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Reply to Mulhauser's Review of The Conscious Mind
David J. Chalmers
Department of Philosophy
University of California
Santa Cruz, CA 95064
USA
chalmers@paradox.ucsc.edu
Copyright (c) David J. Chalmers 1996
PSYCHE, 2(35), November 1996
http://psyche.cs.monash.edu.au/v2/psyche-2-35-chalmers.html
KEYWORDS: consciousness, qualia, materialism, dualism, functionalism, computation,
zombies, information.
RESPONSE TO: G.
Mulhauser, 'Bridge Out' On The Road To A Theory Of Consciousness: A Review
of The Conscious Mind: In Search of a Fundamental Theory. Oxford
University Press, $29.95 hbk., pp. xvii + 414, ISBN 0-19-510553-2.
Gregory Mulhauser's vigorous review of my book The Conscious Mind
includes quite a few misrepresentations and philosophical misunderstandings.
I would not like these misunderstandings to be perpetuated, so I will make
a few comments in reply.
First, a clarification on "taking consciousness seriously". Mulhauser
characterizes this assumption as the assumption that no cognitive theory
of consciousness will suffice. The latter assumption would indeed beg some
crucial questions, but it is not the assumption that I make. I make an assumption
about the problem of consciousness, not about any solution. To quote
(p. xii):
Throughout the book, I have assumed that consciousness exists,
and that to redefine the problem as that of explaining how certain cognitive
and behavioral functions are performed is unacceptable. This is what I mean
by taking consciousness seriously.
That is, the premise is simply that there is a phenomenon to be explained,
and that the problems of explaining such functions as discrimination, integration,
self-monitoring, reportability, and so on do not exhaust all the problems
in the vicinity. The deepest problem of consciousness, as I understand it,
is not the problem of how all these functions are performed, but rather
the problem of explaining how and why all this activity supports states
of subjective experience.
This isn't to make any assumptions about the nature of the solution -- plenty
of people agree with the premise but still think that one way or another
they can get a cognitive or materialist theory of consciousness to work
-- although of course I do go on to argue that if the premise is
granted, it turns out that such theories will always be incomplete.
Like many people (materialists and dualists alike), I find this premise
simply obvious, although I can no more "prove" it than I can prove
that I am conscious. At the very least, to deny this premise would require
extraordinarily strong arguments, of a type that I have never seen. In my
experience the large majority of people find it obvious; but certainly there
are some that deny it, and arguments over whether the premise is true or
false rapidly descend into table-pounding. Wishing to avoid too much of
that dead end, I prefer to simply state the assumption up front. Mulhauser
complains that the assumption is not "discharged", but of course
that is the whole point of making it a premise. (I do argue for it where
I can, but there is no denying that such arguments -- on either side --
ultimately come down to a bedrock of intuition at some point.) The result,
as I also say up front, is that the minority of people who don't see a "hard
problem" aren't going to find the book of more than intellectual interest.
That's life, though some of them seem to read and review it anyway.
That, I think, is the deepest issue relevant to Mulhauser's review. In the
rest of it I find mostly rhetoric, misunderstanding, and an impressive repertoire
of adjectives. Actually, that's not quite fair. He makes a couple of good
points on minor issues, although nothing that really affects the state of
play.
The first point that looks like a substantial objection is in his discussion
of Chapter 2, where he appears to have an objection to my notion of logical
necessity and its relation to formal systems, but as he does not say what
it is (he simply says that he has an objection), it is hard to evaluate.
This pattern -- highly opinionated criticism without any substantiation
-- is repeated many times in the course of the review.
His discussion of the central Chapter 3 mostly centers around the conceivability
of zombies. I say explicitly in the text that this conceivability argument
is more inconclusive than some of the others (due to the difficulty of assessing
claims about conceivability), and that it does not bear the central burden
of the argument, but commentators often focus on it anyway. In any case:
Mulhauser's description of my zombies as "a particularly strong variety:
a physical, functional, and psychological duplicate", with its
emphasis, makes the claim seem stronger than it is: "psychological"
is being used here in a stipulative sense that adds nothing over and above
"functional". What is relevant to the arguments is that a zombie
be a physical and functional duplicate; that's all.
