Frontal Assault
Nobody has the slightest idea how any thing material could be conscious. Nobody
even know swhat it would be like to have the slightest idea So much for the philosophy of consciousness. (Fodor1992)
One of my clearest memories of early childhood finds me sitting alone in my
bedroom at twilight when I was about five, pondering a curious family of questions. Why does the universe exist? What if it didn't? What would be left over if
it stopped existing? Wouldn't something still exist? What colour would it be?
Even now , the questions elicit the same peculiar twisting sensation from my
stomach. And now, as then, I find the basic mystery of why anything exists the
most unfathomable of all.
Probably it was fortunate for the sake of a happy childhood that the gravity
of the second most difficult question didn't impress itself on me until years later:
how is it that it feel like it does to be me (or anyone else) if that feeling is done
with nothing more than a stringy ball of nerve fibres, glia, and other organic
structures made mostly of water? How can it possibly feel like anything?
It is unusual that I agree significantly with Fodor , especially in print . But I
think his pessimistic prognosis that an unassailable conceptual roadblock separates consciousness and the material world is almost right. After all, conscious
experience seems entirely different from mundane features of material objects
like mass or colour or fuzziness . Such attributes generate comparatively few
deep metaphysical quandaries. While the road from fundamental physics and
chemistry to their macroscopic appearance is, in practice, a very long and complex one which has yet to be explored in every detail, in principle nothing stands
in the way of a complete low level account of, say, the particular bulk, reddishyellow hue, and deceptively appealing fuzziness of a ripe peach. No one puzzles
over the question 'how can a material object like a peach possibly be fuzzy ?' .
But on the face of it, at least, the characteristic features of phenomenal experience stand in nothing at all like the same sort of relationship to low level physics
and chemistry that renders peach fuzz so metaphysically unintriguing.
While a fuzzy peach looks to be a straightforward example of material sub stances arranged in the right way, it isn't easy to see , even in principle, how
Nature could have built something like a conscious mind out of matter. Taking
as a working hypothesis the notion that fundamental particles of matter lack
phenomenal experience entirely, it isn't easy to see how any set of such particles-
however they might be organised, energised, shaken, or stirred could
somehow come to be conscious. Nevertheless, each day we find ourselves surrounded
by creatures who seemingly enjoy conscious experience without incorporating
within themselves any extra 'secret ingredients' beyond myriad ordinary
material particles. (At least, contemporary science has yet to uncover any
such extra ingredients.)
After years of flirting with extravagant but, ultimately, explanatorily bankrupt
nonphysical candidates for a solution to this apparent mystery, some significant
conclusions have finally begun to emerge which lead me to think the
instantiation of conscious minds by purely material structures really may be
fathomable after all. This book explores some of those conclusions and the lines
of thought behind them, constructing a story within which conscious experience
and the material world may plausibly be unified.
Taking the position that understanding the puzzles of conscious experience
cannot proceed without some grasp of who or what the subject of conscious
experience might be, I ultimately defend the view that the conscious subject-
the I-is a materially instantiated structure of dynamically changing information.
On this account, phenomenal experience is 'what it is like to be' such a changing
structure. While it may be true that it is not identical to any material thing, I
suggest that a conscious mind may nonetheless be implemented by matter. For
now, I will say little more about this central unifying idea, apart from noting that
information is understood here in a wholly naturalistic, precise, and objective
sense and quantified within a formal framework provided by the field of algorithmic
information theory. Several chapters of preliminaries-concerning information
and representation, problems of perspective, functionalism, supervenience,
and mental states-must be completed before much sense can be read
into this view of the conscious subject, which doesn't receive full treatment until
the latter half of Chapter 6. Drawing on resources from traditional philosophy,
computer science, mathematics, physics, and neuroscience, the job of developing
and exploring this account amounts to a full frontal assault on the clutch of
confusions which philosophers collectively refer to as 'the mind/body problem'.
Many themes underlie this campaign (some of which receive more attention
below in section 2), but of paramount concern is my aim of embracing the rich
'ineffable feel' of the phenomenal world while still operating within the constraints
set by the laws of physics. The method I advocate here takes the laws of
physics as given and then examines what sort of picture of consciousness and
of cognition might be built up within some framework consistent with those
laws. In other words, we assume for the sake of enquiry that the creatures of
interest, such as humans, are instantiated in a purely physical world and then
attempt to construct a picture of how (or whether) those creatures could possibly
be conscious in such a world. The main task then is to evaluate whether such a
picture accounts fully for the way our conscious experience really does seem to
us in the actual world or whether some significant feature has been left behind.
