I've been reading about the philosophy of the mind, and I'm a bit confused. Everything I've read seems to start with the (unjustified) assumption that there is some aspect of the mind that isn't purely physical or deterministic. For example, take the idea of a philosophical zombie:

[T]hey are exactly like us in all physical respects but without conscious experiences: by definition there is ‘nothing it is like’ to be a zombie. Yet zombies behave just like us, and some even spend a lot of time discussing consciousness.

Few people, if any, think zombies actually exist.

I'm confused about what this means. Isn't a "conscious experience", such as seeing the color red, just a firing of neurons in a certain area of the brain that triggers other neurons and eventually leads to us saying "I see red"?

Why do few people think zombies exist? Aren't we all philosophical zombies? We're just very complex chemical computers, programmed to act in certain ways to certain inputs. What we call "conscious experiences" are just abstractions our brains make to organize and manipulate inputs and memories before producing an output, but it all boils down to biology, chemistry, and eventually physics.

So I guess my question is what the philosophy of the mind is really about. Won't physics, chemistry, and neuroscience eventually fully explain why humans act the way they act?

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    So are you saying the firing of neurons IS the experience of red? Or are you saying the firing of neurons causes the experience of red? Commented Jun 25, 2020 at 20:53
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    Wait, I'm confused. You're taking an assumption (there's no such thing as consciousness - it's all just deterministic interplay of chemical reactions) that some people don't share, and then getting confused that they don't have the same conclusions/beliefs. Is it really that hard to imagine that some people don't believe than consciousness is reducable down to deterministic functions? In which case, why should they come to the same conclusion as you? They see a difference in consciousness and P-Zombies; they have a different stance on mental determinism.
    – Kevin
    Commented Jun 26, 2020 at 1:36
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    You might be a zombie. I'm not.
    – Stewart
    Commented Jun 26, 2020 at 9:55
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    I'll let you in on a secret: everyone starts with one of two positions -- 1) every aspect of the mind is physically determined. 2) some aspect of the mind is not physically determined. Then people of both camps get together in a room and argue. They take their best arguments, write papers in prestigious philosophical journals, and express bafflement at why the other camp assumes what they do. Commented Jun 27, 2020 at 3:11
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    @Alex How do you have such certainty about all these beliefs? Commented Jun 28, 2020 at 7:24

18 Answers 18


The concept of a philosophical zombie is incoherent. Take your quote:

[T]hey are exactly like us in all physical respects but without conscious experiences: by definition there is ‘nothing it is like’ to be a zombie. Yet zombies behave just like us, and some even spend a lot of time discussing consciousness.

Let's imagine, for the sake of argument, two universes:

  • C-world, where people are conscious, and
  • P-world, where all the people are replaced by philosophical zombies that behave just like them.

Also assume that Jungian synchronicity isn't a thing, i.e. cause and effect applies. (I don't think this is particularly controversial, but I am stating my axioms nonetheless.)

The “real” Robert Kirk, in C-world, is conscious. C-Socrates comes along and asks C-Kirk whether he is conscious. C-Kirk hears this question, thinks about it, and replies: “Yes.”

Meanwhile, in P-world…

P-Socrates: Are you conscious?
P-Kirk: Yes.

Therefore, consciousness doesn't play a role in answering the question “Are you conscious?”. P-Kirk is also a professor of philosophy at the University of Nottingham, so consciousness doesn't play a role in publishing philosophy papers.

In fact, by observing the inhabitants of P-world, we find that consciousness doesn't play any part in:

  • Playing sports.
  • Political discourse.
  • Love.
  • Poetry.
  • Music.
  • Despair.
  • Joy.

It turns out that the presence of consciousness has no effect on external reality whatsoever! Which… doesn't really sound like the concept I'm referring to when I say “consciousness”; I am conscious, and I am writing this sentence because I am conscious, so my consciousness does cause things to happen.

I'm going to stop writing “conscious” for now, replacing it with:

  • “wachooey”, for the property that C-people possess but P-people don't; and
  • “mome”, for the property that leads people to say stuff like “I think, therefore I am”.

Here's a causal diagram for "a C-person sees a pen, thinks about writing a book, and goes to get some paper":

                           +--> light enters eye --> ??? -+--> wachooeyness
light emitted from sun     |                              v
        |                  |                  +-- mome awareness of pen
        +------> light hits pen               |
                          +---------- mome thought about writing a book
mome thought about getting paper ---> goes to get some paper

Now, there might be a whole parallel wachooey thought structure, and mome thoughts might constantly feed into it (or something), but whatever it is, wachooeyness doesn't cause anything in reality.

Consciousness (momeness) causes things in reality, or we wouldn't be arguing about it. Therefore, the thing that philosophical zombies do not possess (wachooeyness) isn't what we usually call consciousness. This is just a variant of the "if a tree falls in a forest" problem.

Isn't a "conscious experience", such as seeing the color red, just a firing of neurons in a certain area of the brain that triggers other neurons and eventually leads to us saying "I see red"?


Nothing is 'mere'. – Richard Feynman

Yes, in all likelihood, human brains are made of mere neurons, made of mere atoms. But that doesn't mean you can put any old chain of neurons together, trigger the first and produce a conscious experience.

By way of analogy, Portal (2007) is a long sequence of bits, plus a description of a processor architecture (x86) and graphics interface (DirectX). Does that mean that it is just a long sequence of bits, plus a description of a processor architecture and graphics interface? That description is not enough to give you a homicidal science-addicted rogue AI, mute protagonist or series of puzzles in an abandoned testing facility; you're unlikely to even get an executable program.