Mulhauser's objection to the argument is the standard "how do we know
we can really conceive this". He doesn't face up to the real point,
which is the challenge to isolate an inconsistency in the notion, and in
particular to demonstrate the aspect of the concept of consciousness which
could ground an conceptual entailment from the physical facts to the facts
about consciousness. He neither comes out and embraces a functional definition
of consciousness (equating what needs to be explained with reportability,
integration, or some such complex function), which would require facing
up to all the problems with such a definition, nor does he even hint at
another way that such an entailment might go through, which would require
facing up to the fact (stressed in the book) that structure and function
only ever adds up to more structure and function. So we are left in a position
of assertion without enlightenment.
His discussion of epistemic asymmetry makes his first good point: that a
logical entailment from physical facts to facts about consciousness requires
a grasp of the concept of consciousness, so the mere fact that someone without
consciousness wouldn't derive facts about consciousness from the physical
facts can be explained away by the observation that they lack the concept.
This is a minor point -- there is still a striking disanalogy here between
our epistemic access to consciousness and other phenomena -- but nevertheless
I should have rephrased things in a way that brings that disanalogy out
more directly. In any case, I also point out the epistemic asymmetry of
consciousness in ways that aren't vulnerable to this objection, e.g. by
giving the observer the concept of consciousness and noting that the facts
about consciousness in others remain underdetermined.
His second interesting point is the idea that the explanatory gap may arise
for reasons of formal undecidability or computational intractability. There
are obvious problems to be addressed: either consciousness is a structural/functional
concept, in which case (a) it is most unclear why the facts about it should
be any more undecidable or intractable than the facts about any other such
concept (learning, reportability, or whatever), and (b) the view will presumably
be vulnerable to arguments just like mine, establishing a gap between the
structural/functional concept and consciousness while leaving the "intractable"
physical details to one side; or it is not a structural/functional concept,
in which case there are systematic reasons why it cannot be logically necessitated
by the physical facts, intractability/undecidability or no. So I think even
this sort of position is vulnerable to the sort of critique I provide. But
in any case it would be very interesting to see such a view worked out in
detail, and the project of doing so would be sure to be enlightening. I
do address this view briefly on my pp. 138-40 -- not in much depth, as the
view has not been explicitly set out in the literature as far as I know,
so I had to more or less make it up -- but there is no doubt that there
is more to say about it, and it would be a very useful service to see the
view worked out systematically.
Mulhauser's discussion of "explanatory exclusion" is off the point.
His claim that my intuitions about consciousness are based in "explanatory
exclusion" intuitions that apply equally to planets, dolphins, and
so on ignores the many pages of argument earlier in the book analyzing the
disanalogy in depth. Indeed, none of the arguments I give about consciousness
would have a hope of getting off the ground when applied to planets, dolphins,
and the like.
His discussion of the epistemological problems of consciousness adds nothing
of substance. There are, of course, serious problems here -- the first-person
epistemology of consciousness poses some of the deepest questions in the
field, and questions to which I have at best tentative and incomplete answers.
But Mulhauser gives no reason to believe that these answers must be bad
ones; he simply reiterates the problems, as I have laid them out. He is
of course absolutely right that many of these problems can be avoided if
we embrace a reductive functionalist view of consciousness (where all that
needs to be explained is discrimination, integration, reportability, and
other complex functions). In fact, if we embrace such a view, almost all
the problems of consciousness are removed! For those who think this sort
of solution-by-stipulation provides any enlightenment, they are welcome
to it.
The entire second half of Mulhauser's review is thrown deeply astray by
his "discovery" of my "little secret" that I think functional
awareness is logically necessary for consciousness: a "discovery"
based solely on my statement "awareness is necessary for consciousness".
But in context it is obvious that natural necessity is at issue -- what
is under discussion are the bridging laws connecting processing and consciousness
-- and the sentence at the end of the paragraph makes it clear that logical
necessity couldn't possibly be what is meant. Indeed, this "discovery"
is so much at odds with everything else in the book that its invocation
suggests that the reviewer is holding a principle of charity far in abeyance.
