Conceivability,
Possibility and the Mind-Body Problem
The feeling of an
unbridgeable gulf between consciousness and brain-process: how does it come
about that this does not come into the considerations of our ordinary life?
This idea of a difference in kind is accompanied by slight giddiness—which
occurs when we are performing a piece of logical sleight-of-hand.
–
Wittgenstein, Philosophical Investigations,
§412
I
want to take on the question of what a class of arguments, usually called the
Conceivability Arguments, have to say about the mind-body problem. These arguments
have two different versions. In one version, considerations of conceivability
are taken to support the claim that phenomenal consciousness is not identical
to, realized by, or supervenient on physical properties (for example, Kripke
1972, Nagel 1974, Robinson 1993, White 1986, Jackson 1998, and Chalmers 1996).
According to the other version, there is an explanatory gap between phenomenal
and physical levels of description that does not exist with respect to other
higher-level descriptions and that may have metaphysical ramifications.[1]
My claim is that these arguments do not succeed in establishing their
conclusions. That is because (and I take this to be the primary lesson of the
Conceivability Arguments) what they reveal does not have to do with phenomenal
consciousness itself, but rather with
the nature of phenomenal concepts.
In
what follows, I will focus on the most elaborate and sophisticated version of
the Conceivability Argument for dualism. First I provide a general exposition
of the structure of Conceivability Arguments, then I proceed to describe in
greater detail Frank Jackson’s and David Chalmers’s new Conceivability
Argument. Finally I construct a reductio that at the same time reveals where
the arguments went wrong.
1 Introduction
Phenomenal
consciousness—the what it’s like[2] feature of experience—can appear to a
scientifically inclined philosopher to be deeply mysterious. It is difficult to
conceive of how the swirl of atoms in the void, the oscillation of field
values, or anything physical can add up to the smells, tastes, feelings, and so
forth that constitute our phenomenal experience.
The
most important argument for the claim that there is no place for phenomenal
consciousness in a completely physical reality relies on considerations of conceivability. The argument, which goes
back at least to Descartes (Sixth Meditation, in Cottingham, Stoothoff, and
Murdoch 1984, 2:50-63), begins with the premise that we can conceive of any physical or
functional facts obtaining without there being any phenomenal experience at
all.[3]
This is sometimes expressed by saying that zombies (that is, beings that are
our physical and functional duplicates, but possess no phenomenal experiences)
are conceivable.[4]
From this assertion of conceivability it is inferred that zombies are genuinely
possible. And this conclusion is incompatible with physicalism as that doctrine
is usually understood.
The
claim that zombies are conceivable
does not have to do with our powers of imagination, or our psychological constitution in general, but rather with the nature
of physical and phenomenal concepts.
The relevant notion of conceivability is this:
(Con) A statement S is conceivable if it is consistent with the totality
of conceptual truths, that is, if –S is not a conceptual truth.
Conceptual
truths (or analytic truths) are truths in virtue of meaning.[5]
It is usually assumed that if S is conceivable then it is knowable a priori—at least in principle, by an
ideal logician—that S is conceivable. In other words, someone who can entertain
the thought that S can come to know whether S is conceivable without empirical
investigation. Further, failure to detect a priori any contradiction in S is
taken as a defeasible reason to hold that S is conceivable. It is defeasible
since further a priori reasoning may lead one to see that S is inconsistent
with analyticities after all.[6]
To
support the premise that zombies are conceivable, it is claimed that there is
no contradiction, detectable a priori, in describing a possible world as being
physically exactly like our world, yet containing no experiences. Some
philosophers have denied this: they claim that our concepts of various kinds of phenomenal states (for example, pain)
are physical, functional, or behavioral concepts (Lewis 1966, Ryle 1949, White
1986). For example, a crude functionalist account of the concept pain is that
it is the concept internal state produced
by stimuli associated with harm and typically causing aversive behavior. Of
course, if it is analytic that an internal state satisfying a certain
functional specification is pain, then zombies are inconceivable.[7]
It
seems to me that behaviorist and functionalist analyses of phenomenal concepts
are quite implausible. When I think (the same for you, I submit) I am in pain I am not thinking that I am
behaving or disposed to behave in some way, or that I am occupying some
particular neurophysiological state or functional state. Of course, this is not
to say that the property of being in pain is not a physical or functional
property, but rather that the concept pain
is not a functional or physical concept. Whatever the ultimate nature of
phenomenal experience, when I judge that I am having an experience of a particular
sort on the basis of actually having that experience, the concept I invoke is
not a behavioral, physical, or functional concept. Rather, it seems to be a
concept that I apply directly and spontaneously to the experience.[8]
There
is another line of reasoning that can be seen as aiming to show that
zombie-worlds are inconceivable. I have in mind Wittgenstein=s private language argument.[9]
The argument relies on certain a priori considerations concerning the nature of
meaning. The basic idea is that first-person direct uses of a phenomenal
concept presuppose that the concept has links with publicly observable behavior
(or other physical phenomena) that provide criteria for third person uses.
