p-zombies are inconceivable. With notes on the idea of metaphysical possibility.

zombiesby Massimo Pigliucci

Philosophy of mind and the nature of consciousness are fascinating topics, which recur both here at Scientia Salon [1] and at my former writing outlet, Rationally Speaking [2]. And of course we can hardly talk about consciousness for long before running into one of the most famous (and, in my mind, pernicious) thought experiments in philosophy of mind: the philosophical zombie! [3] (Now you should hear ominously sounding music in the background…)

In this essay I propose to do the following: we are first going to take a look at Chalmers’ zombie argument (one of a number of instances of zombification in philosophy of mind) to see exactly what it says and why I find it utterly unconvincing. Next, we’ll use p-zombies to broaden the discussion to parse the differences among different types of possibilities, especially logical, metaphysical and physical/nomological (with a nod toward two other types: epistemic and temporal/historical/contingent). Finally, we’ll use whatever we think we have learned in the process to talk even more broadly about the very nature of philosophical inquiry — or at the least the sort of analytic-type [4] metaphysics that Chalmers and his supporters indulge in.

What, if anything, are p-zombies?

The first thing to be aware of when we talk about p-zombies is that the concept has a long history and has been used in different ways for different purposes. It can be traced back to Saul Kripke’s arguments in the 1970s against type-identity theory in philosophy of mind as presented in his Naming and Necessity [5]. Versions of it were elaborated upon during the same decade by both Thomas Nagel and Robert Kirk. But we won’t go into any of that, focusing instead on the more famous Chalmers’ version of 1996.

Also to keep in mind is the fact that p-zombies have been deployed against different targets, the most important of which are behaviorism [6] and physicalism [7], though they have also been used to argue for the existence of an epistemic gap in our understanding of consciousness (the so-called “hard problem” [8], very much related to the issue of physicalism). Anti-behaviorism p-zombies are not particularly interesting, in my mind, because they beat a dead horse: while behaviorism survives as a useful practice in psychology, it has gone the way of the dodo as a theory of mind decades ago. Besides, it seems to me trivially true that one could face a being that behaves like a human and yet is internally constructed very differently from a human. So what?

As for the epistemic problem concerning consciousness, if by that one simply means that we don’t yet fully (or even very partially!) understand how consciousness can be produced in a physical system, that is obviously the case. But such observation licenses precisely nothing about the future likelihood, or even the in-principle possibility, of such knowledge. Accordingly, we will set this one aside as well.

Instead, I’ll tackle the best known deployment of p-zombies, by Chalmers, whose target was physicalism itself. Here is his argument, formalized:

  1. According to physicalism, all that exists in our world, including consciousness, is physical.
  2. Thus, if physicalism is true, a metaphysically possible world in which all physical facts are the same as those of the actual world must contain everything that exists in our actual world, including conscious experience.
  3. We can conceive of a world physically indistinguishable from our world but in which there is no conscious experience. It follows that such a world is metaphysically possible.
  4. Therefore, physicalism is false. (Because 4 follows from 2 and 3 by modus tollens.)

As plenty of commentators have noted, Chalmers’ argument is deductively valid, i.e., if its premises are true, then the conclusion must logically follow. You would think so. Any philosopher caught putting forth an invalid argument should have his license revoked (well, philosophers don’t really have licenses, but you get my drift).

Which means that we need to focus on (1), (2) and (3) above, from which (4) is allegedly derived. (1) is a fair statement of the metaphysical notion of physicalism, so no problem there. (2) is also true, pending further elucidation of what one means by the tricky term “metaphysically possible.” (3) is where Chalmers hits what will turn out to be an insurmountable brick wall.

Let’s look at it more closely, highlighting the potentially problematic bits: we can conceive of a world physically indistinguishable from our world but in which there is no conscious experience. It follows that such a world is metaphysically possible.

What does it mean to be able to “conceive” such world, in this case? And what, exactly, is metaphysical possibility?

The pertinent dictionary definition of “conceiving” is: to form a mental representation of [something]; to imagine. Well, in that sense, I can certainly conceive of a p-zombie, and of a lot of other nonsensical objects as well. Heck, I can fool myself that I can even conceive of a squared circle, which is mathematically impossible. Clearly, something more rigorous has to be in play here for the argument to go through.

One thing that is not in play is physical possibility. Chalmers himself clearly stated: “Zombies are probably not naturally possible: they probably cannot exist in our world, with its laws of nature.” [9] He also wrote: “it certainly seems that a coherent situation is described; I can discern no contradiction in the description” [10] by which I assume he means no logical contradiction. And finally: “From the conceivability of zombies, proponents of the argument infer their metaphysical possibility” [11].

Keep the above distinction among logical, physical and metaphysical possibilities in the back of your mind for a bit, it will turn out to be crucial.

There are, of course, a number of standard responses to Chalmers’ argument. Dan Dennett famously thinks that Chalmers is simply confused about the notion of conceivability: p-zombies are not actually conceivable, because when examined more closely they embed hidden contradictions, just like many other imaginary objects that we are free to conjure up in our mind when we impose few if any constraints. The better response, in this case, came from AI researcher Marvin Minsky, who pointed out that Chalmers’ argument begs the question: in order to work, it has to assume that some characteristics of human beings, namely consciousness, are not produced by physical processes, which is precisely what the argument allegedly sets out to prove. In formal terms, there is a hidden premise in the argument, lurking somewhere between (2) and (3) above. Once this premise is brought to light, the argument is actually shown to be circular (though still logically valid, mind you!).

What is metaphysical possibility?

Which brings us back to the pesky idea of metaphysical possibility. What is it, exactly, and how is it distinct from logical and physical possibility? This is critical, because Chalmers’ whole gambit relies on the proposition that metaphysical possibility is, in fact, distinct from the other two forms, and doesn’t collapse into one or the other. As we shall see, this assumption may be hard to defend.

Let us begin with a little classificatory scheme of possibilities (and, equally, impossibilities):

  • Logical: typically thought of as the broader kind of possibility (and, conversely, the strictest kind of impossibility). “My friend Phil is a married bachelor” is an example of logical impossibility, as the word bachelor is defined as an unmarried man. More intriguingly, it turns out that something called Noether’s theorem [12] mathematically proves that if the laws of physics are invariant through time then the principle of conservation of energy has to hold true. That is, it is logically impossible for a universe to have both time-invariant laws and violations of conservation of energy. (Naturally, it also follows that it is not logically contradictory, as far as we can tell, to imagine a universe whose laws change over time and where the conservation principle does not hold.)
  • Metaphysical: this is the pesky one. It is commonly thought to be either co-extensive with logical possibility, or to be a subset of it. Perhaps the best known example of metaphysical necessity (which is, of course, stronger than mere possibility) is Kripke’s statement that “water is H2O” is metaphysically but not logically necessary. The idea is that there is no logical contradiction is thinking that water might not be H2O (so this doesn’t rise to the level of logical necessity), and yet it seems physically impossible for that to be the case. Hold this particular thought in place while we turn to the next level.
  • Physical (or nomological, i.e., law-mandated): this means that something is possible (or impossible, or necessary) under the laws of physics of our universe. For instance, for me to jump out the window and start levitating is logically possible (i.e., the idea involves no apparent contradiction of any principle of logic), and yet it is physically impossible. Philosophically, what is interesting here is that ever since Hume, many philosophers have treated the laws of physics as metaphysically contingent, in the sense that they could have been otherwise. Indeed, if the concept of the multiverse [13] holds water, this is likely the case. Some philosophers, however, like Sydney Shoemaker [14], think that the laws of physics couldn’t be otherwise, in which case physical and metaphysical possibility would turn out to be the same.

As I mentioned above, there are two other types of possibilities that occasionally enter into these discussions: epistemic and temporal/historical/contingent. Let’s examine them briefly before setting them aside and going back to the all-important concept of metaphysical possibility.

Temporal (or historical, or contingent) possibility simply means that things could have been otherwise not only logically, but also physically (i.e., without contradiction of either logical principles or physical laws). For instance, I could be writing this essay in my office at CUNY’s Graduate Center, rather than at home, as in fact I am. While contingency plays a crucial role in pretty much all the so-called “special” sciences (i.e., anything but fundamental physics), it doesn’t really concern us here. [15]

As for epistemic possibility, this is marginally relevant to our discussion, as hinted at above. For instance, at the moment at least, we do not know whether Goldbach’s conjecture [16] in mathematics is true or not. But, presumably, there is a fact of the matter as to whether it is or it isn’t, regardless of whether we will or will not ever be able to find out.

Back to metaphysics, then. First off, remember that metaphysical possibility lies somewhere between logical and physical possibility. But here is a new question: which logic, and which physics?

The question is not facetious, and indeed I suspect may lead us to a pretty solid conclusion of our quest, which will imply the rejection of Chalmers’ argument above, among other things.

As any above-introductory level student of logic knows, there are many types of logics out there [17], so that, strictly speaking it makes no sense to say that something is logically possible/impossible unless one also specifies which type of logic applies. For instance, in classical Aristotelian logic, the principle of non-contradiction applies: either A is B, or A is not B, but definitely not both [18]. But if one adopts dialethic logic [19] it turns out that certain propositions (typically, those involving logical paradoxes under classical logic) can be both true and not true. (That said, unlike my colleague Graham Priest, I don’t actually buy this, but it will do for the sake of illustration here.)