Only if one or more significant features cannot be accommodated should we
then consider rejecting both the framework itself and perhaps even the original
assumption that consciousness exists in a purely physical world.
This 'world first', or 'physics first', approach, which begins with the
physical and attempts to work toward a phenomenal goal, contrasts starkly with
methods traditionally dear to the hearts of philosophers. More often, the preferred
starting place includes some set of features of phenomenal experience
thought to be 'manifestly clear' to a subject's introspection, and the goal is to
reconcile those features with what we observe in the physical world.
But frequently
these innocuous clear beginnings lead on in very short order to conclu-sions
clearly conflicting with what a physicalist picture can deliver. It shouldn't
be too surprising, however, if starting only with what seems manifestly clear
from heady introspection sometimes leads us to places which are in fact impossible
to accommodate with actual mere physics.
For instance, it is not unusual to include in an initial flotilla of assumptions
the notion that human minds can generate arbitrarily many well-formed English
sentences, or that they can perform addition over the full domain of natural
numbers, or that their conception of a valid proof can be infinitely extended.
Likewise, it is not uncommon to suppose that human minds are capable, in
principle, of perfect rationality-in the sense of being able to find all deductively
valid consequences of a set of beliefs-or even that they are capable of determining
whether any particular proposition (say, in first order logic) follows
from a given set of assumptions. Despite the fact that not one of the above assumptions
finds support from a single scrap of empirical evidence, even many
naturalistically minded philosophers happily invite them on board. A popular
justification for doing so, it seems, boils down to a belief that these 'in principle'
ideals are what really need explaining, and that actual world deviations from
the ideal are little more significant than the noisy boundary conditions which
always blur experimental measurements away from the ideal predictions of a
good theory. As it happens, however, convincing reasons suggest all the above
assumptions are false for any cognizer physically instantiated in the real
world-even though the failure of each is consistent with the appearance, from
the vantage point of the cognizer concerned, that it is true.
Many of the mind/body confusions which this book attempts to clear away
find their roots in just such lavish assumptions about what seems clear from introspection.
For progress to be made on the puzzle Fodor thinks no one should
even hope to understand, it is helpful for philosophers to adopt a little more
modesty about their own capabilities, acknowledging that-in the absence of
some argument to the contrary, and mere appearances aside-the default as4 CHAPTER ONE
sumption should be that we humans are as subject to the constraints of the laws
of physics as any helium atom in the core of a star or any fuzzy peach poised to
fall from a tree. This book, I hope, marks significant moves in that direction.
In view of its interdisciplinary nature, the text has been organised in a way
which I hope will accommodate readers with a wide variety of backgrounds and
personal interests in the material. Below, I outline my attempts to package farflung
topics in an accessible way, describe the book's anticipated audiences,
and briefly preview each chapter.
1.1 Pathways Through the Book
Because perhaps only a minority of readers whose interests happen to coincide
with my own will want to pursue the arguments set out here linearly from start
to finish, I have structured the book with a view to making other reading strategies
as painless as possible. Especially technical remarks are typically flagged in
advance, and in each such case I suggest an alternative route through the text
which will allow readers with less interest in details to skip ahead without
missing central points. Around two hundred cross-references to particular
chapters, sections, or page numbers, together with an extensive index, should
help those taking a nonlinear path through the book to locate other points supporting
key lines of thought.
With a few exceptions, the discussions require little in the way of specialist
background knowledge, but by no means do I intend the book as a comprehensive
introduction to any of the subdisciplines which feature in it, nor to the
mind/body problem itself. Although in places the text still reveals roots in a
doctoral dissertation, the overhead dedicated to one dissertation favourite, reviews
of existing literature, is substantially reduced-particularly in areas (such
as representation) where fresh perspectives are in the offing, perspectives which
may fit only awkwardly or not at all into the categories provided by that literature.
Likewise, I aim mainly to present views positively, largely dispensing
with cautionary lists detailing what they are not and contrasting them with the
many similar cousins for which they might be mistaken. And while I hope the
broad collection of about five hundred references provides a helpful start for
readers following up particular threads, it remains far from complete. I have
tried to avoid the 'my bibliography is bigger than your bibliography' syndrome-
the urge to cite the kitchen sink-which seems to be spreading ram-pantly
through populations of undergraduates and seasoned researchers alike
(perhaps under the influence of easy to use electronic abstract databases).
