Philosophical Zombies- IEP Amber Ross
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Amber Ross
Philosophical Zombies
Internet Encyclopedia of Philosophy,
Under Revision- Please do not quote or circulate.
Introduction
The ‘philosophical zombie’ is a thought experiment in philosophy of mind that
tests our intuitions about the relation between our conscious experience and our
physical nature. Philosophical zombies look and act just like ordinary human beings and
by all outward appearance zombies and humans are indistinguishable. Zombies
resemble us in all our physical respects: they act as we act and speak as we speak. Each
one of us has a hypothetical ‘zombie-twin’, a molecule-for-molecule duplicate of
ourselves. The only difference between human beings and their zombie-twins is that
none of the zombie’s physical activity–inner or outer–is accompanied by any conscious
experience. Our zombie-twins’ senses gather all the same information from the world
that ours gather, but–unlike ourselves–they have no experience of it whatsoever. As our
behavioral twins, zombies will certainly seem to make judgments that are about
conscious experience, judgments indistinguishable from our own, although they have no
conscious experience themselves.
Related thought experiments appear in Gottfried Wilhelm Leibniz (1720) and a
recent forerunner is Keith Campbell’s ‘imitation man’ (1970), whereas the contemporary
notion of the philosophical zombie was introduced by Robert Kirk (1974a, 1974b) and
employed to the greatest extent by David Chalmers (1996), who uses them to argue for a
‘naturalistic’ form of property dualism. The zombie thought experiment also brings to
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light issues regarding the relationship between conceivability (an epistemological
notion) and both metaphysical possibility and logical possibility.
Table of Contents
1. Zombies and the Metaphysics of Mind
2. Support for the Conceivability of Zombies: The Explanatory Gap
3. The Anti-Physicalist Argument from the Conceivability of Zombies a. The Notion of Conceivability in the Zombie Conceivability Argument
4. Physicalist Responses to the Zombie Conceivability Argument a. Taking the Hard Line: Denying the Conceivability of Zombies
i. Do Philosophical Zombies Employ on a Faulty Notion of Consciousness? b. Taking the Soft Line: Grant Conceivability, Deny Possibility
i. The Phenomenal Concept Strategy
5. Questioning the Foundations: Can Conceivability be a Genuinely Rational Notion? a. Yablo’s Criticism of Ideal Conceivability: Any Conceiver could be Mistaken b. Attempting to Idealize Conceivability
i. Potential Problems with Idealizing Conceivability
6. The Anti-Zombie: Has the Philosophical Zombie Met its Match?
7. References and Further Reading
1. Zombies and the Metaphysics of Mind
The philosophical zombie is a curious, yet philosophically powerful creature. It
does seem as though we can imagine at least to some degree the zombie and its zombie
world,. The mere possibility of this kind of zombie may have the power to overthrow
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what was–at least for the second half of the 20th century–an almost universally accepted
position in philosophy of mind: physicalism.
Physicalism, generally speaking, is the view that everything that exists, at its most
fundamental level, is composed of (or reduces to or supervenes upon) only one kind of
property. Physical properties are the kind of properties that compose everything we
think of as ordinary physical objects. If physicalism is true, then any creature physically
identical to a human being will be identical to a human being in all its respects,
including its conscious experience. The world must also be similar to ours in relevant
respects, since, for example, a creature physically identical to a human being, but in a
world with the wrong properties, may be inert rather than conscious. It is widely
thought that, regardless of one’s position on the metaphysics of mind, zombies are at
least conceivable. According to physicalists, zombies are merely conceivable; one among
many conceivable impossibilities.
In addition to defending the conceivability of philosophical zombies, mind-body
dualists argue for the metaphysical possibility of zombies. The possibility of zombies is
most often used to argue for a position called ‘property dualism’. Property dualists
believe that our minds consist of two fundamentally different types of mental states,
each with its own distinct kind of metaphysical properties. On the one hand, there are
the functional, information processing, problem solving, cognitive kinds of mental
properties and these reduce to certain physical, functional and structural properties that
are more fundamental than those cognitive mental states themselves. But, in contrast to
the physicalist view, property dualists argue that the fundamental features of our world
are not exhausted by physical properties alone. They hold that there must be at least one
other type of property, a special kind of mental property called ‘qualia’ or the
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‘phenomenal properties’ of our mental states. These qualia or phenomenal properties
are the properties that constitute the character of our conscious experience and,
according to dualists, they are metaphysically different in kind from our cognitive,
information processing and functional mental states. These special mental properties
neither reduce to nor metaphysically supervene upon any physical, functional, structural
properties or other non-phenomenal properties. Phenomenal properties are
metaphysically fundamental. They are the only kind of property that, by hypothesis, you
do not share with your philosophical-zombie-twin. Having or lacking these phenomenal
properties, the properties that constitute the character of our conscious experience, will
determine whether you are conscious or whether your mind is like that of the zombie–
‘all silent and dark within.’
The most popular contemporary form of mind-body dualism is ‘naturalized
property dualism’. This kind of dualism assumes that there are psychophysical laws in
the actual world, which govern the relationship between our cognitive mental states and
our phenomenal mental states such that, as a matter of empirical fact, conscious
experience will be connected to the physical, functional and structural properties of the
world in a law-like way. But property dualists argue that the phenomenal facts in the
actual world–facts about the character of our conscious experience–are not logically or
metaphysically necessarily connected with physical facts. For phenomenal facts to be
necessarily connected– logically or metaphysically–to physical facts, it would have to be
logically impossible (conceptually incoherent or inconceivable) for the character of one’s
conscious experience to change without some change in the physical properties of the
world. There is a logically necessary connection, for example, between biological facts
and physical facts. We could say, following the dualist David Chalmers, who borrows an
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image from Kripke (1972), that once God fixed all the physical facts of the world, the
biological facts came along for free. But after setting the physical facts in place, God had
‘more work to do to make sure there is a law relating the [physical] facts and the
[phenomenal] facts’ (1996: 38). According to property dualism, biological facts,
chemical facts and facts about our cognitive mental states are logically necessarily
connected to physical facts; whereas phenomenal facts–facts about the character of
conscious experience–stand apart as metaphysically and conceptually independent of
any other kind of fact, including facts about other kinds of mental states.
Physicalism is not merely a mainstream philosophical view but a fundamental
assumption in the scientific study of the mind. If physicalism is false, then our minds
must be more than brains-in-action. Our conscious experience may be nomologically
connected to our cognitive, functional and structural states as a matter of empirical fact,
but if zombies are possible then our world could have turned out differently. If our
world could have turned out differently–physically just the same but phenomenally
different–that is, different where consciousness is concerned, there must be some
additional feature of our world that could have been absent from it, but is in fact
present. Perhaps this feature emerges from our brain activity, but nevertheless it is a
fundamentally different kind of property than our physical properties and it could only
be this additional, non-physical property that accounts for our conscious experience.