These criterial connections are alleged to preclude zombie-worlds. It would be
well beyond the scope of this paper to evaluate this argument. But in any case,
in the following I want to grant to the proponent of the Conceivability
Arguments as much as possible. So I will grant that there is nothing in our
concept of consciousness that would allow us to rule out a priori the existence
of zombies: zombies are conceivable. I do not want the defense of physicalism
to depend on either the private language argument or such a contentious
semantic doctrine as analytic functionalism or analytic behaviorism about
qualia.
The
conceivability of zombies, however, is used to support the claim that zombies
are genuinely metaphysically possible.
This is a powerful result. If it is correct, and if, as I will assume
throughout this paper, there are phenomenal facts, then physicalism is false.
For it would mean that the totality of physical facts obtaining in our world,
including nomological and causal facts, does not necessitate the phenomenal facts that obtain in our world.[10]
But
there is an obvious objection. On the face of it, the mere fact that a state of
affairs is conceptually possible does not entail that it is metaphysically
possible. The mere fact that it is conceptually possible
for F to exist without its being G does not entail that it is metaphysically
possible for F to exist without being G. For example, it is conceptually
possible (at least it was before the eighteenth century) that water is not H2O,
but it is not really metaphysically possible for water not to be H2O,
since water is H2O, and we know from Kripke’s (1972) work
that identities, where the terms of identity are rigid designators, are
necessary. But during the last three decades the relationship between
conceptual possibility and metaphysical possibility has been greatly clarified
(again, especially by the work of Kripke (1972)) so as to take these objections
into account.
This
has led to a revival of interest in Conceivability Arguments, and sophisticated
versions of these arguments have been developed by Kripke (1972, 144-55), Nagel
(1974, 435-50), White (1986, 333-68), Robinson (1993), Jackson (1982, 1993 and
1998, chaps. 2 and 3), Chalmers (1996, esp. 56-123), Levine (1998, 449-80), and
others. Like their predecessors, these arguments rely on there being a link between
conceivability and metaphysical possibility, but in the formulation of this
link they now take into account that conceivability does not always imply
possibility. The proponents of these new Conceivability Arguments claim that
while the conceivability of water’s not being H2O fails to imply
that it is metaphysically possible
for water not to be H2O, the conceivability of a zombie-world does imply that
a zombie-world is a genuine possibility.[11]
As
we will see, the link between conceivability and possibility invoked by
Conceivability Arguments entails that all modal facts are ultimately reducible
to facts about what is conceivable and ordinary empirical facts (including
laws) that play a role in fixing the references of our concepts. In this way
the link provides a very attractive picture of the metaphysics and epistemology
of possibility. In this picture the truth
makers of modal claims are not a realm of possible worlds, but rather facts
about our concepts and ordinary empirical facts. And modal truths are knowable
by a combination of a priori reflection on our concepts and empirical investigation.
In fact the promise of this account may be the strongest reason for accepting
some form of the conceivability-possibility link.
However,
my aim here is to consider the new Conceivability Arguments due to Frank
Jackson and David Chalmers and show that the very principle connecting
conceivability and possibility they rely on is mistaken. While their arguments
are my particular focus, my criticisms extend to the other Conceivability
Arguments as well, since I will be attacking the link between conceivability
and metaphysical possibility that they all presuppose. These arguments are all
refutable by a master argument that I call ‘the Zombie Refutation.’[12]
The reason they fail has to do with the very nature of phenomenal concepts that
gives rise to the conceivability of zombies. Because of the special nature of
these concepts, the principle that links conceivability and possibility turns
out to be self-refuting. Thus, the zombies that antiphysicalists think possible
in the end undermine the arguments that allege to establish their possibility—a
fitting revenge. While these considerations fall short of establishing the
truth of physicalism, they go a long way toward defending it from some of the
most influential arguments against it. Although I agree with Jackson and
Chalmers that there is something puzzling about consciousness, I do not think
that the puzzle adds up to a refutation of physicalism.
