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 necessity, supervenes on the conceptual roles of the relevant
concepts. That means that if ‘KeQ’ is not derivable from
conceptual truths given that Q lacks sufficient conceptual links to physical,
functional, and behavioral concepts, then neither is ‘KeQ+’ derivable from conceptual truths,
since Q+ will also lack the appropriate conceptual ties to physical,
functional, and behavioral concepts.
I
would like now to consider some objections. First, Assumption 1: One might object to it that zombies do not have
intentional states at all. Presumably the reason would be that having
phenomenal states is essential for having intentional states. In other words,
one might object that because zombie‑Jackson does not have phenomenal
states, he does not really have bona fide
intentional states either, and so cannot put forward any argument.[38]
The most prominent exposition of this view is due to Searle (1992, chap. 7); he
attempts to establish that consciousness[39]
is necessary for intentionality. His argument is based on considerations about
the inscrutability of reference originally formulated by Quine (1960, chap. 2).
Searle puts his thesis in the following form:
The
notion of an unconscious mental state implies accessibility to consciousness.
We have no notion of the unconscious except as that which is potentially conscious. (1992, 152;
emphasis in original)
Contrary
to Searle, a good case can be made that zombie‑Jackson does have
intentional states. Zombie-Jackson communicates with his colleagues: he answers
questions, his utterances convey information, his actions are made intelligible
by the assumption that he has beliefs and desires, etc. His cognitive
organization seems to be essentially the same as Jackson’s. On a more technical
note: on all the extant theories of meaning, zombie-Jackson will count as a
thinker. On a Davidsonian interpretationist account, zombie-Jackson will have intentional
states: he is just as interpretable as Jackson is. Similarly with other
theories, like the informational account (for example, Dretske 1988), the
causal-historical account (for example, Kripke 1972), the counterfactual
account (for example, Fodor 1990), the teleosemantic account (Millikan 1989,
Papineau 1993), etc. Zombie-Jackson’s brain states (putting the problem of
phenomenal versus phenomenal+ states aside for the moment) carry the
same information as Jackson’s brain states; they have the same causal history
linking them to entities in the world as Jackson’s brain states do; the same
counterfactuals hold about them as about Jackson=s brain states, etc. The
only account on which zombie-Jackson will not count as a genuine thinker is the
account on which phenomenal consciousness is essential for intentionality.
Although the idea is not absurd, the argument for it does not seem to be very
strong, and the contrary assumption seems far more intuitive. Moreover, the
proponent of the Conceivability Arguments has to hold both that phenomenal consciousness is nonphysical and that it is essential for
intentionality; but then we are owed an explanation of how causally inert,
nonphysical properties can play a role in endowing mental symbols with meaning.
In any case, since the thesis poses a serious challenge to my argument,[40]
I would like to come back to it after I considered some other objections.
One
might also object to Assumption 2,
that is, the claim that the zombie’s term ‘pain+’ refers to a
(physical) state of the zombie.[41] There are
two ways in which Assumption 2 could
be false: first, if ‘pain+’ referred to nonphysical phenomenal pain,
a property alien to the zombie-word; second, if ‘pain+’ referred to
nothing.[42]
Either of these scenarios would be damaging to my argument: if zombie‑Jackson’s
term ‘pain+’ referred to pain, then premise (2*) would be false,
since all phenomenal+ statements would be false in the zombie‑world.
If, on the other hand, ‘pain+’ didn=t refer to anything, then
premise (2*) would be meaningless. Either way, my reductio would not go
through. Let=s look at these scenarios
one by one.
On
the first scenario, the term ‘pain’ and the term ‘pain+’ have the
same meanings. This is not Chalmers=s view: he thinks that the term ‘pain’ and the term
‘pain+’ have different meanings. He argues like this. In spectrum
inverted physical twins, the meanings of phenomenal terms differ. Since, the
twins being physically identical, the difference must be due to acquaintance
with different phenomenal properties, the zombie’s term has to be different
from both since the zombie is not acquainted with any phenomenal properties
(Chalmers 1996, 207-8). This applies equally in the case of pain or any other
phenomenal property.
But
these considerations aside, we can see that this scenario is very implausible.
