2013 - wealthypenis - 博客大巴
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22:15:00 -The Mind/Brain Identity Theory (Stanford Encyclopedia of Philosophy)
The Mind/Brain Identity Theory
The identity theory of mind holds that states and processes of the mind
are identical to states and processes of the brain. Strictly speaking,
it need not hold that the mind is identical to the brain. Idiomatically
we do use &She has a good mind& and &She has a good
brain& interchangeably but we would hardly say &Her mind
weighs fifty ounces&. Here I take identifying mind and brain as
being a matter of identifying processes and perhaps states of the mind
and brain. Consider an experience of pain, or of seeing something, or
of having a mental image. The identity theory of mind is to the effect
that these experiences just are brain processes, not merely
correlated with brain processes.
Some philosophers hold that though experiences are brain processes
they nevertheless have fundamentally non-physical, psychical,
properties, sometimes called &qualia&. Here I shall take
the identity theory as denying the existence of such irreducible
non-physical properties. Some identity theorists give a behaviouristic
analysis of mental states, such as beliefs and desires, but
others, sometimes called ¢ral state materialists&, say
that mental states are actual brain states. Identity theorists often
describe themselves as &materialists& but
&physicalists& may be a better word. That is, one might be
a materialist about mind but nevertheless hold that there are entities
referred to in physics that are not happily described as
&material&.
In taking the identity theory (in its various forms) as a species of
physicalism, I should say that this is an ontological, not a
translational physicalism. It would be absurd to try to translate
sentences containing the word &brain& or the word
&sensation& into sentences about electrons, protons and so
on. Nor can we so translate sentences containing the word
&tree&. After all &tree& is largely learned
ostensively, and is not even part of botanical classification. If we
were small enough a dandelion might count as a tree. Nevertheless a
physicalist could say that trees are complicated physical mechanisms.
The physicalist will deny strong emergence in the sense of some
philosophers, such as Samuel Alexander and possibly C.D. Broad . The
latter remarked (Broad 1937) that as far as was known at that time the
properties of common salt cannot be deduced from the properties of
sodium in isolation and of chlorine in isolation. (He put it too
epistemologically: chaos theory shows that even in a deterministic
theory physical consequences can outrun predictability.) Of course the
physicalist will not deny the harmless sense of "emergence" in which an
apparatus is not just a jumble of its parts (Smart 1981).
The identity theory as I understand it here goes back to U.T. Place
and Herbert Feigl in the 1950s. Historically philosophers and
scientists, for example Leucippus, Hobbes, La Mettrie, and d'Holbach,
as well as Karl Vogt who, following Pierre-Jean-Georges Cabanis, made
the preposterous remark (perhaps not meant to be taken too seriously)
that the brain secretes thought as the liver secretes bile, have
embraced materialism. However, here I shall date interest in the
identity theory from the pioneering papers &Is Consciousness a
Brain Process?& by U.T. Place (Place 1956) and H.
&The "Mental" and the "Physical"& (Feigl 1958).
Nevertheless mention should be made of suggestions by Rudolf Carnap
(1932, p. 127), H. Reichenbach (1938) and M. Schlick (1935).
Reichenbach said that mental events can be identified by the
corresponding stimuli and responses much as the (possibly unknown)
internal state of a photo-electric cell can be identified by the
stimulus (light falling on it) and response (electric current flowing)
from it. In both cases the internal states can be physical states.
However Carnap did regard the identity as a linguistic recommendation
rather than as asserting a question of fact. See his &Herbert
Feigl on Physicalism& in Schilpp (1963), especially p. 886. The
psychologist E.G. Boring (1933) may well have been the first to use
the term &identity theory&. See Place (1990).
Place's very original and pioneering paper was written after
discussions at the University of Adelaide with J.J.C. Smart and C.B.
Martin. For recollections of Martin's contributions to the discussion
see Place (1989) &Low Claim Assertions& in Heil (1989).
Smart at the time argued for a behaviourist position in which mental
events were elucidated purely in terms of hypothetical propositions
about behaviour, as well as first person reports of experiences which
Gilbert Ryle regarded as &avowals&. Avowals were thought of
as mere pieces of behaviour, as if saying that one had a pain was just
doing a sophisticated sort of wince. Smart saw Ryle's theory as
friendly to physicalism though that was not part of Ryle's motivation.
Smart hoped that the hypotheticals would ultimately be explained by
neuroscience and cybernetics. Being unable to refute Place, and
recognizing the unsatisfactoriness of Ryle's treatment of inner
experience, to some extent recognized by Ryle himself (Ryle 1949, p.