2 The Argument
Jackson’s
and Chalmers’s arguments are similar. Their definitions of physicalism are
almost identical, as are the semantical frameworks in which they formulate
their arguments. Although they employ slightly different formulations of the
crucial premise linking conceivability and possibility, for present purposes I
will assume that they employ the same one since it can be shown that Chalmers’s
premise entails Jackson’s.[13] I will be
mainly following Jackson’s exposition, but my reconstruction of the argument is
meant to be attributed to both of them.
2.1
Preliminaries
One
caveat: Whereas Chalmers (1996) eagerly embraces the dualist conclusion of the
argument, Jackson (1993 and 1998) has a more cautious attitude. He himself
presents the argument as a challenge for the physicalist rather than a straight
refutation of physicalism, and recently seems to reject its conclusion. But on
plausible assumptions, shared by Jackson (1982), it can be easily turned into a
refutation. And this is how I will treat it.
In
a nutshell, the argument is the following: Physicalism requires that a
phenomenal statement, like ‘Frank is experiencing a yellow sensation’, must, if
true, be necessitated by truths expressed in the language of physics. Jackson
and Chalmers argue that this necessitation must itself be a priori and that
such a priori truths must be grounded in the nature of phenomenal and physical
concepts. However, phenomenal concepts do not support such a prioricities. It
follows, assuming that there are phenomenal truths, that physicalism is false.
Let us now look at the argument a little more closely.
Physicalism
Jackson
observes that physicalism, at a minimum, requires a commitment that
(P) Any world which is a minimal physical duplicate of our world is a duplicate simpliciter of our world.[14]
Two
worlds are physical duplicates if and only if they agree on all the true
statements expressed in the language of physics.[15]
A minimal physical duplicate of our
world is what we would get if we used the physical nature of our world
(including, of course, the laws) as the sole
ingredient in making a world (see Jackson 1993, 28); so, a minimal physical duplicate of our world
is, by definition, a physicalistic world.[16]
Jackson
intends this to capture the idea that there is nothing over and above the
physical stuff in our world.[17] He suggests
that his formulation of physicalism (P) is equivalent to the claim that every
truth about our world, be it physical, chemical, biological, psychological,
etc., is necessitated by a statement of physics that gives the full physical
description of the world, and is true in all and only the minimal physical
duplicates of our world. For the purposes of this paper, I will use the following
definition:
(E) For any true statement T, ~(KeT),
where
K is a very long conjunction, expressed in the language of physics,[18]
giving the complete physical truth (including truths about the laws of physics)
about our world.[19]
Conceptual
Explanation
According
to Jackson and Chalmers, the necessities ‘KeT’ (where T is a truth)
cannot be brute facts; they need explaining.[20]
Jackson maintains that if T is, for example, a psychological statement, then
analytical functionalism has a story to tell about why the statement is
necessary. As he puts it:
it is
the very business of conceptual analysis to explain how matters framed in terms
of one set of terms and concepts can make true matters framed in a different
set of terms and concepts. (1993, 32)
Jackson’s
view is that in the absence of a conceptual story of how the purely physical
makes the psychological true, the entailment would remain an ‘impenetrable
mystery’. Both he and Chalmers think that the explanation has to be, in an
appropriate sense, conceptual.[21]where K* is the full description of the world in the language of
fundamental discourse, and T is any truth. (In the case of Berkelean idealism,
for example, the fundamental discourse is mentalistic, and all the physical
truths have to be a priori entailed by a complete mentalistic description of
the world.) They argue that if physicalism is true, then ‘KeT’ is not only metaphysically necessary, but it is
also an a priori conceptual truth; that is, they argue that if physicalism is
true, then all truths are a priori derivable from the full physical description
of the world. I will call this the
A Priori Entailment Thesis: If (E) is true, then, for
any true T, statements of the form KeT are conceptual truths.[22]
This
is the key premise in Jackson’s and Chalmers’s argument against physicalism; it
provides the crucial link between conceivability and possibility.
Why
think that the A Priori Entailment Thesis
is true? Jackson provides the following considerations. First of all, he claims
that many truths conform to it, and there is no reason to suppose that some
will not; also, it is immune to the criticism we made earlier with respect to
the naive conceivability-possibility principle. Although it is conceivable simpliciter that water is not H2O,
it is not conceivable consistent with
the full physical description of the world. Building on Kripke’s argument
(1972, 140-162), Jackson observes that, arguably, in all bona fide cases of identity statements where the denial of the
identity statement is conceivable (for example, ‘water is not H2O’),
there are contingent truths, which, together with conceptual truths involving
the terms in question (here, the terms ‘water’ and ‘H2O’), entail the identity statement.
