true. (2–4)

6. So, computers cannot be conscious. (1, 5)

And that’s really nice: the ethical worries about whether AI research will hurt or enslave inorganic persons disappear.

The premise I am least confident about in the above argument is (4). Nomic functionalism seems like a serious dualist option. However, I now think there is good inductive reason to doubt nomic functionalism.

7. No known law of nature makes functional states imply non-functional states.

8. So, no law of nature makes functional states imply non-functional states. (Inductively from 7)

9. If functionalism is false, mental states are not functional states.

10. So, mental states are not functional states. (2, 3, 9)

11. So, no law of nature makes functional states imply mental states. (8 and 10)

12. So, nomic functionalism is false. (11 and definition)

Regarding (7), if a law of nature made functional states imply non-functional states, that would mean that we have multiple realizability on the left side of the law but lacked multiple realizability on the right side. It would mean that any accurate computer simulation of a system with the given functional state would exhibit the particular non-functional state. This would be like a case where a computer simulation of water being heated were to have to result in actual water boiling.

I think the most promising potential counterexamples to (7) are thermodynamic laws that can be multiply realized. However, I think tht in those cases, the implied states are typically also multiply realizable.

A variant of the above argument replaces “law” with “fundamental law”, and uses the intuition that if dualism is true, then nomic functionalism would have to have fundamental laws that relate functional states to mental states.