Now, we¹ don't know where consciousness comes from – ideas range from "only neurotypical humans" (even "only me" is less absurd than this!) to "all sufficiently complex computers" (slightly less absurd, but still absurd, unless "sufficiently complex" is defined circularly). But dismissing it as

just abstractions our brains make to organize and manipulate inputs and memories before producing an output

is… well, unjustifiably dismissive. Not all possible such abstractions are consciousness; you're just glossing over the thing that makes consciousness special. Don't tell me that:

a firing of neurons in a certain area of the brain that triggers other neurons and eventually leads to us saying "I see red"

is a good enough description for you to create the experience of "seeing red", even in theory. That's the standard we need to hold ourselves to before we say we've explained anything. Otherwise, Pythagoras solved all philosophy when he declared "all is number".

¹: By which I mean "I don't know, and I'd expect the world to look different if somebody else knew".

Why do few people think zombies exist?

They're usually in one of two camps:

  • A separate (dualistic, metaphysical) consciousness is required for human behaviour – if you took this away, you wouldn't have something that acted like a human. Therefore, philosophical zombies are impossible.
  • Wachooeyness is not consciousness, so there's no such thing as a zombie – therefore, they're impossible.

I don't think you disagree with the second camp, except in your mapping of words to meaning. You conclude that, since there's no difference between C-people and P-people, we're all P-people. Type-2 zombie deniers conclude that, since there's no difference between C-people and P-people, the concept of P-people is incoherent. Neither position is wrong, but type-2 zombie deniers retain a useful meaning of the word "consciousness" (i.e. momeness), so I personally prefer their standpoint.

So I guess my question is what the philosophy of the mind is really about.

Philosophy of the mind is about answering questions about the mind. Much philosophy of the mind is out of date – philosophers of ages past spent centuries tackling complicated questions that we can now just look at the answers to (and, to their credit, they usually at least identified the right answers as possibilities, and got the right answers often enough that many otherwise groundbreaking discoveries in neuroscience were already old news). Things like "free will" that many amateur philosophers seem obsessed with are solved problems.

Won't physics, chemistry, and neuroscience eventually fully explain why humans act the way they act?

Perhaps. But we're not at the point where mind philosophy is immediately outdated; there's still some really interesting stuff going on at the cutting edge, like the research into ethics and reason. Plus, somebody has to look at the implications of new discoveries, and build up coherent models of what makes humans tick; in my experience, that work's mostly been done by philosophers.

My prediction is that, given sufficiently advanced neuroscience, philosophers will finish the complete explanation of why humans act the way they act before science catches up. (But even then, the explanation won't be complete enough to make non-trivial predictions about human behaviour; humans are just too complicated.)

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    Comments are not for extended discussion; this conversation has been moved to chat.
    – Geoffrey Thomas
    Commented Jun 27, 2020 at 14:06
  • Isn’t there a type of dualist who doesn’t find zombies incoherent? Ones instead of saying consciousness is required for human behavior (p-behavior?), consciousness does something a bit less (co exist) or is only sufficient for? Or is synchronicity ruling that class out?
    – J Kusin
    Commented Jul 14, 2022 at 19:22
  • @JKusin: That's (basically) epiphenomenalism, but IMHO epiphenomenalism is rather uninteresting because its version of consciousness (wachooeyness) is causally inert. You still have the "so what?" problem.
    – Kevin
    Commented Jul 15, 2022 at 19:35
  • P zombies are not incoherent for eliminative reductionists, or for dualist epiphenomenalists. The arguments against both views are not “incoherence” arguments, but instead are arguments based on the utility of empirical inference. For identity theorists, emergent non reductive physicalists, and interactive dualists, p zombies ARE incoherent.
    – Dcleve
    Commented Jul 16, 2022 at 5:15
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    @wizzwizz4, this little essay, summarizes nicely the points brought up by both you and me. Cheers!
    – Nikos M.
    Commented Jul 17, 2022 at 17:22

I'm confused about what this means. Isn't a "conscious experience", such as seeing the color red, just a firing of neurons in a certain area of the brain that triggers other neurons and eventually leads to us saying "I see red"?

Right, you should be confused.

(Def)-Type-Identity reductionism:

"The view that mental state are directly reducible to brain states."

Type-Identity theorists deny there being such a thing as "irreducible" qualia for the same reason you pointed out. So, obviously, if we assume type-identity theory is the best description of cognition, then qualia-as we know it-doesn't exist.

As for the question:

Isn't a "conscious experience", such as seeing the color red, just a firing of neurons in a certain area of the brain that triggers other neurons and eventually leads to us saying "I see red"?

It's not as simple as that. Type-Identity is just one theory out of many in contemporary Philosophy of Mind. In fact, it's a fringe view at this point. It's simply too costly to hold such a reductionist account, and so it's not really popular.

Type-Identity, but at what cost?

1:It's chauvinistic (imagine an alien that is not carbon based). According to type-theorists, supposing the alien shows intelligence, we can safely say it is not conscious because it does not have the same material make-up for his brain. This version is not so problematic, i think. (Commonly referred to as MR or multiple realizability)

2:It raises some huge problems for Cognition (these are unavoidable), and not worth getting into (besides they are outside the scope of this answer).

3:AI, no AI in this view.

