Is physical stuff all there is? If you ask a philosopher that question, it can lead to a discussion that covers things ranging from consciousness to 20th-century physics to whether mathematical concepts are real. That’s what happened when I discussed the subject with Gideon Rosen, professor of philosophy at Princeton and co-author of The Norton Introduction to Philosophy. Gideon is also a friend of mine—which made the conversation even more fun for me than it would have been otherwise.
ROBERT WRIGHT: I've been trying to get you to be on this show for years. You've resisted, but the reason I've wanted you to is that whenever I have a question about philosophy, you provide a very efficient overview of the whole context of my question. You don't always provide a definitive answer, but that's in the nature of philosophy.
GIDEON ROSEN: It is. It's a shame that it's in the nature of philosophy.
It would be nice if we could wheel out definitive answers to these questions and it's a bit of a mystery why we can't, since everybody else manages to provide the occasional definitive answer. We don't. It's a drag, but we do our best.
Do you think it's a mystery? Or do you think it's kind of clear, given the nature of the questions you address, why it would be the case that you don't come up with the same kinds of answers that mathematicians and scientists do?
Yeah, there are some obvious differences that explain why we don't do it the way they do—but, if the questions make sense, if the questions are clear, then they have answers. We don't have a clear sense of why it is that we can't nail them down.
It's not as if we're floundering around. Philosophy produces plenty of opinion, plenty of conviction—even plenty of justified conviction, in the sense that people have arguments for their views and arguments that some people find persuasive. But we don't get as much consensus on the hard questions, even given the arguments we've got, and that's a little mystifying...
I don’t know, I want to give you more credit. I think you're just tackling the hard questions…
I wanted to start out on the question of materialism or, as I guess it's more or less interchangeably called, physicalism. Let me give you the crude definition and then you can correct me. It's...the idea that everything that there is is physical, it's material stuff…
People of a religious or spiritual persuasion…often think of the worldview of materialism as being antagonistic to their worldview, and a lot of people see it as maybe depressing...And a question arises: what is the status of the worldview of materialism within philosophy?..
Why don't you start out by telling me what you think of the words “physicalism” and “materialism” as meaning, and then we can get into the status of the idea.
Hardheaded philosophers who are impressed by the scientific worldview used to call themselves materialists. That's because they thought that what science had shown is that, at the fundamental level, absolutely everything is made of matter, where “matter” is something that we have a pretty good ordinary idea of.
We know what rocks are like. We know what clay is like. That stuff takes up space. It's spread out, it has geometrical properties. It's impenetrable, and so on. The rocks and the clay of ordinary experience may have other features too, like color and smell, which are a sort of subjective contribution on our part.
But you abstract from that, and what's left is this pretty clear conception of material stuff with geometrical properties that takes up space and has properties like mass, and so on. And for a long time, physics seemed to be saying everything at the fundamental level is like that. It's just geometrical space-occupying stuff, maybe spread out in some empty space.
That was materialism. And that was the received view of what physics, or physics and chemistry, had shared about nature for a long time.
And then that view started to fall apart in the middle of the 19th century, because what physics then seemed to be saying was, it's not all like that. There is, for example, the electromagnetic field.
The electromagnetic field is not like a rock. It's spread out. It's everywhere. It's thin. It's filmy. The features that scientists attribute to it aren't features like [knocks on the table] bang-on-the- table impenetrability. So physics is telling you that that's what nature is like at the most fundamental level. It's not telling you that nature is material at the fundamental level. But it is telling you that nature is physical at the fundamental level.
But then what does the term mean at that point?
It's pretty hazy. It's partly negative. They are still telling you that, at the fundamental level, real things, including the electromagnetic field or the more complicated fields that you get in modern physics, don't think—that there is no mind or spirit or soul or anything like that at the fundamental level—that there is no value or meaning, or anything like that at the fundamental level. There is no consciousness or anything like that at the fundamental level. The electromagnetic field doesn't have those features.
That's the negative conception of what the physical would be.
At this point, what we mean by “fundamental” comes into question, of course.