240), Smart soon became converted to Place's view (Smart 1959). In this
he was also encouraged and influenced by Feigl's &"The Mental"
and the "Physical" & (Feigl ). Feigl's wide ranging
contribution covered many problems, including those connected with
intentionality, and he introduced the useful term &nomological
danglers& for the dualists' supposed mental-physical
correlations. They would dangle from the nomological net of physical
science and should strike one as implausible excrescences on the fair
face of science. Feigl (1967) contains a valuable
&Postscript&.
Place spoke of constitution rather than of identity. One of his
examples is &This table is an old packing case&. Another is
&lightning is an electric discharge&. Indeed this latter
was foreshadowed by Place in his earlier paper &The Concept of
Heed& (Place 1954), in which he took issue with Ryle's
behaviourism as it applied to concepts of consciousness, sensation and
imagery. Place remarked (p. 255)
The logical objections which might be raised to the
statement &consciousness is a process in the brain& are no
greater than the logical objections which might be raised to the
statement &lightning is a motion of electric
It should be noticed that Place was using the word
&logical& in the way that it was used at Oxford at the
time, not in the way that it is normally used now. One objection was
that &sensation& does not mean the same as &brain
process&. Place's reply was to point out that &this
table& does not mean the same as &this old packing
case& and &lightning& does not mean the same as
&motion of electric charges&. We find out whether this is a
table in a different way from the way in which we find out that it is
an old packing case. We find out whether a thing is lightning by
looking and that it is a motion of electric charges by theory and
experiment. This does not prevent the table being identical to the old
packing case and the perceived lightning being nothing other than an
electric discharge. Feigl and Smart put the matter more in terms of the
distinction between meaning and reference. &Sensation& and
&brain process& may differ in meaning and yet have the same
reference. &Very bright planet seen in the morning& and
&very bright planet seen in the evening& both refer to the
same entity Venus. (Of course these expressions could be
construed as referring to different things, different sequences of
temporal stages of Venus, but not necessarily or most naturally so.)
There did seem to be a tendency among philosophers to have thought
that identity statements needed to be necessary and a priori truths.
However identity theorists have treated &sensations are brain
processes& as contingent. We had to find out that the
identity holds. Aristotle, after all, thought that the brain was for
cooling the blood. Descartes thought that consciousness is
immaterial.
It was sometimes objected that sensation statements are incorrigible
whereas statements about brains are corrigible. The inference was made
that there must be something different about sensations. Ryle and in
effect Wittgenstein toyed with the attractive but quite implausible
notion that ostensible reports of immediate experience are not really
reports but are &avowals&, as if my report that I have
toothache is just a sophisticated sort of wince. Place, influenced by
Martin, was able to explain the relative incorrigibility of sensation
statements by their low claims: &I see a bent oar& makes a
bigger claim than &It looks to me that there is a bent
oar&. Nevertheless my sensation and my putative awareness of the
sensation are distinct existences and so, by Hume's principle, it must
be possible for one to occur without the other. One should deny
anything other than a relative incorrigibility (Place 1989).
As remarked above, Place preferred to express the theory by the
notion of constitution, whereas Smart preferred to make prominent the
notion of identity as it occurs in the axioms of identity in logic. So
Smart had to say that if sensation X is identical to brain process Y
then if Y is between my ears and is straight or circular (absurdly to
oversimplify) then the sensation X is between my ears and is straight
or circular. Of course it is not presented to us as such in experience.
Perhaps only the neuroscientist could know that it is straight or
circular. The professor of anatomy might be identical with the dean of
the medical school. A visitor might know that the professor hiccups in
lectures but not know that the dean hiccups in lectures.
Someone might object that the dean of the medical school does not
qua dean hiccup in lectures. Qua dean he goes to
meetings with the vice-chancellor. This is not to the point but there
is a point behind it. This is that the property of being the
professor of anatomy is not identical with the property of
being the dean of the medical school. The question might be asked, that
even if sensations are identical with brain processes, are there not
introspected non-physical properties of sensations that are not
identical with properties of brain processes? How would a physicalist
identity theorist deal with this? The answer (Smart 1959) is that the
properties of experiences are &topic neutral&. Smart
adapted the words &topic-neutral& from Ryle, who used them
to characterise words such as &if, &or&,
&and&, ¬&, &because&. If you
overheard only these words in a conversation you would not be able to
tell whether the conversation was one of mathematics, physics, geology,
history, theology, or any other subject. Smart used the words
&topic neutral& in the narrower sense of being neutral
between physicalism and dualism. For example &going on&,
&occurring&, &intermittent&,
&waxing&, &waning& are topic neutral. So is
&me& in so far as it refers to the utterer of the sentence
in question. Thus to say that a sensation is caused by lightning or the
presence of a cabbage before my eyes leaves it open as to whether the
sensation is non-physical as the dualist believes or is physical as the
materialist believes. This sentence also is neutral as to whether the
properties of the sensation are physical or whether some of them are
irreducibly psychical. To see how this idea can be applied to the
present purpose let us consider the following example.