By assumption, phenomenal properties are alien to his world. It is quite implausible
to assume then that when Jackson says ‘that feels good’, referring to the
phenomenal feels produced by a back‑rub, zombie‑Jackson also refers
to a phenomenal feel, even though there is none in his world. Of course, I am
not saying one can never have terms that lack actual reference. The term
‘winged horse’, for example, has reference. All I am claiming is that, in the
particular case of phenomenal+
terms, like the term ‘pain+’, the reference could not be
nonphysical qualia.
‘Pain+’,
like ‘pain’, is a simple term; its reference is not fixed via a description.
Let me engage in a little digression here. Not everybody agrees that ‘pain’ is
a simple term. Georges Rey (1988) suggests that even if the reference of ‘pain’
is not fixed descriptively, there is a descriptive
element to the concept, one that entails that the concept cannot refer to
anything physical. It would follow then that pain+ could not refer to anything physical either. I do
not think that our concept has this descriptive commitment; and moreover, I do
not think that Jackson or Chalmers thinks that either. Their argument depends
on the assumption that we have epistemic warrant to attribute phenomenal states
to ourselves on introspective evidence. If our very term ‘pain’ entailed that
its reference is nonphysical, one need not bother with the Conceivability
Argument; the truth of dualism would follow from the claim that we have
introspective evidence for the occurrence of phenomenal states. But dualism
could not be so cheap. On this construal of the term ‘pain’ we would have to
give up our commitment to introspective warrant in attributing phenomenal
states. But our assumption that our introspective evidence gives us very strong
justification to attribute phenomenal states to ourselves is much more bound up
with our term ‘pain’ than with any claim about its reference being nonphysical.
Consequently, it is much more reasonable to hold that the term ‘pain’ does not
have any such descriptive element.
If
the term ‘pain’ is a simple term, what could make it the case that it refers to
a nonphysical property? None of the possibilities one can think of would give
the result the objector has in mind. It is unlikely that on an interpretationist
account zombies could come out referring with their term ‘pain+’ to
nonphysical properties alien to their world, as it would render most of their
phenomenal+ statements false.[43]
There are no suitable causal, counterfactual, or lawful relations between nonphysical
phenomenal pain and the term ‘pain+’ either. Since there are no
pains in the zombie-world, there could not be any causal relations between pain
and the term ‘pain+’, as such relations would require the existence
of laws connecting physical and nonphysical entities in the zombie-world; but
by stipulation, there are no such laws there. The case is the same with
counterfactual relations. Another way for reference to be fixed in some direct,
nondescriptional manner is for it to be fixed by a relation of acquaintance. Chalmers (1996, 197)
claims that in the case of phenomenal concepts, reference is constituted by acquaintance with the referent, where
acquaintance is not to be cashed out in terms of causal, counterfactual, or
lawful relations. However, this would not help in the zombie-case: zombie‑Jackson
is just not acquainted with phenomenal experiences in any sense of the word. As
the above options exhaust the existing possibilities, we can conclude that the
zombie=s simple term ‘pain+’
could not refer to a nonphysical property.
The
other objection to Assumption 2 was
that even if the zombie has intentional states in general, his term ‘pain+’
in fact does not refer to anything. In my view, this is wrong. This position
has the counterintuitive consequence that all of the zombie’s phenomenal+ talk
lacks truth value. This would be a very uncharitable interpretation of zombies:
it would imply that zombies are massively deluded about their mental life.
Zombies not only seem to use phenomenal+ terms to give reports about
their inner states, they also seem to use them to give explanations of each
other=s behavior, just as we give
explanations of each other=s behavior in phenomenal
terms. So, for example, zombie-Jackson=s friend apparently explains why zombie-Jackson
takes an aspirin by referring to his head-ache+. Also, their phenomenal+
utterances and nonphenomenal+ utterances have intelligible
connections—zombies say, for example, ‘when I had a tooth-ache+ last
time, I went to the dentist,’ etc. These explanations and reports seem to be
accurate, since whenever, for example, zombie-Jackson says that he is in pain+,
he is in a brain state or functional state that is reliably correlated with his
term ‘pain+’ (the same brain state or functional state that is reliably
correlated with Jackson=s term ‘pain’). The natural
candidate for the reference of zombie‑Jackson=s term ‘pain+’ is
this very brain state or functional state.[44]
This means that whenever Jackson’s statement ‘I am in pain’ is true, zombie‑Jackson’s
statement ‘I am in pain+’ will be true as well, being about a brain
or functional state he is in. The plausibility of this claim might be obscured
by the fact that although zombie‑Jackson=s statement, for example, ‘I
am in pain+’, attributes some brain or functional state to himself,
he of course does not conceive of it in this way, that is, he does not think of
this state qua brain or functional
state.
