36N
These “people” have different attributes, such as “age” and “height.” One
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t h E h A R d PR O b l E M
such attribute is “knowledge.” A person has knowledge of something if they
01
can (more or less) answer questions about it correctly, or carry out the ac-
02
tions associated with it effectively. If a reliable person tells us, “Linda knows
03
how to change the tires on a car,” we should have a high credence that the
04
person labeled “Linda” is able to answer certain questions and perform cer-
05
tain actions, including helping us with our flat tire. The existence of knowl-
06
edge in a person corresponds to the existence of certain networks of
07
synaptic connections between the neurons in that person’s brain.
08
So we are told there is a person named “Mary” who has some particular
09
knowledge— all of the physical facts about color. Does she “gain new
10
knowledge” when she steps out of the room and experiences color for the
11
first time?
12
That depends on what you mean. If Mary knows all of the physical facts
13
about color, that corresponds at the level of her brain to possessing the right
14
synaptic connections to be able to correctly answer questions that we ask
15
her concerning physical facts about color. Were she to actually see the color
16
red, that would correspond to the firing of certain neurons in her visual
17
cortex, which would in turn generate other synaptic connections, “memo-
18
ries of having seen red.” By the assumptions of the thought experiment, this
19
hasn’t actually happened to Mary— the appropriate collections of neurons
20
have never fired.
21
When she walks outside her room and those neurons do finally fire,
22
does Mary “learn something new”? In one sense, surely yes— she now has
23
memories that she hadn’t previously possessed. Knowledge is related to our
24
capacity to answer questions and do things, and Mary can now do some-
25
thing she couldn’t before: recognize red things by sight.
26
Is this an argument that there is more to the universe than its physical
27
aspects? Surely not. We have merely introduced an artificial distinction be-
28
tween two kinds of collections of synaptic connections: “ones induced by
29
reading literature and doing scientific experiments in black and white,” and
30
“ones induced by stimulating the visual cortex by seeing red photons.” This
31
is a possible way to carve up our knowledge of the universe, but not a neces-
32
sary one. It’s a difference in the way the knowledge got to your brain, not in
33
the kind of knowledge it is. This is not an argument that should induce us
34
to start adding wholly new conceptual categories to our successful models
S35
of the natural world.
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T H E B IG PIC T U R E
01
Mary could have experienced the color red. She could have rigged a
02
probe that she could insert into her skull, which would send the appropriate
03
electrochemical signal directly to her visual cortex, triggering precisely the
04
experience we think of as “seeing the color red.” (Mary was postulated to
05
be a brilliant scientist, after all.) We can choose not to allow her to do such
06
a thing, as part of her “learning all the physical facts about red”— but that’s
07
an arbitrary restriction on our part, not a deep insight into the structure of
08
reality.
09
Mary’s situation is related to the old chestnut “Is my color red the same
10
as your color red?” Not the wavelengths, but is the experience of redness
11
the same for you as it is for me? In some strict sense, no: my experience of
12
the color red is a way of talking about certain electrochemical signals travel-
13
ing through my brain, while yours is a way of talking about certain electro-
14
chemical signals traveling through your brain. So they can’t be exactly the
15
same, in a very boring reading: the same as “My pencil is not the same as
16
your pencil, even though they look just alike, because this one belongs to
17
me.” But my experience of red is probably pretty similar to yours, simply
18
because our brains are pretty similar. Interesting to think about, but not
19
exactly a vortex of confusion that should lead us to reject the Core Theory
20
as the underlying description for the whole business.
21
Frank Jackson himself has subsequently repudiated the original conclu-
22
sion of the knowledge argument. Like most philosophers, he now accepts
23
that consciousness arises from purely physical processes: “Although I once
24
dissented from the majority, I have capitulated,” he writes. Jackson believes
25
that Mary the Color Scientist helps pinpoint our intuition about why con-
26
scious experience can’t be purely physical, but that this isn’t enough to
27
qualify as a compelling argument for such a conclusion. The interesting task
28
is to show how our intuition has led us astray— as, science keeps reminding
29
us, it so often does.
30
31
32
33
34
35S
36N
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01
02
41
03
04
Zombies and Stories
05
06
07
08
09
10
11
12
d
13
avid Chalmers, who coined the phrase “Hard Problem of con-
14
sciousness,” is arguably the leading modern advocate for the pos-
15
sibility that physical reality needs to be augmented by some kind
16
of additional ingredient in order to explain consciousness— in particular,
17
to account for the kinds of inner mental experience pinpointed by the Hard
18
Problem. One of his favorite tools has been
yet another thought experi-
19
ment: the philosophical zombie.
20
Unlike undead zombies, which seek out brains and generate movie fran-
21
chises, philosophical zombies look and behave exactly like ordinary human
22
beings. Indeed, they are perfectly physically identical to non- zombie people.
23
The difference is that they are lacking in any inner mental experience. We
24
can ask, and be puzzled about, what it is like to be a bat, or another person.
25
But by definition, there is no “what it is like” to be a zombie. Zombies don’t
26
experience.
27
The possible existence of zombies hinges on the idea that one can be a
28
naturalist but not a physicalist— we can accept that there is only the natural
29
world, but believe that there is more to it than its physical properties. There
30
are not, according this view, nonphysical kinds of things, such as immate-
31
rial souls. But the physical things with which we are familiar can have other
32
kinds of properties— there can be a separate category of mental properties.
33
This view is property dualism, as distinct from good old- fashioned Carte-
34
sian substance dualism, which holds that there are physical and nonphysical
S35
substances.
