The zombie argument against physicalism usually goes like this

  1. Physically identical zombies are conceivable.
  2. If zombies are conceivable, they are metaphysically possible.
  3. Therefore physicalism is false.

Many physicalists deny (2), that conceivability implies metaphysical possibility, while accepting (1).

But by accepting (1) there is an explanatory gap, i.e. consciousness does not have a reductive physical explanation.

What is the physicalist response to the explanatory gap?

  • See SEP Qualia and the Explanatory Gap:"it has no consequences for the nature of consciousness and physicalist or functionalist theories thereof... There aren’t two sorts of natural phenomena: the irreducibly subjective and the objective. The explanatory gap derives from the special character of phenomenal concepts. This response to the explanatory gap obviously bears affinities to the second physicalist response... to the Knowledge Argument". Physicalists then proceed to give an account of why phenomenal concepts are perceived as such.
    – Conifold
    Commented Oct 23, 2018 at 17:59
  • 1
    @Conifold -- yes SEP contains the words "it has no consequence for the nature of consciousness ...", etc, but for any empiricists, a phenomenon which exists and one's world model cannot predict nor explain is NOT "no consequence" for the usefullness of that model. How is the SEP claim justified, or is it a rejection of empiricism? The latter portions of that paragraph imply that what is being described may be delusionism, or may be epiphenomenalism -- each of which face empirical refutations.
    – Dcleve
    Commented Oct 24, 2018 at 3:08
  • @Dcleve Your notion of empiricism is not the usual one, most empiricists only consider publicly accessible phenomena to be empirical. Qualia are by definition non-empirical (if we admit them it is unclear why private experiences of revelation from God should be rejected). Physicalists are committed to reducing public phenomena to physics. The existence of private phenomena is public, so they give accounts of how those can emerge. But the "explanatory gap" refers to non-reduction of private content to the physical, which is definitionally true, but moot as far as physicalism is concerned.
    – Conifold
    Commented Oct 24, 2018 at 21:14
  • @ Conifold -- I don't understand why anyone would consider empiricism to be 3rd person. When you awake in the morning, by what means do you determine that you are prone, under covers, what room you are in, that your bladder is full, etc? This is empiricism, and it is a first person activity, based on mostly private content. Are you rejecting first person empiricism because you want to exclude spiritual experiences?
    – Dcleve
    Commented Oct 24, 2018 at 21:24
  • 2
    It may be helpful to define “explanatory gap”. Because it's pretty uncontroversial to simply state that we currently cannot explain the existence of consciousness. “explanatory gap” has to be a stronger notion than that.
    – viuser
    Commented Oct 25, 2018 at 1:48

3 Answers 3


Physicalists have several responses: 16+% of all philosophers actualy disagree with P1. See page 16: https://philpapers.org/archive/BOUWDP The reason would be a belief in the logical necessity of Identity Theory -- and that anyone who held that Identity Theory was untrue was simply confused.

36+% of philosophers reject P2. Our imagination is not rational and based on our ability to imagine irrational things, one cannot infer possibility from imaginability.

Accepting P2 does not necessarily leave an explanatory gap. There are several standard physicalist responses:

a) Knowledge shortfall -- consciousness is identical to either neurology or algorithms of some kind, but we don't know what kind yet, or how this happens. The "explanatory gap" is just a shortfall of current knoweldge, and at some point we will be able to close that gap, and explain how consiousness is Identical to brain or processing states.

b) Deny that we really are conscious, or have qualia. This is the strategy of both Dennett delusionism, and Churchland eliminative reductionism. If humans are zombies, then the "zombie argument" loses all its sting.

Whether any of these arguments are effective or not is something which cannot be addressed in a single reply on a discusison board, and requires reading deep into the Philosophy of Mind literature. I simply outlined the primary physicalist responses above, not whether they work.

Two sources I can recommend to start this process would be: Susan Blackmore's "Consciousness A Very Short Introduction", and Jaegwon Kim's "Physicalism or Something Near Enough". Both are, or were, physicalists, but are highly skeptical of physicalist arguments.

Blackmore focusses on psych lab experiments that refute the neural and algorithmic Identity Theory arguments, and also on the consistency of our knowledge of consciousness. She considers all physicalist models refuted, but physicalism to be proven by physics, so she ends up rejecting that consciousness even exists.