The zombie thought-experiment is at root a philosophical puzzle, but since the
beginning of the 21st century the idea of philosophical zombies has become common
currency in cognitive science and many have taken to heart the notion that, if zombies
are conceivable, there really is some aspect of consciousness that stands outside the
scope of what a thoroughly physicalist science of the mind can explain. These scientific
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explanations do not have room for a non-functional, non-physical and non-structural
fundamental property yet. A basic assumption of empirical science is that the
phenomena of our world can be explained without appealing to anything beyond the
structure and relations between certain physical properties. If zombies are possible then
our current form of scientific explanation, one that can in principle provide a sufficient
explanation for every other fundamental aspect of our world, could not explain
conscious experience. If property dualism is true, the mind stands outside the scope of
empirical investigation. Zombies are so philosophically powerful that their mere
possibility would illustrate that science-as-we-know-it is unable to explain the conscious
mind.
2. Support for the Conceivability of Zombies: The Explanatory Gap
If we assume that facts about the character of our conscious experience are not
logically determined by facts about our physical nature, then it is conceivable for a
subject’s physical properties to be exactly as they are now, while her conscious
experience differs in some essential way. It would be conceivable for you to feel a slight
ache in your left foot that you are not actually feeling now, even though your physical
body–including your brain activity–is in a state that is molecule-for-molecule identical
to its current state. That ache would be a phenomenal property of your experience. If it
is conceivable for there to be a small change, such as this, in your phenomenal
properties, while your physical properties remain the same, then by the same reasoning
large changes should be conceivable as well.
If physical facts do not logically entail phenomenal facts, then it is conceivable for
phenomenal properties–the properties of conscious experience–to change or differ
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without a change or difference in physical properties. If it is conceivable that such
properties could change, it is also conceivable that phenomenal properties could be
absent from a world altogether, while the physical properties of that world may be
identical to those of the actual world.
Worlds that are physically identical to our own but lack phenomenal properties
are ‘zombie-worlds’. According to the proponents of the zombie conceivability argument
(see below), as long as zombie-worlds are genuinely conceivable, it follows that they are
metaphysically possible. And if zombies are possible, physicalism is false. If zombies are
possible, then it is possible that the phenomenal consciousness we find present in the
actual world–the feature that separates our world from zombie-worlds–could have been
absent, while the physical facts remain just as they are now. This is precisely what the
physicalist denies.
If it is impossible in principle for our current form of scientific explanation to
account for conscious experience, there will be a persistent and unbridgeable
explanatory gap between truths about the physical world and truths about the conscious
mind. The more compelling the conceivability of philosophical zombies is, the harder it
is for physicalism to close the gap through giving a satisfying explanation of conscious
experience in physical terms or even to dismiss the gap as being insignificant. This
insignificance could arise from some feature of our concept of the mind and conscious
experience, regardless of the metaphysical nature of consciousness itself. The dualist
takes the persistence of the explanatory gap–the failure of physicalism to give a
transparent explanation of the connection between facts about consciousness and
physical facts–as conclusive evidence for the falsity of physicalism.
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3. The Anti-Physicalist Argument from the Conceivability of Zombies
The anti-physicalist argument from the conceivability of zombies may be the
most compelling argument for mind-body dualism since the beginning of this century.
In its simplest form, it can be stated thus:
1. Zombies are conceivable.
2. Whatever is conceivable is possible.
3. Zombies are possible.
4. Physicalism is false.
Following David Chalmers (2010: 142), the argument can also be laid out more
technically as follows:
1. P&~Q is conceivable.
2. If P&~Q is conceivable, P&~Q is metaphysically possible.
3. If P&~Q is metaphysically possible, physicalism is false.
4. Physicalism is false.
As the conceivability argument is laid out here, P is ‘the conjunction of all
microphysical truths about the universe’ and Q is ‘an arbitrary phenomenal truth’ (ibid:
142). A ‘phenomenal truth’ is a particular fact about conscious experience; it can be a
fact about a particular individual’s conscious experience or about consciousness in
general.
Premise (1) of the conceivability argument states that you can conceive of a
world, in which the phenomenal facts–facts about the character of conscious
experience–are not necessitated by the physical facts. Most physicalists accept premise
(1), agreeing that we can conceive of our world’s physical facts being just as they are
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now, whereas the phenomenal facts differ in some way. Premise (2) of the conceivability
argument is the conceivability-possibility principle. According to this principle,
whatever is genuinely conceivable is possible. If zombies are genuinely conceivable, then
zombies are possible and if zombies are possible, physicalism must be false.
a. The Notion of Conceivability in the Zombie Conceivability Argument
Premise (2) of the conceivability argument is the most controversial instance of
the conceivability-possibility principle, claiming that any state of affairs that is
conceivable is also possible. Spelled out in these simple terms, it seems clearly false,
since myriad instances exist, in which conceivable states of affairs are metaphysically
impossible. For the most part, conceivability is a good, yet fallible guide to possibility.
But why should conceivability be a perfect guide to possibility in the zombie case?
Chalmers’ defense of the conceivability-possibility principle (and the zombie
conceivability argument) involves dividing the notion of conceivability into several
varieties. Positing careful distinctions within the concept of conceivability itself,
Chalmers reformulates the principle in a way that avoids the most obvious objections.
Rather than the overly simplistic and clearly false claim that could be read as ‘whatever
satisfies any criteria for conceivability is possible,’ the conceivability-possibility
principle is the more refined claim that whatever is ideally conceivable is possible or,
more precisely:
Ideal primary positive conceivability entails primary possibility.
The ideal variety of conceivability above is contrasted with prima facie
conceivability; the positive variety is contrasted with negative conceivability and
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primary conceivability with secondary. The distinction between prima facie and ideal
conceivability is intended to separate those scenarios that merely seem conceivable at
first from those, which are actually conceivable. The notion of prima facie
conceivability is fairly straightforward: S is prima facie conceivable for a subject, when S
is conceivable for that subject on first appearance (Chalmers, 2010: 143).
The dimension of positive conceivability and negative conceivability is concerned
with creation and elimination. A scenario is positively conceivable, when it can be
‘created in (modal) imagination’, while ‘negative notions of conceivability hold that S is
conceivable when S is not ruled out’ (ibid: 143). A scenario is prima facie negatively
conceivable, when initial consideration of the scenario reveals no obvious conceptual
contraction within that scenario or hypothesis. A scenario is ideally negatively
conceivable only if ‘the hypothesis expressed by S cannot be ruled out a priori even on
ideal rational reflection’ (2010: 143) and will fail to be ideally negatively conceivable,
when the prima facie conceivability of S is ‘undermined by further reflection showing
that the tests that are criterial for conceivability are not in fact passed’ (ibid: 144).
The notion of forming a ‘positive conception of a situation’ is somewhat more
complicated, since it involves imagination, but not ‘imagination’ in an ordinary sense. S
is ‘positively conceivable,’ when a subject can coherently ‘modally imagine’ a situation
that verifies S. Hence, ‘when one can coherently imagine a situation in which S is the
case’ (2010: 144), which is ‘to in some sense imagine a specific configuration of objects
and properties’ (ibid: 145) and ‘fill in arbitrary details in the imagined situation such
that no contradiction reveals itself’ (ibid).