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    Would you be able to elaborate on some of the costs of a type-identity viewpoint? At present this answer sort of reads as "The skepticism in your question is a natural consequence of a particular philosophy-of-mind framework, but that framework isn't popular any more," which would be more compelling if it included some of the drawbacks and alternatives.
    – Tiercelet
    Commented Jun 25, 2020 at 21:16
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    Thanks for your answer. So if I understand correctly, type-identity reductionism would agree that if we wrote a very complex computer program that acts as a human, ignoring the fact that it works differently (silicon rather than neurons), it's completely equivalent to humans. There's nothing special that a human has (soul, conscious experience, qualia, etc.) that the program doesn't. Right? If yes, then why is this a fringe view? What's the motivation behind people thinking that humans are more than just a very complex computer?
    – Alex
    Commented Jun 25, 2020 at 22:01
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    But love is just triggering of neurons in a certain area of the brain which has an effect on which actions we take. This is the main thing I'm having problems with. Everything I read and almost all the answers here seem to start with the assumption that there's something "special" that can't be reduced to chemical reactions in the brain...
    – Alex
    Commented Jun 25, 2020 at 22:14
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    @wizzwizz4 For type-Identity theorists "reducible" is equivalent to explaining away subjectively inexplicable qualia. Perhaps you can understand it with an example: Thunder just is an electrical discharge. Obviously, this doesn't mean thunder is not a thing. It is, but it is just that: electrical discharge. Type-theorists believe qualia like we think of now is similar to what ancient people thought of lightening: God's wrath. Therefore, just like how we explained away the "God's wrath" part from thunder, we can do the same with qualia. Commented Jun 25, 2020 at 22:40
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    Wait! After your recent edit, I think I misunderstood your answer. You say: "According to type-theorists, supposing the alien shows intelligence, we can safely say it is not conscious because it does not have the same material make-up for his brain." But what I'm saying is the opposite. If you define consciousness to be a synonym of intelligence or self-awareness, then humans, aliens, and even computer programs have it. If you define it to be a "non-physical thing" related to "qualia" and "subjective experience", then no such thing exist.
    – Alex
    Commented Jun 25, 2020 at 23:12

You cannot tell other philosophers apart from well-programmed zombies, that is true. But you can tell yourself apart.

Your knowledge of yourself comes through your subjective experiences and their specific qualities or qualia. Your present experience is in fact the one and only thing you can be absolutely sure of. Everything else - the dynamic flow of experiences, your past, your body, the existence of other philosophers with their own private flows, the speculative existence of zombies, all arise as identifiable substructures within your current focus of attention.

Other philosophers give every appearance of accessing their own private flow of subjective experiences (even when they try to deny its properties).

On the other hand, by definition a zombie has no access to such a flow, therefore it is distinct in kind from you.

Can the appearance of such access be convincingly simulated? Can a zombie actually be that well-programmed and still be a zombie? Well, so far no AI has passed any sensible Turing test. We know that many higher animals - apes, horses, dogs, parrots and corvid birds, even manta rays and some octopuses, show the behavioural hallmarks of conscious experience and possess the necessary neural structures to support it. Why should an AI be any different? When one eventually does pass a Turing test, that will appear to be because it does have its own flow of experience. Since we do not deny the ape or octopus or philosopher their inner experience, why should we deny the AI?

Similarly, in so far as a purported zombie possesses the required functioning neural substrates and displays sentient behaviours, we must credit it with being a philosopher after all.

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    @tkruse Perhaps you should enlighten the signatories to the Cambridge Declaration on Consciousness fcmconference.org/img/CambridgeDeclarationOnConsciousness.pdf By your argument, everything except your own stream of consciousness is conjecture - as I pointed out at the start of my answer. Commented Jun 25, 2020 at 14:23
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    @tkruse Here too is an article explaining what biologists think about animal consciousness newscientist.com/article/… Perhaps you could explain what kind of meaningful "conjecture" they have all fallen into? Commented Jun 25, 2020 at 14:49
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    In psychology and biology, different concepts are relevant, it does not affect the philosophical topic.
    – tkruse
    Commented Jun 25, 2020 at 15:14
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    From a philosophical point of view, it is equally conjecture that other people have consciousness like you do, or that you yourself had consciousness at any moment other than the present one you are experiencing right now.
    – Hypnosifl
    Commented Jun 25, 2020 at 15:19
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    @tkruse - The point I was making was specifically about the unknowability of qualia other than one's own, it has nothing to do with radical skepticism more broadly. One can believe that there is an objective physical world and that it's possible to gather empirical evidence for or against various propositions about physical facts while still thinking the private nature of qualia means one can only offer evidence-free conjecture about any qualia other than one's own.
    – Hypnosifl
    Commented Jun 25, 2020 at 15:43

Do you know about these twin sisters who are joined at the skull and their thalamus , allowing one twin too see, think about, feel what her sister feels and vice-versa. They even have their own different opinions, and yet, a boundary between them appears if you watch them talk. What is this boundary made of? It is still "one system", connected with neurones. As you responded in your comment to @Godless Girl, you complain that just because you don't have your neurons connected to hers, you can never know what her experiences are like, yet in this case, these girls have their neurons connected and distinctively differentiate between their "own" thoughts and the sister's thoughts.

What happens when a person tells you that they're feeling happy? You correlate. These twins do the same, but they have a more direct physical highway to process each other's emotions. In contrast, you must first translate the sound waves into words and then words into correlated emotions and then pass it through the intellect before you can sympathise with what the other feels. "Mirror neurons" are a special class of neuron cells that have evolved just to do this, mirror the other person in one's own mental space.