Mulhauser also seems to think that my suggestions for psychophysical bridging
principles are a priori deductions from the single fact that consciousness
exists. This is simply false: they are inferences drawn from apparent regularities
between facts about functioning and facts about experience, especially in
the first-person case. I start by drawing connections between (1) functional
facts about reportability, behavioral control, and the like, and (2) phenomenological
observations about the structure and properties of experience in the first-person
case. These connections are certainly quite coarse (I make no claim to be
a sophisticated phenomenologist) and I would be all for a project of refining
them. But in all of them phenomenological data -- observations about the
structure of experience, for example, or its presence or absence in different
sorts of cases -- play a significant role. In every case the relevant data
go well beyond "consciousness exists"; Mulhauser is quite right
that no substantial inferences about the nature of psychophysical laws could
be drawn from that datum alone.
(Some may object to using phenomenological data, but I would argue that
without an appeal to such data, a theory of conscious experience as such
cannot even get off the ground -- it will be a third-person theory that
never connects to the first-person. And indeed I would argue that everyone
who draws conclusions about experience from processing data is implicitly
relying on bridging principles that are partly based on first-person knowledge
of phenomenology; I am just trying to bring them into the open.)
Mulhauser's discussion of the fading and dancing qualia arguments makes
a number of mistakes. The arguments cannot come close to establishing that
absent or inverted qualia are logically impossible, for reasons I address
directly: first, nothing in the arguments suggests that fading and dancing
qualia scenarios are incoherent, and second, they all take the empirical
fact of the existence of consciousness as a premise. Mulhauser somehow slides
from this second observation of mine to the reiterated "conclusion"
that my psychophysical principles are all deduced a priori from this observation,
but this is an elementary mistake -- to say that an argument takes something
as a premise is not to say that it takes it as its only premise!
Mulhauser also makes a lot of play out of a tension between my arguments
here and my supposed view that awareness is logically necessary for consciousness;
but as noted above, this view is a product of his imagination.
For what it's worth, Mulhauser's suggestion that this supposed view implies
that dancing qualia are logically impossible seems to commit another elementary
philosophical mistake: someone could believe that awareness is logically
necessary for consciousness but not logically sufficient, and in particular
could believe that facts about awareness do not logically entail facts about
the intrinsic character of specific qualia.
Mulhauser's discussion of the last three chapters of the book is vigorous
but largely free of substance. He complains that I don't appeal to his favorite
sort of information theory, namely Chaitin's. I think Chaitin's work is
fascinating (certainly it is intrinsically much more interesting than Shannon's),
but it is an entirely different creature and I didn't see its application
here. If Mulhauser can find a way to exploit it in a theory of consciousness,
more power to him. His further observations (e.g., that some sorts of information
processing seem to happen without consciousness) simply go over ground already
covered in the book, without addressing my discussion.
His complaints about my chapter on strong AI rest on my "failure to
grasp the vacuity of naive functional theorizing", and on his appeal
to philosophers such as Putnam who have pointed out this "vacuity".
Like many, I am not deeply impressed by these arguments, although they have
some interest. I have a lengthy analysis of the Putnam considerations in
my "Does
a Rock Implement Every Finite State Automaton?" (Synthese
108:309-33, 1996), and the general issues are discussed in "A
Computational Foundation for the Study of Cognition" (of which
a shorter version appeared in Minds and Machines, 1994). Mulhauser
provides nothing more than an appeal to authority here, though, so there
is little I can say in reply. And although Mulhauser suggests that a giant
look-up table might be constructed to satisfy my CSA definition, I would
be very interested to see such a CSA that is naturally possible (remember,
it is natural possibility that is relevant here). As I discuss in my paper
on Putnam's argument, the only such "false implementations" are
probably beyond the bounds of natural possibility.
Mulhauser says nothing of substance in objecting to my discussion of incompleteness
-- once again, he simply spends a long paragraph asserting vigorously that
he has objections. The same for his discussion of discreteness vs. continuity,
in the next paragraph. Those who understand the issues will know that the
Siegelmann/Sontag machine he refers to does not threaten anything I say:
like every other "super-Turing" machine that has been proposed,
it requires an infinite resource or infinitely precise initial conditions
in order to compute a super-Turing number-theoretic function. With bounded
precision, or even with unbounded precision but a fixed finite initial state,
it does no better than a Turing machine. As with many other places in the
review, the argument strategy seems to be "unargued appeal to irrelevant
authority", which ends up merely betraying the reviewer's lack of understanding.
