Supervenient Qualia, Filozofia, Filozofia - Artykuły
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Philosophical Review
Supervenient Qualia
Author(s): Terence Horgan
Source: The Philosophical Review, Vol. 96, No. 4 (Oct., 1987), pp. 491-520
Published by: Duke University Press on behalf of Philosophical Review
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The PhilosophicalReview,
Vol. XCVI,
No.
4 (October 1987)
SUPERVENIENT QUALIA
Terence Horgan
I.
An
increasingnumber of philosophersmaintainnowadays
that
I
L
the metaphysical doctrine of Materialism is
best formulated
as a thesis of general supervenience.' Let us say that a possible
world W is physicallypossible
iff
(1)
the only sorts of fundamental
physico-chemical
properties exemplified in W are properties ex-
plicitly cited by the
fundamental physico-chemical laws of the ac-
tual world; and (2) all
concrete individuals in W are, or are fully
decomposable into,
individuals whose most specific natural-kind
sortal properties either (i) are exemplified
by some concrete indi-
viduals
in the actual
world;
or
(ii)
are explicitly cited in the actual
world's
fundamental
physico-chemical
laws.2 The supervenience
thesis, then,
is
roughly
this:
(S)
There are no two
physically
possible worlds which are exactly
alike
physico-chemically
but which differ in some other re-
spect.3
'See,
for instance, Hellman and Thompson (1975, 1977), Haugeland
(1982), Horgan (1981b, 1982b), Kim (1978, 1979, 1981), Lewis (1983),
and the papers collected in Horgan (1984c). The suggestion that the con-
cept of supervenience is relevant to materialism seems to have originated
with Davidson (1970, 1973, 1974).
2Clause (2) is meant to exclude such entities as phlogiston, entelechies,
Cartesian spirits, and God-unless such beings happen to exist in the ac-
tual world. Most of the natural-kind sortal properties mentioned
in
(2)
presumably will satisfy both of the conditions (i) and (ii). Condition (i)
is
needed in order to ensure that the actual world still will count as
"physi-
cally possible" even if it does contain entities like Cartesian spirits.
And
condition (ii) is non-redundant because the actual world's fundamental
physico-chemical laws might countenance certain natural-kind
sortal
properties which happen not to be exemplified in the actual world,
such as
certain anti-matter sortals.
3I
say that the supervenience thesis is roughlythis because I think there
is
room for disagreement about how best to characterize the
class of physi-
cally possible worlds. For relevant discussion see Horgan (1982b,
1984d)
and Lewis (1983).
491
TERENCE HORGAN
I find this doctrine immensely plausible,
and I think it goes a
long way toward capturing
the materialistic idea that the physico-
chemical facts about the world
determine all the world's facts.
But (S) seems to run
into problems concerning the qualitative,
or phenomenal, aspects
of our mental life. For, it seems we
can imagine two physically
possible worlds which are physico-
chemically exactly alike
but which differ with respect to the quali-
tative content of
the mental lives of certain creatures within those
worlds. For instance,
it seems we can imagine a physically possible
world W1 that is just
like ours except that the persons who are our
counterparts
in W1 have color-experiences that are systematically
"inverted"
with respect to our own; their brain states when
they
look at ripe tomatoes (say) are just like ours; but nevertheless,
phe-
nomenally their experience of looking at ripe tomatoes
is like our
experience
of looking at green tomatoes; and similarly
for all their
other
color-qualia. It also seems we can imagine a physically
pos-
sible world
W2
that is just like ours except that our counterparts
in
W2 lack qualia altogether; they still have all the same
brain states
we do, and they still have most of the same propositional
attitudes
we do (with the possible exception of certain propositional
atti-
tudes whose content involves qualia), and yet
their internal states
lack qualitative content altogether.
If we really can imagine these things,
then presumably the puta-
tive possible worlds W1 and W2 really
exist. After all, doesn't the
imaginability of a possible world
suffice for its existence? But if
there really are such possible worlds, then
thesis (S) is false; that is,
facts about qualia are not supervenient
upon physico-chemical
facts.
I have two objectives in this
paper. First, I shall attempt to de-
fuse objections
to
(S)
that are based upon the putative imaginabil-
ity of putative
worlds like W1 and W2; I shall argue that
in
these
cases, seeming-imaginability
is compatible with metaphysical im-
possibility. Second,
I shall advance an argument in favor of the
supervenience of qualia.