For
example, on the assumption, roughly, that H2O is the unique thing
that plays the water-role, the statement that water is not H2O is
not conceivable, since it is a conceptual truth that the unique thing that
plays the water-role is water.[23]
Jackson generalizes this observation and claims that the denial of all bona fide true statements, in
conjunction with the full fundamental
truth about the universe, is inconceivable. His idea is that the full fundamental
description of the universe always provides enough background information to
fix the reference of any concept in terms of fundamental concepts, and so it is
always possible to derive any true statement from it.
Let=s look at the example
involving water and H2O in some detail. Suppose water covers 60% of
the surface of the Earth. Then, according to Jackson, it can be shown that the
statement
(W) Kewater covers 60% of the
surface of the Earth
is
a priori. Let’s see how. Jackson claims that something like the following is an
a priori truth
(i) Water is the clear, odorless, etc...liquid
around here that fills the oceans and lakes, etc.
It
follows a priori from (i) that
(ii) H2O is the clear, odorless, etc.
...liquid around here that fills the oceans and lakes, etc.eWater is H2O.
But
it is also a priori true that
(iii) (Water is H2O)e((H2O covers 60%
of the surface of the Earth)e(Water covers 60% of the
surface of the Earth)).
From (ii) and (iii) we get
(iv) H2O is the clear, odorless,
etc....liquid around here that fills the oceans and lakes, etc.e(H2O covers 60% of the surface of the
EartheWater covers 60% of the surface of the Earth).
But
this is equivalent to
(v) (H2O is the clear, odorless,
etc....liquid around here that fills the oceans and lakes, etc. & H2O
covers 60% of the surface of the Earth)eWater covers 60% of the
surface of the Earth.
If
this derivation is correct, we have shown that the statement
HeWater covers 60% of the surface of the Earth,
where
H is a conjunction of contingent statements about H2O,[24]
is a priori.[25]
Since, according to Jackson, these contingent statements about H2O
are similarly a priori derivable, perhaps through some intermediary steps, from
contingent truths of microphysics, we have shown that
(W) KeWater covers 60% of the
surface of the Earth
is
knowable a priori. Jackson thinks that most true statements[26]
can be similarly shown to be a priori entailed by the full physical description
of the world.
A
further motivation for the A Priori
Entailment Thesis is that it is a very powerful explanatory claim. Modal
claims of the form
~(KeT)
might
seem metaphysically and epistemically mysterious. If correct, the A Priori Entailment Thesis would explain
these necessities in terms of conceptual truths, and it would explain
metaphysical necessity in general in terms of conceptual necessities and
contingent truths, since, according to it, the statement
KeM,
where
K is the full fundamental description of the world, and M is any metaphysical
truth, is a conceptual truth.[27] This means
that any metaphysically necessary truth M can be conceptually derived from K,
the totality of contingent fundamental truths. This account also provides an
epistemology for modality.
To
recap, the support Jackson (and Chalmers) offer for the A Priori Entailment Thesis is this: there are good explanatory
motivations for it; and in fact many putative necessities of the form KeT do demonstrably conform to the A Priori Entailment Thesis. The claim is
that there is no reason to suppose that there are exceptions to it.[28]
The main goal of this paper is to give such reasons. I will show that, contrary
to Jackson, there are exceptions to
the A Priori Entailment Thesis.
2.2
The Argument
If
the A Priori Entailment Thesis is
true, the physicalist faces trouble vis-à-vis
fitting psychological, and especially phenomenal, properties into the
physical world. The reason is that there are no suitable conceptual analyses of
phenomenal concepts for the relevant supervenience claim
Kex feels pain (or any other statement expressing a
phenomenal proposition)
to
be a priori.
The
derivation of ‘KeWater covers 60% of the
surface of the Earth’ depended on the conceptual truth ‘Water is the clear,
odorless, etc. ... liquid’. The availability of such conceptual truths is
essential to the kind of derivation we are considering, since the derivation
works by finding a contingent statement linking the description to a term of a
lower-level theory, and ultimately to a term of microphysics. Now consider the
statement
Kex feels pain.
