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The Reverse-Zombie Argument against Dualism
Richard Brown
LaGuardia College, CUNY
Abstract
The zombie argument currently advanced by dualists is question begging. It cannot show that
physicalism is false because the first premise of the argument assumes that physicalism is false.
One cannot even conceive of zombies if physicalism is true. I invoke a type-B-ish Kripkean
strategy. The usual type-B defense admits that zombies are conceivable and then denies that they
are really possible. I argue, instead, that what Kripke shows is that it may seem to us as though
we are conceiving something when we are not. To illustrate this I give two reverse-zombie
arguments against dualism. The first invokes zoombies, creatures identical to me in every nonphysical way but which lack qualitative consciousness; the second invokes shombies, creatures
physically and qualitatively identical to me which are solely physical. These are conceivable and
so the dualist is in a dilemma. Either the original-zombie argument was question begging or
dualism is false.
As developed by David Chalmers the zombie argument against physicalism in its
simplest form goes as follows. Where ‘P’ here stands for the description of the world given by a
completed microphysics and ‘Q’ is the complete qualitative facts about us.
1. P and ~Q is conceivable
2. If (P & ~ Q) is conceivable, then (P & ~ Q) is possible
3. If (P & ~Q) is possible then materialism is false
4. Therefore materialism is false
The basic idea then is that it is conceivable that we could have a world that was microphysically
identical to the world that we live in and which lacked qualitative consciousness. Since this is
conceivable in the right way it follows that it is possible. And from this possibility it follows that
materialism is false. This is because the materialist is committed to the strong claim that the
mind-brain identities are (metaphysically) necessary.
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A lot of the debate about this argument has centered on premise (2) and whether or not
conceivability entails possibility. The typical argument that conceivability doesn’t entail
possibility is the standard Kripkean line about a posteriori necessities. So, it is suggested, I can
conceive that water is not H2O but as Kripke argued, it is not metaphysically possible that water
not be H2O. Chalmers argues that there is clearly a sense in which ‘water is not H2O’ is ideally
conceivable and so metaphysically possible. It is conceivable in the sense that if Twin Earth had
turned out to be actual it would have been the case that water was not H2O. If Twin Earth were
actual, as opposed to counter-factual, then water would have been XYZ. Whether we call the
watery-stuff in Twin Earth –that is, the stuff which would have been water if twin Earth were
actual— ‘water’ or not is irrelevant. When we are imagining Twin Earth we really do have
access to some possible situation and if that possible situation had been actual then it would have
been true that water was not H2O.
Chalmers then argues that when we conceive of the zombie world we really have access
to something which is metaphysically possible and since it is metaphysically possible that there
be a zombie world materialism is false. Therefore physicalists who endorse a posteriori identities
between qualitative states and brain states cannot avoid the zombie argument by invoking
Kripke. The dualist is in some sense conceiving a real possibility when they imagine the zombie
world (just like the person conceiving Twin Earth is conceiving something which is
metaphysically possible). Whether we apply our word ‘consciousness’ to it is irrelevant. The
realm of possibilities has not shrunk and ideal conceivability is still a good guide to what is
metaphysically possible.
But are zombies really conceivable? There are those who deny that they are. These are
what Chalmers calls a type-A physicalists. This is an elimitivistic position usually associated
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with Dennett or Churchland. These kinds of physicalists hold that when we have a completed
microphysics we will be able to deduce the qualitative facts from the physical facts and we will
see that the way that we describe the qualitative now is drastically misguided. The people who
adopt the Kripkean strategy are what Chalmers calls type-B materialists. But there is a way to be
a type-B materialist that denies that zombies are conceivable. Consider the classical Twin Earth
thought experiment. An alternative way of describing what happens here is that it seems to us as
though we are imagining a world where water is not H2O but we actually fail at that since it is
impossible. It seems to us that we can imagine this situation but we cannot. What we actually
succeed in imagining is something which looks like water but isn’t.
This is closer to the spirit of Kripke’s remarks. The whole point about Hesperus and
Phosphorus is that once we know they are the same object we realize that we weren’t really
imagining a case where the they were separate. We cannot imagine that one thing is really two
things. Similarly we cannot really conceive that water is other than H2O, since that is to conceive
of H2O as other than H2O which is absurd. What we can conceive of is a different substance
which presents the same contingent appearance properties as H2O does. This is, I believe, the
correct way to respond to the zombie argument. How can we tell whether or not we are really
conceiving of zombies in the relevant sense or whether we are merely conceiving of creatures
which very closely resemble us but which are not conscious? The case of water and H2O shows
us that our seeming to be able to conceive of something does not guarantee that we can really
conceive of the thing in question. It certainly seems to us as though we can conceive of water
that isn’t H2O but we can’t. So too it seems to us as though we can conceive of zombies but we
cannot.