Analogously, we need to be clear on which set of laws of physics we are operating. The obvious one is the set that applies to our universe, but one could imagine situations applicable to other parts of the multiverse (if it exists) that are governed by different laws. Indeed, some physicists have even proposed that the laws of our universe change over time [20], which means that we would have to specify not just which universe we are talking about, but also when (again, personally not buying it, but it’s out there). Consider again Kripke’s assertion that “water is H2O” is not logically, but metaphysically, necessary, because it cannot physically be otherwise. Well, that’s true for our laws, in this particular period of the universe’s evolution. But if one or more physical constants were different, then it would be perfectly (physically) possible for a substance to have the chemical constitution H2O and yet for its behavior to be different from what we call “water.”

The bottom line is that I think that when people talk about metaphysical possibility/impossibility/necessity they can do so coherently, and position metaphysical space in between logical and nomological spaces, only because they are not careful enough to specify which logic and physics they are contemplating. I suggest further that if we are more precise and fix a particular logic and a particular nomology, then metaphysics space collapses into either one or the other (i.e., some metaphysical possibilities/impossibilities/necessities will turn out to be logical, and other, physical).

So, what about analytic metaphysics, then?

All of the above would seem to bode badly for the whole idea of doing anything like analytic metaphysics, the sort of thing Chalmers engages in [21]. Indeed, one could use the above analysis to question the point of philosophical inquiry itself, at least conducted in the above fashion.

Except, of course, that what you just read is an essay in philosophy — not science, not logic, not mathematics, not literary criticism. What we did was to begin with a startling claim, which was apparently presented in a logically solid framework; we parsed it, unpacked it, poked into it, until we found one or two weak points; we then proceeded to explore just how weak those points were and why; and we finally reached some conclusion, which of course is going to be tentative and open to the very same process, which I’m sure my readers will launch into with gusto as soon as this is published. That’s philosophy, folks!

What about metaphysics and metaphysical possibility, however? If it is true, as I’ve argued above, that metaphysical possibility/necessity/impossibility collapse into either their logical or physical counterparts, depending on the particular statement being made and on which logic and physics one considers while making it, what is left to do for metaphysicians?

Here I endorse (with some caution) the now famous approach to metaphysics articulated in a number of fori by James Ladyman, Don Ross, and colleagues [22]. Although these authors refer to what they do as “scientific” or “naturalized” metaphysics, and they openly disdain the Chalmers brand, labeling it as “neo-Scholasticism,” in reality, I hope, they are all doing the same thing (though some better than others). What they are doing is positioning metaphysics at the interface between logic and science, from which it naturally follows that metaphysicians will arrive at conclusions that are constrained by either the principles of logic or the laws of physics, depending on which side of that spectrum of possibilities they happen to be focusing. P-zombies, as it turns out, are physically, and therefore metaphysically, impossible (in this universe), though not logically so. But the fact that they are logically possible is no argument against physicalism at all, since physicalism itself isn’t a logical necessity, it just happens to be the best (in the specific sense of most fecund) metaphysical approach to understanding the world.

_____

Massimo Pigliucci is a biologist and philosopher at the City University of New York. His main interests are in the philosophy of science and pseudoscience. He is the editor-in-chief of Scientia Salon, and his latest book (co-edited with Maarten Boudry) is Philosophy of Pseudoscience: Reconsidering the Demarcation Problem (Chicago Press).

[1] Is quantum mechanics relevant to the philosophy of mind (and the other way around)?, by Quentin Ruyant, SciSal, 21 July 2014; The Turing test doesn’t matter, by Massimo Pigliucci, SciSal, 12 June 2014; Information is the new Aristotelianism (and Dawkins is a hylomorphist), by John Wilkins, SciSal, 1 May 2014.

[2] Three and a half thought experiments in philosophy of mind, by Massimo Pigliucci, Rationally Speaking, 6 September 2013; Computation, Church-Turing, and all that jazz, by Massimo Pigliucci, Rationally Speaking, 5 August 2013; Philosophy not in the business of producing theories: the case of the computational “theory” of mind, by Massimo Pigliucci, Rationally Speaking, 29 July 2013; The zombification of philosophy (of mind), by Massimo Pigliucci, Rationally Speaking, 29 July 2008.

[3] The Conscious Mind: In Search of a Fundamental Theory, by David J. Chalmers, Oxford University Press, 1996.

[4] Is there (still) a continental-analytic divide in philosophy?, by Massimo Pigliucci, SciSal, 17 July 2014.

[5] Naming and Necessity, by Saul A. Kripke, Wiley-Blackwell, 1972.

[6] Behaviorism, by George Graham, Stanford Encyclopedia of Philosophy.

[7] Physicalism, by Daniel Stoljar, Stanford Encyclopedia of Philosophy.

[8] What hard problem?, by Massimo Pigliucci, Philosophy Now, 2013.

[9] Consciousness and Its Place in Nature, by David J. Chalmers, in: The Blackwell Guide to the Philosophy of Mind, edited by S. Stich and F. Warfield, Blackwell, 2003, p. 5.

[10] The Conscious Mind, p. 96.

[11] Consciousness and Its Place in Nature, p. 5.

[12] Noether’s Theorem.

[13] The multiverse as a scientific concept, by Coel Hellier, SciSal, 3 June 2014 & 5 June 2014.

[14] Time Without Change, by Sidney Shoemaker, Journal of Philosophy, 1969, 66:363–381.

[15] Of course, if metaphysically you are a reductive determinist then temporal possibility reduces to physical possibility, because nothing could have happened differently, and our sense that there are stochastic events in the universe is the result of limited epistemic access to reality.

[16] Goldbach Conjecture.

[17] Logics, by John Nolt, Cengage Learning, 1996.

[18] Aristotle on Non-contradiction, by Paula Gottlieb, Stanford Encyclopedia of Philosophy.

[19] Beyond true and false, by Graham Priest, Aeon magazine, 5 May 2014.

[20] Time, laws, and the future of cosmology, by Lee Smolin, Physics Today, 2014, 67:38-43.

[21] Metametaphysics: New Essays on the Foundations of Ontology, ed. by David Chalmers, David Manley and Ryan Wasserman, Oxford University Press, 2009.

[22] Scientific Metaphysics, ed. by Don Ross, James Ladyman and Harold Kincaid, Oxford University Press, 2013.

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148 replies

  1. A zombie wouldn’t have to care about anything though, it would just get out of bed and go to church because getting out of bed and going to church is one of the mechanisms that are built into the zombies, legs. A zombie is just a concept of a complete imposter, but we are surrounded by partial imposters. A sociopath is an emotional zombie. An actress is a personality zombie. A liar is a truth zombie.

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  2. Clearly you have a greater imagination than me. Why did the zombie go to church? Because it had legs. You think this is a good answer?

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  3. Hi Massimo, thank you for the reply!

    “Because they would violate physics (and biology) as we understand them.” Here is the problem: why “they would violate physics (and biology) as we understand them” should justify any conclusion about some necessity (the impossibility of p-zombies) rather than some ordinary actuality since it is assumed that “physics and biology as we understand them” could change? I mean, physics and biology don’t deal with modal matters by themselves. And logic does not tell anything about the modal status of what we take to be true in those fields either. If there is no metaphysical modality (as something irreducible to logical or physical modality), then there is no basis to judge physical modality.

    We can get no substantial conclusion on modal matters without getting serious about metaphysics (and by that I mean doing analytic metaphysics). Quine was right about that: if we want to restrict metaphysics to metaphysics of science (as the guys from naturalized metaphysics want), then we should say goodbye to modal matters (Quine didn’t said this exactly, but I think you get the point).

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  4. Massimo:
    “Nobody doubts that there are explanatory, epistemic gaps. I see no reason to think they are ontological, which is Chalmers’ point. If he were simply saying that we don’t yet understand consciousness the response would be a very loud collective “duh!””

    Yes I agree with you that the conceivability cuts to the heart of the argument. My little example was meant as a joke of how the child conceived the car could run on water because of his lack of knowledge. Likewise Chalmers argument has appeal because we lack the knowledge of how neurons achieve consciousness. The negative conceivability we get from the argument is the fact that it is natural that more complex behavior in nature is accompanied by higher awareness. The positive conceivability point that Chalmers puts in the argument is that “something must be added”. I think what Chalmers is doing is giving us the objective view that if you took a zombie with all of its identical behavior and “added something”, that something would not be consciousness per se, but what Ted Honderich says nature adds to us https://www.youtube.com/watch?v=UDTSPe88d20. Very simple and very elegant that we have conflated something into first person consciousness which Chalmers attempts to unravel with the Zommbie conjecture.

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  5. DM,

    “if metaphysical possibility is an incomplete subset of logical possibility, then it is possible that something is logically possible but not metaphysically possible. Correct?”

    Obviously: physical possibility is a subset of logical possibility. Remember that I am denying that there is such thing as metaphysical possibility as distinct from either logical or physical. The former collapses into one of the other two.

    “This would be a problem for Chalmers’ argument, because showing that p-zombies are logically possible would not show that they are metaphysically possible. If Chalmers’ argument is to work, therefore he has to show that the two are identical, which you have done for him.”