The
adherent of the Conceivability Arguments might object at this point that the
problem with the alleged term ‘pain+’ is not simply that it lacks
reference; the problem is that it does not express a legitimate concept to
begin with. As Frege pointed out, distinct concepts must have distinct senses
or modes of presentation. Following Frege, White (1986) assumes that modes of presentation
have two roles to play simultaneously.[45]
On the one hand, they determine reference. On the other hand, they individuate
concepts. According to this theory, if the same mode of presentation is associated
with two (co-referring) concepts, it must be knowable a priori that these
concepts co-refer. No two concepts, where the concepts lack the appropriate a
priori links, can have the same reference in all possible worlds. This is
apparently because modes of presentations are properties of the referent through which the subject grasps the
referent.
On
this view, zombie-Jackson=s alleged concept ‘pain+’
is not a legitimate one. One could not refer directly to a brain state in the
way I have claimed zombie-Jackson must, since that would violate the above principle
about modes of presentation. I am assuming that ‘pain+’ and, for
example, ‘pyramidal cell activity’ refer to the same state (a brain state), via the same property, since both of
these concepts have essential modes of presentation or reference fixers, yet
the possessor of these concepts would not be able to know a priori that they
co-refer.
Of
course, on my view, concept individuation, and so a priori knowledge of
co-reference, is more fine-grained than reference fixation. Even if we accept
that modes of presentation involve properties of the referent, these properties
being what determines the reference of the concept, we might want to deny that
these properties exhaust all there is to modes of presentation. Different
concepts might employ the same property to provide different routes to the same
referent. In the case of the concept ‘pain+’, the same property (for
example, pyramidal cell activity) is deployed directly to pick out the
referent, whereas in the case of the concept ‘pyramidal cell activity’, this
property is deployed in the way characteristic of scientific terms.
And
since this picture of how concepts work is clearly conceivable—that is, there
is no incoherence in the idea of concepts that refer directly to brain states
in the way I claimed ‘pain+’ does—the burden of proof is clearly on
the adherent of the Conceivability Arguments to show, rather than just declare,
that such concepts are illegitimate.
Finally,
one could object to Assumption 3, the
assumption that a prioricity supervenes on conceptual role. Here is my defense
of it: If a prioricity did not so supervene, then it would be possible that
sometimes we cannot tell, even in principle, after a lot of thinking, and doing
many thought experiments, of an a priori truth that it is true. If a prioricity
did not supervene on actual and potential inferential relations, then we could
not claim any special access to a priori truths—a paradoxical situation.
Moreover, this would undermine whatever certainty we have in premise (3), the
claim that for any true phenomenal statement Q, KeQ is not a conceptual truth.
Denying Assumption 3 would undermine
the Conceivability Arguments by making premise 3 highly contentious.
I
would like now to return to Assumption 1,
the claim that zombies have intentional states, and the objection to it I
raised earlier. The objection was that (phenomenal) consciousness is essential
to intentionality, and since the zombies, by assumption, do not have phenomenal
states, they cannot have thoughts either. Even if it were true that phenomenal
consciousness is necessary for intentionality, that would not damage my
argument. My argument can be run in a way that would make the objection
irrelevant.
In
fact, zombie-worlds are introduced only for expository convenience. They are
not essential to refute Jackson and Chalmers’ argument. My argument against
them only presupposes that there is nothing incoherent about the idea of
referring to a brain state directly, without the mediation of any physical,
functional, or abstract concept, and even without the mediation of a phenomenal
feel figuring as mode of presentation or reference fixer. This will allow me to
construct an analogue of the Zombie Refutation that will prove the
Conceivability Arguments unsound even if phenomenal consciousness is essential
to intentionality.
One
way to do this is to consider a world where there are partial zombies. If Jackson and Chalmers are right that qualia are
nonphysical, then there is a world that is a physical duplicate of our world,
but in which there are creatures that have only some of our phenomenal
experiences. These creatures will act and talk like us—moreover, they will feel
pleasure whenever we do—but they will feel no pain at all (even though they
will claim they are ‘in pain+’ whenever we claim we are in pain).