Suppose that I have a yellow, green and purple striped mental image.
We may also introduce the philosophical term &sense datum&
to cover the case of seeing or seeming to see something yellow, green
and purple: we say that we have a yellow, green and purple sense datum.
That is I would see or seem to see, for example, a flag or an array of
lamps which is green, yellow and purple striped. Suppose also, as seems
plausible, that there is nothing yellow, green and purple striped in
the brain. Thus it is important for identity theorists to say (as
indeed they have done) that sense data and images are not part of the
furniture of the world. &I have a green sense datum& is
really just a way of saying that I see or seem to see something that
really is green. This move should not be seen as merely an ad
hoc device, since Ryle and J.L. Austin, in effect Wittgenstein,
and others had provided arguments, as when Ryle argued that mental
images were not a sort of ghostly picture postcard. Place characterised
the fallacy of thinking that when we perceive something green we are
perceiving something green in the mind as &the phenomenological
fallacy&. He characterizes this fallacy (Place 1956):
the mistake of supposing that when the subject describes
his experience, when he describes how things look, sound, smell, taste,
or feel to him, he is describing the literal properties of objects and
events on a peculiar sort of internal cinema or television screen,
usually referred to in the modern psychological literature as the
&phenomenal field&.
Of course, as Smart recognised, this leaves the identity theory
dependent on a physicalist account of colour . His early account of
colour (1961) was too behaviourist, and could not deal, for example,
with the reversed spectrum problem, but he later gave a realist and
objectivist account (Smart 1975). Armstrong had been realist about
colour but Smart worried that if so colour would be a very
idiosyncratic and disjunctive concept, of no cosmic importance, of no
interest to extraterrestrials (for instance) who had different visual
systems. Prompted by Lewis in conversation Smart came to realize that
this was no objection to colours being objective properties.
One first gives the notion of a normal human percipient with respect
to colour for which there are objective tests in terms of ability to
make discriminations with respect to colour. This can be done without
circularity. Thus &discriminate with respect to colour& is
a more primitive notion than is that of colour. (Compare the way that
in set theory &equinumerous& is antecedent to
&number&.) Then Smart elucidated the notion of colour in
terms of the discriminations with respect to colour of normal human
percipients in normal conditions (say cloudy Scottish daylight). This
account of colour may be disjunctive and idiosyncratic. (Maxwell's
equations might be of interest to Alpha Centaurians but hardly our
colour concepts.) Anthropocentric and disjunctive they may be, but
objective none the less. David R. Hilbert (1987) identifies colours
with reflectances, thus reducing the idiosyncrasy and disjunctiveness.
A few epicycles are easily added to deal with radiated light, the
colours of rainbows or the sun at sunset and the colours due to
diffraction from feathers. John Locke was on the right track in making
the secondary qualities objective as powers in the object, but erred in
making these powers to be powers to produce ideas in the mind rather
than to make behavioural discriminations. (Also Smart would say that if
powers are dispositions we should treat the secondary qualities as the
categorical bases of these powers, e.g. in the case of colours
properties of the surfaces of objects.) Locke's view suggested that the
ideas have mysterious qualia observed on the screen of an internal
mental theatre. However to do Locke justice he does not talk in effect
of &red ideas& but of &ideas of red&.
Philosophers who elucidate &is red& in terms of
&looks red& have the matter the wrong way round (Smart
Let us return to the issue of us having a yellow, purple and green
striped sense datum or mental image and yet there being no yellow,
purple and green striped thing in the brain. The identity theorist
(Smart 1959) can say that sense data and images are not real things in
the world: they are like the average plumber. Sentences ostensibly
about the average plumber can be translated into, or elucidated in
terms of, sentences about plumbers. So also there is having a green
sense datum or image but not sense data or images, and the having of a
green sense datum or image is not itself green. So it can, so far as
this goes, easily be a brain process which is not green either.
Thus Place (1956, p. 49):
When we describe the after-image as green... we are saying
that we are having the sort of experience which we normally have when,
and which we have learned to described as, looking at a green patch of
and Smart (1959) says:
When a person says &I see a yellowish-orange
after-image& he is saying something like this: "There is
something going on which is like what is going on when I have my
eyes open, am awake, and there is an orange illuminated in good light
in front of me".
Quoting these passages, David Chalmers (1996, p. 360) objects that
if &something is going on& is construed broadly enough it
is inadequate, and if it is construed narrowly enough to cover only
experiential states (or processes) it is not sufficient for the
conclusion. Smart would counter this by stressing the word
&typically&. Of course a lot of things go on in me when I
have a yellow after image (for example my heart is pumping blood
through my brain). However they do not typically go on then:
they go on at other times too. Against Place Chalmers says that the
word &experience& is unanalysed and so Place's analysis is
insufficient towards establishing an identity between sensations and
brain processes. As against Smart he says that leaving the word
&experience& out of the analysis renders it inadequate.