As for exceptions to general accessibility, I do assume familiarity with basic
logical connectives, plus a few mathematical and set theoretic symbols, and I
assume experience with the philosophical notions of a priori, a posteriori, intension,
extension, possible worlds, and the like. Prior acquaintance with Turing
Machines is helpful. The 'worst' exception occurs in Chapter 7; the summary
notes on the quantum formalism beginning on page 145, as well as some subsequent
sections, will be most useful for those with at least a passing familiarity
with linear algebra. However, as always, those portions may safely be skipped
by readers preferring to bypass the particulars, and pointers on where to pick up
again are of course included.
Overall, I hope the book will be enjoyable for most people interested in materialist
cognitive science and the challenges of understanding consciousness,
from advanced undergraduates to senior researchers and those whom publishers'
marketing departments sometimes dub 'the motivated lay reader'. It may
find a place in graduate seminars or as a supplementary text in philosophy, cognitive
science, artificial intelligence, or artificial life.
1.2 Chapters Summary
The second chapter is a warm-up exercise. Taking up Dennett's recent challenge
to defend the philosophical relevance of zombies without begging important
questions about their capabilities (or lack thereof), the chapter includes an architecturally
explicit zombie construction and applies it to motivate later explora-tions
not of how conscious subjects behave but of what internal processes bring
about that behaviour. Main outcome: nonconscious zombies with external be-haviour
indistinguishable from that of normal subjects are logically possible, so
conscious experience requires more than the right external behaviour.
Those later explorations of internal processes depend largely on the precise
and objective notions of information and of representation which take centre
stage in Chapter 3. Introducing a purely physical view of information based on
Gregory Chaitin's version of algorithmic information theory, the chapter describes
representation in the general case with a formal measure of mutual information
content between two physical objects. (Note that this appeal is to a
concept of information which differs from Shannon's, used by Dretske 1981.)
Along the way, I outline the modern and easily understood information theoretic
version of incompleteness results, questioning the foundations of
claims occasionally made about incompleteness and its bearing on philosophy of
mind. Main outcome: representation is objectively linked to the physical world.
The next chapter shows why, far from underwriting a convincing argument
against physicalism, the curiosities of Jackson's example of Mary, the colour deprived
neuroscientist, arise naturally within a wholly physicalist setting.
Tricky puzzles of perspective, or points of view, first arise here-to return in
Chapter 6-and the relationship between logic and the physically instantiated
cognizers using it merits brief remarks. Main outcome: the same information
may be physically instantiated in many distinct ways and with disparate ramifications
for conscious experience; Mary's ignorance before seeing red for herself
is not a matter of information, but of state.
Chapter 5 outlines a new formal framework for understanding functional
systems. Problems of mathematical triviality threaten traditional approaches to
functionalism based on correlation or correspondence, while teleofunctionalism
requires links to facts historically removed from the system in question, rendering
it more suitable for questions like 'why is this component here?' than
those like 'how does this system work?'. This chapter's objective method of
functional decomposition, using a formal measure of process complexity called
functional logical depth (inspired by work of Chaitin and Charles Bennett), circumvents
both difficulties. Main outcome: the revised functionalism is now ob-jective
and better disposed for explanatory work.
Within a context featuring arguments about supervenience, perspectives,
and mental states, Chapter 6 outlines the first components of a theory of consciousness
based on the self model, a materially instantiated dynamic data
structure which emerges as a promising candidate for the seat of phenomenal
experience. On this view, one motivated by the need for a conceptual link between
consciousness and the material world yet grounded empirically and thus
falsifiable, conscious experience is 'what it is like to be' a particular kind of
changing data structure. The self is not identical to any of those physical com-ponents
underlying it, yet it is implemented by them; I am a self model. Main
outcome: taking the concept with an appropriate intension, consciousness supervenes
logically on the physical world, with the self model as link.
Taking a brief side trip to debunk a competing class of theories, the so-called
'quantum theories of consciousness', the next chapter describes the work
of Roland and the mechanisms of interactive decoherence which, auto-matically
and extremely efficiently, eliminate the need for a conscious observer
in quantum mechanics and guarantee that special quantum effects are virtually
nonexistent at the levels of description where they are sometimes imagined to
feature in the human brain. As a bonus, interactive decoherence accounts for the
automatic emergence of apparently deterministic quasi-classical reality from a
quantum substrate. Main outcome: quantum physics doesn't need consciousness,
and consciousness doesn't need quantum physics.