As the word suggests, imagination is often imagistic or in some way sensorial and
genuinely conceivable scenarios exist that cannot be ‘imagined’ in these ways. Descartes’
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example was ‘imagining’ a chiliagon (Meditation 6) in visual terms: a polygon with 1000
sides indistinguishable from a circle, even though the concepts ‘chiliagon’ and ‘circle’ are
clearly distinct, while both are conceptually coherent. Modal imagination cannot be
perceptual or sensory, as neither can be imagined from the first-personal subjective
perspective. To ‘modally imagine a scenario’ is not to imagine viewing some scene, but
rather to mentally arrange a set of objects and properties in a certain way that would
either verify or fail to verify a proposition that represents a possible world or potential
scenario.
Insofar as we can conceive of a difference between zombies and conscious human
beings, the scenario cannot be positively conceived by comparing perceptions of the two
creatures in imagination, since a zombie world is identical to a human world in every
observable respect. Neither we nor the zombies could observe that zombies lack
phenomenal states. Zombies themselves cannot observe that they are in any way
different from humans. Zombies, by definition, do not observe any difference between
themselves and their human twins, since one cannot observe a subjective state that is
simply absent, hence the zombie is unable to observe a difference.
Zombie-minds will be prima facie positively conceivable, when a subject believes
that all the details of the zombie scenario can be filled in without revealing a
contradiction or when a subject believes she can ‘imagine a situation with certain
important features specified, notes that a situation of this kind appears to verify S, and
judges that the remaining details are not crucial’ (Chalmers, 2002a: 153).
Property dualists and some physicalists claim that zombies are ideally
conceivable, because the zombie-scenario is conceptually coherent and displays no
contradictions concealed within it. The proponents of the zombie conceivability
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argument believe that, if there is no latent conceptual incoherence in the zombie
scenario, we can infer the possibility of zombies from their conceivability alone. And, if
zombies are possible, physicalism must be false, since, according to physicalism, any
creature, in any possible world that is molecule-for-molecule physically identical to a
human will have human mental properties, both cognitive and phenomenal. This means
that the mere possibility of a zombie-world makes physicalism an untenable position:
physicalism would be false in our world, as well as in all possible worlds. If zombies are
possible, physicalism is necessarily false.
4. Physicalist Responses to the Zombie Conceivability Argument
The common consensus among philosophers is that the zombie-scenario is
conceptually coherent. Property dualists, as well as the majority of physicalists, hold
that they can ‘coherently modally imagine’ zombies and zombie-worlds without
difficulty by ‘fill[ing] in arbitrary details in the imagined [zombie] situation such that no
contradiction reveals itself’ (Chalmers, 2010: 145). Most philosophers would agree that
their positive conception of the zombie-scenario withstands the test for ideal
conceivability, a point crucial for accepting premise (1) of the argument, since no
‘variety’ short of ideal conceivability qualifies as genuine conceivability, as the property
dualist intends it to be understood in the zombie conceivability argument and
interpreted in the conceivability-possibility principle. Very few philosophers argue that
philosophical zombies are not ideally conceivable, but the most compelling arguments
against the conceivability of zombies can be found in Robert Kirk (1974, 2008), Daniel
Dennett (1995, 1999, 2005, 2013), Sydney Shoemaker (1975), Nigel Thomas (1998),
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David Braddon-Mitchell (2003), Allin Botterell (2001), Keith Frankish (2007), Richard
Brown (2010) and Marcus (2004).
a. Taking the Hard Line: Denying the Conceivability of Zombies
A subject may make the prima facie judgment that she can fill in the details of
scenario S, even though the world S described is in fact conceptually incoherent (for
example, inconceivable objects, such as Roger Penrose’s ‘impossible triangle’ or many
drawings by M.C. Escher). [Image of the “impossible triangle” approximately here.]
Most philosophers rejecting the conceivability of the zombie-scenario argue against its
positive conceivability, through attempting to show that zombies are only prima facie
positively conceivable. According to these philosophers, subjects who believe they are
conceiving of a zombie are actually making a mistake of some sort in their imagination:
possibly by ‘filling in’ the scenario with improper details or by failing to notice ‘holes’ in
the details of their imagined creature. (For compelling arguments of this sort, see Kirk
(2008), Dennett on zombies (1991, 2005) and on the knowledge argument (1991), as
well as Marcus (2004) and Ross Inconceivable Minds (2013) chapter 4.)
Popular attempts to explain away the zombie’s apparent conceivability appeal to
empirical facts about the psychology of imagination, arguing that when we take
ourselves to be imagining a philosophical zombie, we imagine, or refrain from
imagining, different aspects of the zombie-scenario. (See Hill (1997), Hill and
McLaughlin (1999), Block and Stalnaker (1999) and Nagel (1974, fn11), among others.
For an overview of this type of response to the conceivability argument, see Tyler
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Doggett & Daniel Stoljar (2010).) It is worth quoting Nagel’s account of imagination
here at some length:
We may imagine something by representing it to ourselves either
perceptually [or] sympathetically. … To imagine something perceptually,
we put ourselves in a conscious state resembling the state we would be in if
we perceived it. To imagine something sympathetically, we put ourselves
in a conscious state resembling the thing itself. …When we try to imagine a
mental state occurring without its associated brain state, we first
sympathetically imagine the occurrence of the mental state; that is, we put
ourselves in a state that resembles it mentally. At the same time, we
attempt to perceptually imagine the non-occurrence of the associated
physical state, by putting ourselves into a state unconnected with the first:
one resembling that which we would be in if we perceived the non-
occurrence of the physical state. Where the imagination of mental features
is sympathetic, it appears to us that we can imagine any experience
occurring without its associated brain state, and vice versa. The relation
between them will appear contingent even if it is necessary, because of the
independence of the disparate types of imagination (1979: 175, fn. 11).
It is no small feat to show that the creature we ordinarily imagine, when we
believe we are conceiving of a zombie, does not have all the properties of an actual
philosophical zombie, but is merely a superficially similar creature, the conceivability of
which is irrelevant to the truth or falsity of physicalism. Nor is it a small task to give a
compelling explanation of our apparent ability to imagine philosophical zombies via an
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account of the psychology of imagination. But the problem with these and similar
attempts to identify the ways, in which we might fail to properly positively conceive of a
zombie, is that they are not actually objections to the zombie conceivability argument.
The proponent of the zombie conceivability argument claims that there is a
genuine sense of ‘modal imagination,’ in which one can ‘imagine an arrangement of
objects and properties’ that form a scenario, in addition to perceptual and sensory or
first-person-subjective imagination (imagining what S is like from the perspective of a
subject in scenario S). If this is correct, then it is irrelevant whether our ordinary
methods of imagination will produce a positive conception of a zombie.