That is, he does not accept the &topic-neutral& analysis.
Smart hopes, and Chalmers denies, that the account in terms of
&typically of& saves the topic-neutral analysis. In defence
of Place one might perhaps say that it is not clear that the word
&experience& cannot be given a topic neutral analysis,
perhaps building on Farrell (1950). If we do not need the word
&experience& neither do we need the word
&mental&. Rosenthal (1994) complains (against the identity
theorist) that experiences have some characteristically mental
properties, and that &We inevitably lose the distinctively mental
if we construe these properties as neither physical nor mental&.
Of course to be topic neutral is to be able to be both physical and
mental, just as arithmetic is. There is no need for the word
&mental& itself to occur in the topic neutral formula.
&Mental&, as Ryle (1949) suggests, in its ordinary use is a
rather grab-bag term, &mental arithmetic&, &mental
illness&, etc. with which an identity theorist finds no
In their accounts of mind, David Lewis and D.M. Armstrong emphasise the
notion of causality. Lewis's 1966 was a particularly clear headed
presentation of the identity theory in which he says (I here refer to
the reprint in Lewis 1983, p. 100):
My argument is this: The definitive characteristic of any
(sort of) experience as such is its causal role, its syndrome of most
typical causes and effects. But we materialists believe that these
causal roles which belong by analytic necessity to experiences belong
in fact to certain physical states. Since these physical states possess
the definitive character of experiences, they must be
experiences.
Similarly, Robert Kirk (1999) has argued for the impossibility of
zombies. If the supposed zombie has all the behavioural and neural
properties ascribed to it by those who argue from the possibility of
zombies against materialism, then the zombie is conscious and so not a
Thus there is no need for explicit use of Ockham's Razor as in Smart
(1959) though not in Place (1956). (See Place 1960.) Lewis's paper was
extremely valuable and already there are hints of a marriage between
the identity theory of mind and so-called &functionalist&
ideas that are explicit in Lewis 1972 and 1994. In his 1972
(&Psychophysical and Theoretical Identifications&) he
applies ideas in his more formal paper &How to Define Theoretical
Terms& (1970). Folk psychology contains words such as
&sensation&, &perceive&, &belief,
&desire&, &emotion&, etc. which we recognise as
psychological. Words for colours, smells, sounds, tastes and so on also
occur. One can regard common sense platitudes containing both these
sorts of these words as constituting a theory and we can take them as
theoretical terms of common sense psychology and thus as denoting
whatever entities or sorts of entities uniquely realise the theory.
Then if certain neural states do so too (as we believe) then the mental
states must be these neural states. In his 1994 he allows for tact in
extracting a consistent theory from common sense. One cannot
uncritically collect platitudes, just as in producing a grammar,
implicit in our speech patterns, one must allow for departures from
what on our best theory would constitute grammaticality.
A great advantage of this approach over the early identity theory is
its holism. Two features of this holism should be noted. One is that
the approach is able to allow for the causal interactions between brain
states and processes themselves, as well as in the case of external
stimuli and responses. Another is the ability to draw on the notion of
Ramseyfication of a theory. F.P. Ramsey had shown how to replace the
theoretical terms of a theory such as &the property of being an
electron& by &the property X such that...&. so that
when this is done for all the theoretical terms, we are left only with
&property X such that&, &property Y such that&
etc. Take the terms describing behaviour as the observation terms and
psychological terms as the theoretical ones of folk psychology. Then
Ramseyfication shows that folk psychology is compatible with
materialism. This seems right, though perhaps the earlier identity
theory deals more directly with reports of immediate experience.
The causal approach was also characteristic of D.M. Armstrong's
careful conceptual analysis of mental states and processes, such as
perception and the secondary qualities, sensation, consciousness,
belief, desire, emotion, voluntary action, in his A Materialist
Theory of the Mind (1968a) with a second edition (1993) containing
a valuable new preface. Parts I and II of this book are concerned with
conceptual analysis, paving the way for a contingent identification of
mental states and processes with material ones. As had Brian Medlin, in
an impressive critique of Ryle and defence of materialism (Medlin
1967), Armstrong preferred to describe the identity theory as
&Central State Materialism&. Independently of Armstrong and
Lewis, Medlin's central state materialism depended, as theirs did, on a
causal analysis of concepts of mental states and processes. See Medlin
1967, and 1969 (including endnote 1).
Mention should particularly be made here of two of Armstrong's other
books, one on perception (1961), and one on bodily sensations, (1962).