    I have not done any such thing. I have argued that p-zombies are logically possible only insofar logical constraints are *very* loose anyway. But they are physically impossible, end of story.

    “If he doesn’t think zombies are naturally possible, then he is not talking about natural possibility.”

    He doesn’t deny their physical possibility, he simply is on record saying that he thinks it’s unlikely. There is a difference.

    Richard,

    “I don’t think Massimo has succeeded in showing that zombies are inconceivable.”

    It’s interesting that so many commenters think that’s what I tried to do. Obviously, my mistake for not being clear: my point is that metaphysical conceivability is not a thing at all: it either collapses into logical or into physical possibility/impossibility, which means that statements such as “p-zombies are conceivable” are meaningless, unless one frames them in either rigorously logical or empirically verifiable terms.

    “he will also insist that there are natural laws that connect the physical correlates of consciousness to the phenomenally conscious experiences”

    And where does he get those laws from? A hat? There are no additional laws other than the laws of physics, as far as I can tell.

    “We might say that something could have been true of our world if a(n ideal) reasoner does’t find that it entails a contradiction when taken together with the appropriate formal statement of the actually true laws of physics that hold (at the time, etc)”

    No reason to bring in ad hoc semantics here, this is the same as contingent/historical possibility as discussed in my essay, and as well understood in philosophy of science.

    “We might also say that something could be true of a world in general when there is no contradiction in (or following from) the description of the world (to any arbitrary level of detail one wishes)”

    Yes, and that’s logical possibility. And there’s nothing else in between…

    “This seems like a metaphysical possibility in the sense that, though it could not have been true of our world given its actual laws that we think hold now”

    It is a logical possibility, not a metaphysical one (unless, again, one simply equates the two). But, again, logic imposes very loose constraints on the way the world is, so it really doesn’t get us very far in these discussions. And it certain doesn’t get us anything like the challenge to physicalism that Chalmers ultimately wants.

    “there is a possible world in which ‘lightning is electrical discharge’ come out to be false”

    Right. Such scenarios are described by modal *logic*, no need to bring metaphysics into it.

    “if you really could build a world that had just our physics, whatever that turns out to be (I vote for quantum field theory/string theory btw), and if at the end of that process you don’t have consciousness, as it exists right now, then how can you say that consciousness is one of these physical process?”

    But you couldn’t! In order to get a world without consciousness you’d have to change *something* in the world as it is, because otherwise you get a physical impossibility.

    “if you could show that zombies are physically impossible (rather than naturally impossible) that would amount to showing that the concept of a zombie entailed a contradiction.”

    No, because there are all sorts of things that are not physically possible (travel at speeds higher than that of light) that entail no logical contradiction whatsoever.

    Coel,

    “I see a difference between logic and physics in the same way that I see a difference between physics and biology. All three are descriptions of the world.”

    Sorry, no. There is no world described by a lot of topologies in mathematics, and no world compatible with an infinity of logical possibilities. At best logic and mathematics describe all possible worlds, only one of which is actually instantiated (save the multiverse, of course).

    “”physical constant” means “value that has seemed constant to us so far”. So a better understanding could cause us to move an item from the “constant” category to the “locally contingent” category”

    Agreed. But you have to admit that this would be a *big* deal, if it turned out to be true of, say, the speed of light, or the mass of the proton.

    “the idea of “laws of physics” or “physical constants” being different elsewhere is merely a re-drawing of that boundary, rather than being anything radical.”

    Oh no, I think it would be pretty radical. Nobel-winning radical, in fact.

    Robin,

    “But Chalmers is deriving metaphysical possibility (indirectly) from conceivability rather than logical possiblity.”

    And that’s the whole problem in my view, as should be clear by now.

    “Chalmers has recast his argument in terms of his own two dimensional semantics”

    Yeah, I’m not going there. If someone has to invent a whole new semantics in order to defend a highly questionable and fuzzy notion, I’ve got better things to do.

    james,

    “I would be grateful if you, or anyone else, could provide a meaning for “information” that does not require physical substance for an “information process””

    I can’t think of any, but it doesn’t follow that everything is information in any meaningful sense. I suggest the following readings: http://goo.gl/5Krpgp and http://goo.gl/BlyqUS.

    “I would also be grateful for a definition or description of Consciousness that does not involve pattern recognition, (I.e., that does not involve feeling, sensing, perceiving.)”

    Not possible, that’s what consciousness is: the phenomenal experience of certain internal states of the organism.

    SelfAware,

    “The question for me is whether those logically possible universes allow us to make conclusions about ours. I can see where working through them might be a valuable exercise for thinking outside the box, but any conclusions from that type of reasoning alone would be suspect, at least to me.”

    Well, all conclusions arrived at by human thoughts are fallible and therefore tentative. But I do think thinking about logical possibilities is, as you put it, a valuable exercise.

    David,

    “Not sure what you mean by semantics here”

    Semantics deals with meaning, grammar with structure. Just think of logic, for instance, where it’s all done in terms of the structure of reasoning, regardless of the content, i.e., without semantics.

    “but to locate a category mistake, these statements must be richly meaningful. They are confused but not nonsense.”

    No, category mistakes are nonsensical, although in a different way from the nonsense of grammatical gibberish.

    Gregory,

    “why “they would violate physics (and biology) as we understand them” should justify any conclusion about some necessity (the impossibility of p-zombies) rather than some ordinary actuality since it is assumed that “physics and biology as we understand them” could change?”

    Because we can only meaningfully talk about the physics and biology we understand. So, any statement of the type X is physically/biologically impossible is assumed to imply “given the epistemic warrant we currently have concerning physical/biological possibility.”

    “If there is no metaphysical modality (as something irreducible to logical or physical modality), then there is no basis to judge physical modality.”

    Why? We know that perpetual motion machines, for instance, are physical impossible. Why isn’t that good enough?

    victor,

    “Likewise Chalmers argument has appeal because we lack the knowledge of how neurons achieve consciousness.”

    But to me that’s essentially an argument from ignorance. We may found out, one of these days. Or not. Nothing metaphysically compelling follows from it.

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  6. Massimo,

    It is a mistake to think that Chalmers introduces a third kind of possibility. He has the two I talked about, and you say that these are in fact the two you had in mind. Given your terminology Chalmers’ argument is that zombies are logically possible and that this is enough to refute physicalism. You say that this doesn’t get us a challenge to physicalism but it does. To illustrate suppose that a version of the identity theory is true. Then my conscious experience of red, say, will be identical to some specific neural event. So, if the identity claim is true it is necessarily true (this follows from the fact that it is necessary that everything is self identical and Leibniz’s law). Now if there is a possible world where there is physical duplicate of me but which lacks consciousness then we do in fact have a contradiction. This world will have a creature with all of my physical states, so it will have the physical state which is identical to the conscious experience of red, and so will consciously experience red. But we described the world as one where it doesn’t consciously experience red. So if consciousness is identical to a brain process then there is a contradiction entailed by the conceiving of zombies. It is in that sense that zombies must be logically impossible; there must be some kind of contradiction entailed by the assertion of P&~Q (where P is a complete description of the fundamental microphysics of our world and Q is an arbitrary statement about consciousness, like that I am consciously seeing red).

    The same is true in the case of lighting and electrical discharge. If you tell me that you can conceive of a world that is physically just like ours but in which lightning is not electrical discharge I would say that you cannot conceive of that, since given the way our world is it entails a contradiction (i.e. that there is and isn’t electrical discharge in that world). What is logically possible is that there is a world that has physical laws similar to ours but which are not exactly the same.

    You seem to endorse this line when you responded to me as follows,

    “if you really could build a world that had just our physics, whatever that turns out to be (I vote for quantum field theory/string theory btw), and if at the end of that process you don’t have consciousness, as it exists right now, then how can you say that consciousness is one of these physical process?”

    But you couldn’t! In order to get a world without consciousness you’d have to change *something* in the world as it is, because otherwise you get a physical impossibility.

    if this is true then zombies cannot be possible in any sense. So I still don’t see how you have defused the argument. If you allows that zombies are logically possible (in your sense) then Chalmers wins.

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  7. Hi Massimo,

    This comment is rather long but I urge you to read it carefully as I’m 99% sure you’re making a basic error in your treatment of Chalmers’ argument because you’re misinterpreting what he means by metaphysical possibility.

    I was very bewildered by your argument but now I think I understand where you’re coming from.

    Tell me if the following paragraph represents your view (I’m going to concentrate on the possibility that metaphysical possibility collapses into logical possibility because this is the interpretation I endorse myself).

    Chalmers’ argument depends on the idea that p-zombies are metaphysically possible, but since metaphysical possibility may collapse into logical possibility, metaphysical possibility as a distinct concept is nonsense. Since Chalmers’ argument depends on a nonsensical idea, it is fatally flawed.

    There’s a big problem with this argument because you don’t consider what metaphysical possibility actually means. You take an incomplete definition from Wikipedia which just says that it’s a subset of logical possibility and gives one example, but this is not enough.

    This is from the SEP:

    “Φ is metaphysically possible if and only if Φ is true in some metaphysically possible world.
    Example: It is metaphysically possible that some physical particle moves faster than the speed of light.”