Where Chapter 6 focused mainly on the conceptual territory between the self
model and supervening consciousness, Chapter 8 sets out in the opposite direction,
from the self model down toward the sorts of lower level materials-neural
tissue, in the case of humans and other terrestrial life forms which may implement
such data structures. After tidying the information theoretic description
of self models given in Chapter 6 and introducing basic tools from neuroscience,
the chapter shows how one particular research programme, Stephen
Grossberg's adaptive resonance theory, bears especially on the task of implementing
self models in real neural systems. Main outcome: the right neural systems
can do the representational work which self models require, and real organisms
may plausibly have evolved so as to implement them.
Turning from cognitive models to the mathematical presuppositions underlying
them, Chapter 9 examines the relationship between models and properties
of the physical systems being modelled. In particular, the chapter examines re-cent
work by Hava Siegelmann and Eduardo Sontag suggesting that analogue
models (based on the real numbers) may display computational capabilities
which exceed those of digital models (based on the rational numbers). To the
extent that the two sorts of models differ in their capabilities, an interesting
question then arises as to whether one or the other makes for a better match with
reality. Main outcome: contrary to popular dogma, the choice of number sys-tems
does make a difference for models of cognitive systems, but the significance
of that difference for the real world has yet to be established.
Finally, Chapter 10 recaps some of the text's central themes and reflects on
the broader significance of the mind/body problem for understanding who we
are, as individuals and as a civilisation. It finishes with some remaining open
questions and possible directions for future research.
Readers who find my attempts in each of these chapters to situate the discussion
within an overall picture a little too obscure might also want to skim
through that last chapter's section 2, starting on page 243, which, unlike the
above summary, surveys the principal developments of each discussion on the
assumption that readers will already have acquired some familiarity with them.
Although the book treats many distinct topics, all are united both in the sense
that they relate to some aspect of the mind/body problem and in terms of under-lying
themes. Below I begin with a theme I specifically attempt to sidestep and
move on to two more positive ones. Readers less interested in comparatively
dull methodological issues should skip ahead to section 3 below.
2.1 Dynamics and Computation
One fracas I hope to avoid is the war raging between advocates of dynamical
and computational methods in cognitive science. At a recent workshop marking
the opening of Sussex University's Centre for Computational Neuroscience and
Robotics, for example, I was astonished at the number of participants who ap-peared
quite abruptly to have rediscovered dynamical systems and were vigor8 CHAPTER ONE
ously promoting a dynamical approach to artificial life and related fields as the
greatest new advance-perhaps 'revelation' would be more fitting-in decades.
Worse than the hype
was the impression that one should be exclusively either
dynamicist or computationalist and that for the sake of scientific purity the two
must not be mixed-a notion asserted with characteristic vehemence by Tim
Smithers, the well known 'non-representationalist' roboticist from the University
of the Basque Country. I hardly dared raise a voice for a hybrid view for
fear of witnessing my own public stoning!
Typically, allegiances to a particular approach run deep, often it seems to
such an extent that what appears at a glance a straightforward observation supporting
one or the other position becomes utterly invisible to those favouring the
opposing viewpoint; all too frequently, arguments are simply ignored or contradicted
rather than rebutted. I hope in this book to challenge both sides while incensing
neither. For my part, while generally inclined more in the direction of a
dynamical approach, I believe tools of both types play a valuable in cognitive
science: both dynamics and a computationally defined variety of representation
feature crucially in my own view. In Chapter 3, I outline a method of quantifying
information content (and representation) which, while itself wholeheartedly
computational, applies equally well to all physical systems, whether interpreted
as computational or dynamical entities. Later, in Chapter 6, I argue
against the typical computationalism-friendly notion of an instantaneous mental
state in favour of an inherently temporal replacement, advancing a view of consciousness
itself which, while described in 'computational' information theoretic
terms, subsequently receives a dynamical account of neural instantiation in
Chapter 8. (For readers harbouring strong feelings on the debate and an irrepressible
urge to categorise this book in the language of it, the approach I adopt
here might be verbosely labelled, with tongue in cheek, as 'computationally described,
dynamical semi-representationalism'.)