But before we get to that (assuming we ever do) let me just say that one thing I would have retreated to, if I were trying to defend materialism in the light of these developments in physics, is I would say: "What it really means is that the world is a regular, predictable place. And these concepts, like a field and so on, they're kind of these aspects of reality that permit us to make the predictions, and in that sense affirm the predictability. They're part of the gears of the universe. And it's by understanding them that we are able to predict it."
So I might've said "what we really mean is regularity: no spooky interventions that are, in principle, unpredictable." Is that not a satisfactory retreat?
I think it's a little bit less, and a little bit more than what physicalism is supposed to be.
For a time, around the beginning of the 20th century, philosophers and some scientists played with the idea that, at the fundamental level, again, what you have instead of material objects spread out in space, is a set of mental qualities spread out in a mental space. This view was called a phenomenalism.
The world is really an array of colored shapes, like the colored shapes you experience when you open your eyes and have a visual experience, and not a bunch of invisible particles with geometrical or mathematical qualities.
So then color is just not a takeaway of ours from the material world, it's actually there.
That's right. So this was a view that the objects of immediate experience, which were sometimes called sense data, are real things that exist independently of our awareness of them. They occasionally come into view, but that's what reality is like at the fundamental level, and the world of physics is a kind of superstructure that we derive from that.
These philosophers didn't deny that, at the fundamental level, nature was regular. They thought there would be laws governing the evolution of the sense data, or the phenomenal qualities. So they believed in regularity at the fundamental level, but they weren't physicalists.
And what is the connection of these people to, broadly speaking, idealism, as most famously embodied, I guess, in Berkeley? Are they really doing a fundamental inversion and saying, well, what's most fundamental is actually consciousness, subjective experience, and what we think of as the material world is a construct, or what?
Yeah, so this is a subtle point.
These guys—I'm thinking of Bertrand Russell at certain points, and also William James, who converged on similar ideas around the same time—unlike the idealists like Berkeley and maybe Hume, they did not think that the objects we’re aware of in sensory experience—the colored bits and pieces that you entertain—depend on the mind. They thought that they were there anyway, and consciousness is a relation to them—you become aware of them—but consciousness doesn't create them, they're not creatures of consciousness.
So they thought that the world was independent of consciousness, but was sort of fit to be revealed to consciousness as it actually is. So when you open your eyes and see the world, you don't see some image or some illusion or some misleading, mentally constructed picture of reality; you see some fragment of reality, the array of colored shapes that you're aware of.
So those guys weren't physicalists. They weren't idealists, either. They sometimes called themselves “neutral monists.” There was only one fundamental stuff; it was the stuff that we are immediately aware of in experience, but it wasn't [stuff] in the physical, chemist's sense.
It's almost hard for me to imagine what they're saying.
I mean, yeah, the color is inherent in the apple in the sense that it has the physical properties such that when light bounces off of it and interacts with the parts of my eyeball, I have this conscious experience.
They're clearly not just saying that. Right?
No, they're not just saying that. They're saying that, although that story of color perception is certainly correct as a matter of psychophysics, as a matter of metaphysics that process that we just alluded to is a process, by means of which some parts of the phenomenal world become aware of other parts of the phenomenal world.
So you—or your brain, or whatever it is—considered at the most fundamental...This is a crazy view, I should say. Some people, I guess, take this seriously now...
Yeah, I'm surprised to hear that Russell did. I had always thought of him as a pretty concrete, sober, meat-and-potatoes, conservative thinker, but maybe I'm wrong.
Russell was an extremely ambitious metaphysician. He was responsible—in large part, not in whole part—for the intense respect, with which mathematical physics and so on is regarded by philosophers. But he himself was totally open to the idea that, at the fundamental level, reality was so freaking weird that physics wasn't going to disclose it to us.
That seems possible to me. It seems almost likely, given the process that created us, natural selection.
So there's that, but then that kind of passed away. I'm not sure I totally get it, but it's not idealism. It's not the idea that, in some sense, consciousness is more fundamental than the physical world.
Right. You could put it like this: the objects of consciousness are more fundamental than the physical world, but not consciousness of them. But we shouldn't give this view more credit than it deserves.
Challenges: physics, math, morality
Physics makes what you might call naive or simple physicalism increasingly problematic. At some point it threatens even the version I threw out—that you use these people to question the idea that we just mean regularity by physicalism. With quantum physics, we get to the idea that...there are truly unpredictable things in the universe. Things happen in the universe, for which there is no cause in the universe; there's no predicting them. In the long run, the odds even out—the number of heads equals the number of tails, so to speak—but still, it's not regular in the conventional sense.