    This is the sense in which Chalmers means it.

    So, unlike logical possibility and physical possibility, which define what is possible according to some rules (logical axioms or laws of physics), metaphysical possibility is defined by its role — it is the kind of possibility we need when we discuss what could exist in some possible world. It doesn’t vanish when you show it collapses to logical possibility any more than the President of the USA vanishes when you show it is (currently) co-extensive with Barack Obama. Metaphysical possibility collapsing to logical possibility just means that all logically possible worlds can exist. By distinguishing metaphysical possibility from logical possibility, Chalmers is actually being modest. If there are some logically possible worlds which are not metaphysically possible, then showing that p-zombies are logically possible does not automatically show that they could exist in some possible world.

    If we do not assume that metaphysical possibility collapses to logical possibility, then Chalmers’ original argument can be attacked on the grounds that just because something is conceivable (by which I interpret Chalmers to mean logically possible) doesn’t mean that it could actually exist.

    If we assume that metaphysical possibility collapses to logical possibility (i.e. that all logically possible worlds could actually exist), then this objection is not available and Chalmers’ argument becomes the following (although I’ve made a few other adjustments too):

    1. According to physicalism, all that exists in our world, including consciousness, is physical.
    2. Thus, if physicalism is true, a logically possible world in which all physical facts are the same as those of the actual world must contain everything that exists in our actual world, including conscious experience.
    3. A world which is physically indistinguishable from our world but in which there is no conscious experience seems to entail no logical contradictions. If so, it follows that such a world is logically possible and is a possible world.
    4. Therefore, physicalism seems to be false. (Because 4 follows from 2 and 3 by modus tollens.)

    The problem with this argument is in my view point 3. Just because we can’t see logical contradictions does not mean there are none (which is why I modified 3 and 4 to use the word ‘seems’). This is precisely Dennett’s objection, and this objection is the correct one in my view.

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  8. Hi Richard,

    I now realise your objection to Massimo’s post is essentially the same as mine, phrased differently. Could you read my comments to Massimo and confirm that we agree?

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  9. Richard Brown gets it.

    If you allows that zombies are logically possible (in your sense) then Chalmers wins.

    That’s exactly right. And reading his other comments more carefully again I think that he is essentially making the same points as I, although in a more technical way.

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  10. Wins what? C’mon people, go back to the basics: Chalmers want to say that the conceivability of p-zombies amounts to a potential blow for physicalism. If indeed what he means by metaphysical conceivability is simply logically possible then he’s got nothing, because it would follow that all sorts of other things that are logically possible but physically impossible would pose the same threat. That simply cannot be what he means, or he is terribly confused. (And I think he is confused, but not so terribly.)

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  11. In response to Richard Brown, Massimo said:

    But you couldn’t! In order to get a world without consciousness you’d have to change *something* in the world as it is, because otherwise you get a physical impossibility.

    Not according to the view Chalmers advocates. Chalmers thinks there is natural law which is something separate to physical law. You can think of natural law as magic pixie fairy dust. Magic pixie fairy dust has no physical effects whatsoever. All physical events happen just the same with or without it.

    But without magic pixie fairy dust, you don’t get consciousness. Magic pixie fairy dust is what brings phenomenality into physical interactions, which otherwise would be entirely unconscious. So you can have a world which is physically the same, both in terms of laws and physical events, but without consciousness.

    If you need to visualise how it might be possible to have a world with all the same laws of physics but no consciousness, just consider a simulation which perfectly implements the laws of physics. You think that simulation would contain no consciousness, even though within the context of the simulation, the laws of physics are just the same as in the real world. So the laws of physics are not enough to give rise to consciousness. To make these laws of physics give rise to consciousness, we need something more — we need the equivalent of Chalmers’ natural law. On biological naturalism, that natural law mandates that consciousness requires that we have actual physical particles interacting in actual biological brains and not only representations of them in computers.

    This is why Chalmers is your natural ally. The only way biological naturalism is tenable is if Chalmers is right.

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  12. Hi Massimo,

    because it would follow that all sorts of other things that are logically possible but physically impossible would pose the same threat. That simply cannot be what he means, or he is terribly confused.

    That wouldn’t follow at all.

    Look at the version of the syllogism I posted a couple of comments up.

    For Chalmers’ argument to work, he has to show that it is logically possible for the same physics to obtain and the same physical events to occur but for the world to be different in some way. Showing that something is logically possible but not physically impossible is nothing like this.

    An example of an alternative argument against physical might involve moral realism. If we assume moral realism, then we could perhaps imagine another possible world with the same physics but in which the morally right thing to do is to murder babies. If we assume that it is not morally right to murder babies in this world but it is in that world, and the physics of the two are the same, then physicalism would have to be false.

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  13. DM, this is going to be my last comment for a while, since I’ve got a book to finish. Please try to read what I write charitably and with understanding. There is no meaningful distinction between natural laws and physical laws, regardless of whatever Chalmers says.

    As for biological naturalism, one more (last?) time: it does NOT involve any kind of magic. It is a pretty darn straightforward statement that the materials with which you do X matter to how X comes out, or to whether it functions at all. Ask any engineer about this. My position is that consciousness requires certain materials to work precisely because we have laws of physics that limit what biological organisms can and cannot do. No magic, no bizarro “natural” laws required. Cheers.

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  14. Hi Massimo,

    “There is no meaningful distinction between natural laws and physical laws, regardless of whatever Chalmers says.”

    I agree. Which is why I characterise Chalmers’ view disparagingly as “magic pixie fairy dust”.

    “As for biological naturalism, one more (last?) time: it does NOT involve any kind of magic. ”

    I understand that is your position. I disagree with it, because you require not only the laws of physics for consciousness (because these can be implemented on a computer) but also something extra, that they be implemented natively in the universe itself. If this is so, then that requirement could charitably be called natural law, but it is not a physical law because a physical law could be implemented on a computer.

    That’s a side issue though. I would ask that you ignore that and pay close attention to Richard’s and my arguments because you are getting Chalmers’ argument badly wrong. There are some very important points against your post which remain unanswered — namely the logical possibility variant of the syllogism and the charge that you misunderstand the implications of Chalmers using logical possibility directly.

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  15. “Because we can only meaningfully talk about the physics and biology we understand. So, any statement of the type X is physically/biologically impossible is assumed to imply ‘given the epistemic warrant we currently have concerning physical/biological possibility.’”

    If the truth of statements of that kind is relative to their epistemic warrant, then you will have to accept some kind of verificationism (I wouldn’t argue against that here, but I take any form of verificationism to be false). If its not the truth of the statements that is relative, then probably you will get something trivial that will not answer my point.

    “Why? We know that perpetual motion machines, for instance, are physical impossible. Why isn’t that good enough?”

    It’s not good enough because it begs the question. The statements “Perpetual motion machines are impossible” and “Mutable physical laws are possible” can’t be both inside physics without ambiguous modality (and so we would open the door to metaphysical modality).

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  16. OK let me just throw my opinion in again. I think Massimo is correct that the heart of the argument is in the conceivability premises, not the conclusion. Many processes in my senses are “zombies” or purely physical i.e. when the light level in a room changes or I look at a distant object my eyes automatically adjust or these reactions can be explained in purely physical terms (physicalism is true). However when I am walking around feeling and perceiving the environment (not dark inside), I am “non-zombied” and since this is not purely/intuitively explainable in physical terms (yet?), then physicalism must be false. Why the Chalmers argument is intriguing and why it is popular because he points to the gap between the purely physical unconscious behavior and conscious behavior in our nervous systems. Maybe it sounds mundane but I think it is the locus that all of these discussions and controversies revolve around.

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  17. As to the conceivability of philosophical zombies, let’s imagine a human being who has his consciousness switched off. Let’s call them a sleeper. We can even imagine them talking or even walking. Are they indistinguishable from conscious human beings? I don’t think so, so I’m not sure that it is really conceivable that philosophical zombies can exist. I think anything that moves from one place to another is aware of its environment to some degree. I don’t think they’re human consciousness, but movement without awareness of some sort is I think distinguishable.

    I think the notion that a philosophical zombie really is conceivable carries the assumption that the Turing Test is wrong because true consciousness, the ego, is not a product of material reality, therefore no behavior, no matter how complex can count as signs of a soul? And the flip side, apparent zombies, we cannot rely upon any signs of brain behavior as signs of consciousness, in persistently vegetative coma patients…or for that matter, in fetuses. Aren’t we really talking about souls here?

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  18. Paul Braterman: “There is something very wrong with the idea that there is any necessity to the fact that water is H2O. Firstly, it is at best contingently true, given our laws of nature, that there exists a compound with this formula, but under different laws of nature this would not have been the case.”
    “… is Kripke’s statement that “water is H2O” is metaphysically but not logically necessary. The idea is that there is no logical contradiction is thinking that water might not be H2O (so this doesn’t rise to the level of logical necessity), and yet it seems physically impossible for that to be the case.”

    I have read this type of statement many times before without giving a hoot about it as I simply discounted it as simply nonsense. Yet, it is seemingly becoming a widely accepted great wisdom. Thus, I would like to say something about it now. I will talk about it on three levels.

    One, linguistically: is H2O as water, as ater, as terwa,… ? It does not make one bit of difference.