Eric Marcus (2004) argues against the conceivability of zombies by claiming that,
when we take ourselves to conceive of zombies, we are not actually forming a positive
conception of a non-phenomenally-conscious creature physically identical to ourselves.
Instead, we are positively and perceptually imagining something physically identical to a
human being and then refraining from imagining its conscious experience. Since
‘refraining from imagining’ does not suffice for forming a positive conception of a
scenario and the only way to conceive of an absence of subjective experience is to refrain
from imagining subjective experience, he claims we cannot positively conceive of
zombies.
In order to positively conceive of the absence of a subjective experience, we would
need to ‘sympathetically imagine’ the zombie’s experience (to use Nagel’s terminology)
and to ‘put ourselves in a state that resembles it mentally’. And exactly this is
impossible, since there is no state that resembles the zombie’s subjective state mentally,
given that no subjective state for it to mentally resemble exists. As Marcus says:
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The problem for this thought-experiment is not that there is something
imaginable, only we can’t quite conjure it up. The problem is that there is
nothing to be imagined. To ‘imagine’ creatures that are objectively
identical to us with all subjectivity removed is neither an act of third-
person imagining, nor an act of first-person imagining. No, to ‘imagine’ a
zombie is not really to imagine at all (2004: 483).
The problem with Marcus’ argument against the conceivability of zombies is that
neither ‘sympathetic imagination’ nor ‘first-person imagination’ are modal imagination
and this is the kind of imagination at issue in the zombie conceivability argument.
According to Marcus, ‘it is crucial for the argument in favor of the possibility of zombies
that the conceivability of zombies be in part a matter of first-person imagining’ (ibid:
483), whereas a proponent of the zombie conceivability argument would deny this. In
order to modally imagining a scenario, a subject must be able to imagine particular
properties themselves having certain properties. To modally imagine a zombie world, a
subject must imagine that the properties that constitute conscious experience are or at
least could be such that a creature could share all our physical properties but lack our
conscious experience. And conceiving of mental properies as bearing, or not bearing,
certain relations to other properties (for example physical properties) does not require
any first-person imagination, as it only requires conceptual analysis.
Marcus’ interpretation of Chalmers’ notion of ‘modal imagining’ highlights the
notion’s deceptive simplicity:
[A]ccording to Chalmers, positive imagining need not be perceptual. I can
imagine what is ‘beyond the scale of perception: for example, molecules of
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H2O or Germany winning the Second World War’ [Chalmers 2002, 151]. In
such cases, there are no mental images, instead ‘we have an intuition of (or
as of) a world in which S, or at least of (or as of) a situation in which S,
where a situation is (roughly) a configuration of objects and properties
within a world’ [Ibid., 151]. In the case of modal imagining, then, the
mediating object is an intuition that represents the possibility in a way
analogous to that of the image in the case of perceptual imagining (Marcus
2004, 479).
The footnote following Marcus’ quote states that ‘I don’t see exactly how an
intuition could be an object analogous to an image; but I won’t digress by disputing that
here’ (ibid: 479). In failing to see how an intuition is analogous to an image, Marcus
reveals something important about modal imagination: images and intuitions may both
be a sort of mental representation, but beyond this there is no illuminating analogy
between the two. The terms intuition, image and imagination all serve to make the
extraordinary task of modally imagining a scenario look like the commonplace act of
imagining a character in a scene, through attempting to precisify the content of certain
concepts (such as consciousness, conscious experience, physicality and so forth) and
judge whether certain properties could bear certain relations to other properties.
Regardless of whether Marcus’ argument addresses the zombie conceivability argument
as Chalmers poses it, Marcus’ main point is still significant: to positively conceive of the
zombie-scenario is in fact harder than it seems.
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i. Do Philosophical Zombies Employ on a Faulty Notion of Consciousness?
Philosophical zombies are defined as void of conscious experience. But different
interpretations of the meaning of consciousness and conscious experience will generate
different conclusions about the conceivability of zombies. These different
interpretations not only separate physicalists from dualists, but account for the division
between different physicalist positions as well. All dualists and the majority of
physicalists interpret having a conscious experience as something like ‘being in a state
that has a certain phenomenal feel’ or ‘there being something it’s like to be in this
particular state.’
A minority position within physicalism called ‘thin materialism’, according to
Graham and Horgan’s (2000) delineation of physicalist positions, takes the notion of
‘seeming’ to be essential to the concept of conscious experience. These physicalists
believe for a subject to have a conscious experience means to be in a state that seems to
the subject to have a certain character, quality or feel to it. In the descriptions of zombie-
worlds, zombies claim to be conscious, they write about consciousness, complain when
they feel pain in their lower back and so forth. All parties to the zombie-debate agree
that there is a philosophically significant sense, in which it seems to the zombie that she
has conscious experience.
If seeming plays an essential role in the concept of conscious experience itself,
the definition of a philosophical zombie will be incompatible with the concept of
conscious experience, since it will certainly seem to the zombie that she is conscious and
has conscious experiences. If it seems to the zombie that she is having a conscious
experience, then, according to this interpretation of the meaning of consciousness, the
zombie is having a conscious experience. Thus the notion of a philosophical zombie
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contradicts the thin physicalist’s concept of consciousness, since if all that is required for
consciousness to exist is for it to seem to the subject that she is conscious then zombies
are conceptually incoherent and inconceivable. (It should be noted that such accounts
are typically categorized as ‘anti-realist’ accounts of conscious experience, even though
proponents of thin materialism would disagree with this characterization.)
Thin physicalists deny the primary assumption, on which the conceivability
argument is based, namely the claim that zombies are genuinely conceivable. The
apparent conceivability of zombies may stem from a conceptual confusion about the
nature of consciousness, the latent disagreements over what it means for a scenario to
be conceivable or from a lack of imagination. The thin physicalist holds that in some way
or another the ease, with which one can describe a philosophical zombie is obscuring the
actual complexity of the zombie-scenario and this complexity in turn hides the zombie’s
conceptual incoherence. These physicalists think that zombie-stories induce something
resembling a conceptual hallucination, in which what you seem to be conceiving is not
actually what you conceive. According to thin physicalism, such conceptual
hallucinations might be corrected through the discovery of a yet unknown, but in
principle possible, a priori connection between phenomenal facts about conscious
experience and physical facts. Though prima facie philosophical zombies seem to make
sense, the thin physicalist holds that they are not conceptually coherent. This seems to
be Dennett’s (1995) take on the notion of zombies. In The Unimagined
Preposterousness of Zombies, he compares the concept of consciousness to that of
health:
Supposing that by an act of stipulative imagination you can remove
consciousness while leaving all cognitive systems intact — a quite standard
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but entirely bogus feat of imagination — is like supposing that by an act of
stipulative imagination, you can remove health while leaving all bodily
functions and powers intact. … Health isn't that sort of thing, and neither is
consciousness.
b. Taking the Soft Line: Grant Conceivability, Deny Possibility
Dualists and the majority of physicalists take the meaning of consciousness to be
something like ‘having phenomenal feel’. This group of physicalists is called ‘thick
materialists’, according to Graham and Horgan (2000) or ‘type-b materialists’,
according to Chalmers (2002b) and endorses premise (1) of the conceivability
argument, granting that philosophical zombies are conceptually coherent. According to
type-b physicalists, there is no conceptual contradiction within the zombie-scenario, in
which it seems to a subject that she is having a conscious experience with a certain
phenomenal content, despite lacking conscious experience whatsoever. If having a
conscious experience means ‘being in a state with a certain phenomenal feel’ and
seeming to be in a state with a phenomenal feel is not conceptually sufficient for having
a conscious experience veridical or otherwise. Then a subject may believe that she is in a
state that has a phenomenal feel, but holding this belief will be conceptually consistent
with the subject not actually being conscious. Despite the subject’s potential to hold a
false belief about her mental state, the scenario itself is still conceptually consistent.