Is quantum physics thought of as posing a distinctive and new kind of danger to the worldview of materialism?
I wouldn't have thought that the indeterminism that may be part of quantum physics is a threat to materialism. It should always have been an open question, how regular or law-governed the material world was.
It was a sort of a real surprise of classical physics that it looked like the sprawling complexity, the incredible chaos and hodgepodge that we observe in physical nature is in fact governed by strict deterministic laws. That's how it seemed to physics. But that was a shocking possibility.
As that began to fall apart with 20th century physics, a materialist or a physicalist should have said "Ah! So it turns out that the physical world, which is the only real world, is a little more chaotic or a little more indeterministic than we had suspected, but the metaphysical view is still fine. It's just the laws have a different kind of probabilistic character.”
Of course, it was true that, in the early days of quantum mechanics, people thought that, for other reasons, there was some tension between physics and physicalism.
And they don't think that anymore?
Well, they thought the consciousness had to play a special role in the dynamics of quantum mechanics.
You know, the cat's only determinately alive.
The observation forces reality into definite existence.
Right. So that was a view that was apparently held—though I guess it's a controverted historical question whether the architects of quantum mechanics really held it—but anyway, that was a view that seemed to emerge from a mid-20th century physics that would have elevated consciousness to this very special role in the cosmos.
I don't think that view is especially current these days.
Yeah. In physics, I don't think that many people hold that the actual conscious observation of the measurement, as opposed to the physical measuring apparatus, brings resolution.
So is the current status that it's harder to defend materialism than it was a hundred years ago, or harder to even say what it means, or what? And what is the landscape of opinion within philosophy in terms of what percentage of philosophers would say, "yes, I'm a proud materialist"?
So there is a lingering, slightly embarrassing question about how to formulate physicalism. If you're going to sign onto it, you should have a clear statement of it.
The thing I said before—”at the fundamental level, nature is consciousness-free, mind-free, value-free”—that's kind of negative. It doesn't bring out what all of the physical stuff as physical stuff is supposed to have in common. What do the particles of 17th century atomism and the quantum fields of 21st century physics have in common that makes them genuinely physical entities? It's a little hard to say.
So there's this embarrassment about what exactly we're signing onto when we say "at the fundamental level, everything is like that." But I think the main sticking point isn't this definitional thing...
It's that there seem to be aspects of reality that can't be fit into a physicalist picture of the world.
Just to mention one that's not so central to the debate: I'm not a physicalist, because I think that mathematical objects are real. That is, I think that the subject matter of pure mathematics, the numbers and functions and sets and algebras and spaces with which pure mathematics is concerned—I don't think those are parts of the natural world at all. I don't think they're spread out in space. I don't think that they have properties like mass, or electric charge, or anything like that. But mathematics is a body of knowledge, so it must have a subject matter, and its subject matter must exist. So, because that subject matter is, as far as I'm concerned, obviously not part of the physical world, I wouldn't call myself a physicalist. I believe in mathematical entities too.
That's not the sexiest reason for rejecting physicalism...
No, I think there are people who will be disappointed if that's the only reason. Although it's interesting to me that you see those two as in tension.
I mean, I know there's this old debate about whether, in some platonic sense, mathematical truths are out there. I've never been able to totally wrap my mind around the question.
It's also kind of related to something you said earlier and just kind of repeated, which is that part of the idea of physicalism is that the fundamental stuff out there is just physical—there's no value out there, right?
I mean, here we're talking about the concept of moral realism: do moral laws and truths have kind of some kind of reality? I would've thought that you can defend a version of moral realism without asserting that moral truths, like, occupy space, as if they're competing with atoms, right?
Do you see the issue I'm raising with respect to both the math question and the moral realism question?
Yeah, though I do think they're slightly different.
The math question is the question about things that…If you think about it, nobody ever thought that those things were parts of the natural world. If you believe in them at all, they were, you know, a separate sort of category and so on. So when people are arguing about physicalism, that stuff's not what's on their mind.