To
derive ‘x feels pain’ a priori from K, there must be some conceptual truth
connecting ‘pain’ with a nonphenomenal
description such that satisfaction of the description is a
priori sufficient for ‘feels
pain’. But, arguably, there are no
such conceptual truths.[29] For any
such nonphenomenal description we can conceive
of its being satisfied without anyone feeling pain. ‘Pain’ is, as Loar (1990)
calls it, a direct recognitional term; we do not apply the term, at least in
our own case,[30]
on the basis of any evidence, sensory, behavioral, or physical, distinct from
what the term picks out, that is, distinct from the experience itself. ‘Pain’
refers to pain directly, or rather, via an essential feature of it, say,
painfulness.[31]
But it follows from the A Priori
Entailment Thesis that if ‘x feels pain’ cannot be derived a priori from K, then
~(Kex feels pain)
is
false, and so if ‘x feels pain’ is true[32],
then physicalism is false.[33] To put it
more formally:
(1)
If
physicalism is true, then for any true T, statements of the form KeT are conceptual truths.
(2)
There
are some true statements Q to the effect that phenomenal conscious experience
occurs (eliminativism about phenomenal experience is false).
(3)
If
Q is a phenomenal statement, then ‘KeQ’ is not a conceptual
truth.
So
(4)
Physicalism
is false.
This
is a really remarkable result. One might wonder, however, about its conclusion.
What would the world be like if dualism were true? First, the dualist has to
account for why psychophysical correlations occur even though phenomenal states
do not metaphysically supervene on the physical. Nomological correlations have
to be posited to hold the two realms together; but that leads to an ontology
with a multitude of fundamental laws connecting complex physical states with
apparently simple phenomenal states. These fundamental laws would be different
from any laws of nature we know from science. Second, a dualist would either
have to deny the causal closure of physics, countenance implausible causal
overdetermination, or accept epiphenomenalism for phenomenal states.[34]
None of these options is very attractive, however. Chalmers seems to prefer
epiphenomenalism, but that would make it completely mysterious how we know about
our own phenomenal states.[35] Third,
although the new Conceivability Arguments rely solely on the conceivability of
worlds exactly like ours physically, but lacking any phenomenal properties instantiated,
and not on the converse, that is, the conceivability of worlds exactly like
ours phenomenally, but lacking in any physical properties instantiated, it
appears that an advocate of the Conceivability Arguments would have to condone
the existence of purely phenomenal worlds.[36]
It is barely intelligible what a world like that would be like. All these
considerations make dualism very implausible. Fortunately, it can actually be
shown that the arguments for dualism we have been considering are unsound.
3 Zombies Deceived
I
now introduce the Zombie Refutation. This argument will show that the
Conceivability Argument as formulated by Jackson and Chalmers is
self-undermining, that is, that with the addition of some plausible further premises
we can derive a contradiction from it. Suppose that Jackson’s argument is sound.
Its conclusion, that physical facts do not necessitate phenomenal facts, would
then be true. And it would follow that there is a possible world that is
exactly like our world physically, but in which no phenomenal, or other,
nonphysical, facts obtain.[37] Let me
emphasize: I make this assumption only for the sake of a reductio. Of course,
if physicalism is true, as I think it is, then such a world is impossible. But
my strategy is to show that the very assumption that there is such a world
undermines the argument that leads to positing the existence of such a world.
In
the world we are imagining there exists a zombie‑Jackson, physically just
like Jackson, but not the subject of any phenomenal states. Professor
zombie-Jackson appears to give a series of lectures in zombie-Oxford (as
Jackson did in Oxford) arguing for the A
Priori Entailment Thesis. What are we to make of his words?
First
of all, plausibly, zombie-Jackson will have intentional states. When he talks,
his words are not mere meaningless sounds. I will argue that it is plausible to
assume that zombie-Jackson has intentional states even if he lacks phenomenal
states. Moreover, I will argue that it is plausible to assume that
zombie-Jackson’s intentional states will be identical with Jackson’s intentional
states except for intentional states that, in Jackson, involve phenomenal
concepts. Those of zombie-Jackson’s intentional states that, in Jackson,
involve phenomenal concepts will refer to states of affairs present in
zombie-Jackson’s world. On this view, zombie-Jackson’s argument will be just as
meaningful as Jackson’s, though not quite identical
to it. Although the argument is word by
word identical to Jackson’s argument, some of the words (those that express
phenomenal concepts in Jackson’s language) have different meanings in Jackson’s
and zombie-Jackson’s mouths. I mark these words with a ‘+’. ‘Pain+’,
for example, stands for a term of zombie‑Jackson that corresponds to
Jackson’s term ‘pain’. They will use the same words to express different concepts;
whereas Jackson’s concept is phenomenal, zombie‑Jackson’s concept, by
assumption, is not. We will come back to the exact nature of the difference
shortly.