Since they do have phenomenal states, and, we might even stipulate, all of
their intentional states are accompanied by phenomenal consciousness, there is
no reason to deny that they have intentional states. However, on considerations
discussed in reply to earlier objections, the most natural thing to say is that
their term ‘pain+’ refers to a brain state.
There
is another way to make the point in a slightly different way. I submit that the
following scenario is at least conceivable—and so, on Jackson and Chalmers=s view, possible. Imagine a
world where there are creatures in many respects like us. They have the same
physical and mental constitution we have, except that there are some among them
that are capable of forming concepts we are not capable of; let us call these
people yogis. The yogis are capable of directly detecting certain states of
their brains, even though they do not conceive of these states as brain states. In some ways, these
yogi-concepts will work the way our phenomenal concepts work; they are applied
to their referents directly, without the mediation of any physical, functional,
or abstract concept. What is peculiar to them is that in the case of the
yogi-concepts reference is not even mediated by a phenomenal feel. The yogis
will notice that they are capable of detecting some inner state of theirs, even though they do not have any idea
how they are doing it. Let us call one of the brain states that they can detect
in this way state A, and let us suppose that they use the term >flurg= to refer directly to state
A.
Yogis
can formulate a variant of the Conceivability Argument. There are true
statements in their world involving the concept ‘flurg’—for example, ‘flurg occurred
at t’. These statements will not be derivable from the full fundamental
(physical, or if dualism is true, physical cum
phenomenal) description of their world, since yogis apply their concept ‘flurg’
directly to brain state A; just like phenomenal concepts, the concept ‘flurg’
lacks conceptual links to physical, functional, and behavioral concepts
sufficient to ground the a prioricity of ‘Keflurg occurred at t’. Yogis
then can use the A Priori Entailment
Thesis to argue that there is a possible world exactly like theirs
physically and phenomenally, but where no, as they say, ‘flurgs’ occur. But
such a world is impossible, since, by stipulation, the term ‘flurg’ refers to a
state of their brain. The yogi=s argument is unsound. But
among its premises the only contentious one is the A Priori Entailment Thesis.
This
argument has the advantage of making the same point as the Zombie Refutation,
only making it even clearer that the Conceivability Arguments arise not out of
any feature specific to phenomenal consciousness, but rather because of a
certain peculiarity of our phenomenal concepts,
a peculiarity that can conceivably be shared by concepts undisputably referring
to physical states.
To
sum up, even if the objection that phenomenal consciousness is essential for
intentionality were sound, it would not succeed in disarming my refutation of
the Conceivability Argument. The Zombie Refutation, and its analogues, the
partial-Zombie Refutation, and the Yogi Refutation, show that there is
something wrong with the Conceivability Argument. It is plausible even on the
Zombie Refutation that the premise that has to be given up is the A Priori Entailment Thesis; and on the
Yogi Refutation this conclusion is inevitable. My arguments then not only show
that the conceivability arguments fail. They also prove that Jackson and
Chalmers’s principle linking conceivability and possibility is false, and so
they prove that hopes for grounding all necessities in conceptual and empirical
truths were ill founded.[46] Moreover,
they help diagnose where things went wrong. The Yogi argument has the advantage
over the Zombie Refutation of making it even clearer that the conceivability of
zombies arises not out of any feature specific to phenomenal consciousness, but
rather because of a certain peculiarity of our phenomenal concepts. This peculiarity, that is, referring to a state directly, can plausibly be shared by
concepts undisputably referring to physical states, and so with regard to these
concepts the A Priori Entailment Thesis
is inapplicable.
4 The Aftermath
We
have seen that the Conceivability Arguments against physicalism are
unsuccessful. In fact, even Jackson, one of the most forceful original proponents
of the argument, now thinks that there must be something wrong with it. He
thinks that for a dualist, epiphenomenalism is the most reasonable position,
given the plausibility of the causal closure of physics. But epiphenomenalism
is more implausible than any of the premises are plausible, except the premise
claiming that phenomenal states exist. Jackson says that there must be a reply
to the Conceivability Arguments, although one cannot quite say what. He calls
this the ‘There must be a reply’ reply (Jackson 1996, 134-35).