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T H E B IG PIC T U R E
01
The idea is that you can have a collection of atoms, and tell me every-
02
thing there is to say about the physical properties of those atoms, and yet
03
you haven’t told me everything. The system has various possible mental
04
states. If the atoms make up a rock, those states might be primitive and
05
unobservable, essentially irrelevant. But if they make up a person, a rich
06
variety of mental states come to life. To understand consciousness, on this
07
view, we need to take those mental properties seriously.
08
If these mental properties affected the behavior of particles in the same
09
way that physical properties like mass and electric charge do, then they
10
would simply be another kind of physical property. You are free to postulate
11
new properties that affect the behavior of electrons and photons, but you’re
12
not simply adding new ideas to the Core Theory; you are saying that it is
13
wrong. If mental properties affect the evolution of quantum fields, there
14
will be ways to measure that effect experimentally, at least in principle—
15
not to mention all of the theoretical difficulties with regard to conservation
16
of energy and so on that such a modification would entail. It’s reasonable to
17
assign very low credence to such a complete overhaul of the very successful
18
structure of known physics.
19
Alternatively, we could imagine that mental properties just go along for
20
the ride, as far as physical systems are concerned. The Core Theory can be a
21
complete description of the physical behavior of the quantum fields of
22
which we are made, but not a complete description of us. Such a description
23
would need to specify our mental properties as well.
24
Zombies would be collections of particles in exactly the same arrange-
25
ment as would ordinarily make up a person, obeying the same laws of phys-
26
ics and therefore behaving in precisely the same way, but lacking the mental
27
properties that account for inner experience. As far as you can tell by talk-
28
ing to them, all of your friends and loved ones are secretly zombies. And
29
they can’t be sure you’re not a zombie. Perhaps they have suspicions.
30
•
31
32
The big question about zombies is a simple one: can they possibly exist? If
33
they can, it’s a knockout argument against the idea that consciousness can
34
be explained in completely physical terms. If you can have two identical
35S
collections of atoms, both of which take the form of a human being, but
36N
one has consciousness and the other does not, then consciousness cannot
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z O M b I E S A n d S t O R I E S
be purely physical. There must be something else going on, not necessarily
01
a disembodied spirit, but at least a mental aspect in addition to the physical
02
configuration.
03
When we talk about whether zombies are possible, we don’t necessarily
04
mean physical y possible. We don’t need to imagine that we could find an
05
honest-to-goodness zombie here in our real world, made out of the same
06
particles that you and I are made from (if you’re not a zombie, which I’m
07
going to assume henceforth). We’re just imagining a possible world, with a
08
different fundamental ontology, even though it might have very similar-
09
seeming particles and forces. What it would be lacking is mental properties.
10
As long as zombies are conceivable or logically possible, Chalmers argues,
11
then we know that consciousness is not purely physical, regardless of whether
12
zombies could exist in our world. Because then we would know that con-
13
sciousness can’t simply be attributed to what matter is doing: the same be-
14
havior of matter could happen with or without conscious experience.
15
Of course, Chalmers also then says that zombies are conceivable. He has
16
no trouble conceiving of them, and maybe you feel the same way. Can we
17
then conclude that there is more to the world than just the physical uni-
18
verse?
19
20
•
21
Deciding whether something is “conceivable” is harder than it might seem
22
at first glance. We can conjure up an image in our mind of someone that
23
looks and acts just like a human being, but who is dead inside, with no in-
24
ner experiences. But can we really do so without imagining any differences
25
in the physical behavior of them versus an ordinary person?
26
Imagine a zombie stubbed its toe. It would cry out in pain, because
27
that’s what a human would do, and
zombies behave just like humans. (Oth-
28
erwise we would be able to recognize zombies by observing their external
29
behavior.) When you stub your toe, certain electrochemical signals bounce
30
around your connectome, and the exact same signals bounce around
31
the zombie connectome. If you asked it why it cried out, it could say, “Be-
32
cause I stubbed my toe and it hurts.” When a human says something like
33
that, we presume it’s telling the truth. But the zombie must be lying, be-
34
cause zombies have no mental states such as “experiencing pain.” Why do
S35
zombies lie all the time?
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T H E B IG PIC T U R E
01
For that matter, are you sure you’re not a zombie? You think you’re not,
02
because you have access to your own mental experiences. You can write
03
about them in your journal or sing songs about them in a coffee shop. But
04
a zombie version of you would do those things as well. Your zombie dop-
05
pelgänger would swear in all sincerity that it had inner experiences, just as
06
you would. You don’t think you’re a zombie, but that’s just what a zombie
07
would say.
08
•
09
10
The problem is that the notion of “inner mental states” isn’t one that merely
11
goes along for the ride as we interact with the world. It has an important
12
role to play in accounting for how people behave. In informal speech, we
13
certainly imagine that our mental states influence our physical actions. I am
14
happy, and therefore I am smiling. The idea that mental properties are both
15
separate from physical properties, and yet have no influence on them what-
16
soever, is harder to consistently conceive of than it might first appear.
17
According to poetic naturalism, philosophical zombies are simply in-
18
conceivable, because “consciousness” is a particular way of talking about the
19
behavior of certain physical systems. The phrase “experiencing the redness
20
of red” is part of a higher- level vocabulary we use to talk about the emergent
21
behavior of the underlying physical system, not something separate from
22
the physical system. That doesn’t mean it’s not real; my experience of red-
23
ness is perfectly real, as is yours. It’s real in exactly the same way as fluids and
The Big Picture Page 60