But now coming to your Q:

Isn't a "conscious experience", such as seeing the color red, just a firing of neurons in a certain area of the brain that triggers other neurons and eventually leads to us saying "I see red"?

In stritctly reductionist vocabulary, words like "red", "see", "know" don't exist any other than a high-level phenonmenon. When I see red, all I do is I correlate the words red and the sensation of 700nm light as a unit and act it out. There seems to be no requirement for an awareness of this happening. If you hold on to the fact that when you see red, all that is happening is a bunch of neurones are firing, and that "seeing red" is equivalent to "a few hundred thousand neurones firing", then you're silly - the non-reductionist argues. For you can use an MRI to "see" the exact 3D pattern of neuronal firing that goes off in another person, or your own brain, but you can't quite see a "red" there can you?

Reading your question, seems to me like you put a lot of faith on the assumptions that reductionism assumes. We should only consider those theories and philosophies as valid which resolve paradoxes, not create one. Consciousness of quale, in a materialisitc Universe, is a paradox. With that said, let us look specifically at the P-zombie.

Yes it is true that if you really believe that reductionism is true, you must assume that when you say I see red, all that is happening is what is known as downward causation. Downward Causation in action

Photons are like billiard balls, hitting your retinas, throwing off the energy equilibrium in your brain circuits, leading to a cascade of particle movements and energy shufflings until you blurt out the words "I see red". So far this is true. Yet one tiny fact has been overlooked: you actually see the red. What?

Consider this to be what happens when you look at red Neural correlate of responding to 700 nm light

the actual red you look at Red

If looking at the two pictures, you see the same thing, then you've already answered your question. Either you must conclude that what red feels like in your mind is the same thing as a 4D geometrical structure of charges OR, that it is separate and of a completely different character.

  • I think it confuses the issue to connect the question of qualia to the question about reductionism/downward causation, after all plenty of philosophers who think qualia are "something extra" metaphysically are nevertheless epiphenomalists who don't believe qualia/first-person consciousness have any causal role in physical processes, and that reductionism and downward causation are perfectly true as far as the physical world goes.
    – Hypnosifl
    Commented Jun 25, 2020 at 15:17
  • @Hypnosifl It is my particular understanding, that any theory which claims to be a universal model, yet fails to account for even a single phenomenon within the universe, is an incomplete theory if not outright wrong. Reductionism is based on the axioms of some fundamental unit of the universe existing and manifesting in different shapes giving rise to different interactions. Yet somehow, we find ourselves in a habitable universe of not just p-zombies but conscious p-zombies. Yet I can think of no dynamics that will analogize with conscious experiences that "I" am having right now.
    – Weezy
    Commented Jun 25, 2020 at 15:23
  • One might distinguish "reductionism" in the physical sense from metaphysical reductionism--when physicists talk about reductionism they just mean that all physical behavior and phenomenon are in principle explainable in terms of the basic physical units and the laws governing them, they aren't necessarily ruling out that there could be metaphysical truths which are independent of all measurable physical phenomena, like truths about mathematical objects that don't correspond to anything physical, or truths about qualia. And what would "downward causation" mean if not about physical causation?
    – Hypnosifl
    Commented Jun 25, 2020 at 15:29
  • @Hypnosifl I agree with your wording of physical causation, however regarding the truths of mathematics, which is again derived from principles of logic, I'm not too sure. Logic depends a lot on analogies with the physical universe, which is the source of intuition for the mathematician. It can be argued that qualia too, is like logical intuition, derived from the physical universe. After all, logic is another type of qualia that feels "correct". No one decided why it had to be correct. Logic is "correct" as long as it is consistent. Thus, it shouldn't be relied on as a source of truth.
    – Weezy
    Commented Jun 25, 2020 at 15:49
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    @Taladris what the OP questions about is what I've mentioned in my answer. Mechanically all processes are obeying physical laws, but the physical laws themselves are in consciousness. Are you going to deny that something blue exists, distinct from the mechanistic implications those photons cause you? How do you even know anything? When you read a book all you did was reshuffle some cells and particles in your brain. So does that imply that the difference between a knowledgeable and ignorant person is simply an accumulation of extra particle motion? If you don't accept that, you see my point.
    – Weezy
    Commented Jun 28, 2020 at 9:50

So I guess my question is what the philosophy of the mind is really about. Won't physics, chemistry, and neuroscience eventually fully explain why humans act the way they act?

It might fully explain the way humans act, but this is what David Chalmers calls the "easy problem" of consciousness ('easy' from a philosophical point of view, not a scientific one), in contrast to the "hard problem" which is supposed to be about qualia/experience. So clearly the question of qualia is not meant to be about behavior at all, many philosophers like Chalmers fully accept that it would be possible to create something like a simulation of a brain on a deterministic computer that would behave just like a real brain, and Chalmers speculates about "psychophysical laws" that might imply the simulation would have the same sort of qualia as an organic brain as well. But for him there are still facts about what the qualia of such a simulation would be like that are not simply equivalent to facts about measurable physical behavior, so that you need some extra set of bridging laws to connect the facts about qualia to the facts about behavior. And one of his main arguments is that there's a logically possible world where all the physical facts are identical but the facts about qualia are different (same physical laws and phenomena, but different psychophysical laws), like a "zombie world" perfectly identical to ours in every physical sense but where none of the physical processes are associated with any qualia at all.