    Two, is H2O logically necessary? For heaven’s sake, what ‘logic’? Logic of induction? Logic of deduction? Logic of physics? Logic of math? Logic of ‘heaven’s sake’? Before they make such a strong statement “… not logically necessary…”, they should at least show “what the damn logic they are talking about?” The only logic which makes H2O not logically necessary is the multiverse argument. Yet, multiverse can be ruled out by simply showing that the key nature constants (Alpha, Cabibbo and Weinberg angles, ħ, etc.) are not bubble-dependent, (see http://tienzengong.wordpress.com/2014/02/18/damage-control-for-the-multiverse/ ).

    Three, is H2O a metaphysically necessary? What the heck is metaphysics? This will quickly turn into the chicken/duck argument, and thus, there is no point to argue over this issue. Today (yes, today, not the time of Aristotle or Hume), the physics knows about a lot of facts (truth) which will stay true for long time to come (in fact, eternally). I will list only five of them below while ignoring all the other nitty-gritty.
    1. Four forces
    2. Forty-eight ‘matter’ particles
    3. Quantum principle
    4. Relativity
    5. Some key nature constants (Alpha, Cabibbo and Weinberg angles, ħ, Planck data, etc.)

    Now, let’s put the metaphysics aside but discuss only two ‘physics’ issues.
    A. How did these ‘five’ come about?
    B. Can a different set of ‘five’ be ‘produced’?

    There is a good chance that these two issues become one if the ‘five’ can only be produced with ‘one’ way. This is in fact a ‘physics’ issue, not about metaphysics.

    If ‘procedure A (PA)’ produces the ‘known five’, can PA produce a ‘new five’?
    If a ‘procedure B (PB)’ produces a ‘new five’, can PB produce the ‘known five’?

    If we can show that for any (arbitrary) PB, PB = PA, then PA is universal, no multiverse. Yet, what is PA? In fact, this is not a very important question. If we know the ‘attributes’ of PA and PB, we can do a great deal of analysis on them without knowing exactly what they are. In fact, we can simplify the issue one step further. Instead of being a ‘procedure’, we can view the PA as an ‘object’ first. But, what are the key attributes for PA?

    For any PB, PB = PA. This equation holds only if PA is ‘unchangeable’ and ‘unsubstitutable” which could be expressed as ‘timeless’ and ‘immutable’. However, they are not terms of philosophy or theology. They are the terms of physics, that is, they must be ‘operational’ defined (not philosophical concepts or theological ideas). Can we find an ‘object’ in this universe which is both timeless and immutable (unchangeable and unsubstitutable)? Yes, ‘infinity’ is an object in math, and it is both unchangeable and unsubstitutable. However, for the ‘current mainstream physics’, the infinity is not an object as a physics-reality. Yet, infinity has another ‘side’ {0 = 1/infinity}. Yet, can ‘nothingness (0)’ be a physics-timeless-and-immutable entity?

    In short, is zero (0) [nothingness] a physics-reality? Seemingly, the answer is no. At the moment of this universe came into being, it has an ‘arrow of time’ which is something, not nothing. That is, in the entire lifetime of this universe, there is always ‘something’, not one moment in the state of ‘nothing’. In this physics-universe, the best ‘nothing (0)’ is the Cosmology-constant (with at least 120 zero after the decimal point). But, there is no guarantee that a non-zero digit won’t pop out after that. In short, we have not found a physics-zero in this universe thus far. If this is the case, then there is no ‘timeless and immutable’ object (let alone a process) in ‘this’ universe. Then, there is no way to guarantee that PA is timeless and immutable, that is, there could have many PB(s) which are not PA (thus, multiverse prevail). And, ‘the H2O, not logically necessary’-nonsense might no longer be a nonsense.

    Now, the issue is very clear. The only way to rule out the ‘multiverse’ is ‘if the PA is indeed timeless and immutable’. Of course, PA could be timeless and immutable even while this universe is not. But, if we can find ‘one’ item in this universe which is timeless and immutable, then we can show that PA is definitely timeless and immutable. Now, we know that the only chance of finding a thing in this universe is timeless and immutable is by crashing the ‘arrow of time’. At least, we must show that the ‘arrow of time’ is only an ‘emergent’ from a ‘fundamental’ which is timeless and immutable. So, our task has two parts.

    First, to ‘derive’ the ‘known five’ from a PA (the process which gives rise to the laws of physics), see the link above.

    Second, to show that that PA is timeless and immutable (not as concepts and ideas, but must be processes). So,
    a. Timeless ‘process’
    b. Immutable ‘process’

    I will not show these two ‘processes’ in this short comment but will make a statement here.

    Statement: Yes, these two processes are realities in this universe.

    Thus, there will definitely be no multiverse and ‘the H2O, not logically necessary’-nonsense is definitely a nonsense.

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  19. Richard,
    I think Massimo’s got hold of a little more than you let on here.
    “Now if there is a possible world where there is physical duplicate of me but which lacks consciousness then we do in fact have a contradiction.”
    No doubt. But that is a statement about possibility not inconceivability.
    “So if consciousness is identical to a brain process then there is a contradiction entailed by the conceiving of zombies.”
    Here you neatly substitute “conceivable” for “possible” in a way that Massimo is problematizing. You more or less assume that what is conceivable is possible which is contradicted by square circles, highest prime numbers, perpetual motion machines etc etc. And no, appeals to idealized reflectors will not do, simply because we do not have any. At any rate, the many philosophers who reject physicalism are motivated by the reflections of the decidedly less than ideal reflector named David Chalmers (or Peter Jackson or Thomas Nagel or whatever). Yet, as Dennett would say, we may not have enough information to properly conduct the thought experiment, such that what seemed perfectly separable to us (the physical and mental) would not seem so in possession of all the facts.

    If anyone is interested this has me remembering my Wittgenstein:
    “But in a fairy tale the pot too can see and hear!” (Certainly; but it can also talk.)
    “But the fairy tale only invents what is not the case: it does not talk nonsense.” — It is not as simple as that. Is it false or nonsensical to say that a pot talks? [Here’s the crucial bit] Have we a clear picture of the circumstances in which we should say of a pot that it talked? (Even a nonsense — poem is not nonsense in the same way as the babbling of a child.)
    PI 282
    Before anyone gets snarky I realize Ludwig is contradicting what I said about meaning above. I think he’s wrong, but the point stands.

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  20. Hi Massimo,

    (quote in reply to my claim that logic, physics and biology are all descriptions of the world)

    Sorry, no. There is no world described by a lot of topologies in mathematics, and no world compatible with an infinity of logical possibilities. At best logic and mathematics describe all possible worlds, only one of which is actually instantiated (save the multiverse, of course).

    The real division here is between rules/descriptions that are universal and those that are not universal. Suppose it is the case that the “universal” set includes logic, maths and some of physics. In that case we would not expect the “infinity of logical possibilities” to be extant, because everything would also be obeying the physical rules/description, which narrows things down a lot. In this case the absence of worlds matching all logical possibilities and all mathematical topologies is entirely in line with my claim.

    Now suppose that the “universal” set is logic and maths alone (with all physics being local and contingent). In that case, it more or less follows that there *are* worlds out there matching all mathematical topologies and all logical possibilities. (At least, I don’t see how you know that there aren’t.) So, again, your counter is not a counter.

    The last possibility is that even logic is local and contingent, in which case “all possible worlds” far exceeds “all logical possibilities” (presuming we take logic to mean our logic).

    In any of these cases, I don’t see any counter to the idea that logic, maths, physics, biology and history are all descriptions of the world (but differing in universality).

    Oh no, I think it would be pretty radical. Nobel-winning radical, in fact.

    So a once-a-year degree of radicality then? OK, I’ll agree with that!

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  21. Hi David,

    Here you neatly substitute “conceivable” for “possible” in a way that Massimo is problematizing. You more or less assume that what is conceivable is possible which is contradicted by square circles, highest prime numbers, perpetual motion machines etc etc.

    It is my view (and I believe Richard’s) that Chalmers is using “conceivable” to mean “seems to be logically possible” and from this assuming that p-zombies are in fact logically possible.

    Please read my rewording of his argument to clarify how I understand him if we assume that metaphysical possibility is the same as logical possibility. I’ll repeat it here.

    1. According to physicalism, all that exists in our world, including consciousness, is physical.
    2. Thus, if physicalism is true, a logically possible world in which all physical facts are the same as those of the actual world must contain everything that exists in our actual world, including conscious experience.
    3. A world which is physically indistinguishable from our world but in which there is no conscious experience seems to entail no logical contradictions. If so, it follows that such a world is logically possible and is a possible world.
    4. Therefore, physicalism seems to be false. (Because 4 follows from 2 and 3 by modus tollens.)

    Now, what is wrong with this version of the argument? It is not what Massimo is focusing on, certainly. Rather, it is Dennett’s criticism that stands.

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  22. I think one issue here is whether we interpret “the world” to mean our universe or “the world” to mean all that exists, which may entail multiple universes.