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The zombie argument begs the question against this kind of Kripkean response. If
physicalism is true then it will --of course-- be the case that qualitative states are just physical
states. That is simply because if physicalism is true then everything is physical and since it is
undeniably true that consciousness exists it will be undeniably true that consciousness is physical
(if physicalism is true). So if this turns out to be true of our world then we cannot really conceive
of zombies in the way that the zombie argument requires. Therefore the zombie argument cannot
be an argument against materialism of this type unless we have already shown that dualism is
true. The problem is that the proponents of the zombie argument, and some of those against it,
just assert that zombies are conceivable. But we need some evidence that this is actually the case.
You’re telling me that you seem to be able to do it is not evidence that you are really doing it. I,
for instance, find that I can’t do it.
To illustrate this I will present the Reverse-Zombie argument against dualism. There are
two kinds of reverse-zombies that I call ‘zoombies’ and ‘shombies’. Each of these corresponds to
a way of being ‘the opposite’ of the traditional philosophical zombie. A zoombie is a creature
which is identical to me in every non-physical respect but which lacks any (non-physical)
conscious experience. I don’t merely mean that the zoombie exists in a world where there are
different bridge laws and the link between the physical and the mental is severed. I am
conceiving of the zoombie world as having any appropriate laws. If there were non-physical
properties that resulted from the microphysics of the zoombie world they would be linked in the
right way. Thus a zoombie is the dualist equivalent of a zombie: a creature just like me in the
right respect that lacks (non-physical) qualitative consciousness. Zoombies are conceivable and
so dualism is false.
One may object to the zoombie argument in the following way.
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Look, the question here is one of whether or not the qualitative facts can be deduced from
the complete micro-physical facts or not (like, say, table facts can). Let’s say that
answering ‘yes’ means that the mental is reduced to the physical. The original zombie
argument then shows that the mental cannot be reduced to the physical. What the
zoombie argument shows is that neither can qualia be reduced to any non-physical facts
that are not themselves qualitative; but no dualist has ever thought that! Therefore the
zoombie argument doesn’t truly parody the original zombie argument and so doesn’t
show that there is anything wrong with the original argument.1
But there are actually two separate questions here. One question is whether our mental concept
words, like ‘pain’ or ‘belief’, can be linked to the brain and its states. This is a question of intertheoretic reduction. This is a separate question from the ontological question of whether there is
anything more to the world than the physical. There are some physicalists who think that mental
concepts cannot be reduced to physical concepts even though ontologically speaking all there is
that exists is the physical state.2 One famous version of this kind of theory is Davidson’s
anomalous monism. Davidson held that the mind and the brain were identical but that we could
not reduce one set of concepts to the other in the sense that we could not deduce mental facts
from physical facts.3 If this is all that one takes the original zombie argument to be showing then
one has admitted that you haven’t shown that physicalism is false. What you have shown is that a
certain kind of physicalism is counter-intuitive. Namely, the kind which holds that you can
deduce the mental facts from the physical facts, but one may admit that while still holding that
all there is in the world are physical things.
One may try one more time.
Look, the issue is whether we need to add anything to a completed microphysics or not.
The dualists says ‘yes’ we need to add non-physical properties. The classical zombie
argument is what shows this. The dualist says the same in the zoombie case. In such a
world we still need to add non-physical qualitative properties explicitly. So the issue of
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I am grateful to –name withheld-- for pressing this objection, if not for the manner in which he did it.
Jose Luis Bermudez’s recent book Philosophy of Psychology: a Contemporary Introduction provides a nice
discussion of this point.
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Because, Davidson famously argued, one set of concepts was essentially normative and the other essentially
descriptive.
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reduction is beside the point; the zoombie argument still doesn’t parody the zombie
argument.
But this just begs the question again. I say that I can conceive of a creature just like me in all
relevant respects (the non-physical ones) which lacks non-physical qualitative properties and
doesn’t need any additional non-physical qualitative properties added. It is a complete nonphysical duplicate of me that lacks qualitative consciousness. This is the zoombie and its
conceivability shows that qualitative consciousness is not a non-physical property or that the
original zombie argument makes the same mistake as the zoombie argument. What we need is
some reason to think that we are really conceiving of a zombie world as opposed to a world that
is very similar to ours but not micro-physically identical.
But still this issue of reduction can get in the way. It is better to avoid it altogether. To do
so consider the other kind of reverse-zombie: the shombie. A shombie is a creature that is microphysically identical to me, has conscious experience, and is completely physical.4 Shombie pain
is just as painful as my pain is and shombie orgasms are every bit as pleasurable as mine are. My
shombie twin and I have all of the same experiences. The only difference, if it is a difference, is
that shombie pain is completely physical. That doesn’t make it any different from the inside.
What it is like for me to have a pain and what it is like for my shombie twin to have a pain are
identical in all respects. We have stipulated that shombie pain is just like my pain in every
respect (qualitatively) and that my shombie twin is a complete micro-physical duplicate of me.
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Shombies are not zimboes. According to Dennett a zimbo is a zombie that is able to monitor its internal states. For
Dennett a zombie is a creature that is behaviorally indistinguishable from a a creature that has conscious states but it
itself doesn’t. A zimbo is a zombie that has a certain functional organization. According to Dennett we are zimboes.