Contra Smithers, I emphatically do not believe that one should decide in advance
to adopt one framework or the other, on pain of tainted science. Whether
a good explanation of observed phenomena should be dynamical, computational,
or hybrid in nature is a question properly evaluated in light of empirical
evidence and the resulting matches between candidate theories and reality; it is
not, to my mind, a matter of evaluating empirical evidence in light of a preexisting
conviction that explanation is to be found in one and only one particular
form. Likewise, contra van Gelder (see note 4 above), I find very little ontological
mileage in the methodological distinction between dynamical and computational
approaches to cognitive science. As far as I can see, whether we
speak in computational language, dynamical language, or little green men language,
we still talk about the same actual world. ('World first', not 'words
first'!) In the terminology of Chapter 6, the 'things' talked about supervene
logically on the physical world. Depending on the needs and aims of any given
situation, we might find it useful sometimes to describe cognitive processes
computationally, while at other times dynamical or hybrid descriptions will
prove most helpful. There may be a de facto rough cultural division between
cognitive scientists who generally prefer computational tools and those who
generally prefer dynamical tools, just as there is a de facto rough division between
those who prefer reverse Polish notation calculators and those who prefer
algebraic calculators, but such a division needn't necessarily reflect ontologically
significant facts about the real world of cognizers which they are studying.
2.2 Priorities and the Naturalistic Urge
Closely related to the business of choosing appropriate languages of explanation
are questions about the goals of research itself and the choices of tools which
those goals motivate. One opinion popular in the United Kingdom, at least,
counts the task of furthering the cause of a particular discipline or even department
as, if not quite an end in itself, at least a highly significant component of
academic research. On this view, a central aim of the philosophy researcher
should be to advance the understanding of philosophy for philosophy's sake;
the general field of philosophy is primary, while the particular issues to be explored
take a back seat. A diametrically opposed tack shapes my own research
in general and this book in particular.
My main interest lies not with furthering a particular discipline (or, even
less, a department), but with examining fascinating questions, whatever disciplines
may count as their own those questions or their solutions. I make no
apologies for importing methods or conclusions from outwith traditional philosophy,
particularly from scientific fields, in the course of exploring the
mind/body problem.
Although many philosophical colleagues in the United
Kingdom are quick to dismiss my own work as "science, not philosophy!"-as
though the two were mutually exclusive-I am only too happy to recruit for
'philosophical' purposes the tools of other fields. (Were I to encounter tomorrow
some good reasons for believing the art of pottery held the key to understanding
problems of consciousness, I would learn to make pots!) In the spirit
of thinkers like Kitcher (1992) and those featured in Kornblith (1994), I take
philosophy and the natural sciences as forming a continuum. The eloquent
words of E.W. Hobson, Sadleirian Professor of Pure Mathematics and Fellow
of Christ's College in Cambridge, speaking at the conclusion of his 1921-22
Gifford Lectures at the University of Aberdeen, express the idea succinctly:
If we were in possession of, and able to grasp, a unified view of the Universe, in
which all the elements of existence and valuation were completely synthesizedwe
should not require to mark out frontiers between Science and Philosophy or Theology
The untrammelled freedom which must be allowed to workers in all depart10 CHAPTER ONE
ments of the great cultural work of humanityshould notinvolve the erection of
rigid impassable barriers which shall mark off domains which hold no communication
with one another. On the contrary, workers in one department will often receive
the most valuable enlightenment, and most important suggestions, from quarters outside
their own special line. (Hobson 1923, p. 501)
Borrowing the contemporary words of Sussex researcher Inman Harvey
(personal communication), I also agree wholeheartedly with the notion of
"doing philosophy of mind with a screwdriver"-testing philosophical ideas
with robotics and artificial life in real world laboratories. In an article entitled
'Artificial Life as Philosophy', Dennett (1994) advocates a similar view.
But despite a distinguished tradition of positive and mutually beneficial interaction
between philosophy and the sciences, philosophy of mind is, perhaps
more than at any time in its history, feeling the heat from scientific areas as
those fields 'encroach upon' the study of questions still considered by many to
be philosophers' territory. Quite justifiably, methods and strategies from areas
like quantum physics, chaos theory, neuroscience, and artificial life have been
stirring up the field, eliciting responses from the philosophers' camp ranging
from the sort of dismissiveness recalled above to enthusiastic endorsements of
method x as that which will at last naturalise the study of mind. Although my
own tendencies draw me firmly in the naturalistic direction, explicitly arguing
the case for the relevance of scientific fields to 'philosophical' questions really is
not my battle. I hope others will simply evaluate my judgement in choosing the
tools I have in light of the lines of argument they support, rather than under the
shadow of some pre-existing prejudice as to how best to secure the borders of
philosophy against infiltration.