Armstrong thought of perception as coming to believe by means of
the senses (compare also Pitcher 1971). This combines the
advantages of Direct Realism with hospitality towards the scientific
causal story which had been thought to have supported the earlier
representative theory of perception. Armstrong regarded bodily
sensations as perceptions of states of our body. Of course the latter
may be mixed up with emotional states, as an itch may include a
propensity to scratch, and contrariwise in exceptional circumstances
pain may be felt without distress. However, Armstrong sees the central
notion here as that of perception. This suggests a terminological
problem. Smart had talked of visual sensations. These were not
perceptions but something which occurred in perception. So in
this sense of &sensation& there should be bodily
sensation sensations. The ambiguity could perhaps be resolved by using
the word &sensing& in the context of &visual&,
&auditory&, &tactile& and &bodily&,
so that bodily sensations would be perceivings which involved
introspectible &sensings&. These bodily sensations are
perceptions and there can be misperceptions as when a person with his
foot amputated can think that he has a pain in the foot. He has a
sensing &having a pain in the foot& but the world does not
contain a pain in the foot, just as it does not contain sense data or
images but does contain havings of sense data and of images.
Armstrong's central state materialism involved identifying beliefs
and desires with states of the brain (1968a). Smart came to agree with
this. On the other hand Place resisted the proposal to extend the
identity theory to dispositional states such as beliefs and desires. He
stressed that we do not have privileged access to our beliefs and
desires. Like Ryle he thought of beliefs and desires as to be
elucidated by means of hypothetical statements about behaviour and gave
the analogy of the horsepower of a car (Place 1967). However he held
that the dispute here is not so much about the neural basis of mental
states as about the nature of dispositions. His views on dispositions
are argued at length in his debate with Armstrong and Martin
(Armstrong, Martin and Place, T. Crane (ed.) 1996). Perhaps we can be
relaxed about whether mental states such as beliefs and desires are
dispositions or are topic neutrally described neurophysiological states
and return to what seems to be the more difficult issue of
consciousness. Causal identity theories are closely related to
Functionalism, to be discussed in the next section. Smart had been wary
of the notion of causality in metaphysics believing that it had no
place in theoretical physics. However even so he should have admitted
it in folk psychology and also in scientific psychology and biology
generally, in which physics and chemistry are applied to explain
generalisations rather than strict laws. If folk psychology uses the
notion of causality, it is no matter if it is what Quine has called
second grade discourse, involving the very contextual notions of
It has commonly been thought that the identity theory has been
superseded by a theory called &functionalism&. It could be
argued that functionalists greatly exaggerate their difference from
identity theorists. Indeed some philosophers, such as Lewis (1972 and
1994) and Jackson, Pargetter and Prior (1982), have seen functionalism
as a route towards an identity theory.
Like Lewis and Armstrong, functionalists define mental states and
processes in terms of their causal relations to behaviour but stop
short of identifying them with their neural realisations. Of course the
term &functionalism& has been used vaguely and in different
ways, and it could be argued that even the theories of Place, Smart and
Armstrong were at bottom functionalist. The word
&functionalist& has affinities with that of
&function& in mathematics and also with that of
&function& in biology. In mathematics a function is a set
of ordered n-tuples. Similarly if mental processes are defined directly
or indirectly by sets of stimulus-response pairs the definitions could
be seen as &functional& in the mathematical sense. However
there is probably a closer connection with the term as it is used in
biology, as one might define &eye& by its function even
though a fly's eye and a dog's eye are anatomically and physiologically
very different. Functionalism identifies mental states and processes by
means of their causal roles, and as noted above in connection with
Lewis, we know that the functional roles are possessed by neural states
and processes. (There are teleological and homuncular forms of
functionalism, which I do not consider here.) Nevertheless an
interactionist dualist such as the eminent neurophysiologist Sir John
Eccles would (implausibly for most of us) deny that all functional
roles are so possessed. One might think of folk psychology, and indeed
much of cognitive science too, as analogous to a &block
diagram& in electronics. A box in the diagram might be labelled
(say) &intermediate frequency amplifier& while remaining)
neutral as to the exact circuit and whether the amplification is
carried out by a thermionic valve or by a transistor. Using terminology
of F. Jackson and P. Pettit (1988, pp. 381&400) the &role
state& would be given by &lifier&, the
&realiser state& would be given by &thermionic
valve&, say. So we can think of functionalism as a &black
box& theory. This line of thought will be pursued in the next
Thinking very much in causal terms about beliefs and desires fits in
very well not only with folk psychology but also with Humean ideas
about the motives of action. Though this point of view has been
criticised by some philosophers it does seem to be right, as can be
seen if we consider a possible robot aeroplane designed to find its way
from Melbourne to Sydney. The designer would have to include an
electronic version of something like a map of south-eastern Australia.