The basic intuition is that there are facts about what my experience is like that go beyond the most complete possible causal description of my brain activity and behavior, so that even if some superintelligence could hold in its mind a complete set of facts about every physical event in my brain and their causal interconnections, they might still be missing some understanding of "what it is like" to actually have my experiences. Suppose this superintelligence has been colorblind all their lives for example--would complete physical knowledge of my brain processes give them an inner sense of what it's like to see the color yellow, for example? See The Knowledge Argument, which was influenced by Thomas Nagel's "What Is It Like to Be a Bat?" paper (where the idea is that we are in pretty much the same boat as the hypothetical colorblind brain researcher when it comes to the bat's sonar sense, and what it would be like to experience the world through that sense).


The Knowledge Argument might be a good thought experiment for seeing why many people believe qualia exist.

Mary is a brilliant scientist who is, for whatever reason, forced to investigate the world from a black and white room via a black and white television monitor. She specializes in the neurophysiology of vision and acquires, let us suppose, all the physical information there is to obtain about what goes on when we see ripe tomatoes, or the sky, and use terms like "red", "blue", and so on. She discovers, for example, just which wavelength combinations from the sky stimulate the retina, and exactly how this produces via the central nervous system the contraction of the vocal cords and expulsion of air from the lungs that results in the uttering of the sentence "The sky is blue". ... What will happen when Mary is released from her black and white room or is given a color television monitor? Will she learn anything or not?

Basically, Mary knows everything physical there is to know about the color red and the human experience of seeing it. Yet most people would agree that, after knowing this, she still learns something new the first time she actually sees red herself. This is the qualia, the part of the experience that interacts with her consciousness and not the physical word.

A p-zombie would simply not have this separate experience. To a p-zombie, nothing new happens when it actually sees red vs just understanding red. It would be like a computer getting a signal from the internet after it had already process an internally-emulated version of the same signal.

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    The color neurons of her brain have never been linked to the neurons for color words because they have never been fired, which is why she is not able to name the color red when she sees it. Whether she lacked knowledge or didn't gain knowledge depends on whether you consider that missing link "knowledge".
    – Alex
    Commented Jun 27, 2020 at 0:02
  • @Alex It's not so much being able to name the color red. It's that she's still learning something new by experiencing red, but she knows everything there is to know about the physical characteristics of red and how humans view it, therefore what she learned must be something else. One simple answer is that it's the interaction with consciousness.
    – Cain
    Commented Jun 29, 2020 at 16:29
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    @Cain that is a simple answer, but a wrong one. Actually receiving the photon gives data which is saved as additional information in her memory. It shows her some processed form of the input photon. The form of the visualization is physical information (on her own internal machinery). It is clear that this is a change in the physical state of her memory. With perfect technology the changed bits in her memory could be detected.There is no reason to treat the reception of that information in any other way than other information she received.
    – Kvothe
    Commented Sep 13, 2020 at 20:01
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    @Kvothe I agree that her brain will undergo a physical change upon seeing red. And in fact the existence of qualia does not preclude physical views of the mind. Qualia could be produced by a certain physical configuration of neurons, we could detect the bit flip, yet the "redness" of red is still something tied to consciousness. Essentially, the experience of seeing red cannot reduced to pure knowledge, as it is impossible to do without that specific alignment of neurons occurring the first time she sees it.
    – Cain
    Commented Sep 15, 2020 at 14:37
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    @Cain, well this was not your point but in that case of course the exact experience of red can be created without her receiving any red photons simply by recreating the alignment of neurons some other way. (If in the hypothetical we have perfect reading capabilities it is not a far stretch that we can also write neurons perfectly.) Anyway, my point was more that the "alignment of neurons" is the thing that she observes when she "sees" red. It tells her something about the internal state of her brain (in addition to any information on the locations of photons).
    – Kvothe
    Commented Sep 15, 2020 at 14:48

P-zombies are supposed to be a thought experiment to show the privacy of the mind. Experiences are subjective and we don't have access to what it is like to be something else. That is what consciousness is - what it is like to be X. Unless you think consciousness is physical then no matter how much of the physical facts we had we could never have access to what it is like to be that thing. Some would argue we can't even make justified inferences about it. Belief that another person is conscious is just an intution and cannot be justified.

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    If it's not physical then consciousness is immaterial. There is also transcendental idealism which I am not sure about. It's not true that if it were physical that you would never be able to speak about another's experiences. If consciousness were physical and you had all the physical facts and laws that entails you would know what it is like to be another person. Commented Jun 25, 2020 at 8:32
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    Replacing "non-physical" with "immaterial" doesn't really help me... I just can't imagine what it means for something to not be physical. Are you saying that it's non-deterministic?
    – Alex
    Commented Jun 25, 2020 at 8:37
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    @Alex Have you not heard of the idea of souls? Spirits? Gods and/or spiritual beings? Lots of people (including philosophers) may reject the existence of any or all of these, but I don't think anyone here could claim they've never heard of them before! Commented Jun 25, 2020 at 14:08
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    @Alex : In "Humans are completely composed of physical particles that act based on a set of rules to produce intelligent behavior." What is your falsifiable test of "Humans are completely composed of physical particles"? What is your basis for the article of faith "act based on a set of rules"? What is your definition of "produce intelligent behavior" and how do you avoid the distinction "produce intelligent behavior" versus "have intelligence"? Commented Jun 25, 2020 at 22:18
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    @Alex you say "I just can't imagine what it means for something to not be physical" and that is your issue. You're looking at these extremely complex ideas and problems from a very limited point of view and dismissing a lot as a result. there are people that think consciousness may work on some higher plane of existence, or be something that they call spiritual. You want to dismiss them, that's fine, but we may end up finding there is something there that won't be explained by mere particles. Our understanding is very young at the moment, and it seems foolish to limit what we don't know to it. Commented Jun 27, 2020 at 6:24

Your question seems to boil down to whether existence is purely physical, with science destined to eventually fully understand self-awareness; or whether there could be a metaphysical aspect to our existence.