    But how we count universes is also somewhat arbitrary. By some definitions something is in a different universe if it’s merely far enough away. The bubble universes of inflation are all part of one whole, one continuous conjoined reality, so calling the whole ensemble “the world” seems to be reasonable. Similarly with the many worlds interpretation of quantum mechanics — despite the name — this view holds that the actual fundamental reality of the universe is one wave function evolving deterministically in Hilbert space. The reality we see is just one shard of this single world or universe. The universe itself doesn’t split, but we do along with every other object in it (at least from one perspective).

    To return to Massimo’s point…

    At best logic and mathematics describe all possible worlds, only one of which is actually instantiated (save the multiverse, of course).

    At best, logic and mathematics describe all that exists, and all of it is instantiated. We can call this the multiverse or we can call it the world. It depends how you use the term. If it’s all really one whole and it all exists, then calling the whole thing “the world” seems reasonable to me.

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  23. Hi DM,
    For clarification, in my above comment I used “world” to mean what we observe, and “worlds” (plural) to refer to possible other worlds with different physics or logic. “Universal”, as I used it, would refer to the ensemble of all worlds.

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  24. Because it is programmed to fool people into thinking it is human. That’s what a p-zombie is. If you say that a zombie wouldn’t go to church by themselves, then you are begging the question by smuggling in facts about the actual world and using them to affirm the very theory that is in question. Humans go to church because consciousness is not a mechanism. Zombies could go to church for whatever reason we like, but the fact of their going to church can exist as the blind product of programmed physical behaviors.

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  25. Yes, exactly, where my thought was taking me. We can conceive of a p-zombie, but only if it doesn’t do anything; as soon as it engages in non-vegetative behavior, it is no longer distinguishable from us, and becomes useless for the sake of the argument. Chalmers’ understanding of ‘consciousness’ is an additive (to behavior, physiological processes, etc.,) that doesn’t add anything. Of the theories of additive consciousness that would really add something, the strongest, oldest, and most strenuously argued for are theological theories of the soul. And unfortunately one has to accept an awful lot of rubbish when one buys into any of them.

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  26. Hi DM,

    “When we think we can imagine a creature that behaves like a human being but is not conscious I think we are kidding ourselves.”

    I understand Peter J when he says “a creature that behaves like a human being” to mean the similarity between that creature and a human is very high, so I have little reason to not assume it would be conscious.

    “If a computer behaves indistinguishably from a human (as assessed by text-based conversation), then it is assumed to be conscious”

    In that comparison I think the behavioral similarity between the computer and a human implied by the statement “indistinguishably as assessed by text-based conversation” could be very low, so for that case I see little reason to assume it would be conscious.

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  27. Tienzengong – What you say makes sense to me, both in regard to the water problem, which I cannot comprehend at all, and about what I can only assume is the Tao from your description of it. Is this where you’re heading? If so it’s a fascinating argument you’re making.

    A timeless and immutable phenomenon could never be in this universe or a part of physics. I don’t think we need to test for this or wonder for very long. It would have to be unmanifest. It would very definitely be a part of metaphysics and mysticism, however, and we must be careful not to rule it out just because it is not part of physics.
    .

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  28. I’m willing to buy that talk of “metaphysical possibility” really collapses into talk of “logical possibility given logic L”, where the logic in L is something far more robust than first order logic.

    Let’s call this “R-Possibility”, meaning “what analytic metaphysicians meaningfully call ‘metaphysical possibility’ or ‘genuine possibility’, but which in fact is logical possibility relative to a robust logic L”.

    Still, a physicalist cannot accept that Zombies are R-Possible.

    Here’s why.

    1. First, notice that your defense that “physicalism itself is not a logical necessity” misses the point. No, physicalism itself is not an R-necessity. But physicalism is a claim about some kind of R-necessity. At the maximum it’s a claim about identity: conscious properties are R-necessarily identical to physical properties. At a minimum it’s a claim about supervenience: any world with the same physical properties R-necessarily is a world with the same conscious properties. (Though it’s recognized now that supervenience may not be sufficient for physicalism, it’s widely supposed to be required by all forms of physicalism).

    2. As you note, Chalmers accepts that any world with the same physical properties and laws of physics is a world with the same conscious properties. That is, he accepts that physical properties physically necessitate conscious properties, but denies that they R-necessitate conscious properties. There are two possibilities: (a) either Chalmers is a misguided physicalist, on your view or, (b) physicalism requires something further that Chalmers accepts, on your view.

    3. OPTION (a). Let’s suppose Chalmers’s position is really a physicalist position, and he’s misguided about his own view, for physicalism only requires that physical properties physically necessitate conscious properties. Physicalism is compatible with the R-possibility of a world in which my body exists without my mind. Why is this a problem?

    Consider the following theorem of modal logic:

    (RBM) if A = B, then necessarily A = B

    That is to say, if two things are identical, they’re necessarily identical. Here ‘necessarily’ clearly does not refer to physical necessity but to some form of logical necessity. Clearly (RBM) entails that if A=B, then R-necessarily A=B, since R-necessity is supposed to be a robust sort of logical necessity.

    If it is R-possible that my body should exist without my mind, then my body is not identical to my mind even in the actual world. If it is possible for these physical properties to exist without these conscious properties, then these physical properties ain’t these conscious properties, actually. If holding that consciousness is something over and above the physical properties and that the body and the mind are not identical is a physicalist position . . . then dualism is a physicalist position.

    4. ON KRIPKE. You might want to reject reading (RBM) as involving R-necessity – and instead read it as involving physical necessity. You seem to think this is possible by holding that Kripke’s arguments really only involve physical necessity. First, note that (RBM), while used by Kripke in his argument, does not depend on Kripke’s arguments about reference and pre-dates Kripke by a few decades. Second, trying to reinterpret Kripke as truthfully concerned with physical necessity is very much backwards. Kripke’s point is not that H2O is necessarily identical to Water because it “seems physically impossible” for something to be water-like but not H2O or H2O and not water-like. Much the opposite: Kripke grants that it is physically conceivable (and physically possible) that there might be a substance which acts just like water for all intents and purposes but isn’t H2O, or there might be a world in which H2O fails to do the things we associate with water. Nonetheless, Kripke argues that because “Water” historically refers to H2O in our world, Water is identical to H2O in our world. And if he’s right that Water is identical to H2O in our world, then by RBM if follows that water is R-necessarily identical to H2O — even in those worlds in which something else acts like water, or in which H2O acts like something else.

    It’s possible to reject Kripke on reference and hold some form of descriptivism. But you can’t reject the distinction between logical and metaphysical necessity on the grounds that Kripke failed to consider that H2O could have non-watery properties in a world with different physical laws, since that’s actually part of Kripke’s argument.

    5. OPTION (b). So, let’s suppose instead that physicalism is true even though zombies are R-possible, but that physicalism requires something more than just accepting that zombies are physically impossible. . . . Well, the ball’s in your court. What is it? What more does it require?

    You see, historically, the distinction between logical and genuine metaphysical possibility was supposed to be an aid to the *physicalist* for this reason. The possibility that physicalism involved a posteriori metaphysically necessary (but logically contingent) connections between brain and mind was brought it for the sake of the physicalists – against Chalmers and (at that time) Frank Jackson. This new brand of physicalist was supposed to be able to say in response to Chalmers, “well, Zombies are logically possible, but they’re not a *geniune* *metaphysical* possibility”. Removing the distinction between metaphysical and logical necessity makes Chalmers’s job a good deal easier. No more need for the last 15 years of that messy two-dimensional semantics stuff!

    Because if both you and Chalmers share the position that zombies are logically possible but physically impossible, and Chalmers is a dualist for pretty straightforward reasons given in (3), then it’s up to you to say what it is that the physicalist holds that a dualist like Chalmers can’t hold. And I don’t see anything left.

    6. TRUTH IN ADVERTISING. But to be honest, from your own description, it sounds like your view is really neither physicalist or dualist, but rather a kind of anti-metaphysical view. And anti-metaphysicians can’t meaningfully take sides in metaphysical disputes, since these disputes make assumptions and distinctions they either reject or admit they do not understand. So your readers should not think that you’ve somehow undermined Chalmers and vindicated Chalmers’s physicalist critics. Rather, they should understand that your position is that one ought to ignore the physicalist/dualist dispute entirely and replace it with a different (and in your view, more productive) conversation. Meanwhile, both Chalmers and his physicalist critics will go on with their unproductive metaphysical conversation, unconcerned with anything you’ve brought up here.

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  29. 1. You say, “I think that anything that moves form one place to another is aware of its environment to some degree”. But what is your basis for thinking this? Is it from the concept of “awareness”; that is, by “aware” you just mean “responsive to its environment”? In that case, you’re not talking about what philosophers are talking about when they use the word “consciousness”. Or do you mean by “aware” having some sort of subjective, phenomenological experiences? If that’s what you mean, then it seems like your only reason for linking these up with bodies moving in a certain way is observation of the contingent world around you. So, you believe this on empirical grounds.

    But empirical truths are the sorts of things we can conceive of being otherwise. I can conceive of the Earth having oceans of pea soup; I know it doesn’t on empirical grounds. I can conceive of a world in which all of the things that look like cats are really alien robots with psychic powers; I know this isn’t the case on empirical grounds. Chalmers says: Zombies are conceivable; we know there are no zombies on empirical grounds,

    Perhaps by “conceivable” you mean “easy to imagine” or “unsurprising”.