2.3 Description Complementarity and Puzzles of Perspective
After the central goal mentioned at the start of the chapter, that of embracing the
'ineffable feel' of phenomenal experience while simultaneously heeding the
constraints of physical law, the next most significant thread running through
this book concerns the relationships between different levels of description
the same cognitive system and between first and third person perspectives on
cognitive systems. I believe both relationships bear crucially on the project of
understanding how (or whether) matter can implement a mind.
With respect to the first, a good many problems in the history of philosophy
originate, in my opinion, with a failure to appreciate the complementarity between
alternative descriptions of the very same thing-a failure which, at times,
borders on stubborn-minded silliness. Throughout the explorations of the topic
which appear here, I have in mind a background context of working hypotheses
inspired by the likes of Davidson (1973) and Hellman and Thompson (1975); I
opt for what the latter call 'ontological determination'-the physical is all there

is, and everything that happens physically is governed entirely by the low level
laws of physics-coupled with 'explanatory anti-reductionism'. In other words,
nothing ever happens which is not, at the lowest level, entirely a result of the
laws of physics;
yet, in giving intelligible explanations of processes, we may
well have to rely on entities constructed at a higher level of description commensurate
with that at which we describe the processes themselves.
For instance, it would be no explanation of how a clock keeps time with its
hour and minute hands to describe the interactions, in accordance with the laws
of physics, of every single subatomic particle within it. A good explanation
would describe instead the interactions of cogs and pendulums or transistors
and quartz crystals (depending on the clock) and the relationship of those interactions
to the movements of the hands. Yet nothing ever happens to (or be-tween)
cogs, pendulums, transistors, quartz crystals, or arms of a clock which
doesn't follow straightforwardly from the lowest level laws of physics. The approach
to explanation favoured in this book embraces both observations to-gether.
The view contrasts starkly with those of Durkheim (1938) or Radcliffe-Brown
(1952), for instance, who maintain that good explanations require not
only an appropriate level of description, but a new independent level of things
whose causal properties, significantly, do not follow from those of their constituent
In the guise of a discussion of evolution and Conway's Game of
Life (Poundstone 1985), Dennett (1995c, pp. 166-75) offers the tidiest look at
levels of description I have encountered to date.
Interest in the relationships between alternative descriptions of the same
thing doesn't end with different levels; a special case of complementary descriptions
exists in the distinction between first and third person perspectives on
cognitive systems. Just as I believe there is a common failure to appreciate the
relationships between levels of description, so, too, is there a common failure to
appreciate the factors underlying the truism that reasoning about a system as a
third person differs greatly from being that system in the first person. If, for
instance, I cannot come to know 'what it is like' for me to be in a particular state
until I have actually been in that state or one relevantly similar to it, why should
it be at all puzzling that I cannot come to know what it is like for someone else
to be in such a state? And is there any reason to think I should be able to grasp
what it is like for me to be in a particular state before having actually been in
such a state? Such perspectival issues figure in a wide range of questions about
the relationship between mind and the physical world. My direct quarrel with a
standard view that problems of perspective support a case against physicalism
begins in Chapter 4 and returns in Chapter 6, but a reluctance to accept the standard
view underlies much of the rest of the book.
It was in one of the first philosophy texts I encountered as an undergraduate,
Richard Taylor's (1963) Metaphysics, that I vividly recall reading the tale of a
poor fellow called Osmo, who perishes while trying to escape a future foretold
for him in a special book. With perfect accuracy, the mysterious volume describes
every event in Osmo's entire life, from his birth through to the present
and on into the future and his eventual death. Like the protagonist in a Greek
tragedy, Osmo cannot escape his Fate: eerily, whatever the book foretells always
comes to pass, and try as he might, his every failed struggle to forge a
new and different future for himself only underscores the book's apparent infallibility.