If we are purely physical, then it stands to reason that only sufficiently complex structures (such as our brain) can become self aware. Or else the odds of us living in a state where we are in control of our bodies, rather than just existing as a nerve in our arm or leg. What I'm trying to say is, is every piece of our nervous system self aware? OR just the brain that controls it? It would seem to be just the brain since we are self aware as in control of our brains and therefore in control of our entire body. Simpler organisms, (such as single cell organisms) that are made up of much smaller nervous systems which are similar to subsets of our own, would have to be classified as unaware then. Then complexity and life are linked, but is it life due to complexity or did they both come to exist at the same time? Back to your point about whether we are just chemical reactions, if life was defined exclusively as a complex enough chemical reaction, then the computers we have built could be deemed alive. They react to stimuli from their environment, and reason in their own way. But then they have to be self aware somehow, which they are not. They cannot think outside of the bounds of their material, or in anyway other than how they are programmed. If we were purely chemical, we would just happen. We wouldn't be aware our lives were happening, because we would just be chemicals. This leads me to believe that there is a metaphysical aspect to our existence that allows for us to be aware.


Another thought experiment that is useful to consider here is the inverted spectrum scenario. The thought experiment is as follows: suppose you and I are neurophysiologically alike, but somehow, unbeknownst to us, the subjective experience that I have when I see red is the same as the subjective experience that you have when you see green, and vice versa. If this is so, we will never find out about it, because we will still agree on which objects in the world are green and which are red.

The point of the scenario is not that this is likely. The point is that it is conceivable, and the mere fact that it is conceivable tells us that there is something that we do not understand about how our neurophysiology leads to what it is like to perceive colors, and it is not clear how any progress in neuroscience, at least of the kind that we usually see, would resolve this for us. This suggests that there is more to the conscious experience of seeing the color red than just neurons firing and saying "I see red."

The knowledge argument makes a similar point.

  • 2
    I don't see how this is conceivable... If we are neurophysiologically alike, then how exactly are we different? What more is there than the way neurons are linked in the brain? It's like saying "here are two color-recognition programs with exactly the same source code, yet one has a 'subjective experience' that's different than the other one". With humans, it's the same thing, but the programs (encoded in the way neurons are linked) are much more complex.
    – Alex
    Commented Jun 25, 2020 at 22:10
  • 1
    Are you sure "the mere fact that it is conceivable" relates more to the thing you're conceiving than to our conceiving machinery?
    – wizzwizz4
    Commented Jun 25, 2020 at 22:29
  • 1
    @Alex right, the question is precisely in what way we could still be different under those conditions. From a third-person perspective, it's not clear how we could be different. But from a first-person perspective, there is something it is like for me to see green, just the experience that results from that, which doesn't seem to naturally relate to the state of the neurons in my brain, and for all I know it's not the same for you. Maybe this paper helps: link.springer.com/article/10.1007/s10670-018-9979-6
    – present
    Commented Jun 26, 2020 at 1:34
  • 1
    @Alex the idea is tht a softare AI, no matter how advanced, even if it seemed similar to a human in all ways, may still be fundamentally lacking something humans have. You want to know what that is, and assume if it can't be reduced down to particles and chemical reactions then it must not exist, which is rather naive IMO. Our understanding of our reality is so incredibly primitive, and there well may be solutions that tie into consciousness that have nothing to do with particles or chemical reactions. We can't explain gravity entirely yet you're ready to put your foot down re consciousness? Commented Jun 27, 2020 at 6:27

When I see something red, I have a conscious internal experience of "redness". Presumably this experience is caused by neurons (or whatever), but that doesn't mean I don't feel it as a conscious being. You could say, "Hammers are just bunches of molecules," but that doesn't mean hammers aren't hammers. It just means molecules are a (partial) explanation of how hammers work.

Philosophical zombies, if they existed, would able to point their eyes at something red and say, "This is red," despite lacking the internal conscious experience we would expect to happen in between.

To believe in p-zombies is to believe that conscious experiences aren't a necessary part of the process of brains turning sensory inputs into intelligent outputs.

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    I understand that, but I just don't understand what you mean by "conscious internal experience of redness". I think that a human is just a very complex computer that acts in certain ways to certain inputs, I don't see what else there is, and what a philosophical zombie is missing compared to a normal human.
    – Alex
    Commented Jun 25, 2020 at 21:43

The problem is simple: OP's conclusions do not follow. A lot of logical issues.

So I guess my question is what the philosophy of the mind is really about. Won't physics, chemistry, and neuroscience eventually fully explain why humans act the way they act?

Absolutely not!

You can't reduce love, religion or mysticism -or consciousness- to physics, chemistry and neuroscience.

Can you? Can you express the problem of consciousness with equations in https://physics.stackexchange.com and ask for a solution? In such case, why are you in this forum? (just joking)

Worst even, in any of such disciplines, we don't have enough knowledge, and we don' t know the extension of our ignorance.

In such case, you would be telling that the problem of consciousness belongs to an unknown domain, and it must be addressed from such perspective... That would be like saying "there's a non-philosophical problem that can't be described with electromagnetism, what is the electromagnetic solution?"