This would provide the &belief& side. One would also have
to program in an electronic equivalent of &go to Sydney&.
This program would provide the &desire& side. If wind and
weather pushed the aeroplane off course then negative feedback would
push the aeroplane back on to the right course for Sydney. The
existence of purposive mechanisms has at last (I hope) shown to
philosophers that there is nothing mysterious about teleology. Nor are
there any great semantic problems over intentionality (with a
&t&). Consider the sentence &Joe desires a
unicorn&. This is not like &Joe kicks a football&.
For Joe to kick a football there must be a football to be kicked, but
there are no unicorns. However we can say &Joe desires-true of
himself "possesses a unicorn" &. Or more generally &Joe
believes-true S& or &Joe desires-true S& where S is
an appropriate sentence (Quine 1960, pp. 206&16). Of course if one does
not want to relativise to a language one needs to insert &or some
samesayer of S& or use the word &proposition&, and
this involves the notion of proposition or intertranslatability. Even
if one does not accept Quine's notion of indeterminacy of translation,
there is still fuzziness in the notions of &belief& and
&desire& arising from the fuzziness of
&analyticity& and &synonymy&. The identity
theorist could say that on any occasion this fuzziness is matched by
the fuzziness of the brain state that constitutes the belief or desire.
Just how many interconnections are involved in a belief or desire? On a
holistic account such as Lewis's one need not suppose that
individuation of beliefs and desires is precise, even though good
enough for folk psychology and Humean metaethics. Thus the way in which
the brain represents the world might not be like a language. The
representation might be like a map. A map relates every feature on it
to every other feature. Nevertheless maps contain a finite amount of
information. They have not infinitely many parts, still less continuum
many. We can think of beliefs as expressing the different bits of
information that could be extracted from the map. Thinking in this way
beliefs would correspond near enough to the individualist beliefs
characteristic of folk and Humean psychology.
The notion &type& and &token& here comes by
analogy from &type& and &token& as applied to
words. A telegram &love and love and love& contains only
two type words but in another sense, as the telegraph clerk would
insist, it contains five words (&token words&). Similarly a
particular pain (more exactly a having a pain) according to the token
identity theory is identical to a particular brain process. A
functionalist could agree to this. Functionalism came to be seen as an
improvement on the identity theory, and as inconsistent with it,
because of the correct assertion that a functional state can be
realised by quite different brain states: thus a functional state might
be realised by a silicon based brain as well as by a carbon based
brain, and leaving robotics or science fiction aside, my feeling of
toothache could be realised by a different neural process from what
realises your toothache.
As far as this goes a functionalist can at any rate accept token
identities. Functionalists commonly deny type identities. However
Jackson, Pargetter and Prior (1982) and Braddon-Mitchell and Jackson
(1996) argue that this is an over-reaction on the part of the
functionalist. (Indeed they see functionalism as a route to the
identity theory.) The functionalist may define mental states as having
some state or other (e.g., carbon based or silicon based) which
accounts for the functional properties. The functionalist second order
state is a state of having some first order state or other which causes
or is caused by the behaviour to which the functionalist alludes. In
this way we have a second order type theory. Compare brittleness. The
brittleness of glass and the brittleness of biscuits are both the state
of having some property which explains their breaking, though the first
order physical property may be different in the two cases. This way of
looking at the matter is perhaps more plausible in relation to mental
states such as beliefs and desires than it is to immediately reported
experiences. When I report a toothache I do seem to be concerned with
first order properties, even though topic neutral ones.
If we continue to concern ourselves with first order properties, we
could say that the type-token distinction is not an all or nothing
affair. We could say that human experiences are brain processes of one
lot of sorts and Alpha Centaurian experiences are brain processes of
another lot of sorts. We could indeed propose much finer
classifications without going to the limit of mere token
identities.
How restricted should be the restriction of a restricted type
theory? How many hairs must a bald man have no more of? An identity
theorist would expect his toothache today to be very similar to his
toothache yesterday. He would expect his toothache to be quite similar
to his wife's toothache. He would expect his toothache to be somewhat
similar to his cat's toothache. He would not be confident about
similarity to an extra-terrestrial's pain. Even here, however, he might
expect some similarities of wave form or the like.
Even in the case of the similarity of my pain now to my pain ten
minutes ago, there will be unimportant dissimilarities, and also
between my pain and your pain. Compare topiary, making use of an
analogy exploited by Quine in a different connection. In English
country gardens the tops of box hedges are often cut in various shapes,
for example peacock shapes. One might make generalizations about
peacock shapes on box hedges, and one might say that all the imitation
peacocks on a particular hedge have the same shape. However if we
approach the two imitation peacocks and peer into them to note the
precise shapes of the twigs that make them up we will find differences.