Briefly, the argument is this: qualia are
causally efficacious, and
their supervenience is a necessary condi-
tion for this causal
efficacy; hence they are supervenient.
II.
I
begin
with some preliminary points. First,
I shall take
qualia
to
be properties
exemplified by creatures with mentality-in par-
492
SUPERVENIENT QUALIA
ticular, by humans. These are properties like sensing redly, or the
experiential property one exemplifies when smelling Chanel #5
(sensing in a Chanel #5 manner), or the experiential property one
exemplifies when the dentist's drill hits an unanesthetized nerve
(sensing [sharp
pain in the tooth]-ly).4
Second, my
discussion here will be
independent
of
certain other,
more specific,
materialist theses concerning mentality
in
general
and
qualia
in
particular.
One such
thesis is functionalism-the
doctrine, roughly, that our mental terms (including qualia terms)
can be exhuastively analyzed by
reference to the typical causal
roles of the events and states to which those terms apply. Another
is the psycho-physical identity theory, which has both type-type
and token-token versions. Elsewhere (Horgan 1984a, 1984b) I
have argued against functionalism regarding qualia, on the basis
of less radical inverted-spectrum cases than the one envisioned
above (viz., cases of creatures who are functionally indis-
guishable from one another, but who differ from each other both
neurally and phenomenally-where the neural differences are the
basis for the phenomenal differences); I also have defended a
type-type identity theory regarding qualia. But my present discus-
sion will be independent of those claims.
Third, although I shall focus here upon qualia, largely because
qualia seem especially troublesome for the supervenience thesis
(S), nevertheless I believe that my arguments are generalizable to
other kinds of mental properties-in particular, to propositional
attitudes.
Fourth, I want to distinguish the kind of supervenience ex-
pressed by (S)
from
a weaker kind of supervenience thesis. Let a
world
W be nominallypossible
iff
(i) all the laws of the actual world
are true in
W, and (ii) all the concrete individuals
in
W are,
or
are
fully decomposable
into,
individuals whose most
specific
natural
kinds are actual-world natural kinds.
(Thus, every nomically pos-
sible world is a
physically possible world,
but the converse
may
not
be true.)
Suppose
there are certain laws
linking physico-chemical
properties to qualia, and that these laws would be violated
in worlds like W1 and W2 described above. Then someone might
hold that even if (S) is false (by virtue of the existence of counter-
4I
take seriously these adverbial constructions as indicators of under-
lying logical form. So does Michael Tye (1984a, 1984b, 1984c).
493
TERENCEHORGAN
nomological worlds like W1 and W2), nevertheless the following
supervenience thesis is still true:
(S') There are no two nomically possible worlds which are exactly
alike physico-chemically but different in some other respect.
Let us call (S') the thesis of nomicsupervenience, and (S) the thesis
of strict supervenience. Now, I claim that facts about qualia are
strictly supervenient upon physico-chemical facts
-not
merely
nomically supervenient upon them. One reason
I
advocate (S),
over and above (S'), is that I don't think (S') does justice
to
the
materialistic idea that the physico-chemical facts alone
determine
all the other facts. At most, (S') expresses the idea of determina-
tion on the basis of physico-chemical
facts
together
withvarious inter-
theoretic or inter-level "bridge laws" (such as physico-chemical/
phenomenal bridge laws). Yet is seems that a full-fledged materi-
alism should not treat bridge laws as being on a par with the fun-
damental laws of physics-chemistry; rather, it should treat them as
belonging to the truths which are determined by physico-chemical
truths. Furthermore,
I
shall
be
arguing
below that there is another
reason
for
claiming that qualia are strictly supervenient
upon the
physico-chemical, rather than merely nomically supervenient: viz.,
that
otherwise
qualia
will turn out to be
epiphenomenal.
Fifth, it will be convenient to have before us two supervenience
theses which are special cases of (S) and (S') respectively, and
which deal specifically with the supervenience of qualia:
(SQ) There do not exist any two physically possible worlds which
are exactly alike physico-chemically
but
different with re-
spect
to
the way qualia are instantiated.
(SQ') There do not exist any two nomically possible worlds which
are exactly alike physico-chemically but different with re-
spect to the way qualia are instantiated.
Principle (SQ') expresses the thesis that qualia are nomically su-
pervenient upon the physico-chemical. (SQ') leaves it open
whether or not there can be two physicallypossible worlds which do
not differ physico-chemically but do differ with respect to the in-
stantiation of qualia; it merely says that
if
there are two such
494
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