Type-b physicalists insist that zombies are merely conceivable, but that it does
not follow that zombies are metaphysically possible, targeting premise (2) of the
conceivability argument. Even though facts about possibility and conceivability are
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related, they are separate matters. Type-b physicalists reject the claim that the
conceivability of scenario S straightforwardly entails that S is possible, stipulating
conceivability as a guide to possibility, but nonetheless a defeasible one.
Premise (2) of the zombie conceivability argument, ‘whatever is (ideally
positively) conceivable, is possible,’ is the most widely disputed premise. The plausibility
of premise (2) depends on the inconceivability of metaphysical impossibilities. Most
type-b physicalists hold that premise (2) is undermined by Kripke’s notion of a
posteriori necessity.
According to type-b physicalists, we can conceive of zombies, not because they
are possible, but because the structure of our cognitive economy isolates our
phenomenal concepts (for example, the concept of what it is like to see red) from our
physical, functional, cognitive, and otherwise non-phenomenal concepts (for example,
the physical concept brain event b or the cognitive concepts focusing attention and
identifying a percept). Our ability to conceive of zombies reflects only the nature of our
concepts, just as our ability to conceive of water as distinct from H2O does not entail the
metaphysical possibility that water is not H2O. Therefore our ability to conceive of
zombies says nothing about the metaphysical possibility of zombies. According to type-b
physicalists, the conceivability of the zombie-scenario does not itself show that
physicalism is false in our world.
The most widely accepted view among physicalists is that physicalism is
contingently true of our world. They hold that the mental facts of our world supervene
upon the physical facts, but maintain that physicalism is not the only conceptually
coherent theory of the relationship between mind and world. Most physicalists admit
that it is conceivable that physicalism might have been false of our world and a smaller
Philosophical Zombies- IEP Amber Ross
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set of physicalists treat it as a necessary or conceptual truth (for example, Davidson
(1970)).
Whether the psychophysical conditional (‘P →Q’, where P is the set of all physical
facts in a world and Q is the set of all phenomenal facts in that world) is intended to be
taken as a necessary or as a contingent truth of our world, the fact that certain mental
states supervene upon or are identical to certain physical brain states certainly appears
to be contingent. In either case, those who interpret physicalism as either a necessary or
contingent truth widely appeal to Kripke’s (1972) introduction of ‘a posteriori necessity’
to defend physicalism against the zombie conceivability argument.
To borrow Frege’s example: the terms ‘Morning Star’ and ‘Evening Star’ both
refer to the planet Venus, but both pick out their referent through different modes of
presentation or descriptions. Morning Star picks out its referent by means of some
description such as ‘the last heavenly body we see in the morning’, while Evening Star
picks out its referent by the description ‘the first heavenly body we see in the evening’.
The difference between the way these two terms pick out their shared referent indicates
a difference in the meaning of these two terms; that is, a difference between the
concepts’ content.
Since identity is a necessary relation, the Morning Star is necessarily the Evening
Star. Still, the identity of the Morning Star with the Evening Star may appear
contingent, because this identity is not an a priori truth. The fact that the Morning Star
is the Evening Star is not true in virtue of the content of the constituent concepts alone.
Since their identity is an empirical fact rather than a priori truth, it will seem as though
conditions could have turned out differently. It seems as though the Morning Star might
have turned out to be some heavenly body other than Venus. But an identity discovered
Philosophical Zombies- IEP Amber Ross
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a posteriori is still an identity and since the relation is necessary it holds in every
possible world.
A posteriori necessary truths seem contingent, because we must first gain
empirical knowledge, in order to see their truth. A person who does not know that the
Morning Star and Evening Star are Venus, who does not know that ‘the last heavenly
body we see in the morning’ is the very same thing as ‘the first heavenly body we see in
the evening’, can conceive of the Morning Star and the Evening Star being distinct
objects. It is consistent with everything this person knows that the Morning Star and
Evening Star may be two separate entities.
Whether or not one is actually aware that these ‘stars’ are the planet Venus, there
is still a sense in which it is conceivable for the Morning Star to be distinct from the
Evening Star. Within the modality of possible worlds, we can express the divergence of
conceivability from possibility by postulating two independent sets of worlds: the first
containing ‘conceptually possible worlds’ (for example, worlds that are merely
conceivable), while the second set contains only ‘metaphysically possible worlds’, the
kind of ‘worlds’ that matter to the truth or falsity of physicalism. Because the identity
relation is metaphysically necessary, the Morning Star will be identical with the
Evening Star in every metaphysically possible world. But because their identity is not a
priori, it is not a conceptually necessary truth and as such there will be conceptually
possible worlds (conceivable scenarios or epistemically possible worlds), in which the
Morning Star and the Evening Star are distinct entities.
Most physicalists are a posteriori physicalists in the sense that they claim we can
conceive of brain events occurring in the absence of phenomenal events, even though
the brain event and phenomenal event are identical. They furthermore claim that we can
Philosophical Zombies- IEP Amber Ross
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conceive of zombie-scenarios even though they are impossible, for the same reason that
we can conceive of the Morning Star and Evening Star being distinct entities, even
though their identity is metaphysically necessary. Just as the concepts Morning Star
and Evening Star have different content, but both refer to planet Venus, the concepts
we use to denote our conscious experiences (for example, ‘what it is like to see red’) and
the concepts we use to refer to brain or cognitive events (for example, ‘identifying the
red percept’) have different content, but refer to the same properties. Appealing to two
independent sets of possible worlds allows type-b physicalists to claim that the identity
of the conscious experience ‘seeing-red’ with the brain or cognitive event ‘identifying-
the-red-percept’ may be an empirical fact, only known a posteriori, yet nonetheless
metaphysically necessary.