Whether we say that two things are similar or not is a matter of
abstractness of description. If we were to go to the limit of
concreteness the types would shrink to single membered types, but there
would still be no ontological difference between identity theory and
functionalism.
An interesting form of token identity theory is the anomalous monism
of Davidson 1980. Davidson argues that causal relations occur under the
neural descriptions but not under the descriptions of psychological
language. The latter descriptions use intentional predicates, but
because of indeterminacy of translation and of interpretation, these
predicates do not occur in law statements. It follows that mind-brain
identities can occur only on the level of individual (token) events. It
would be beyond the scope of the present essay to consider Davidson's
ingenious approach, since it differs importantly from the more usual
forms of identity theory.
Place answered the question &Is Consciousness a Brain
Process?& in the affirmative. But what sort of brain process? It
is natural to feel that there is something ineffable about which no
mere neurophysiological process (with only physical intrinsic
properties) could have. There is a challenge to the identity theorist
to dispel this feeling.
Suppose that I am riding my bicycle from my home to the university.
Suddenly I realise that I have crossed a bridge over a creek, gone
along a twisty path for half a mile, avoided oncoming traffic, and so
on, and yet have no memories of all this. In one sense I was conscious:
I was perceiving, getting information about my position and speed, the
state of the bicycle track and the road, the positions and speeds of
approaching cars, the width of the familiar narrow bridge. But in
another sense I was not conscious: I was on &automatic
pilot&. So let me use the word &awareness& for this
automatic or subconscious sort of consciousness. Perhaps I am not one
hundred percent on automatic pilot. For one thing I might be absent
minded and thinking about philosophy. Still, this would not be relevant
to my bicycle riding. One might indeed wonder whether one is ever one
hundred percent on automatic pilot, and perhaps one hopes that one
isn't, especially in Armstrong's example of the long distance truck
driver (Armstrong 1962). Still it probably does happen, and if it does
the driver is conscious only in the sense that he or she is alert to
the route, of oncoming traffic etc., i.e. is perceiving in the sense of
&coming to believe by means of the senses&. The driver gets
the beliefs but is not aware of doing so. There is no suggestion of
ineffability in this sense of &consciousness&, for which I
shall reserve the term &awareness&.
For the full consciousness, the one that puzzles us and suggests
ineffability, we need the sense elucidated by Armstrong in a debate
with Norman Malcolm (Armstrong and Malcolm 1962, p. 110). Somewhat
similar views have been expressed by other philosophers, such as Savage
(1976), Dennett (1991), Lycan (1996), Rosenthal (1996). A recent
presentation of it is in Smart (2004). In the debate with Norman
Malcolm, Armstrong compared consciousness with proprioception. A case
of proprioception occurs when with our eyes shut and without touch we
are immediately aware of the angle at which one of our elbows is bent.
That is, proprioception is a special sense, different from that of
bodily sensation, in which we become aware of parts of our body. Now
the brain is part of our body and so perhaps immediate awareness of a
process in, or a state of, our brain may here for present purposes be
called &proprioception&. Thus the proprioception even
though the neuroanatomy is different. Thus the proprioception which
constitutes consciousness, as distinguished from mere awareness, is a
higher order awareness, a perception of one part of (or configuration
in) our brain by the brain itself. Some may sense circularity here. If
so let them suppose that the proprioception occurs in an in practice
negligible time after the process propriocepted. Then perhaps there can
be proprioceptions of proprioceptions, proprioceptions of
proprioceptions of proprioceptions, and so on up, though in fact the
sequence will probably not go up more than two or three steps. The last
proprioception in the sequence will not be propriocepted, and this may
help to explain our sense of the ineffability of consciousness. Compare
Gilbert Ryle in The Concept of Mind on the systematic
elusiveness of &I& (Ryle 1949, pp. 195&8).
Place has argued that the function of the &automatic
pilot&, to which he refers as &the zombie within&, is
to alert consciousness to inputs which it identifies as problematic,
while it ignores non-problematic inputs or re-routes them to output
without the need for conscious awareness. For this view of
consciousness see Place (1999).
