This is the draft of a paper that will be published in
its fully developed form in my book Lines of Thought: Rethinking
Philosophical Assumptions (Cambridge: Cambridge Scholars Publishing, 2014)
ANSWERING
THE TWO MAIN OBJECTIONS AGAINST IDENTITY THEORY: MULTIPLE REALIZABILITY AND IRREDUCTIBILITY OF QUALIA
There
are two main objections against the identity theory of mind: the objection of
multiple realizability and the objection of the irreductibility of qualia.
In this paper I will answer both of them, beginning with the objection of
multiple realizability.
I
The concept of type, as distinct from token,
may require a greater or lesser degree of similarity among things that are
tokens of the same type. For example: two similar round patches of pure
ultramarine blue can be regarded as two tokens of the same type, distinguished
only by the different spaces they occupy. A round patch of ultramarine blue and
a round patch of sky blue can likewise be distinguished by differences in their
shades of colour, although they have the same blue colour type. We can clarify
this point by saying that types can be more abstract relative to
their tokens in ways that tend to be directly proportional to the number of
properties that are abstracted, namely, those that are left out of
consideration because they aren’t necessarily common to all their tokens.
According
to the well-known multiple realisability objection to type-type identity
theory, there is no way to identify a mental state with a neurophysiological
type, because a mental state of a mental type is in fact realizable in tokens
of very distinct physical types. In searching for a reason to dismiss the
multiple realisability objection, some philosophers have considered the
property of types that they are more or less abstract. What these philosophers
have discovered is that the supposed identity between mental and neurophysiological
types can be much more abstract than was initially
supposed by the advocates of the multiple realisability objection, which allows
realisations in many different types of tokens belonging to the domain of the
intended more abstract type.[1]
I agree with this position, but I also
agree with those who say that this would not be enough. Consequently, my first
aim here is to call attention to an insight about the nature of the properties
that identify a token as a token of the same type. In the case of the colour
blue, we are usually speaking about a certain phenomenally identifiable range
of the visible spectrum. In this case, as in the case of a stone, a
mountain, a cloud, etc., the identifying properties can be regarded as qualitative
and intrinsic, what we could call material properties. However,
not all the properties that identify types are material properties in this
sense, since as a rule many kinds can only be identified by means of what in
contrast may be called functional properties, that is, by what
they are able to do. In what follows, I will give three very common examples of
functional definitions of types:
(i) Consider the natural kind concept of mammal.
There are many different sorts of mammals: human beings, whales and bats are
all mammals. How can the concept include such different kinds of living
creatures? The reason is that its definition draws much more on functional characteristics
than on material ones. Typically, mammals are warm-blooded vertebrate
animals that maintain a constant body temperature. They have hair, and females
have milk-producing glands used to nourish their infants. There are several
other specifically mammalian features, such as a lower jaw directly hinged to
the skull, etc. ... However, this definition doesn’t include a precise material
determination, for example, of the chemical composition of milk. It is functions
(combined with some general material determinations) that make a token a token
of the mammalian type.
(ii) Artefacts are good examples of functionally
defined things. Consider the concept of knife. One can define a (real)
knife as ‘an instrument with a handle and a sharp blade designed for cutting
things’. This is essentially a functional definition. In addition to this, a
minimal material specification can also be made. When one says that a knife is
a solid, hard, very sturdy object, one is delimiting, in a generous way, a
domain of possible materials. Real knives can be made of hard materials such as
steel, flint, silver, bronze, aluminium, maybe fibreglass, plastic, wood… but
not of soft, easily deformed materials such as paper, marzipan, butter, liquids
and gases in general. Of course, one could complete the definition with a list
of hard-and-not-easily-broken materials that can be used to make knives, a list
that would unavoidably remain open-ended.
(iii) Consider now the much-discussed concept of chair
– another artefact. In general, this concept can be adequately defined as ‘a
seat with a back, designed for one person to sit on’. A stool isn’t a
chair because it has no back; a park bench isn’t a chair, because it is wider
and designed to seat more than one person.[2] Although mainly
functional, the definition of a chair cannot be entirely functional because a
chair must be made of materials that are rigid and stable. One can easily
imagine a chair made of wood, steel, fibreglass, plastic, etc. But one cannot
easily imagine a chair made of chocolate, butter, sea-water (at room
temperature) or air (except for inflatable plastic furniture…).
What these cases first demand is a sufficiently
precise specification of their function; to this we can add an indeterminate
qualitative identification of the material, but not the other way around.