Physicalism, you might think, is a view about what nature is like: what's there in the natural world, the world of space and time. Is it all physical? That stuff about numbers, it's not a direct address to that question.
The moral realism question, on the other hand, is.
Picture some morally hideous human action. You've got some human beings doing painful medical experiments on cats for the cosmetic industry. Just picture it.
You can give a scientific description of what they're doing: how their bodies are moving, what's going on in the bodies and brains of the animals they're interacting with. And then there is the fact that what they're doing is wrong, that there is a moral standard that they are violating in doing this.
That claim attributes a further property to that human action. In addition to the properties that a psychologist or a physiologist might take an interest in, the action has a moral property, the property of being wrong.
If that property is fundamental—if we cannot somehow reduce the wrongness of the act to other more basic features about what it causes and what its effects are and so on—then there's a feature of a natural object, a human action, that isn't a physical feature: moral wrongness.
And if that's true, then physicalism is false. Because physical entities, natural entities, have features that physics doesn't capture.
If it's inherent in physical phenomena that they're right or wrong, then physicalism is inadequate...because “inherent in” means “it's part of them,” and physicalism doesn't account for any non-physical part.
Exactly. So, if the wrongness is irreducible, then, in a certain sense, physicalism is false. Because there's more to the natural world of events unfolding in space and time than a morally neutral physical theory like quantum mechanics or anything else that gets served up in the physics department, the chemistry department, or the biology department would describe.
I'm not sure I'm willing to buy that, but I guess, if I were going to try to articulate an objection—and this would maybe embody the math question as well—it would just be: leave aside math, leave aside morality, when we just describe what's going on in the physical world, obviously the description itself is not part of the physical world.
If that's going to be sufficient to dismiss physicalism, then physicalism should've surrendered a long time ago, because obviously we make statements about the world, and those statements are not part of the world—they’re not part of the physical system we're talking about, right?
So it seems to me that math and moral assertion and sheer description are all things that exist by virtue of our being observers and articulators.
But the physicalist will say: the descriptions you produce—they could be marks on paper, they could be sounds in the air, or they could be representations in your brain—they are part of the physical world. And it's true that fundamental physics doesn't talk about things like that, but linguistics does, and audiology does, and eventually all of those sciences are just capturing complex features of the physical world.
So it's not just that descriptions emerge that's a challenge to physicalism; it's when you get features of the world that really can't be, as far as we can tell, reducible to—or fully captured in terms of—the kinds of things that do show up in physics and chemistry.
It's unclear whether there's anything in the theory of representation, linguistics, cognitive psychology, and so on that’s problematic there.
Certainly, one distinction is that, if I describe the physical world, the truth or falseness of my description should in principle be determinable, unambiguously, by examining the physical world. We wouldn't say the same thing about moral claims.
But you know, math is interesting because all of its application is to the physical world. Certainly its roots, historically, arise from observing the physical world and trying to figure stuff out. So what is it that makes you think that there's some part of math that's out there beyond the physical world?
Two rather different kinds of things.
One is that it's true that, for example, geometry was originally the study of physical space or objects in physical space, and there wasn't much of a difference between geometry and the physics that employs the geometry—so, if you would ask Archimedes what he did, it would have been not so different from what the geometers were doing.
But, with the discovery of non-Euclidean geometry, it became clear that the study of mathematical geometry is one thing, and the study of physical geometry is another. So Euclidean geometry is still good mathematics, even if the physical space we inhabit is not Euclidean.
At that point, mathematics becomes no longer the study of physical structures. It's the study of pure mathematical structures, which may sometimes be more or less perfectly realized in the physical world.
And the other thing is that mathematics is thoroughly, completely, up to its ears committed to the infinite. The structures that are of most mathematical interest are wildly infinite. Huge, huge by comparison with anything that could fit in ordinary nature, as far as we know.
If you think that the infinite is real, then you think that what we study when we study the infinite probably isn't anywhere instantiated in physical nature.
Accounting for consciousness
So what about—as a challenge to physicalism, I mean—just the very existence (if you think it exists) of consciousness?
I think almost all of us believe that there is such a thing as subjective experience. It's like something to be us. Therefore, we have consciousness.