With
the Zombie Refutation and its companion arguments, we can actually do better.
The arguments actually showed where the antiphysicalist went wrong. However,
the physicalist, if she wants to make her position attractive, must have an
answer to two questions. One is the question of what explains the physicalistic
supervenience claims captured in the Entailment
Thesis:
(E) For any true statement T, ~(KeT).
The
explanation that Jackson puts forward of why E holds is that all instances of E
are conceptual truths. He thinks that the reduction of higher-level concepts to
lower-level concepts has to be perspicuous.
This, however, is unwarranted. The only assumption needed to explain E is
that metaphysical reductionism
is true; that is, the only explanation needed is the assumption that there is
some appropriate metaphysical
relationship (identity, or the realization relation, or perhaps some other, yet
unknown relationship) between the referents of higher-level and basic physical
concepts. There is no reason such a relation could not hold between physical
and phenomenal properties, even in the absence of conceptual connections that
would make this relationship perspicuous.
But
now, the physicalist also owes an explanation of why phenomenal statements
appear to be so different from other higher-level statements in their connections
with lower-level discourse. Many of us are convinced (partly by the
Conceivability Arguments) that there is something special about phenomenal
statements. It seems right that it is not conceivable, after all the physical
truths are in, that water is not H2O. But it is still conceivable
that any phenomenal statement is false, no matter how much physical information
we have. And the question of the explanatory gap remains as well.
However,
there is no mystery about all this. The explanation of this should be rather
obvious by now. Physicalists who adopt a direct recognitional account of
phenomenal concepts will not be in the business of trying to close the gap, or
explaining away the conceivability of zombies, since, on this account of
phenomenal concepts, it is to be expected
for a physicalist that there will be an explanatory gap, and that zombies are
conceivable. In the Yogi Refutation I have constructed a concept that refers to
a physical state even though the fact that it does so is not derivable a priori
from the full physical description of the world. There is even less a priori
reason to rule out the possibility that something like this is the case with
phenomenal terms. On this account, we get the following picture.[47]
Phenomenal concepts are direct recognitional concepts and they employ as their
reference fixer the very state they are denoting: the itchy feeling of an itch
serves to fix the reference of the phenomenal concept itch. Phenomenal concepts, on the other hand,
refer to the very same property as some
neurophysiological (ultimately, microphysical) concept: assuming that an
itch just is a certain
brain/functional state, there will be an appropriate neurophysiological/functional
concept whose reference fixer will involve the same property (a certain
neurophysiological/functional property that is identical to an itch); only the
reference fixer is deployed in the way characteristic of scientific terms. A
phenomenal concept and a concept of microphysics, each of which picks out its
referent through an essential reference fixer (say, some neurophysiological
property), could then refer to the same property, even in the absence of the
kind of conceptual connections required by the A Priori Entailment Thesis.
But
what about the persistent intuition that, despite every argument in favor of
it, physicalism just can’t be true? I
think that it can be explained by the intuitive pull of the Transparency
Thesis, roughly, the thesis that if we have two concepts, both of which refer
via an essential reference fixer, then we must
be able to tell whether they co-refer. After all, we have an insight into the nature of their referent through their
reference fixers; so how could we be wrong about our judgment (as it is in the
phenomenal/neurophysiological case) that they do not co-refer?[48]
But in the light of the picture of phenomenal concepts given above, this
intuition is shown to be misplaced.
One
might object that this explanation does not do justice to our Yogi thought
experiment. In the Yogi Refutation I have hypothesized that there could be
beings that possess concepts directly referring to (nonphenomenal) physical
states. Given my refutation of the Conceivability Arguments, I cannot claim,
merely on the basis of their conceivability, that they are possible. But I see
no reason why they would not be. Yogis can make statements that are true in
their world even though these statements are not derivable a priori from the
full fundamental description of their world.
Yet
it is plausible to speculate that yogis would not be inescapably drawn to
dualism. But should not they be, given our claim that a belief in the
Transparency Thesis is enough to explain antiphysicalist intuitions?