Kim depends on philosophical consensus, plus logic -- primarily related to causation. He too assumes physics has proven causal closure of matter. He holds that the consensus of the last 50 years of Philosophy of Mind is that qualia exist. He shows using causal logic that Supervenience must either reduce to neural identity theory or break his Causal Closure assumption (and he thinks that algorithmic identity theory is a dualist worldview, despite the protests of the algorithmecists). And he cites the consensus of Philosophy of Mind that experiential qualia cannot be reduced to neurons. This leads him to an epiphenomenal dualism for portions of consciousness.

These two authors are in conflict with each other, but that is where Philosophy of Mind is today. There is no consensus view.


Question: The zombie argument against physicalism usually goes like this

  1. Physically identical zombies are conceivable.
  2. If zombies are conceivable, they are metaphysically possible.
  3. Therefore physicalism is false.


  1. Physically identical zombies are conceivable. ...This assertion is wrong.
  2. & 3. follow from the physically invalid 1., so they are also physically invalid.


The assertion 1. is wrong because a zombie as defined as *“a being that is physically identical to a normal human except that it lacks qualia and consciousness (conscious awareness and experience)”[Ref 1-5] is physically impossible to exist. This article p-Zombies explains this matter in an easy-to-understand way as follows:

Although this definition is philosophically possible, it is not certain that it is physically tenable. This is because, if qualia and consciousness have physical effects, there might be something else that is physically associated with them disappears or changes in the p-zombie too when it lacks qualia and consciousness, and this will make the clause “physically identical to a normal human except that it lacks qualia and consciousness” impossible to be true physically. This problem will become obvious if we consider this definition in the form of equations:

A human = a being with qualia and consciousness and their effects … (1)

A p–zombie (philosophical definition) = A human – qualia – consciousness

= a being without qualia and consciousness but with their effects … (2)

Thus, if qualia’s and consciousness’s effects exist, Equation (2) will define a being that is impossible to exist physically because qualia’s and consciousness’s effects cannot occur without qualia and consciousness. Therefore, if we want to do an experiment to see whether, physically, a being with qualia and consciousness and a being without them are behaviorally identical or not, we must use the definition that all the beings in the experiment can definitely exist physically. In doing so, we must take the possibility that qualia and consciousness may have physical effects into account. Thus, the appropriate definition must instead be a p-zombie is “a being that is physically identical to a normal human except that it lacks qualia and consciousness and their effects”, as in the following equation:

A p–zombie (physical definition) = A human – qualia – consciousness – their effects

= a being without qualia and consciousness and their effects … (3)

Whether qualia’s and conscious experiences’ effects exist or not is to be proved by separate investigations.

The article goes on to show that qualia and consciousness have physical effects:

That qualia and consciousness have physical effects is simply because both qualia and consciousness have effects on the consciousness neural process: they induce the consciousness neural process to function to create conscious awareness and conscious experiences of themselves (this is evident by the fact that we do have conscious awareness and conscious experiences of both the qualia and our consciousness). Because the consciousness neural process is a physical process and because its function is affected, these effects are physical effects. And they are the physical effects that are to occur, at the minimum.

Therefore, because qualia and consciousness have physical effects, the philosophical definition is not physically valid, and the results (including the conclusions or deductions like 2. & 3. in the question above) of the thought experiment pertaining to this philosophical definition, although philosophically valid, are physically invalid and irrelevant to the physical (real-life) world.

Again, you can read a more detailed discussion of this matter here, and you can read more detailed proof that qualia and consciousness have physical effects here at section 5.4. and here at section 6.4..