"Consciousness" and "subjective experience" are nouns, right? It's not the same as…when you see a person running, how is the “runningness” different from consciousness? Well, I think it actually is, dammit, for reasons I'm not sure I'm prepared to articulate…
But I assume a lot of philosophers would say that yes, consciousness, subjective experience, deserve to be nouns in a deep and significant sense that arguably could be a challenge to physicalism.
Yeah. I think the challenge arises even if you don't lean on the idea that consciousness is an abstract noun.
But before we start reifying or making a thing out of consciousness itself, as if consciousness were like milk or styrofoam—this sort of substance that we somehow have to account for—just start with the idea that people are conscious.
When I say that you are conscious—that you have a certain conscious experience, or that it feels a certain way at a certain time to be you—I'm not reifying consciousness as stuff when I say that, but I am attributing a feature to you: the feature that you possess when you are tasting pineapple, say, for the first time. At that moment, you're the subject of an event, an episode, the experience itself.
That experience may in some sense be constituted by an event in your brain, an event that a neuroscientist could study, but it looks like, when you have that experience, you are aware of other features of it, its distinctive feel.
Those features need to be located somehow in the natural physical world if physicalism is going to be true. And the problem of consciousness—what Chalmers calls the "hard problem of consciousness”—is the problem of finding the qualitative features of experiences in the physical world.
So, if there's this identical version of me—physically identical, and behaves as I do—but it's not like anything to be it, [then] it lacks a feature that I have—and that's the source of the challenge, because you can't locate the feature I have in physical space.
Right. So those guys, those things that are allegedly exactly like you in every physical respect, but don't have conscious experience at all—”philosophical zombies,” as they're called—if those guys are possible, physicalism is false. Because you have a property that your physical duplicate wouldn't have, so there must be some property that isn't a physical property.
See, here's the sense in which I think scientific materialism can't win. ...[Because, if the philosophical zombies] are not possible, it seems to me scientific materialism is in trouble in another sense…
Let's start at the way we think of evolution, which I think is basically true. The account is: there's these physical molecules that start replicating; the ones who do the best job are favored; so it turns out that building cell walls is favored by natural selection; you get genes for that, blah, blah, blah. Ultimately, you get these super complex creatures, and, according to the fundamental theory of natural selection, you can account for all of the behavior in physical terms. That’s just, like, has to be the case.
And to bring that up to the present world, that means that—and most behavioral scientists would think this is true—that when I get my hand too close to a fire and retract it, you can have a strictly physical account. All this evolved equipment—there are sensors on my fingers, physical information gets sent up my arm, and so on—in theory, the machinery should work without me feeling the pain, without it being like anything to be me.
And if that's not the case, if it's not this physical system, then somewhere in the account I just gave you, we have a serious problem. Right?
So it seems to me that scientific materialism is in trouble either way.
The only hope for the materialists (and I don't think it's an entirely vain hope) is to find something in that causal sequence in your brain—not some micro-event, but some largish sort of event—that plays a role in between the activation of your sensory neurons in your finger when you get too close to the flame, and the activation of your motor neurons when you pull your hand out of it.
Somewhere in between, something happens in your brain, that also happens when you get stuck with a pin, and that also happens when you stub your toe, and that also happens when you get a headache.
If there's a physical thing—something that could in principle be identified in neuro-physiological or in structural terms—that is plausibly identified with the pain; if the physicalist can say, "I'm not denying the existence of pain—I've found it. I have told you what feature of physical reality pain is: it's this one”—if they can make compelling identifications like that, then there's no tension between scientific materialism and the existence of consciousness, just as there's no tension between scientific materialism and the existence of life.
Some things are alive and others aren't, right? Rocks aren't, hamsters are. That's a line we draw.
But, as we now think, to be alive is just to have a set of fairly complicated, high-level capacities: to metabolize energy sources in the environment, to self-regulate, to maintain shape, to maintain form, to maintain other processes characteristic of life and so on. It's not a deep mystery how something that was ultimately made up of inanimate unthinking matter could have those high-level capacities, and that's what life is—so there's no tension between the existence of life and physicalism.
If consciousness turned out to be like that, the mystery would go away.
I’m not sure it would. So the account that the physicalist resorts to as a last resort here—isn't that still a purely deterministic account?