In his discussion of my analysis of the Everett interpretation of quantum
mechanics, Mulhauser asserts quite correctly that (1) a similar analysis
might be available to a materialist (assuming a materialist theory of consciousness
could work at all), and (2) that these considerations do not provide knockdown
support for the interpretation (as I say in the book, they simply remove
one sort of objection, and thus give it indirect support; the interpretation
still has serious problems, and indeed I am not sure whether I believe it).
He apparently intends these remarks as criticisms, but it is hard to see
why. The chapter is not intended as religious warfare either for this interpretation
or for dualism; it is simply an exploration of the issues.
I will end with a few comments on the more unusual aspects of Mulhauser's
review. Mulhauser seems much concerned to point out everywhere that an argument
I use has appeared in the literature before. I am not sure why, as I acknowledge
my multiple debts right up front, and I cite every debt as the book goes
along (it's not for nothing that the book has a 400-entry bibliography).
Apparently he is spurred on by "the widespread publicity...suggesting
it would contain startling new arguments and thought experiments".
He would not be the first reviewer to review the media rather than the book,
but it would be nice to have the book reviewed for what it is.
In reality, it's a book written by a mere mortal, and a book which tries
to present the arguments -- some old, some new -- as carefully and as completely
as possible. There's no question that anti-reductionist arguments have been
around a long time, and negative arguments with the same general thrust
as mine have been seen before, though they have usually been presented in
a very piecemeal way. In the book, I try to really make the case properly:
maybe I succeed and maybe I fail, but I make no apologies for retreading
old ground at those points where I think it is the best way to do things.
I must respond to one particularly odd remark of Mulhauser's in this context.
A characterization of my fading and dancing qualia arguments -- "both
of which, contrary to popular tale, have appeared in one form or another
elsewhere in the literature" -- seems to suggest that I have borrowed
someone else's arguments unacknowledged. In fact both arguments are accompanied
by citations to every item I know in the literature to which they bear even
a remote similarity. The fading qualia gradual-replacement scenario is of
course an old folk tale in the literature, and in the paragraph where it
is introduced I cite a number of papers that use it (although they use it
in somewhat different ways), and I footnote some more. The dancing qualia
argument, as far as I know, was original with me in my 1993 Ph.D. dissertation,
although there do exist a couple of distantly related scenarios used to
argue for quite different conclusions, and a more closely related version
was formulated independently by Arnold Zuboff in a 1994 article. So as with
much of the rest of the book, there are a number of elements which are familiar,
and a number which are new. That's the way it usually is in philosophy.
Finally, let me express my bemusement at the religious tone that is so common
in this sort of discussion. I don't know why discussions of consciousness
provoke this tone, which is not nearly so pronounced in other areas of science
and philosophy. I don't feel any particular emotional commitment to my conclusions
myself (I may be a materialist in my heart, if not in my mind); I have come
to the conclusion that they more or less have to be true, for systematic
reasons, but if someone thinks they have a better option, that's fine. I
tried to write a book setting out the lay of the land as I see it, laying
out what seemed to me to be a promising approach, and openly acknowledging
the various problems my approach faces along the way. If someone disagrees,
then I'm interested to hear about it. It's a fascinating area of intellectual
inquiry. But cheap point-scoring and unargued rhetoric are uninteresting.
Mulhauser does make a couple of points of substance along the way; I suggest
that we are all best served if substance is what we stick to.
References
Chaitin, G.J. (1990). Information, randomness, and incompleteness.
(2nd ed.). World Scientific.
Chalmers, D.J. (1994). A computational foundation for the study of cognition.
PNP Technical Report 94-03, Washington University. [http://ling.ucsc.edu/~chalmers/papers/computation.html].
Shorter version published as "On implementing a computation".
Minds and Machines, 4, 391-402.
Chalmers, D.J. (1996). The conscious mind: In search of a fundamental
theory. Oxford University Press. [http://ling.ucsc.edu/~chalmers/tcm.html]
Chalmers, D.J. 1996. Does a rock implement every finite-state automaton?
Synthese, 108, 309-33. [http://ling.ucsc.edu/~chalmers/paper/rock.html]
Putnam, H. (1988). Representation and reality. MIT Press.
Siegelmann, H.T. & Sontag, E.D. (1994). Analog computation via neural networks.
Theoretical Computer Science, 131, 331-60.
Zuboff, A. (1994). What is a mind? In P. French, T. Uehling, & H. Wettstein
(Eds.),Philosophical Naturalism. University of Notre Dame Press.