Zombie-Jackson’s
argument will go like this:
(1*)
If
physicalism is true, then for any true T, statements of the form KeT are conceptual truths.
(2*)
There
are some true statements Q+ to the effect that a phenomenal+
state occurs (eliminativism about phenomenal+ states is false).
(3*)
If
Q+ is a phenomenal+ statement , then ‘KeQ+’ is not a conceptual truth.
So
(4*)
Physicalism
is false.
My
plan is the following: Given the assumptions I have made, I will argue that if
a premise of Jackson’s argument is true, the corresponding premise formulated
by zombie-Jackson will be true as well. We know, however, that the dualist
conclusion of zombie-Jackson’s argument is false in the zombie‑world.
Remember, physicalism, [or anti-physicalism], on the notion that is relevant
here, is not a necessary doctrine; it is true about some worlds and false about
others. The zombie-world, by stipulation, is a minimal physical duplicate of
our world, so its minimal physical
duplicates will be duplicates simpliciter of
it. According to our formulation of physicalism, this is what it takes for
a world to be physicalistic. Consequently, we know that zombie-Jackson’s
argument cannot be sound. Since, given that it is meaningful, it is clearly
valid, one of its premises has to be false. It follows then that one of the
premises of Jackson=s argument has to be false
as well.
This
plainly amounts to a reductio of Jackson’s argument. It turns out that it is
possible to derive a contradiction from Jackson’s original premises, taken
together with a few plausible additional assumptions. I will argue that these
assumptions are indeed plausible, and that, given these assumptions, premises
(1*)–(3*) follow from Jackson’s original premises. But then the dualist
conclusion of zombie-Jackson’s argument follows as well, which contradicts the
claim, also a consequence of Jackson’s original argument, that the zombie-world
exists and that it is physicalistic.
The
fact that one can derive a contradiction from the original argument, together
with the added premises, shows that one of the premises must be false. Since, I
argue, [my added premises] are extremely plausible, the fault must lie with one
of the premises of zombie-Jackson’s argument (and, consequently, with the corresponding
premise in Jackson’s argument): the obvious candidate is the A Priori Entailment Thesis. While this
does not necessarily mean that the dualist conclusion is false, it does mean
that the argument used to establish it is not effective.
Let’s
now formulate these auxiliary assumptions more precisely. I am going to state
them briefly right at the start; they will be discussed and defended in detail
later, after the argument is given. Let me point out here that these
assumptions do not by themselves imply physicalism (indeed, a dualist might
very well accept them).
Assumption 1: Jackson and zombie-Jackson share most of their intentional states
except those involving phenomenal concepts.
Assumption 2: Those concepts of zombie-Jackson that correspond to Jackson’s
phenomenal concepts will refer in the zombie to some (physical) state of the
zombie.
Assumption 3: A prioricity for thoughts supervenes on the conceptual roles of their
constituent (and related) concepts.
Let=s see how these assumptions,
together with Jackson’s premises (1)-(3) will suffice to derive
zombie-Jackson’s premises. As we said, zombie‑Jackson, being Jackson’s
physical twin, offers an argument that is identical, word for word, to
Jackson’s argument. On Assumption 1, Jackson and zombie-Jackson mean the
same by their words, except where phenomenal terms are involved. This means
that premise (1*) in the zombie=s language expresses the A Priori Entailment Thesis, which, if
true, is necessarily true, so if it was true in the actual world, it will be
true in the zombie‑world as well. On Assumption
2, we get premise (2*), that is, the claim that eliminativism about
phenomenal+ properties is false. Given Assumption 3, premise
(3*) of zombie‑Jackson’s argument,
(3*)
If
Q+ is a phenomenal+ statement, then ‘KeQ+’ is not a conceptual truth,
has as much claim to be true as premise (3) in Jackson’s argument even though >KeQ+’ has a different meaning from ‘KeQ’. The reason is that Jackson’s phenomenal concepts and zombie-Jackson’s phenomenal+ concepts have parallel conceptual roles. Q+, like Q, lacks conceptual links to physical, functional, and behavioral concepts sufficient to ground the a prioricity of ‘KeQ+’. On Assumption 3, a prioricity, or conceptual