  1. Chalmers DJ. Consciousness and its place in nature.
  2. Flanagan O, Polger T. Zombies and the function of consciousness.
  3. Kirk R. Zombies.
  4. Nigel J.T. Thomas. Zombie killers.
  5. Seager W. Are zombies logically possible? And Why It Matters.
  • Your assertion that P1 is wrong depends on a) our imagination being accurately rational, which it is not, and b) that consciousness and qualia are causal rather than epiphenomenal, which is not universally accepted. Your links do include arguments for the causal nature of consciousness and qualia, but the justificaiton they use-- that our neurology does not have any mechanism to create or recieve non-neural signals, is just a restatement of causal closure -- I.E. your link is assuming its physicalist conclusion as a precondition to the argument, and is explicitly circular.
    – Dcleve
    Commented Oct 24, 2018 at 8:51
  • The assertion that P1 is wrong is based on solid objective evidence. At present, the evidence from clinical neurology, neurophamacology, cognitive neuroscience studies, etc. all confirm that our brain, and the nervous system on the whole, does not have any mechanism to create or receive non-neural signals. This is the sole basis for the argument that P1 is wrong and is not circulatory on anything else.
    – user287279
    Commented Oct 24, 2018 at 10:16
  • What is the evidence to the contrary that the brain can ceate/receive non-neural signals? Those who object the assertion of my answer should provide solid, objective evidence against it, not just their belief or beliefs of other philosophers, which are not objective evidence.
    – user287279
    Commented Oct 24, 2018 at 10:17
  • 1
    You say that because consciousness has 'physical effects', we can't conceive of a zombie without consciousness. But couldn't something else in the zombie play the causal role of consciousness without actually being consciousness?
    – reeeeee
    Commented Oct 24, 2018 at 10:47
  • @user287279 -- "solid objective evidence" does not conflict with P1. That is an empirical test, which is only a challenge to whether actual humans are wired such that zombiehood is possible or not, which isn't even a challenge to P1 or P2, but a downstream challenge to an unstated P3. Meanwhile, your reference does not provide any evidence to reject P3, and you have the burden of proof here, shifing the burden of proof is a fallacy.qcc.cuny.edu/socialsciences/ppecorino/phil_of_religion_text/…
    – Dcleve
    Commented Oct 24, 2018 at 14:33

I would suggest that you examine this question without reference to zombies. They will do your head in and are not necessary to the argument. It is obvious that zombies as defined by Chalmers cannot exist even if we could conceive them. No zombie would have this present discussion.

The explanatory gap has nothing to do with zombies, which are just a way of thinking about it. This gap is the reason why Mind-Matter is and always has been a metaphysical problem. Physicalists have no way to solve it and they never will.

It is surely obvious that consciousness does not have a reductive physicalist explanation but all this stuff about zombies confuses the issues. It seems designed to tie us all in knots and prevent clarity. Chalmers' 'hard' problem is an ancient metaphysical problem and long predates his zombie argument.

Physicalism does not work in metaphysics so its proponents tend to ignore metaphysics and close their ears to logical argument like any good dogmatic theist, and perhaps this is what drove Chalmers to find a new argument to which they they might pay attention. Nice try but not a success.

Imagine a world that is just like this one except that consciousness gives rise to matter. You would be unable to distinguish it from this one. This will always be true. So perhaps it is this one.

You might like this. The discussion has been going on a long time.

"If the flesh was produced because of of the spirit, it is a wonder. But if the spirit was produced because of the body, it is a wonderous wonder. Rather, I am amazed that this great richness was placed in this poverty."

Jesus Gospel of Thomas V. 34

  • Is it really "obvious that consciousness does not have a reductive physicalist explanation"? Sure it doesn't right now, but perhaps we are just missing some physical facts? And isn't the explanatory gap an epistemic gap, not a metaphysical gap?
    – reeeeee
    Commented Oct 24, 2018 at 12:49
  • @PeterJ -- you argue for interactive dualism, and that is incompatible with Chalmer's zombies, which are based on his epiphenomenal dualism. An interactive dualist zombie would have different neurology, such that it does all human actions unconsciously. It would not be IDENTICAL to existing humans, but only subtlely different. Note that humans ARE zombies of this sort in 99% of what their brains do, and our zombiehood for most of our neuro and algorithmic activity, refutes both types of identity Theories.
    – Dcleve
    Commented Oct 24, 2018 at 16:26
  • @reeeeee -- I agree with you that the physicalist response is to assert the explanatory gap is only a temporary epistemic gap. I added a few references that bring that into question to my comment. I agree with PeterJ that all physicalist models are refuted, but it takes a lot more to show this than one short response in Stack Exchange.
    – Dcleve
    Commented Oct 24, 2018 at 16:29
  • @Dcleve Chalmers claims that zombies don't presuppose epiphenomenalism. See "(4) Zombies presuppose epiphenomenalism." in consc.net/papers/2dargument.html
    – reeeeee
    Commented Oct 25, 2018 at 2:08
  • @Dcleve - I'm certainly not arguing for dualism of any kind. You say we are zombies as far as out brains go, which may well be the case, but they are used as a way to examine consciousness, not brains. If we assume consciousness is a product of brains then zombies become plausible, but we cannot then use them to justify our assumption. .
    – user20253
    Commented Oct 26, 2018 at 11:35

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