We might say that the type-b physicalist’s modal universe contains two types of
worlds: the merely conceivable and the genuinely possible. The property dualist cannot
accept this distinction between two sets of worlds, because, in order to defend the
zombie conceivability argument, he must maintain his claim that conceivability entails
possibility by showing how every conceivable world can be a metaphysically possible
world. If the type-b physicalist is correct and some conceivable worlds are not
metaphysically possible, the conceivability of zombies may have no metaphysical
implication.
i. The Phenomenal Concept Strategy
Physicalists hold that the conceivability of zombies and the existence of the
explanatory gap only provide prima facie support for the claim that there is an
Philosophical Zombies- IEP Amber Ross
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ontological difference between physical and phenomenal mental properties and that the
evidence thereof is actually defeasible. One might ‘explain away’ this prima facie
evidence against physicalism by showing that the conceivability of zombies and
existence of the explanatory gap are merely benign consequences of the way our mind
organizes and draws connections between our concepts of consciousness and
physicality. Similar to the appeal to ‘a posteriori necessity,’ this sort of alternative
explanation would prohibit the dualist from making a direct inference from the
conceivability of zombies and the existence of the explanatory gap to their metaphysical
possibility and the falsity of physicalism.
For the possibility of a scenario S to be entailed by the conceivability of S, further
criteria must be satisfied beyond the ideal positive conceivability of S. In particular,
there can be no viable alternative explanations of S’s conceivability. There may be
‘blockers’, such as multiple scenarios, which are all ideally positively conceivable
explaining the conceivability of zombies without appealing to an additional class of
ontologically properties, thus ‘blocking’ the inference from zombie-conceivability to
their possibility.
Dualists and type-b physicalists agree that phenomenal and non-phenomenal
concepts are isolated from one another. It follows that facts couched in phenomenal
terms cannot be inferred from facts couched in entirely physical terms and that
statements expressed in phenomenal terms cannot be translated into statements
expressed in entirely physical or functional (non-phenomenal) terms without some loss
of meaning. Some physicalists, applying what has come to be called “The Phenomenal
Concept Strategy” (Loar, 1990), claim that this conceptual isolation explains why Mary
the Color Scientist cannot know what it is like to see red simply in virtue of knowing all
Philosophical Zombies- IEP Amber Ross
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the physical facts about her world. Physical facts are facts expressed with physical
concepts and while physical concepts and phenomenal concepts may have the same
referent, they do not share their meaning. Therefore, no knowledge of facts expressed
with physical concepts will close the explanatory gap. Physicalists who support the
phenomenal concept strategy believe that the isolation of phenomenal concepts from
physical concepts can account for the explanatory gap between physical facts and facts
about conscious experience.
There is no single definitive version of the phenomenal concept strategy (see
Stoljar (2005)), but all forms have two basic steps in common. The first is to claim that
the psychophysical conditional (‘P →Q’, where P is the set of all physical and Q is the set
of all phenomenal facts in that world) is a necessary a posteriori truth and grant that it
appears to be contingent. The second step is to acknowledge the conceptual isolation of
phenomenal concepts from physical concepts and argue that conceptual isolation
accounts for both (1) the absence of any a priori entailment of phenomenal facts from
physical facts and (2) the apparent contingency of the psychophysical conditional.
If the phenomenal concept strategy works, that is if the source of the explanatory
gap is simply the isolation of physical concepts from phenomenal concepts, then the
existence of irreducible, non-physical and phenomenal properties is not entailed by the
explanatory gap or by the conceivability of zombies simpliciter. If this is correct, then
the nature of the relationship between our physical and phenomenal concepts will
deflate the metaphysical significance of the gap. This solution to the zombie problem is
neither intended to close the explanatory gap nor should it. If our physical concepts and
phenomenal concepts are isolated from each other, we should expect to see an epistemic
gap, even if the phenomenal states, to which those concepts refer, are identical to, or
Philosophical Zombies- IEP Amber Ross
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supervene upon, physical states. If the phenomenal concept strategy succeeds here,
neither the conceivability of zombies nor the explanatory gap more generally would
provide evidence for the claim that property dualism is true of our world.
5. Questioning the Foundations: Can Conceivability be a Genuinely Rational
Notion?
Marcus’ argument against the conceivability of zombies has shown that, at the
very least, positively conceiving of a zombie is a much more demanding task than it first
appears. But, in principle, whether or not the zombie is ideally positively conceivable
does not depend on our fallible powers of imagination. In practice, an ordinary
epistemic agent’s conceivability judgments are ‘tied to [that] subject’s contingent
cognitive limitations’ (Chalmers, 2010: 143), but genuine conceivability is not dictated
by our limited cognitive capacities. ‘Ideal conceivability’, the ‘variety’ of conceivability at
work in the conceivability-possibility principle, ‘abstracts away from those limitations’
(ibid: 143). In ‘modally imagining’ a scenario, we are attempting to determine whether
an ideal conceiver would judge that certain properties could bear certain relations to
other properties.
A fundamental assumption of the zombie conceivability argument is that the
concept of ‘ideal conceivability’ is coherent, without which a rational notion of
conceivability would fail the conceivability-possibility principle and there would be no
link between epistemic and metaphysical facts. Chalmers writes that
if we are looking for a notion of conceivability such that conceivability
tracks possibility perfectly, we must focus on ideal conceivability. In this
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sense conceivability is not a merely psychological notion; it is a rational
notion, in much the same way that a priority and rational entailment are
rational notions. If there is to be a plausible epistemic/modal bridge, it will
be a bridge between the rational and modal domains (2002a: 160
emphasis original).
Facts about epistemic agents are irrelevant to a priority and entailment. The a
priori truth of a proposition is neither relative to the subject evaluating the proposition
nor is entailment relative to a subject’s beliefs about the relation between propositions.
Though conceivability is (in some cases) relative to a speaker or thinker, for there to be
any instance, in which conceivability entails metaphysical possibility, there must be
some variety of conceivability, according to which the conceivability of S is not relative
to an epistemic agent’s beliefs. For the conceivability-possibility principle to hold, there
must be some ‘variety’ of conceivability that is a rational, rather than a psychological or
subjective notion.
Carving conceivability into several distinct notions gives the proponent of the
zombie conceivability argument the opportunity to explain and explain away the
appearance of subjectivity in conceivability-judgments. If there are in fact several types
of conceivability, it might be plausible that only certain varieties are subject-dependent.
The truth of some conceivability-judgments are clearly relative to a conceiver (for
example, prima and secondi facie conceivability-judgments), but the more finely we
discriminate between types of conceivability, the more plausible it will seems that there
could be a conceiver-independent variety of conceivability, according to which the
conceivability of S can be knowable a priori. This conceiver-independent variety of
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conceivability would allow us to judge whether scenario S is conceivable simply in virtue
of the concepts’ content that compose the scenario.
a. Yablo’s Criticism of Ideal Conceivability: Any Conceiver could be
Mistaken
Positive conceivability involves imagining a certain configuration of objects and
properties and to then decide whether that modal imagining verifies a particular
scenario, by making a considered judgment whether all the details of that scenario could
be ‘filled in’ without any contradiction revealing itself. But any ordinary epistemic agent
can be ignorant of some fact relevant to the scenario she believes she can conceive.