Taylor's point in articulating the story-apart, perhaps, from terrorising impressionable
young philosophers-is to suggest that we all should view the fu-ture
with the eyes of a fatalist. Fatalism should appeal, Taylor argues, for purely
logical reasons: since some complete description of all my life's future events is
true right now, and since that description could already have been written down
in a book (say, by an omniscient and prolific author), I lack any sort of freedom
to change it, and I ought just to stop worrying about it! Despite Taylor's protests
to the contrary, the argument for fatalism seems a textbook example of
modal fallacy. But nevertheless, I think I can almost grasp what might have led
him to suggest the line of thought, despite his fluency with the logic of modal
operators. Although most philosophers reject Taylor's reasoning, the years have
not dulled my impression that something remains deeply disturbing about the
fantasy scenario he describes; a book accurately foretelling my every experience-
perhaps even my every thought-for the rest of my life truly would be a
frightening prospect.
That peculiar discomfort, I believe, bears a possibly illuminating likeness to
the distaste many express for the idea that human cognition and consciousness
might one day be explained within a purely materialist framework. I am not
suggesting that those unhappy about such a possibility are confused about modal
logic! Rather, although the analogy is imperfect with respect to logical
structure, there seems to me an appealing kind of symmetry between the two
cases. On one hand, it is disturbing to think that some book could in principle
expose, for all to see, every single event in my entire life-even though I know
perfectly well that the logical possibility of such a volume, in and of itself, in no
way diminishes my freedom in bringing about the events described within it.
There might be other reasons why I lack freedom, but the possibility of such a
book is certainly not one of them. And on the other hand, some may likewise
find it disturbing that a complete materialist theory of consciousness could in
principle expose, for all to see, the underlying physical foundation of every sinFRONTAL ASSAULT 13
gle pain or taste or visual impression (or hope or lust or intuition) throughout a
subject's entire life. This might seem disturbing even though such a prospect
would in no way diminish the painfulness of the pain or the lustfulness of the
lust; that rich phenomenal experience might have a physical explanation would
render it no less rich phenomenal experience.
A usually unarticulated further worry might grow from the notion that any-thing
which admits of a physical explanation is no different in principle from
any other physical thing. The possibility of a book explaining my entire conscious
existence in the language of physics threatens to reduce that experience
itself to nothing more than mere physics, siphoning off its value down to the
level of some least common denominator appropriate for other physical things
like bricks and globules of sludge. Probably it is only natural to feel some discomfort
at the idea that the very sciences which our own ingenuity created could
drain away our fundamental value in this way. On this view, perhaps our value
can only be preserved by finding it a nonphysical refuge categorically separate
from (and impossible to unify with) the merely mechanical transactions of
bricks and balls of sludge.
Needless to say, these are worries I do not share. On the contrary, I feel that
such a naturalistic physical explanation could only add to the sheer marvellousness
of phenomenal experience. There can be little doubt that it would be amazing
if it turned out instead that the subject of my phenomenal experience was
really an independent, immaterial, ethereal spirit of some sort-that I was such a
spirit and my consciousness one of that spirit's properties. But how much more
truly amazing it would be to discover that the conscious 'I' is instantiated purely
physically-that somehow, despite having nothing but that stringy ball of nerve
fibres and other organic matter with which to do it, I still manage to enjoy my
full remarkable repertoire of rich conscious experience! That matter simply organised
in the right pattern and changing in the right ways could actually instan-tiate
me, with all my vivid phenomenal experience intact: that is a marvel worthy
of the name. And, indeed, if what really counts is its in enabling our conscious
lives, why should a pattern be of any less value than an immaterial spirit?
In the next nine chapters, I set out what I believe are some useful steps toward
understanding the sorts of links between mind and matter which might
make such a view attractive in its own right and which may allay Osmo-style
discomfort. Do I believe I have given a rigorous, complete, and definitive solution
to the mind/body problem(s)? Of course not! But I do think a 'solution'-
or, rather, a set of solutions to a cluster of related problems-will eventually be
found to share the general form, and perhaps some of the details, of what I outline
here. Many times in these pages I deliberately reach far out on a limb while
constructing some view or other. In so doing, I aim to lay out a sort of tree of
possibilities; not all of its branches will ultimately bear fruit, I am sure. But I'm
convinced that while some limbs will eventually need cutting out and others will
benefit from considerable reshaping, the central thematic trunk is healthy and
planted just about where it ought to be. I hope that laying out the tree as I have
will provide new opportunities for progress through the process of evaluating
and snipping back those bits which don't belong, strengthening those which do,
and shaping this nascent theory into something robust and comprehensive.
1 Nowhere do I argue positively for any particular rendition of material monism; I find it hard
to grasp what a good argument for material monism would even look like.