I mean, I certainly grant that there are physical events that correlate with my feeling of pain. They may be generic in some sense—and so, yeah, it's the same thing when a pin sticks me and when my hand's in a flame. But it’s still a purely deterministic and mechanical account we're talking about, right?
Right. So, If pain, for example, just is a complicated brain state, then pains are caused physiologically and they have their effects physiologically.
So you're talking about the mind-brain identity position?
Yeah. But that is unintelligible to me, so I dismiss it. (Laughs.)
I mean, I'm not alone, right?
The whole thing about the issue of consciousness, mind-body problem, is like…It's one of these areas where it's such a fundamental issue that when people disagree, sometimes it's not just that they disagree—it's like they don't even understand what the other person is talking about.
And when they say, these mind-brain identity people—is Dan Dennett currently in this realm of mind-brain identity? I'm not sure if he is—but to say they're one in the same is...I almost literally don't understand what they're talking about. To say that my subjective experience is the same as the physical thing…
Because you can see the physical thing, Gideon. You can look into my brain and see the physical thing. You cannot look into my brain and see the subjective experience. Ergo, they cannot be the same thing.
That way of putting it begs the question against the materialist who likes this sort of view.
...so they would say, but anyway, elaborate on their dubious position.
I think it's a good sign that it's taking you longer to formulate the sentence. I take that to mean that I am ascendant in this argument, but go ahead.
Wittgenstein thought that in certain kinds of philosophical conversations, the question that ought to be at the front of your mind is "what sort of medicine does my interlocutor need"?
It's not "What sort of argument do you need? What sort of evidence do you need"? It's "What's the right turn of phrase that will jolt you into seeing that your confusion was a confusion."
I've been looking for that medicine. There are people I want to give it to.
So I'm trying to think of an analogy.
Oh, you want to give it to me? You want to give the medicine to me? I think that’s hopeless.
I want to try on the hat of the reductive materialist. I should say, I don't have a view about this. It's not like I have in my back pocket some vindication of reductive materialism.
I do find the worldview on which reductive materialism is false, and there are these other qualities unknown and unknowable to physics strewn throughout at least some parts of the natural world, these subjective qualities that are only accessible from the inside.
That's weird, too.
Oh, it's all weird. It’s definitely weird, yeah.
So, materialism is hard to understand. So is the alternative.
The alternative is hard to conceive, but I do think I have a clear conception of why the materialism is, in the sense that I described, inadequate. I feel clear on that. I don't feel I have a clear view of the alternative.
The materialist picture is something like…This is a rough analogy: imagine some aliens who live in a world where there is no water—an arid world where somehow they get by without liquid water.
But they have chemistry, so they've concocted a theory which allows them to describe this stuff that may exist on other planets at the molecular level. So they have a detailed quantum chemistry description of H2O and how it would behave and so on.
Then they come to a wet planet like this, they start stepping in puddles, and they say, what's this stuff? We've never seen anything like this before. And it takes them a while to realize that the stuff they're bouncing around in is the stuff they'd been studying for years under another name, under another description—H2O, rather than water.
According to the materialists, that's how it is with the consciousness in the material world. We have two ways of thinking about it. We can think about it in the ordinary way as the feature we're acquainted with when we step on a rock—a pain we feel—and then there's this other description of the very same phenomenon in the language of neuroscience or whatever it is. And it may take us a while to realize that it is one and the same phenomenon that we're describing in two different vocabularies.
That's what the materialist thinks would vindicate his view. That's sort of what happened with life, and with other high-level phenomena that were accommodated within the physicalist worldview. They think that could happen with consciousness.
It still does seem to me that it should be the case that, if two things are exactly the same, any feature one has the other should have.
And the physical workings of my brain an outsider can observe in principle, and the subjective experience correlated with that they cannot observe. So subjective experience has a feature that is not shared by the physical working of the brain.
Yeah. You know how this goes. The materialist is just going to say it's not true that an external observer cannot come to know the qualitative features of your subjective experience. They can, it's just that the description they give with them will be more like the chemist description of water than like the everyday description of water.
This is the impasse.
This is the impasse. As so often, the impasse is that I'm right and they're wrong. I don't know why it always winds up like that, it's weird. And you're agnostic.
Yeah, I am.
Illustration by Nikita Petrov.
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