If you agree that philosophy is the proper level of abstraction to address the problem of consciousness, then address it in such level. In consequence, no, we're not philosophical zombies at all. At least not those who have once wandered why cogito ergo sum.

Philosophy, seeking for the truth, has still not the answer, but has far more perspectives of possible solvable parts of the problem. Some of them reduce to the knowledge of electromagnetism, chemistry or physics we do have (that is the key difference of this approach: in philosophy, problems are expressed, and sometimes solved with what we do know, and that has a logical coherence).

  • 1
    "Can you? Can you express the problem of consciousness with equations in physics.stackexchange.com and ask for a solution?" Lack of knowledge of the details of one model of reality does not imply that it is not true. Can you back your claim that your proposed model is instead true, that "You can't reduce love, religion or mysticism -or consciousness- to physics, chemistry and neuroscience."? Commented Dec 7, 2020 at 14:38

The answer to your question, “Won't physics, chemistry, and neuroscience eventually fully explain why humans act the way they act?” is, of course, yes and no. It depends on what you mean by “fully explain,” and what you’re up to by asking the question. For instance, why include “chemistry and neuroscience,” which are themselves reducible to physics, in your formulation.

It should by now be obvious to all who have perused this post, that no "progress" will be made in this discussion. If you believes that qualia can be reduced to physics (to which, as mentioned, chemistry and neuroscience are reducible), you can define your terms in such a way that, even by the lights of your antagonists, you would be “entitled” to do so. You are entitled to find Frank Jackson's Mary the neurophysiologist color scientist thought experiment unpersuasive. Reduction “works” in many contexts and for many purposes. https://plato.stanford.edu/entries/scientific-reduction/#TypIde. The issue here, while different, is reminiscent of the contemporary free will v determinism conundrum. You would say that the motions of atoms in the void are determined by the laws of physics, and “free will” is but an epiphenomenon. As so it is.

What we have on display in this post it seems to me is akin to dueling epistemic communities with numerous incommensurable sets of normative and principled beliefs (including beliefs about the meaning of their constituent terms), notions of validity, and epistemic norms and paradigms. https://en.wikipedia.org/wiki/Epistemic_community). (It is worth noting that in the current ethos of “big data” and dearth of universal normative epistemic criteria, instances of such radical polarity, often as a result simply of people simply standing in one another’s blind spot have become increasingly commonplace.)


Yes we are. Or at least, that the simplest solution.

There's no meaningful difference between a P-zombie and a "real human". How do you know you're not a zombie? "But I experience senses" yes you do, but you have no way to compare this experience with a gold standard "conscious human".

For consciousness to be a meaningful idea, first you need individuality to be a meaningful idea. Already this is an impassable wall: your mind emerges from a structure which is not meaningfully separate from everything else in the universe. It's made of stuff which is not only indistinguishable from everything else but actually the same in every way. If you stopped time and switched your fundamental particles with that of the Eiffel tower but keeping the same structure, nothing special would happen after restarting time. The universe evolves in terms of fundamental particles. Everything else is human interpretation.

If consciousness exists, then it must be that certain parts of the universe must be called conscious and others not. You may find that a very large number of subsets and super sets of your matter may qualify as "having conscious experience". In particular, these subsets don't necessarily overlap fully. And even if they share a common kernel, that kernel alone isn't sufficient to qualify.

But then if many different structures could be the seat of your conscious experience, which one is it that actually provides it?

Consciousness is on a spectrum, it isn't binary. If you go sufficiently far back in time, you will be confronted with the ancestor that "became conscious". You can make the same observation about human development before birth. If you start arguing that an embryo has qualia, you'll soon find yourself arguing over whether a teapot has qualia too. The teapot has no way to tell us and apparently no way to probe the universe either, but that doesn't mean it lacks some sort of inaccessible experience of the world.


I think this question is actually easiest to answer backwards:

So I guess my question is what the philosophy of the mind is really about. Won't physics, chemistry, and neuroscience eventually fully explain why humans act the way they act?

That is the point of the concept of Philosophical Zombies. It is a challenge to limit the nature of the "specialness" of consciousness. It basically offers two options:

  • Recognize that no physical action, or set of actions in gestalt, can be used to demonstrate one's consciousness
  • or recognize that that which makes us demonstrably conscious is producible using what might be called "mechanical" means.

For an individual who subscribes to physicalism, where everything supervenes on physical properties, this is a non-statement. That approach clearly supports using the second option. However, for those who argue that consciousness is another substance entirely must be careful in what they state about the observability of consciousness in others, or risk declaring that a P-zombie can meet their criteria for consciousness.

This is a big deal because many schools of thought, especially in the Western world, put the conscious human mind in a special class above all other things. The philosophical value of such thoughts are limited when one considers the possibility of P-zombies.

As for why most people believe they do not exist: we can easily divide people into two camps. There are those who believe that humans are conscious (and perhaps a few other species), and thus there is no need for a mechanical concept which is conscious. And there are those who already believe that consciousness supervenes on physical properties, in which case the concept of a P-zombie is an absurd waste of time when one can merely declare that entity conscious.

The people who do not fit in either camp are the interesting question, and I do believe it is reasonable to argue that they are very few in number. This provides your answer for why so few believe it exists.

  • Good points, see my answer as well.
    – Nikos M.
    Commented Jul 17, 2022 at 22:40

I would like to offer another answer.

P-zombie argument rests crucially on simply being conceivable, thus the philosopher claims, it is conceivable, it is metaphysically possible.

But really is anything conceivable (eg by me) possible? What if I conceive of "square circles"? Or conversely is something not conceivable (eg by me) impossible? So at some point in history, people could not conceive the earth as moving, is it impossible then?