2 Philosophers, understandably concerned to be clear about what it is they're trying to explain
before setting out to explain it, frequently adopt the convenient assumption that our first hand,
direct experience of consciousness suffices to fix the concept appropriately well. But to paraphrase
an example due to Aaron Sloman, the assumption is as unjustified as the claim that
even before Einstein's analysis of the concept of simultaneity, we really all knew what it was
anyway just through our first hand experience. As for the case of simultaneity, Sloman suggests,
it may be that only after constructing some good theories, capable of supporting coherent
concepts, will we be able to grasp properly what it was we were trying to explain in the
first place!
3 Since endnotes are easily found at the end of each chapter, when cross-referencing them I usually
mention the page number for the discussion which is endnoted rather than giving the page
number for the endnote text itself.
4 Not all the excitement is hype. While I am dubious about his tendency to overstate the ontological
significance of what amount to different dynamical (or non-dynamical) descriptions of
physical entities-see section 3 of Chapter 9-Tim van Gelder (1995a, b) offers a sober but
provocative analysis of each approach. In a forthcoming target article for Behavioral and Brain
Sciences, he succinctly maps out distinctions between the computational hypothesis-
roughly, the view that cognizers are digital computers-and the dynamical hypothesis-
roughly, the view that cognizers are dynamical systems.
5 Very often it is expedient to import science into philosophical discourse-nothing clinches
an existence proof like empirical evidence, for instance!-but some of the really difficult problems
of philosophy might well be those which either cannot be naturalised or which would be
very difficult to naturalise. (Ethics comes to mind as a possible example.) I have the utmost
respect for these sorts of areas, but my temperament generally tempts me more in the direction
of those where some 'easier' progress can be made.
6 Although I usually refer to 'levels', I mean also to include parallel or otherwise complementary
descriptions which may not exist in an hierarchical relationship with one another.
7 In the language of Chapter 6, everything supervenes on microphysics; see section 1 of that
chapter in particular.
8 On the last especially, also compare the emergentists such as Alexander (1920), Broad
(1925), or Pepper (1926); see McLaughlin (1992) for recent discussion.
9 Specifically, the purported argument to the contrary requires shifting the scope of a necessity
operator from a whole conditional to just the consequent of the conditional. But although it is
necessarily true that if such a book correctly proclaims that I will perform action x, then I will
perform action x, from this it simply does not follow that such a correct proclamation entails
that I necessarily will perform action x.
Zombies and Their
It is an embarrassment to our discipline that what is widely regarded among philosophers
as a major theoretical controversy should come down to whether or
notphilosophers' zombiesare possible/conceivable. (Dennett 1995b, p. 325)
Zombies of analytic philosophy, unlike the voodoo victims of Haitian folklore,
are hypothetical creatures entirely bereft of conscious experience who nonethe-less
behave indistinguishably from the rest of us. Philosophers' zombies walk
and talk as if they're conscious, they appear to wake up in the morning, and
over breakfast they even speculate on the meaning of dreams they claim to have
had. They don't realise they're zombies, of course-no feeling of peculiarity
spoils the pristine emptiness of their barren phenomenological landscapes-and
an enterprising philosopher engaging one in conversation about the topic might
well hear all manner of insightful commentary about what the notion of zombies
reveals about philosophy of mind.
Daniel Dennett says zombies don't exist. Most people, no doubt, would
agree. But more importantly, he suggests they are logically impossible: misguided
philosophers who claim they are conceivable merely fail to imagine the
full repertoire of zombie behaviours. All too often, philosophers define zombies
as above and then proceed to argue for some behavioural clue or other which
would give them away. But of course there can't be any such clue. "The philosophical
tradition of zombies would die overnight", Dennett says (1995b, p.
325; Dennett 1995a is similar), "if philosophers ceased to mis-imagine them". It
is unusual that I disagree significantly with Dennett, especially in print
(Mulhauser 1997a). But I think his pessimistic prognosis can't be quite right.
Dennett's challenge offers a tailor-made warm-up exercise for the rest of this
Show me, please, why the zombie hypothesis deserves to be taken seriously, and I
will apologize handsomely for having ridiculed those who think so If the philosophical
concept of zombies is so important, so useful, some philosopher ought to
be able to say why in non-question begging terms. I'll be curious to see if anybody
can mount such a defence, but I won't be holding my breath. (Dennett 1995b, p. 326)


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