Although there is no hard and fast
distinction between material and functional definitions, they can easily be
distinguished. One could object that each material property can be further
defined in a functional way. The colour blue, for example, is a qualitatively
perceptible property, but usually it is scientifically defined in terms of its
wave-length, functionally determined by means of instrumentally measured
diffraction, etc. Nevertheless, the point is that material properties like the
colour blue aren’t in fact accessed in this way, but rather in a way
that for us is more direct, by the perception of their qualitative aspects,
while the reverse isn’t the case: Functional properties, like ‘being designed
to cut things’, cannot be materially defined.
I
Now, I will show that the neurophysiological side of
the identities foreseen by identity theory requires a functional definition,
and that this fact has implications for the multiple realisability objection.
Restricting our considerations to phenomenal states, my point is that qualia
must be seen as constituted not of precise material elements, but rather of
more specific neurofunctional elements added to indeterminate, vague or
open-ended material conditions.[3]
We can try to defend this proposal by
pointing out the deficiencies of hypothetical counterexamples. Consider the
identification of the neurophysiological type corresponding to the sensation of
pain. This identification has similarities with those presented above. It
should be done using a sufficiently precise functional identification added to
an indeterminate material identification that refers to biophysical,
neurochemical, histological and anatomical commonalities. We already know
something about them. We can say something about the relevant centres in the
limbic system. We can also say something about the neuronal processes that produce
what we call pain. This is the beginning of a neurofunctional identification,
but it also brings us to the borders of the unknown. Neuroscience is still in
its infancy, and our ignorance of the real workings of the brain tends to be
much greater than we are able to imagine. Up to now all that we have really
accomplished is to describe the neurophysiology of pain in a manner similar to
naïve scientific thinking: A child may try to understand how a steam locomotive
works after seeing one, indigenous peoples may try to understand the flight of
an airplane that has crashed in their jungle. An inquisitive child might
conclude that the forward movement of a locomotive has something to do with men
shovelling coal into a firebox and water heated in a boiler, and perhaps even
guess correctly that in some way steam pressure causes the wheels to turn...
The indigenous peoples could rummage through the smouldering wreckage of the
airplane and perhaps guess that it was able to fly because of its engine and
wings. In the same way, we can already offer vague, hypothetical and
superficial neurophysiological proto-definitions of mental states
like pain. One of these could be the following:
Pain sensation (P-Df.) = a kind
of pre-cortical response, resulting from the stimulation of peripheral sensory
structures called ‘nociceptors’ (which are neuronal cells activated by noxious
stimuli and inhibited by analgesic drugs), usually leading to some sorts of
cortical activation and appropriate avoidance reactions…
As a definition, this would be plainly
insufficient. But it already serves to expose some of the confusion that
philosophers have caused by applying the multiple realisability objection to
the case of pain. Consider the ‘definition’ of pain as the activation of C fibres,
once seriously proposed by philosophers when discussing identity theory. It is
true that this can be intended as an as if definition. The problem,
however, is that this as if definition is also misleading, because it is
based on the already named material elements of the definition, tempting us to
think that an adequate definition of pain must identify something materially in
a much more specific way than is needed or expected. An analogous case would be
that of someone insisting that nothing can be a knife that isn’t made of steel.