    2. Understanding why the turing test is not a good test for consciousness just takes understanding what philosophers mean by “consciousness” — namely, that subjective experience you’re having right now, not the degree to which you are responsive to stimuli. It takes no deep assumptions about the physical world or souls, just understanding what the conversation is about.

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  30. Well, perhaps it’s just the case that the proper determination of what constitutes consciousness will be determined by practitioners in the laboratory – in neurophysiology, biochemistry, genetics, and neuroscience – and related sciences – because apparently philosophy can’t get us there. Logic and metaphysics cannot determine reality – which is, as it always is, just what it is..
    Of course when that happens, the physicalist position will be vindicated, and will be incorporated in textbooks as part of the standard explanation. For better or worse, that seems to be the historical relationship between philosophy and science.

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  31. Hi SAP,

    *Within* the universe, your reasoning, your logic, holds,

    Or yours, so you cannot use logic to infer that you exist – just what I was saying. But that is just what you did.

    I am not talking about the universe existing and not existing in a superposition – I am talking about the universe not existing at all – no superposition, no nothing.

    So how do you know that anything at all exists?

    Well, you start with the fact that you exist.

    Then you infer that if you exist then something exists.

    But you have just assumed the validity of the axioms of identity and non-contradiction.

    But, if you are saying that these might not hold outside of our universe then it is circular to use then to infer that something exists.

    So you would have to take seriously the proposition that nothing exists at all – no universe, no superposition, no nothing.

    So, I am asking you, do you take seriously the proposition that nothing whatsoever exists?

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  32. Or, as I meant to say, do you take seriously the possibility that nothing whatsoever exists?

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  33. Hi Coel,

    Is that a claim about what cannot be done with current instruments and experiments (in which case it is mostly a statement about our current limitations) or is it a claim applying however advanced our scientific capabilities (in which case how do we know this, isn’t it simply begging the question?)?

    No matter how detailed our models become and no matter how perfect our instruments become – we would still have a mathematical model which predicts observations – it will always be conceivable that those mathematical models describe something which happens without any consciousness happening.

    That is just in the nature of empiricism – we can directly observe the consciousness of one and only one organism.

    I suppose some new epistemology could come along which would have a different way of knowing than empiricism – but that is like saying that maybe we will discover magic or God or something.

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  34. PeterJ: “… It would very definitely be a part of metaphysics and mysticism, however, and we must be careful not to rule it out just because it is not part of physics.”

    Thanks for your comment. But, you have misunderstood me.

    The ‘timeless (eternality) and immutable’ were only the concepts of philosophy and theology, and they are not a part of the ‘current mainstream physics’. But, they must be parts of the ‘nature physics’. And, I emphasized that they both must be ‘physics’-issues and must be defined ‘operationally’ (as physics-processes). That is, they are in fact parts of this physics-universe. Of course, I have not yet discussed these two physics-processes at the comments of this thread.

    Coel: “In that case we would not expect the “infinity of logical possibilities” to be extant, … Now suppose that the “universal” set is logic and maths alone (with all physics being local and contingent). In that case, it more or less follows that there *are* worlds out there matching all mathematical topologies and all logical possibilities. (At least, I don’t see how you know that there aren’t.)”

    Well, you have presumed that the physics-universe is different from the logic/math-universe while you did not show any argument on that presumption. I will argue that the logic/math-universe is ‘identical’ to the physics-universe. Of course, the burden of proof on this is on me. But, if you want to disagree with me before reviewing my proofs, then the burden of proof will be transferred to you.

    In order to prove that ‘all’ math-possibilities do not go beyond this physics-universe, I must show two proofs.

    Proof one, a process A (PA) which gives rise to the ‘five known’ physics, listed below.
    a. Four forces
    b. Forty-eight ‘matter’ particles
    c. Quantum principle
    d. Relativity
    e. Some key nature constants (Alpha, Cabibbo and Weinberg angles, ħ, Planck data, etc.)

    Proof two, this PA is ‘timeless and immutable’, and these two must be expressed as ‘processes’ (not just concepts). With this proof, it will be easy to show that ‘all’ math (or metaphysics) possibilities are subset of this ‘physics’-universe.

    I have showed a big portion of the proof one (1) at your article (see, https://scientiasalon.wordpress.com/2014/06/05/the-multiverse-as-a-scientific-concept-part-ii/comment-page-1/#comment-3158 ). You did not reply my comment there. But, it is the only way to keep arguing your claim if you reply my step one (1) argument first, and then it will be my turn to show my proof two (2).

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  35. HI Massimo: ” At best logic and mathematics describe all possible worlds, only one of which is actually instantiated (save the multiverse, of course).”

    So who or what decides what is logically/metaphysically/physically possible in the multiverse? And how can any claim in this regard be tested?

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  36. I disagree with it, because you require not only the laws of physics for consciousness (because these can be implemented on a computer) but also something extra, that they be implemented natively in the universe itself.

    It’s worth mentioning that if you have a complete simulation of the universe – a simulation in which causality is defined by the (complete) laws of physics – then “matter”, as it exists in our universe, *is also being simulated*. The computer is not the “substrate” in the same sense that matter is the substrate of physical processes in our universe. The computer is a meta-substrate, and *simulated* matter is the substrate of physical processes.

    When people conjecture that our actual universe might be a simulation, they are talking about the existence of a meta-substrate.

    So when you say that consciousness requires the physical substrate as it exists in our universe, it does not rule out a simulation, because the substrate you need is there, and it acts exactly as it does in our universe.

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  37. Richard and DM are surely correct to maintain (despite Massimo’s incredulity) that Chalmers’ argument comes down to logical possibility: “if you allow that zombies are logically possible … then Chalmers wins”. After all, Chalmers insists in “The Conscious Mind” (p. 41) that for physicalism to be correct the phenomenal facts must logically supervene on the physical facts. The argument that zombies are conceivable is one of a number which he then puts forward (CM pp. 94-99) to show that there can be no such logical supervenience: if the phenomenal facts were indeed logically supervenient on the physical facts, then we should be able to ascertain some logical contradiction in the notion of a p-zombie (and that section is actually titled “The logical possibility of zombies”).

    The version of Chalmers’ argument against physicalism that most clearly shows the underlying logic of his case is, I think, that given in his 1999 “Mind and modality” seminar (http://consc.net/class/596b/week2.txt), because it is explicitly formulated in terms of a priori entailment:

    “(1) Physical concepts are all structural-dispositional concepts;

    (2) If B truths are to be entailed a priori by structural-dispositional truths, there must be some analysis of B concepts in structural-dispositional terms;

    (3) There is no analysis of phenomenal concepts in structural-dispositional terms; so

    (4) Phenomenal truths are not entailed a priori by physical truths

    (where ‘B’ stands for some domain that is to be subject to reductive explanation).”

    Chalmers takes something like (3), the key premise, to be self-evident, noting that: “To analyze consciousness in terms of some functional notion is either to change the subject or to define away the problem. One might as well define ‘world peace’ as ‘a ham sandwich’” (CM, p. 105). The orthogonal nature of the two different types of concept means that there appears to be no “conceptual hook” (The Character of Consciousness, p. 123) by which a purely phenomenal concept can be linked to physical or functional concepts.

    However (to briefly summarize a suggestion I make at http://www.holli.co.uk/hardproblem.htm), even if we were to accept for the sake of argument everything that Chalmers supposes in connection with his various anti-physicalist arguments, they all fail anyway: because on Chalmers’ own account of meaning, what is important for a concept’s role in inference is the concept’s intension (more specifically its primary, or epistemic, intension), i.e. the implicit criteria by which we apply that concept. So what Chalmers actually needs to demonstrate, if he is to prove that a phenomenal concept cannot have an inferential role which could conceivably ground a priori entailments from physical or functional facts, is that the concept’s intension, its applicability criteria, cannot be analysed or formulated in physical or functional terms. And that he simply does not do: as John Perry and Peter Alward have both pointed out, albeit in rather different contexts, Chalmers does not actually investigate the applicability criteria for a phenomenal concept in the way that his general discussion of primary intensions would suggest – even in his lengthy discussion of phenomenal concepts in Chapter 8 of “The Character of Consciousness”. Instead, he just takes it for granted that the applicability criterion is simply the instantiation of the some phenomenal property.

    I’m therefore completely in agreement with DM’s conclusion: “just because we can’t see logical contradictions does not mean there are none.”

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  38. Hi Marc,

    I think we have very different intuitions on that. I think the capacity to be indistinguishable from a human in a text conversation implies having all the cognitive faculties of a human because there is very little in the way of cognitive ability that cannot be assessed by text.

    But if it’s the text part of it that bothers you, then you can imagine putting the computer program in control of a robot body similar to a human body, with senses and motor control similar to a human. For purposes of the thought experiment you can imagine the robot body even looks human if you like. Meanwhile the computer itself is in some basement controlling the robot over WiFi.

    Can we not say that it is conceivable that the computer would behave like a human, as assessed by observing and chatting with the robot body? If so, would it necessarily be conscious?

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  39. Hi ejwinner,

    We can conceive of a p-zombie, but only if it doesn’t do anything; as soon as it engages in non-vegetative behavior, it is no longer distinguishable from us, and becomes useless for the sake of the argument.