Yablo (2003) objects to the immediate inference from conceivability to metaphysical
possibility across the board:
If ignorance of an individual's essential properties can generate modal
error, why not ignorance of a property's essential properties? Imagine that
my grasp of a property S fails to reflect the fact that it is essentially
uninstantiable (S might be the property of being sodium-free salt).
Nothing to prevent me, then, from conceiving it as possible that Ss should
exist: a de dicto conceivability error rather than a de re one. Likewise the
de dicto impossibility that some Qs are Rs will be conceivable, if my
understanding of Q omits its essential property of having no Rs in its
extension. Probably there is no proposition for which a worry like this
cannot be raised (Yablo, 2003:17).
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Nothing is to prevent a subject from believing she can ‘modally imagine’ a
scenario, if she is ignorant of some essential property of a property or concept involved.
No epistemic agent can prevent herself from making such a mistake and no community
of likewise-ignorant epistemic agents could correct that mistake. Chalmers
acknowledges this problem with the rational notion of conceivability in certain cases.
Indeed, it is arguable that one can modally imagine S when S involves an a
priori contradiction. An example may be a case in which one imagines a
geometric object with contradictory properties. In cases like this, one
imagines a situation in something less than full detail (2002a).
The overarching problem is that a subject’s intrinsic cognitive limitations will
always prevent her from knowing with certainty whether she has in fact ideally
positively conceived of a scenario that verifies scenario S or whether she merely believes
that she has positively conceived of S and that her conception of S passes the test for
ideal conceivability. In the same vein, a subject’s intrinsic cognitive limitations will
prevent her from knowing whether she has imagined a situation in full detail or she has
left pertinent details unspecified (allowing a priori contradictions to go unnoticed). As
Yablo (2003) warns, there is probably no scenario for which such worries cannot be
raised.
This is why positive conceivability must be idealized. But the question remains as
to how ideal conceivability ought to be explained.
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b. Attempting to Idealize Conceivability
So far the notion of ‘ideal conceivability’ has been left under-determined, but
defending its status as a rational notion (like a prioricity and entailment) depends on
there being some method of idealizing conceivability that ‘abstracts away’ from the
subjective judgments of limited and fallible epistemic agents. At the same time, it would
be of no use to idealize conceivability by appealing to an omniscient conceiver, since, by
hypothesis, whatever an omniscient agent believes is true. Introducing an omniscient
conceiver runs the risk of reducing ideal conceivability to a triviality; the claim that an
omniscient conceiver would find scenario S conceivable is tantamount to simply
stipulating the coherence of the concepts that compose the scenario, granting it ideal
conceivability by fiat rather than by argument.
There are several methods, from which one might explicate the notion of ideal
conceivability. Chalmers (2002a) considers two: the first is to appeal to an ideal, though
not omniscient conceiver; and the second to an ideally reasonable epistemic agent.
One could try to define ideal conceivability in terms of the capacities of an
ideal reasoner — a reasoner free of all contingent cognitive limitations.
Using this notion, we could say that S is ideally conceivable if an ideal
reasoner would find it to pass the relevant tests (if an ideal reasoner could
not rule out the hypothesis expressed by S a priori, for example) (2002a:
148, parenthetical remark original).
Chalmers’ explicit worry with this first account is that an ideal reasoner may be
impossible and even incoherent. He reasons that ‘it may be that for every possible
reasoner, there is a more sophisticated possible reasoner’ (ibid: 148), rejecting the
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notion of an ideal reasoner and pursuing the second elucidation of ideal conceiving. This
is the one Chalmers eventually endorses, which does not appeal to the judgment of an
epistemic agent, but rather to the notions of justification and defeasibility, properties
that appear to be reasoner-independent.
[O]ne can dispense with the notion of an ideal reasoner, and simply invoke
the notion of undefeatability by better reasoning. Given this notion, we can
say that S is ideally conceivable when there is a possible subject for whom
S is prima facie conceivable, with justification that is undefeatable by
better reasoning (2002: 148).
Employing the notion of ‘undefeatability by better reasoning’ may avoid the
regress of ‘more sophisticated reasoners’, since ideal conceivability would rely on a
reasoner only insofar as there must be some epistemic agent who makes the judgment
that S is prima facie conceivable.
The idea is that when prima facie conceivability falls short of ideal
conceivability, then the claim that the relevant tests are passed will either
be unjustified, or the justification will be defeatable by further reasoning.
For ideal conceivability, one needs justification that cannot be rationally
defeated (ibid).
i. Potential Problems with Idealizing Conceivability
There are several potential problems with Chalmers’ rejection of the ideal
reasoner explanation of ideal conceivability. The first is that the account he endorses
instead–invoking the notions of ‘undefeatability’ and ‘justification’–may be open to a
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regress analogous to the problem, for which the ideal reasoner option was rejected in
the first place. The strength of justification for a particular belief (whether it is
‘defeatable by further reasoning’ or ‘cannot be rationally defeated’) is determined by
several factors, one of which will be the means by which the subject acquires the belief.
This may open the possibility of a regress of ‘better means of belief acquisition’,
analogous to the regress of ‘the more sophisticated reasoner’. For any given means by
which a subject acquires a belief, it is possible (or at least conceivable) for there to be
some superior means by which that belief could be acquired: a means that would create
a stronger rational connection between the believer and the object of her belief,
conferring stronger justification on that belief.
To stop this regress of ‘better means of belief acquisition’, a proponent of ideal
conceivability might appeal to a notion of acquaintance, such as Russell’s account of
acquaintance with sense data. Subjects may be related to the object of their phenomenal
beliefs (for example, the phenomenal properties of their conscious experience) by being
acquainted with them, whereas the dualist might claim that knowledge by acquaintance
is the ultimate justification for a belief. Whether an appeal to ‘acquaintance’ will
successfully stop the regress of ‘better means of belief acquisition’ will depend on one’s
views on acquaintance in general.
Defining ideal conceivability in terms of ‘undefeatable justification’ rather than
what ‘an ideal reasoner could not rule out,’ does not conclusively remove the conceiving
subject from conceivability. This may be unavoidable, since the notion of a reasoner may
be conceptually necessarily connected to the notion of conceivability. If that is the case,
then ideal conceivability stands apart from the exemplary rational notions of ‘a
prioricity’ and ‘entailment’. ‘Being true a priori’ and ‘being entailed by’ are properties of
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propositions themselves. In the first case, the property can belong to an individual
proposition, whereas in the second case, the property belongs to a set of propositions
(for example, proposition P entails proposition Q). To be a ‘rational notion’, it seems
that ideal conceivability should be a property of propositions themselves, as Chalmers
(2002a) has claimed it to be. But unlike purely rational notions, conceivability–even
ideal conceivability–is not a property of propositions or sets of propositions in
themselves. The property of ‘being justified’ belongs to a belief, claim or judgment.