And just as maintaining that a knife must be made of steel excludes many things
usually called ‘knives’, it must be similarly misleading to claim that as
peripheral nociceptors, C fibres are a necessary condition for experiencing pain,
so that animals lacking C fibres could not possibly feel pain. This would lead
all too easily to the species-chauvinistic conclusion denounced by Hilary
Putnam, according to which only human beings can experience pain. Now, it is
this kind of mistake that pervades Putnam’s multiple realization argument, at
least insofar as it concerns phenomenal qualities. To quote a well-known
passage by Putnam:
Consider what the brain-state theorist has to do
to make good his claims. He has to specify a physical-chemical state
such that any organism (not just a mammal) is in pain if and only if (a)
it possesses a brain of a suitable physical-chemical structure; and (b)
its brain is in that physical-chemical state. This means that the
physical-chemical state in question must be a possible state of a mammalian
brain, a reptilian brain, a mollusk’s brain (octopuses are mollusca, and
certainly feel pain), etc. At the same time, it must not be a possible
(physically possible) state of the brain of any physically possible creature
that cannot feel pain. Even if such a state can be found, it must be
nomologically certain that it will also be a state of the brain of any
extra-terrestrial life that may be found that will be capable of feeling pain
before we can even entertain the supposition that it may be pain.[4]
These comments, intended to reduce to absurdity the
hypothesis of an identity between pain and certain physical states of the
brain, can easily be shown to be misleading by considering our proto-definition
of pain. For the material specifications in it are restricted to a minimum,
consisting in a reference to (non-specified) cortical and pre-cortical centres,
along with peripheral cells called nociceptors, which are only functionally
defined as cells activated by noxious stimuli and inhibited by analgesic
drugs. And even the functioning of these cells is not a necessary condition,
since some animals (including human beings) can feel pain simply through direct
neuronal activation of the reticular formation and the thalamus. Indeed, once
our proto-definition of pain is accepted, the objection of inter-specific
multiple realisability loses its relevance. It is very probable, for example,
that an octopus can experience pain, and that this involves the activation of
paleo-encephalic cells, which usually results from the stimulation of
nociceptors… Indeed, the anatomical and histological elements of the
proto-definition are vague enough to make this possible. Even octopuses have
neuronal cells, they must have pre-cortical centres, and it is obvious that
they also have nociceptors, defined as cells excitable by noxious stimuli like
heat that can be inhibited by at least some analgesic blockers. (If it should
be found that their nociceptors were not blocked by any known analgesic substance,
physiologists would want to broaden the concept of nociceptor, since we are
convinced that octopuses also feel pain.)
We conclude that, at least concerning
inter-specific cases, the multiple realisability objection to identity theory
is misleading, because it relies on a mistaken notion of how we specify types,
assuming that we identify types on the basis of material properties, ignoring
neurofunctional properties. Here the multiple realisability objection is to
blame for what we could call a fallacy of false specification. We
commit this fallacy when we define something using an unsuitable parameter of
specification that sets the boundaries of the concept either too broadly or too
narrowly. Often it is committed when people do not sufficiently understand the
functional nature of things and consider them only or primarily in terms of
their material aspects. For example, we find this fallacy when it is assumed
that since insects lack retinal cells, they cannot have eyes. The obvious
mistake is to define the concept of eye not based on the functional
property of having vision, but instead on the material property of having
retinal cells. The thesis that the neurophysiological type of pain in other
species is different from that in humans exemplifies the fallacy of false
specification. It is possible for different types of pain to arise from the
same type of neurophysiology, because pain must be defined mainly in terms of
its neurophysiological function, and only secondarily and vaguely in material
(anatomical and histological) terms.
If the inter-specific argument of multiple realisability
is equivocal when applied to pain, and pain is a phenomenal quality, we may ask
if we cannot say the same of other phenomenal qualities. Consider the case of
anxiety. One can give a proto-definition of anxiety by saying that it is a
cortical effect resulting from the reverberation of neuronal firing in circuits
belonging to the limbic system (in this case, we exclude the possibility that
insects could experience anxiety – because they don’t have a limbic system –
but we are more cautious when considering the possibility of anxiety in fish
and birds.) What about visual images? We can say that these are a sort of
effect of the isomorphic activation of brain cells, normally caused by the
stimulation of the visual organs by light (this case is very inclusive: even
insects have some kinds of visual images). It seems that it is always possible
to justify general attributions of phenomenal qualities (like pain, anxiety and
visual images) by means of a sufficiently broad neurophysiological
characterization matching our phenomenally and behaviourally based use of the
concept.
The upshot of our considerations is that,
regarding phenomenal qualities, we have sufficient reason to believe that the
proposal of inter-specific multiple realisability concerning phenomenal
qualities is a philosophical fantasy made possible by our lack of knowledge of
how the brain really works.
However, there are other philosophical
fantasies about the multiple realisability of phenomenal states. Consider the
case of phenomenal states in hypothetical extra-terrestrial beings with a
non-carbon based physiology, as Putnam suggests at the end of the cited
passage. In my view, the question: ‘Why are sophisticated non-carbon based
brains not physio-chemically possible?’ is naively motivated. Anyone who has
studied biochemistry realizes this. It is like asking: ‘Why is there no life on
the other planets of our solar system?’ The obvious answer is that life is an extremely
complex and rare phenomenon. The earth is the one place in our solar system
where all the myriad necessary conditions were present that made possible and
led to the emergence and evolution of an order of reality we call life.
Furthermore, the evolutionary knowledge that led biologists to formulate the
fundamental principle of convergence between different
species suggests that life on other planets in other solar systems would
probably not be very different from life on ours. But if life is a complex
phenomenon, conscious life is a much more complex and demanding phenomenon.