Mention should here be made of influential criticisms of the identity
theory by Saul Kripke and David Chalmers respectively. It will not be
possible to discuss them in great detail, partly because of the fact
that Kripke's remarks rely on views about modality, possible worlds
semantics, and essentialism which some philosophers would want to
contest, and because Chalmers' long and rich book would deserve a
lengthy answer. Kripke (1980) calls an expression a rigid designator if
it refers to the same object in every possible world. Or in counterpart
theory it would have an exactly similar counterpart in every possible
world. It seems to me that what we count as counterparts is highly
contextual. Take the example &water is H2O&. In
another world, or in a twin earth in our world as Putnam imagines
(1975), the stuff found in rivers, lakes, the sea would not be
H2O but XYZ and so would not be water. This is certainly
giving preference to real chemistry over folk chemistry, and so far I
applaud this. There are therefore contexts in which we say that on twin
earth or the envisaged possible world the stuff found in rivers would
not be water. Nevertheless there are contexts in which we could
envisage a possible world (write a science fiction novel) in which
being found in rivers and lakes and the sea, assuaging thirst and
sustaining life was more important than the chemical composition and so
XYZ would be the counterpart of H2O.
Kripke considers the identity &heat = molecular motion&,
and holds that this is true in every possible world and so is a
necessary truth. Actually the proposition is not quite true, for what
about radiant heat? What about heat as defined in classical
thermodynamics which is &topic neutral& compared with
statistical thermodynamics? Still, suppose that heat has an essence and
that it is molecular motion, or at least is in the context envisaged.
Kripke says (1980, p. 151) that when we think that molecular motion
might exist in the absence of heat we are confusing this with thinking
that the molecular motion might have existed without being
felt as heat. He asks whether it is analogously possible that
if pain is a certain sort of brain process that it has existed without
being felt as pain. He suggests that the answer is
&No&. An identity theorist who accepted the account of
consciousness as a higher order perception could answer
&Yes&. We might be aware of a damaged tooth and also of
being in an agitation condition (to use Ryle's term for emotional
states) without being aware of our awareness. An identity theorist such
as Smart would prefer talk of &having a pain& rather than
of &pain&: pain is not part of the furniture of the world
any more than a sense datum or the average plumber is. Kripke concludes
(p. 152) that the
apparent contingency of the connection between the mental
state and the corresponding brain state thus cannot be explained by
some sort of qualitative analogue as in the case of heat.
Smart would say that there is a sense in which the connection of
sensations (sensings) and brain processes is only half contingent. A
complete description of the brain state or process (including causes
and effects of it) would imply the report of inner experience, but the
latter, being topic neutral and so very abstract would not imply the
neurological description.
Chalmers (1996) in the course of his exhaustive study of
consciousness developed a theory of non-physical qualia which to some
extent avoids the worry about nomological danglers. The worry expressed
by Smart (1959) is that if there were non-physical qualia there would,
most implausibly, have to be laws relating neurophysiological processes
to apparently simple properties, and the correlation laws would have to
be fundamental, mere danglers from the nomological net (as Feigl called
it) of science. Chalmers counters this by supposing that the qualia are
not simple but unknown to us, are made up of simple proto-qualia, and
that the fundamental laws relating these to physical entities relate
them to fundamental physical entities. His view comes to a
rather interesting panpsychism. On the other hand if the topic neutral
account is correct, then qualia are no more than points in a
multidimensional similarity space, and the overwhelming plausibility
will fall on the side of the identity theorist.
On Chalmers' view how are we aware of non-physical qualia? It has
been suggested above that this inner awareness is proprioception of the
brain by the brain. But what sort of story is possible in the case of
awareness of a quale? Chalmers could have some sort of answer to this
by means of his principle of coherence according to which the causal
neurological story parallels the story of succession of qualia. It is
not clear however that this would make us aware of the qualia. The
qualia do not seem to be needed in the physiological story of how an
antelope avoids a tiger.
People often think that even if a robot could scan its own
perceptual processes this would not mean that the robot was conscious.
This appeals to our intuitions, but perhaps we could reverse the
argument and say that because the robot can be aware of its awareness
the robot is conscious. I have given reason above to distrust
intuitions, but in any case Chalmers comes some of the way in that he
toys with the idea that a thermostat has a sort of proto-qualia. The
dispute between identity theorists (and physicalists generally) and
Chalmers comes down to our attitude to phenomenology. Certainly walking
in a forest, seeing the blue of the sky, the green of the trees, the
red of the track, one may find it hard to believe that our qualia are
merely points in a multidimensional similarity space. But perhaps that
is what it is like (to use a phrase that can be distrusted) to
be aware of a point in a multidimensional similarity space. One may
also, as Place would suggest, be subject to &the phenomenological
fallacy&. At the end of his book Chalmers makes some speculations
about the interpretation of quantum mechanics. If they succeed then
perhaps we could envisage Chalmers' theory as integrated into physics
and him as a physicalist after all. However it could be doubted whether
we need to go down to the quantum level to understand consciousness or
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an incomplete paper by U.T.
Place, published in the Field Guide to Philosophy of Mind
Acknowledgments
I would like to express my thanks to David Armstrong, Frank Jackson and
Ullin Place for comments on an earlier draft of this article and David
Chalmers for careful editorial suggestions.
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