Beliefs, claims and judgments are not propositions, but rather propositional attitudes
and as such they conceptually require belief-holders, claim-holders and judgment-
makers. These require a subject who forms and holds those beliefs and in whose
cognitive economy that belief can be instantiated.
Insofar as beliefs are the kind of things that can be justified, beliefs are not
merely propositions. ‘Being justified’ is a property of a proposition, only insofar as that
proposition is a belief. And the kind of justification that belongs to a particular belief, or
the extent to which that belief is justified, depends on the kind of epistemic relation that
holds between a believer and the object of her belief. The believer is not something with
which we can dispense without losing precisely that entity to which the property ‘being
justified’ belongs: the belief itself.
Acts of conceiving and reasoning–ideal or otherwise–are epistemic acts. As such,
the notion of an epistemic agent or subject is integrated into the very concepts of
conceiving and reasoning. Conceiving, reasoning, and modally imagining require some
subject who possesses concepts and can make inferences. Thus it is unavoidable that a
coherent notion of ideal conceivability will be one, in which there is a conceiver.
Therefore, the problem Yablo poses for ideal conceivability is still present: nothing is to
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prevent a subject from believing she can modally imagine a scenario and finding it
ideally conceivable, if she is ignorant of some essential property of a property or concept
involved.
6. The Anti-Zombie: Has the Philosophical Zombie Met its Match?
At root, the zombie conceivability argument relies on the intuition that zombies
and non-physical mental properties are conceivable. This is the starting point for the
argument that zombies are conceivable in either the ideal or rational sense.
Sophisticated philosophical arguments follow this initial intuitive judgment, but without
the intuition that mental properties are non-physically conceivable, the zombie
conceivability argument would have no foundation. As a response, several ‘anti-zombie’
parity arguments have emerged, which use the same resources as the zombie
conceivability argument to construct arguments from the conceivability of anti-zombies
to the truth of physicalism (see Brown (2010), Frankish (2007), Sturgeon (2000) and
Marton (1998)).
Anti-zombies are molecule-for-molecule duplicates of human beings, who are
made conscious by physical facts alone. The anti-zombie is nothing over and above the
picture that results from embracing physicalism about the mind. If physicalism is true,
then we are made conscious by our physical facts alone and anti-zombies are merely
human beings viewed from a physicalist perspective. The conceivability of zombies has
intuitive support, but the intuitive support for anti-zombies may be equally strong. As
long as physicalism is no less intuitively plausible than property dualism (or the
possibility of zombies), the same conceivability argument that shows zombies to be
possible, will equally show anti-zombies to be possible.
Philosophical Zombies- IEP Amber Ross
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The property dualist claims that the zombie is ideally positively conceivable; that
is, if any reasonable epistemic agent were to modally imagine the zombie-scenario, she
could fill in all the details of that scenario without encountering a contradiction. If there
is no reason not to extend that same charity to the physicalist, then any reasonable
epistemic agent should be able to modally imagine the anti-zombie scenario without
encountering a contradiction. Assuming that the conceivability-possibility principle
holds, the conceivability of anti-zombies entails their possibility. Therefore, it would be
possible for creatures physically identical to ourselves to be made conscious by physical
facts alone. If physicalism and property dualism are both intuitively plausible, and if the
conceivability-possibility principle holds, then both zombies and anti-zombies are
possible.
But this result is a contradiction, because if physical facts alone make an anti-
zombie conscious, and the same physical facts hold in the zombie world, then the
physical facts of the zombie-world would make the zombie conscious. And the concept
conscious zombie is clearly internally inconsistent.
At this point, there are three options. To avoid contradiction, those who find both
zombies and anti-zombies intuitively conceivable may:
(a) reject the conceivability-possibility thesis
(b) deny the genuine conceivability of physicalism
(c) deny the genuine conceivability of dualism
Most physicalists endorse (a) by denying that conceivability implies possibility,
hence being able to grant that both zombies and anti-zombies are conceivable without
Philosophical Zombies- IEP Amber Ross
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contradiction. The only option available to the proponent of the zombie conceivability
argument is to endorse (b) by denying the conceivability of physicalism. In response to
the anti-zombie argument, Chalmers (2010: 180) accepts this and denies the
conceivability of physicalism in any philosophically significant way:
It may be prima facie negatively conceivable that materialism is true about
consciousness, but [the truth of physicalism] is not obviously conceivable
in any stronger sense. Many people have noted that it is very hard to
imagine that consciousness is a physical process. I do not think that this
unimaginability is so obvious that it should be used as a premise in an
argument against materialism, but likewise, the imaginability claim [i.e.
the imaginability of materialism] cannot be used as a premise [in an
argument for materialism], either (2010: 180).
The anti-zombie argument shows that endorsing the genuine conceivability of
zombies leads to a stronger commitment than might have been initially obvious. Rather
than merely denying the truth of physicalism, one must deny that physicalism is a
conceptually coherent position. Proponents of the zombie conceivability argument must
allow that the dualist’s prima facie judgment, that zombies are conceivable, can support
the stronger claim that zombies are conceivable in the rational sense, which is required,
in order for the conceivability-possibility principle to establish the truth of dualism. At
the same time, they must deny that the physicalist’s prima facie judgment that
physicalism is conceivable can support the stronger claim that physicalism is
conceivable in the rational sense, which in turn is required, in order for the
conceivability-possibility principle to establish the truth of physicalism. If physicalism
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were conceptually coherent, then according to the conceivability-possibility principle,
physicalism would be logically possible and the zombie conceivability argument would
collapse in contradiction.
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7. References and Further Reading
Block, N. and Stalnaker, R. (1999). ‘Conceptual Analysis, Dualism, and the Explanatory
Gap.’ Philosophical Review 108: 1–46.
Botterell, A. (2001). ‘Conceiving What is Not There.’ Journal of Consciousness Studies
8: 21-42.
Braddon-Mitchell, D. (2003). ‘Qualia and Analytical Conditionals.’ Journal of
Philosophy 100: 111–135.
Brown, R. (2010). ‘Deprioritizing the A Priori Arguments Against Physicalism.’ Journal
of Consciousness Studies 17 (3-4): 47-69.
Campbell, K. (1970). Body and Mind. London: Macmillan.
Chalmers, D. J. (1996). The Conscious Mind: In Search of a Fundamental Theory. New
York and Oxford: Oxford University Press.
Chalmers, D. J. (2002a). ‘Does Conceivability Entail Possibility?’ Conceivability and
Possibility. T. S. Gendler and J. Hawthorne (eds.). Oxford: Clarendon Press.
Chalmers, D. J. (2002b). ‘Consciousness and its Place in Nature.’ Philosophy of Mind:
Classical and Contemporary Readings. D. Chalmers (ed.). Oxford: Oxford
University Press.
Chalmers, D. J. (2010). The Character of Consciousness. Oxford: Oxford University
Press.
Davidson, D. (1970). ‘Mental Events.’,Essays on Actions and Events. D. Davidson.
Oxford: Oxford University Press: 207–223.
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