    If that is your view, then I don’t think you understand what consciousness means in Chalmers’ mind and in the minds of many thinkers (including Massimo and Matean Oghbergutean above).

    I am inclined to agree with what you imply, that consciousness is just what it feels like to be an intelligent being. Any being with that kind of intelligence will feel conscious the way we do to ourselves.

    But this view is controversial. Many people think that the outward appearance of intelligence and the inner experience of phenomenal consciousness are two different things and have no necessary connection. They believe, for instance, that one might be able to make a computer that can do everything a human can do (including claim itself to be consciousness and find itself attracted to deep philosophical questions about consciousness) without actually being conscious.

    So Chalmers’ p-zombies are similar to simulations of humans in this respect. They are non-vegetative, they walk around and are responsive to their environments. But they are supposed to be unconscious automatons. Simulacra of conscious beings with no actual inner life.

    You are quite right in my view that this position seems to imply something like a soul, however Chalmers and biological naturalists would both vehemently disagree with you. Chalmers thinks there is some kind of natural phenomenon pervading the universe that brings brains to consciousness, and is open to the idea that all matter may be conscious to some extent (panpsychism). Biological naturalists just think that all we know is that consciousness requires a brain like ours and any suggestion that it could exist on other substrates (even if they processed information and so behaved identically) is wild speculation.

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  40. Hi Matean,

    But what is your basis for thinking this? Is it from the concept of “awareness”; that is, by “aware” you just mean “responsive to its environment”? In that case, you’re not talking about what philosophers are talking about when they use the word “consciousness”.

    That’s not necessarily true. There are philosophers who think that consciousness and awareness in the sense of responsiveness are not really two different things. The difference may be one of degree, of complexity or sophistication. The position you endorse — that consciousness really is a distinct phenomenon separate from sensitivity and information processing — is a controversial one (as is the opposing view).

    Understanding why the turing test is not a good test for consciousness just takes understanding what philosophers mean by “consciousness”

    Not so. I understand what philosophers mean by consciousness and I think the Turing test is a good test for consciousness. I think philosophers who think it is not are mistaken, because I think their concept of what consciousness is is confused. My view — and as controversial as it may be it is not an especially radical or uncommon one — is that consciousness is just what it feels like to be a system processing information in a certain way. If this kind of information processing is required to behave like a human (and I think that likely), then the Turing test can be used to infer that information is being processed so. If we can infer that information is being processed as in a mind, and if consciousness is just what it feels like to be such an information processing system, then the Turing test can be used to infer consciousness. I believe Dennett, for example, would agree with me.

    The point is that it is a mistake to assume that others are not aware of the issues just because they express a view you disagree with.

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  41. Quoted for truth:

    You see, historically, the distinction between logical and genuine metaphysical possibility was supposed to be an aid to the *physicalist* for this reason. The possibility that physicalism involved a posteriori metaphysically necessary (but logically contingent) connections between brain and mind was brought it for the sake of the physicalists – against Chalmers and (at that time) Frank Jackson. This new brand of physicalist was supposed to be able to say in response to Chalmers, “well, Zombies are logically possible, but they’re not a *geniune* *metaphysical* possibility”. Removing the distinction between metaphysical and logical necessity makes Chalmers’s job a good deal easier.

    Well said. This is exactly the point I have been making. The distinction between logical and metaphysical possibility makes Chalmers’ argument harder. Collapsing the distinction plays into Chalmers’ hands.

    The problem seems to be that Massimo forgets that metaphysical possibility is by definition the kind of possibility we mean when we talk about what can actually exist. Collapsing it to logical possibility therefore doesn’t destroy it as Massimo seems to think — rather it just means that any logically possible world can exist. Once this is made clear Massimo’s argument falls apart.

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  42. Hi Robin,

    it will always be conceivable that those mathematical models describe something which happens without any consciousness happening.

    Being conceivable is not the same as being possible (since I can conceive of all sorts of impossible things). Thus saying that it is *possible* is begging the question.

    That is just in the nature of empiricism – we can directly observe the consciousness of one and only one organism.

    It’s more that we can *experience* the consciousness of only one organism, but experiencing something is different from observing it.

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  43. Hi Robin,
    This is an interesting discussion. It seems like we’re talking across a conceptual barrier here. (And perhaps I’m on the wrong side of it, but of course I don’t think so 🙂 )

    “Or yours, so you cannot use logic to infer that you exist – just what I was saying. But that is just what you did.”
    Exactly, within our universe.

    “I am talking about the universe not existing at all”
    From within the universe, it certainly exists. From outside the universe? Existence outside the universe may be a meaningless concept. Consider that to a video game character, her universe exists, but from outside the game, it’s just a game. We can say the game universe “exists”, but only within the game.

    “So, I am asking you, do you take seriously the proposition that nothing whatsoever exists?”
    From within the universe, no. (It’s not clear to me that “nothing whatsoever” is a meaningful concept in our universe.) From outside of the universe, I recognize that the question itself may not have meaning. “Existence” may be a concept local to our universe.

    My point on this is that once we start talking about outside of our universe where our natural laws end, everything we expect about reality becomes suspect. We can pick and choose what we think persists outside of our universe, but we’re doing so in mid air with nothing but structures within our universe to justify our choices, structure which are not guaranteed to continue beyond the boundaries of our universe.

    But, I’m curious of what your line of reasoning might be if I said either “yes” or “no” to the nothing question.

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  44. I’m not sure that it’s right to say that Chalmers is engaging in analytic metaphysics in the metametaphysics volume. In his paper in that volume he’s very much on the anti-metaphysics side, along with around half of the other authors in the volume (albeit for different—but not incompatible—reasons from Ladyman et. al.).

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  45. “The ‘timeless (eternality) and immutable’ were only the concepts of philosophy and theology, and they are not a part of the ‘current mainstream physics’. But, they must be parts of the ‘nature physics’. And, I emphasized that they both must be ‘physics’-issues and must be defined ‘operationally’ (as physics-processes). That is, they are in fact parts of this physics-universe.”

    Tienzengong. I don’t know the difference between physics and ‘;nature physics’. You seem to be saying that physics needs an immutable phenomenon but does not have it at present. I was suggesting that it does not need it and can never have it. Any such phenomenon would have to belong in metaphysics, where it is indispensable.

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  46. Hi DM,

    “I think we have very different intuitions on that”

    Maybe not all that different.

    “But if it’s the text part of it that bothers you, then you can imagine putting the computer program in control of a robot body similar to a human body, with senses and motor control similar to a human. For purposes of the thought experiment you can imagine the robot body even looks human if you like. Meanwhile the computer itself is in some basement controlling the robot over WiFi. Can we not say that it is conceivable that the computer would behave like a human, as assessed by observing and chatting with the robot body? If so, would it necessarily be conscious?”

    Either way, text conversation with computer or a human like robot, I think I could be fooled. So I don’t think it would necessarily be conscious.

    “I think the capacity to be indistinguishable from a human in a text conversation implies having all the cognitive faculties of a human because there is very little in the way of cognitive ability that cannot be assessed by text”

    I see lots of problems. Like: the lower the quantity of sensual data (a text base conversation) one uses to judge humanness implies the higher, or more thorough, the testing standard for “indistinguishable from a human” must be. And who is doing the testing, by what methods, how long can the test go on for, etc.

    And humans can pretend to be a computer, so if computers could model humans in a reliable fashion they could pretend to be non-human, and why did I bring up digestion: because if I really think it is a human based on a text conversation, then I will probably also be thinking it can digest food, be conscious, and type.

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  47. Massimo, by framing it this way…

    “we don’t yet fully (or even very partially!) understand how consciousness can be produced in a physical system,”

    You are, despite all the good work of your article, giving Chalmers everything he wants. Why? Because you are framing the notion of consciousness as though it were a thing that is produced, as though it were a single thing. By slicing off consciousness from all the other things that a properly functioning brain does, you are granting him the ghost in the machine. Isn’t consciousness a bunch of different, complimentary, reinforcing brain functions?

    I mean, Chalmers could just as easily talk about the Hard Problem of Walking. Sure, you might be able to describe all the mechanics of walking, even down to the neurons and muscle fibers, but that’s all the easy problem of walking. But no matter what you do, you will never find the one thing that makes walking feel like walking.

    Yes, Chalmers could say, we could make a machine that walks exactly the way we do, but it won’t feel like it’s walking. And we can imagine a universe where the humans are identical to us, except they don’t have the first person feeling of walking. All of which proves that there is no single physical explanation for the sensation of walking.

    The proper response to the Hard Problem of Walking or Walking Zombies is to say there is no one sensation associated with walking. We would ask Chalmers if the walking zombie is aware, at least as far as his spinal chord goes of the angle and pressure of his ankle joints. Sure, he’d concede. That sensation or awareness is an essential part of the feedback loop associated with the complex of behavior called walking. Then we’d ask if the walking zombie is aware of his bodily orientation. He’d have to concede that as well. And so on, until we’ve gotten him to concede that all the sensations of walking are necessary to any human walking in any universe. But, he’d probably foolishly stick to his point, “you haven’t described the ONE thing that it feels like to walk.”

    Consciousness is not a single thing. It is not a single process. Therefore it’s a circular argument to insist that the one thing that it is can likely never be described.

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