Presumably, yogis are just as attracted by the Transparency Thesis as ordinary
humans are. But there is no contradiction here. The yogi can be attracted by
the Transparency Thesis, and still not be drawn to dualism, just on the basis
of her special conceptual repertoire. There is a difference between us vis‑à‑vis phenomenal concepts
and the yogi vis‑à‑vis
the yogi concepts; the yogi, as opposed to us, does not have a temptation to
think that she has direct insight into the nature of what her concept flurg refers to. In a sense, she does
not have a handle on the concept; the reference fixer of her concept might be
an essential property of the referent, but she does not have access to it, the
way we have access to the phenomenal reference fixers of our phenomenal
concepts.
We
started with the question of what the Conceivability Arguments can teach us
about the mind-body problem. On the present picture of phenomenal concepts, the
conceivability of zombies is a symptom of the unique role phenomenal concepts
play in our conceptual repertoire, but it is not a guide to their possibility.
This is not the lesson intended; but, all the same, it is an important one.
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I would like to thank John Biro, Ned Block, David Chalmers, Jennifer Church, Jerry Fodor, Gary Gates, Tamar Gendler, Joe Levine, Brian Loar, Barry Loewer, Colin McGinn, Brian McLaughlin, Karen Neander, Jesse Prinz, Georges Rey, Howard Robinson, Zoltán Szabó, Gene Witmer, and four anonymous referees for helpful comments and conversation.
[1]This
argument is formulated by Joseph Levine (1998), although he does not endorse
the conclusion.
[2]The
expression is coined by Thomas Nagel (1974).
[3]Sometimes
it is argued that the opposite is also conceivable, that is, that it is conceivable
that mental facts, especially experiences, occur without any physical or
functional facts occurring (see Descartes, Sixth Meditation). It is not
necessary, however, for the arguments under consideration, that conceivability
go both ways.
[4]I
will use the terms ‘experience’, ‘phenomenally conscious state’, and
‘phenomenal state’ interchangeably. The phenomenal aspect of a mental state is
the same as its experiential character, or, in Nagel’s (1974) words, its ‘what
it is like’ feature.
[5]The
nature of concepts, what determines whether a statement or thought is true in
virtue of meaning, and even whether there are any conceptual truths at all are
vexed and disputed matters; see Fodor 1997. Since the proponents of
Conceivability Arguments rely on the notion of conceptual truth, I will as
well.
[6]The
claim that whether S is conceivable is always
knowable a priori is not quite correct, since logical consistency is not
effectively decidable and, if the underlying logic is higher order, not even
effectively axiomatizable. But this observation has no effect on the
Conceivability Arguments.
[7]Another
view contrary to the conceivability of zombies relies on the claim that, while
concepts of kinds of experience—for example, pain, nausea, etc.—do not have a
functionalist analysis, the concept conscious
experience does. For example, Shoemaker (1981) holds that zombies are
inconceivable, but that inverted qualia are conceivable (indeed, possible).
This is an interesting view, but in itself is not enough to block the Conceivability
Arguments.
[8]Loar
(1997) characterizes phenomenal concepts as ‘direct recognitional’ concepts.
[9]Wittgenstein
1953, §§ 207-384. The argument is usually invoked in the discussion of ‘other
minds.’ But of course the question of whether another being has a mind is just
the question of whether she is a zombie.
[10]There is a
form of this argument that does not aim at a metaphysical conclusion but merely
at an epistemic one. In this form the argument aims to establish that there are
features of conscious states that will forever elude scientific explanation.
The position originates with Levine (1983, 1993).
[11]Of course,
they will argue that the difference is between kinds of statement. The claim is, as it will soon be clear, that
there is a kind of statement for which conceivability implies possibility. The
statement that a zombie-world exists is supposed to fall under this kind.
[12]For the
extension of the refutation to other Conceivability Arguments see Balog 1998.
[13]See Balog
1998.
[14]Chalmers
gives essentially the same definition (1996, 41-42). Their formulation is
similar to Lewis’s definition in his 1983. For expository reasons, I will stick
with Jackson’s formulation throughout the paper.
[15]The exact
content of physicalism depends on exactly how
physics is understood. Current physics is almost certainly not exactly true or
complete and we have no idea how to characterize future physics. But it
suffices for Jackson’s (and my) purposes to assume that the language of physics
includes no mentalistic (that is, phenomenal or intentional) vocabulary (see Papineau
1993, 29-32).
[16]Unless, of
course, there are nonphysical entities or properties that are connected, with
metaphysical necessity, to physical entities or properties. But this is a
complication I wish to ignore for now.