Probably extra-terrestrial beings, in order to be conscious and have phenomenal
states, would need to be so biochemically similar to us that it would be
possible, if not to use the same neurofunctional definitions for their
phenomenal states, at least to extend our definitions in a natural way in order
to include them.
Finally, what about the future
possibilities of phenomenal states in advanced silicon-based computers? Here
the answer is that the belief that phenomenal states such as pain could occur
in computers or robots is an even more naïve fantasy that became popular at the
beginning of the computer era. Robots can replicate the external manifestations
of psychological states like sensations and feelings, but cannot intrinsically experience
real sensations or real feelings. For one thing, they don’t belong to the same
order of physical reality that makes such phenomena possible, but instead to a
far less complex physical order. Computers and robots with human feelings such
as pain are the stuff of science fiction films by Hollywood producers like
Steven Spielberg or Stanley Kubrick (e.g., A.I.: Artificial Intelligence;
2001: A Space Odyssey). Influenced by such fanciful ideas but lacking an
understanding of the real dimensions of the biological nature responsible for
the incredible sophistication of real brains, people simply project human
consciousness and mental faculties into supercomputers, with their enormous
databases and capability to make extremely rapid calculations involving vast
numbers of variables. However, this is in fact not so very different from the
anthropomorphic projection of human feelings and thoughts into the animal
kingdom that has been found in totemic societies.
We conclude that at least concerning
phenomenal qualities the neurofunctional interpretation of the constitution of
mental states immunizes the identity thesis against the multiple realisability
objection.
II
Now, what about the multiple realisability objection
on the level of cognitive states like thoughts, beliefs,
intentions, etc., which from Aristotle to Aquinas were seen as belonging to the
more abstract and general dimension of the mental? Here I have real doubts as
to whether the same kinds of answers are suitable. It remains implausible that
a particular thought, for example, that Kauai is the oldest Hawaiian island,
should have similar neurofunctional paths in both my brain and yours. Moreover,
a chain of reasoning, understood as a logical sequence of thoughts, seems to be
at least structurally reproducible in the form of a mechanical manipulation of
symbols according to an algorithm. Indeed, there must be something that allows
us to say that computers can think in some derivative sense of the word,
since they are able to solve complicated mathematical problems or play chess.
Even if the biological process of human thinking is very different, it could be
maintained that there is no reason why the symbolic manipulation of a computer
couldn’t at least in some respects resemble what occurs in the mind of a
mathematician or a chess player.
Nevertheless, the idea that a computer
would be able to think or reason in the strict and proper sense
of the word remains intuitively implausible. Why is this the case? – Mere
prejudice? I don’t think so. It seems to me that when we speak about thinking
and reasoning we are not restricting ourselves to the generation of sequences
of symbols in accordance with algorithms. We are assuming that these are
integrated into a whole which includes in its foundations the lower levels of
the thinker’s emotions, desires, sensory experiences and memories, that is,
things that must involve phenomenal states depending on our biology and life
form.[5]
The necessary involvement of our emotions
and desires in reasoning was famously pointed out by David Hume, who
maintained that reason is the slave of passion, for our reasoning must have
changeable aims originally grounded in the emotional and volitional nature moulded
in our life form. But these are not the sorts of phenomena that a computer
could duplicate. Moreover, the necessary engagement of sensations as grounding
elements for our reasoning processes was already pointed out by Kant, who
concluded that thoughts without any association to sensible intuitions are
empty, that is, lacking a semantic basis. Indeed, if artificial reasoning and
thinking were possible, then from a wider perspective they would be seen as
irrational and in the end thoughtless, because they would not be adequately
grounded in the phenomenal states constitutive of our biologically-rooted and
socially-moulded nature, the only things able to make full sense of them. It
seems, consequently, that in order to reason or think in the full sense of the
word, a mind would need to possess appropriate phenomenal states that could
give content to its reasoning and thinking. However, as already explained, a
true phenomenal state for consciousness and thinking must necessarily be a
biological, neurophysiological state.