One can argue, rather successfully, about the incoherence of the p-zombie argument itself. But arguing over that eventually we return back to how it is conceived and whether it is really possible. In fact other responses to the zombie (eg anti-zombie, zoombie, or zimboe), simply conceive the opposite or some other variation.

In this respect, I present the following solid analysis of arguments from conceivability (like the p-zombie) and when, if ever, they can be used soundly.

The Unsoundness of Arguments From Conceivability

[..] the inability of our ancestors in the fourteenth century to imagine, say, genetic engineering does not show that genetic engineering is impossible, any more than their belief that they could conceive of lead being transmuted into gold by the application of the appropriate chemical process (consistently with all the actual laws of physics) showed that this is in fact logically possible.

[..] No matter how these details are fleshed out, my main point for present purposes is that the following is a necessary condition on any plausible account of ideal conceivability: one’s conceiving of X can count as ideal only if the removal of any existing epistemic distortions (of the general sort described above) would not result in X’s ceasing to be conceivable. For example, if we could come to see X as inconceivable through acquiring a new piece of knowledge, then X cannot now be for us ideally conceivable. This is not by any means an overly ambitious criterion for ideal conceivability. In particular, it does not require that some X can only be for us ideally conceivable if we are already in relevantly epistemically ideal conditions—a tall order indeed. It merely requires that if we were in relevantly epistemically ideal conditions we would continue to see X as conceivable. Indeed, this condition is simply a requirement of the fact that ideal conceivability is supposed to be a reliable a priori indicator of logical possibility: this requires minimally that its judgements should be stable in the face of the acquisition of new knowledge, or the shedding of false beliefs.

[..] The systematic problem with arguments from conceivability, then, is the following: unless we are already in relevantly epistemically ideal conditions, the justification of the modal sub- conclusion of an argument from conceivability can in principle never be completed.

[..] I shall focus on the case of zombie worlds. Chalmers’ argument, then, rests on two claims:

  1. “If a physically identical zombie world is logically possible, it follows that the presence of consciousness is an extra fact about our world, not guaranteed by the physical facts alone” (1996, 123).
  2. Physically identical zombie worlds are logically possible.

What makes Chalmers’ argument an argument from conceivability is that his defence of both of these claims rests ultimately on considerations about what is and is not conceivable. In order to establish Claim 1—that the logical or conceptual possibility of zombie worlds is sufficient to falsify materialism—Chalmers must answer philosophers who claim that materialism is content to rule out metaphysically possible zombie worlds, and is consistent with the ‘logical possibility’ of zombie worlds. In other words, Chalmers must show that the relevant modal judgements are a priori rather than a posteriori. 12 And in order to establish Claim 2, Chalmers must show that zombie worlds are in fact logically possible.

For further arguments regarding the (in-)conceivability of the p-zombie see related entry at SEP


Isn't a "conscious experience", such as seeing the color red, just a firing of neurons in a certain area of the brain that triggers other neurons and eventually leads to us saying "I see red"?

Likely yes, but there could be a similar way for neurons to fire and trigger other neurons that on the outside looks similar, but works different in the inside, lacking the kind of consciousness we experience ourselves.

Assume that there are some humans without emotion, without empathy, without fear, without long-term memory ... Just because a human has a brain and can walk and talk does not mean they have all same abilities as everyone else. So there could be a special disease, disability or genetical "defect" for humans to live without the kind of consciousness other people have. That's one example to better imagine p-zombies.

  • 3
    Having different abilities like no long-term memory would be a behavioral difference, the notion of a philosophical zombie is specifically about an entity that behaves identically to a normal person in every respect, but lacks qualia. See the opening paragraph of the Stanford Encyclopedia of Philosophy article, for example.
    – Hypnosifl
    Commented Jun 25, 2020 at 18:26
  • Yes, those examples I give may just be helpful to the OP to realize a functioning brain can still have differences to other brains. Also generally note, p-zombies could have slight differences in behavior, all that matters is that despite any difference, they appear to behave acting rationally. If all p-Zombies were never dreaming as an example, that would not change their philosophical use. But that's not even part of my explanation.
    – tkruse
    Commented Jun 25, 2020 at 21:04

   “I see dead people. They don’t know they’re dead... They only see what they want to see!”

  -- Cole Sear, "The Sixth Sense"

I don't think seeing color red implies consciousness.1 What p-Zombies lack is rationality -- the rational/conscious Self, the Self-awareness, the ability to think for them-Selves.2

To understand p-Zombies, it's important to realize that:

  1. Their raison d'être is to pass as [rational] human. To that end, they themselves must believe that they are the epitome of being human. For example, they would not shut up about love, even tho love being understanding before anything else, there is no love in them.
    Their suffering is immense.
  2. It takes a human tribe to raise a human. Failing that, most children turn p-Zombie hard. A small minority manages to retain their conscious Self, but in the absence of a fully rational system of beliefs it's "cogito ergo sum miser".
  3. When they have no humans to imitate, they start to imitate each other, creating a totally messed up system of feedback loops that keeps getting out wack -- a p-Zombie Apocalypse we call "civilization".

1 if anything, it is the ability to have a mental model of red-ness, before actually experiencing it, that suggests consciousness in Mary

2 Does it means Buddha was a p-Zombie? I have little choice but to answer "yes, he must have been".


It's an unjustified assumption that the mind is physical. Try opening an introductory text on physics. You will be hard put to find any physical description of mind.

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