[17]The
definition also captures the intuition that physicalism is a contingent
doctrine, that is, that physicalism is true in some worlds, but false in
others. For example, a minimal physical
duplicate of a world containing ghosts will not be a duplicate simpliciter of
the ghost-world, since the ghosts will be missing in the minimal physical
duplicate world. On the other hand, a minimal physical duplicate of a
physicalistic world will be a duplicate simpliciter of that world.
[18]This
definition is not strictly equivalent to (P). Statements that make reference to
special kinds of property—to put it crudely, global properties—are not
necessitated by the full fundamental description of the world K; they are only
necessitated by the conjunction of K with the statement that K is the full fundamental description of
the world. However, consciousness, among many others, is arguably not such a
property. Whether I am in pain is a positive fact that does not seem to depend
on any other fact except local facts about me. So, for the purposes of this
paper, this issue can be safely ignored.
[19]More
formally, the definition is: (E) (Y)(Ye~(KeY)),
where Y is a sentential substitutional quantifier.
[20]The point
is, actually, not just that (E) (and (P)) needs an explanation; it is that
there are explanations of (E) that
are actually incompatible with physicalism. For example, (E) could be true in
virtue of some strange set of ‘quizzical’ properties that underlie both
physical and nonphysical property instantiations (see Witmer 1997, 137). But
this issue will not affect the main argument. Even if (E) is not sufficient, it
is still necessary to make physicalism true, so if it can be refuted by Jackson and Chalmers, physicalism is refuted.
(And, I might add, if it cannot be
refuted, then we have no reason to doubt physicalism, since Jackson and
Chalmers provide no further reasons against physicalism.)
[21]This, of course, is not an arbitrary requirement for physicalism alone. Jackson is explicit that any metaphysical theory that makes a distinction between fundamental and nonfundamental properties—for example, Berkelean idealism, or Cartesian dualism—has to be able to produce, for any true T, appropriate derivations of the respective entailment claims K*eT, 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.)
[22]More
formally: (Y)(Ye~(KeY))e(Y)(Ye‘KeY’
is a priori knowable), where Y is a sentential substitutional quantifier.
[23]That it is a
conceptual truth follows from Jackson’s semantics. Here we do not have space to
give it the full treatment it deserves.
[24]H is a
conjunction of statements like, for example, ‘H2O is clear, odorless
liquid.’
[25]Of course,
the derivation, as it stands, is incomplete. To
complete it, we would have to have the requisite conceptual truths that link
the concepts ‘Earth’, ‘surface’, ‘clear’, ‘odorless’, etc. to terms of
lower-level discourse, and, ultimately, microphysics. According to Jackson, it
is clear that such conceptual truths exist.
[26]With the
exception of phenomenal statements. But, of course, he thinks that even those
would be entailed a priori by the full
fundamental description of the world.
[27]This
statement has to be qualified somewhat. Metaphysical claims like ‘universals
are prior to tropes’ or ‘fundamental properties are categorical’ apparently can
be denied without conceptual incoherence. Since it is implausible that the full
fundamental description of the world will settle their truth, they are not
going to be a priori derivable from that description. It is an interesting
question how, on Jackson’s view statements of this type should be handled; but
we cannot discuss this here.
[28]Jackson and
Chalmers also supply a much more sophisticated and elaborate argument for the A Priori Entailment Thesis, based on
the so-called two-dimensional semantic framework. They seem to suggest that
two-dimensional semantics, together with uncontroversial claims, entails the A Priori Entailment Thesis. However, it
can be shown that the argument is question-begging (see Balog 1998).
[29]One might think that, on the model of our derivation of ‘Water covers 60% of the surface of the Earth’, we can derive a priori, for example, ‘x had pain’ from contingent truths, if we allow just any contingent truths to figure in the derivations. For imagine the following argument:
(a) x has C-fibre firing (contingent empirical truth).
(b) Pain is the originating cause of pain-behavior (contingent empirical truth).
(c) C-fibre firing is the originating cause of pain-behavior (contingent empirical truth).
From (b) and (c) we get
(d) Pain is C-fibre firing.
From (a) and (d) we get
(e) x has pain.