People object to this because they feel as though Dennett is leaving something out. This is where shombies come in.
Whatever is thought to be left out on Dennet’s account is included in the shombie world. Shombies are not zombies
of any kid with or without anything added or subtracted. Shombies are creatures that are completely physical and
have qualitative consciousness of the very same kind as I do. This seems very different from a zimbo. A zimbo is the
human being as the elimativist imagines them. So a zimbo is a type of shombie (or could be if I am getting this
right). But a shombie need not be an elimativist model. There is still the issue of reduction or not and one kind of
shombie is the anomalous monist kind that has distinct mental and physical concepts that cannot be reduced to each
other.
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The shombie is NOT a zombie. A zombie lacks qualitative consciousness; a shombie doesn’t,
though both are micro-physical duplicates of me. So am I my own shombie twin?5 I do not want
to beg that question here so I will take no stand on whether I am a shombie or not. The point is
that shombies are conceivable. The qualitative does, therefore, logically supervene on the
physical and dualism is false. Zombies are metaphysically impossible.
We can now formulate the reverse-zombie argument with shombies. Let ‘P’ be a
complete micro-physical description of the world and ‘MQ’ be a complete description of the
qualitative facts that either follows from P, ‘(Q(d))’ for ‘deductive’, or doesn’t, ‘(Q(a))’ ‘for
anomalous’, but is still just a different way of describing P (i.e. both ways of construing Q are
purely in keeping with physicalism. To keep things simple I will just say that,
MQ= (Q(d) or (Q(a)).
Given this we can formulate an exactly analogous argument against dualism as follows.
1’. P and MQ is conceivable
2’. If (P & MQ) is conceivable, then (P & MQ) is possible
3’. If (P & MQ) is possible then dualism is false
4’. Therefore dualism is false
Premise (1’) says that the Shombie world is conceivable, premise (2’) concludes from that fact
that the shombie world is possible and from that we conclude that dualism is false. This
argument is in every way parallel to the original zombie argument.
In closing let us briefly consider how a dualist might respond to this argument. Well,
Chalmers is committed to accepting premise (2’). Conceivability entails possibility for him so if
shombies are conceivable then they are possible. How about premise (3’)? Might a dualist allow
that shombies are possible but dualism was still true? Such a position would hold that it might be
true at some possible world that there are non-physical properties but that there were also
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I am if physicalism is true.
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possible worlds where consciousness was a physical property. But if this is the case then we
loose all of our motivation for being dualists in the first place. Why should we posit mysterious
non-physical properties if we could have a completely physical account of consciousness? And if
such a physical account of consciousness is possible shouldn’t we primarily be focused on seeing
if it is true of the world we live in? So, it seems to me that Chalmers should accept premise (3’).
Besides this to reject premise (3’) would require an argument that identity was not
metaphysically necessary which is a completely different story.
This brings us to the first premise. Is (1’) really conceivable? Can we really imagine a
world where consciousness is a completely non-mysterious physical property? It seems to me
that I can. Since it seems like I can do this I cannot really imagine the traditional zombie scenario
anymore. It no longer seems to me that I can coherently conceive of a creature that is physically
identical to me but which lacks qualitative states. It seems to me that I must be overlooking some
small subtle difference in my imagined physical world. If you find yourself thinking “hey, but
the shombie argument just assumes that consciousness is physical!” or “yeah, but the zoombie
argument just assumes that a non-physical duplicate of me can lack (non-physical) qualitative
consciousness even with the same laws of physics!” then you are starting to see my point. The
way you think the world is shapes what seems conceivable to you. It cannot be the case that
intuitions about zombies are evidence for or against any theory of consciousness. All it can do is
to let us know where our sympathies lie, or to draw out some implicit commitment that we did
not know that we had. But what it cannot do is show that physicalism is false.
Dualism is therefore false or the original zombie argument is question begging. It will
only have any pull on you at all if you think that zombies are conceivable. But to concede that is
already to concede that physicalism is false. Type-B materialists should then adopt the present
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strategy. The question is begged right when Chalmers says that whether we call the zombie
world one which lacks consciousness or not we clearly have conceived something and that is
enough to show that physicalism is false. He has only succeeded in imagining a zombie world if
our world is not a shombie world. Chalmers must hold that the shombie world is not really
conceivable. I hold that this is an empirical question that we do not yet know the answer to. But
even so there is a lot of evidence which suggest that the world we live in is in fact the shombie
world. That is, there is a lot of evidence that we are shombies. But strictly speaking we really are
not in a position to say which world we are imagining when we try to imagine the zombie world.
We may be succeeding in imagining a world that is truly physically identical to ours, in which
case we are really imagining the shombie world, or we do not in which case we imagine a world
that looks as though it is physically identical to ours but is not.
Either way the zombie argument does not threaten physicalism unless one has already
assumed that qualitative properties are not physical.