This derivation uses only contingent empirical truths and conceptual truths; it shows that
Pex has pain,
where P is a conjunction of
contingent facts of neurophysiology and psychology, is knowable a priori. The
problem with this derivation, however, is that one of the conjuncts in P,
premise (b), is not itself a priori
derivable from K; and if physicalism is true, according to Jackson, (b) could
be true only if it were so derivable.
[30]And for
phenomenal concepts, application to others is arguably derivative on the
first-person use of the term (see Loar 1990).
[31]See Loar
1990 and Sturgeon 1994 for a discussion of this. In fact, on a Kripkean direct
reference theory, this also applies to proper names, demonstratives, natural
kind terms, etc. The point is that on Jackson
and Chalmers=s
view, this feature is unique to phenomenal concepts.
[32]Another way
to block the argument is to deny that there are phenomenal states; see, for example,
Rey 1988. But, again, I put this objection to the Conceivability Argument
aside, since I do not want a refutation of it to depend on such a controversial
claim.
[33]As we have
already pointed it out, Jackson is not explicit
about this. But in his 1982 he provides the tools to generate trouble for the
physicalist from the A Priori Entailment
Thesis. In that paper Jackson maintained that Mary is not able to deduce,
even from the full physical description of the world, that a certain phenomenal
experience, for example, red phenomenal experience, occurs. There are
indications that he might have changed his mind on exactly this issue (see his
1996, 142.)
[34]The most
important formulations of the argument that shows this are by Papineau (1993),
Loewer (1995), and Witmer (1997). They intend this as an argument for physicalism.
[35]Chalmers
says that a person is acquainted with
her phenomenal states and that this relation is not a causal one. But this
seems to just put a label on the mystery.
[36]Descartes
actually did in the Meditations.
[37]In fact,
this world would be a minimal physical duplicate of our world.
[38]The
objection can be made more general by simply claiming that intentionality does
not supervene on the physical. In this case, however, the argument for dualism
based on qualia would already presuppose
dualism about intentionality.
[39]Searle does
not distinguish between phenomenal consciousness and the cognitive aspects of
consciousness; he probably thinks that the two are metaphysically connected. In
any case, I take him to say that all intentional states have to be at least
potentially phenomenally conscious. This is the reading on which Searle’s
thesis causes a prima facie problem for my argument.
[40]Incidentally,
this thesis is perfectly compatible with physicalism, even though, if true, it
would render the Zombie Refutation in its present form ineffective.
[41]Wittgenstein’s
private language argument, if sound, would show that it is not possible to refer
to an inner state (be that a brain state or a nonphysical phenomenal state) by
a concept that does not employ external criteria for its application; so it
would show that there could not be a concept like the concept ‘pain+’.
However, this would not count in favor of the Conceivability Arguments, since,
as I have pointed out earlier, these same considerations would make zombies
inconceivable.
[42]Strictly
speaking, there is another way in which Assumption
2 could turn out to be false: if ‘pain+’ referred to a physical
state that could not be instantiated by zombies. But that is a very unlikely
scenario; I am going to deal with it I when give support to Assumption 2.
[43]Most, but
not all; when one of them says ‘I am not in pain+,’ she would speak
the truth.
[44]In fact,
Shoemaker (1998) has similarly argued that zombies will refer to a brain or
functional state by their phenomenal+ concepts. He uses the point to
a different effect, however; he argues for the view that our phenomenal
concepts also refer to physical states, since we are physically identical to
our zombie-twins.
[45]A very
similar argument was formulated by Smart (1959). He introduced his ‘topic neutral
analyses’ of mental terms in response to this argument.
[46]It is
arguable that one can save the spirit, while rejecting the letter, of the A Priori Entailment Thesis. In my view,
the A Priori Entailment Thesis might
be correct about all truths except phenomenal truths. This has to do with the
special nature of phenomenal concepts. So metaphysical necessity might be
reducible to conceptual truth cum
empirical truths in all cases except cases involving phenomenal concepts (plus
the cases mentioned in note 29), and the exceptions themselves might be covered
by principles that make modality sufficiently ‘un-mysterious’. How exactly to
deal with the exceptions, however, is beyond the scope of this paper.
[47]The
following originates in Loar 1997. See also Sturgeon 1994.
[48]This is a
close relative of the theory of concepts I attributed to White (1986) earlier,
where I was considering the viability of the concept ‘pain+’.