The result of these considerations seems to
be that even if the multiple realisability objection were applicable to
cognitive processes, forcing us to accept only a token-token identity on
that level, this would not necessarily lead us to the fanciful conclusion that
some minds could be very different from our own, perhaps transcending the
biological realm. It is true that a token-token identity is the identity of
something with something else, which can be simply anything,
insofar as the kind of identity always remains open. However, the reason to
reject the conclusion that at the cognitive level the multiple realisability hypothesis
trounces all its rivals is that the cognitive states of conscious minds would
always have to be grounded in phenomenal states. Since in this way cognitive
states would depend on something identifiable with definite functional
neurophysiological states by means of a type-type identity theory, this would
allow us to restrict the objection of multiple realisability for cognitive
states in a satisfactory way, limiting them to biological brains.
With this conclusion, we reach the point
where we can make a speculative wager about the right form of an identity
theory of mind. It would be a double-edged solution that could be motivated by
and against the medieval doctrine that only the intellective soul – but
not the sensitive soul – could survive the destruction of the body. Mind
has indeed both a cognitive and a phenomenal dimension. The phenomenal
dimension, as we have seen, is connected to the brain by type-type identities,
because of the concrete singularity of its proper neurofunctional states. However,
because of its abstract nature the cognitive dimension is structurally linked
to the physical realm only by a token-token identity. Nevertheless, contrary to
the medieval doctrine, the cognitive mind continues to depend on the living
brain. And the reason for this is that the cognitive mind is rooted in the
phenomenal dimension of the mind. This in turn is inextricably dependent upon
our biological brain and life form. In short: the phenomenal mind is the glue
that cements the cognitive mind in the brain.
III
After the multiple realisability objection, the second
main objection to type-type identity theory consists in the claim that this theory
is unable to reduce phenomenal qualities in the sense of identifying
them with neurophysiological properties. The sentence ‘I have a visual
experience of red’ seems to say something different from ‘Such and such
brain-cells and centres are being activated in such and such ways’. This is
made clear by the fact that a blind person could know everything about how
these brain cells work to produce the experience of the colour red, without
knowing, as we do, what the colour red looks like, since she has
no access to the qualia of red.
Since we have answered the first main objection, it
makes sense to finish this paper with a tentative answer to the second. In my
view, the second objection arises from a confusion as old as that between sense
and reference. The sentence
(1)
Having
the visual experience of the colour red is the same as having
such and such neurofunctional phenomena.
is in some sense analogous to
(2)
The
roundness of this tennis ball that I experience by seeing it is the same
as the roundness of this tennis ball that I experience by touching it.
The roundness of the tennis ball is the object of knowledge,
which remains one and the same, although differently experienced. However, we
have here two different senses, or, as I prefer to call them, two different perspectives
of access: the visual and the tactile experiences of roundness.
Obviously, we could also take these perspectives of access as objects of
our knowledge. Since these two perspectives are different, there is no question
about their numerical identity. The sentence
(3)
The
visual experience that I have when I speak of the roundness of a tennis ball is
the same as the tactile experience that I have when I speak of
the roundness of the tennis ball.
is obviously false, since here the objects of knowledge are the
different perspectives of access.
Now, my
suggestion is that the objection that phenomenal qualities cannot be reduced to
neurophysiological properties arises from our perception that, even if the
object is the same, there is an irreducible remainder in the fact
that the associated perspectives of access remain different.
My answer to the objection is that it is misleading,
for the perspectives of access are also reducible, so that there is no need for
a non-identical remainder. To show this, all we need to do is to choose a
perspective of access as our object of knowledge and consider attentively what
occurs in experiencing something. In this case, we can show, for example, that
the chosen psychological perspective of access is identical with a further
physical-physiological object of description that has its own proper public
perspective of access. For example:
(4)
The
visual experience that I have of a tennis ball is the same as a
computing process integrating spatial extension, perspective, form and colour
in certain centres of my brain.
Unlike (3), (4) is a true sentence. If the subjective psychological
perspective of access can also be described as a new public physical-neurophysiological
phenomenon, we see that this perspective, taken as an object of knowledge,
could also be reduced with no remainder. We can, I am convinced, also detect
different perspectives of access to a given perspective of access taken as an
object… But it is plausible that we could give the same answer regarding any higher
order perspective of access. The conclusion of this argument is that when we make
ourselves aware that any supposed psychological remainder responsible for what
an experience is like can always be equated with some public physical-physiological
state of affairs, the objection breaks down that phenomenal qualities are
non-reducible.
[1] See William Bechtel & Jennifer Mundale, ‘Multiple
Realizability Revisited: Linking Cognitive and Neural States’, Philosophy of
Science 66 (1999), 175-207. See also chapter 1 of T. W. Polger’s book, Natural
Minds (Cambridge: MIT Press, 2004). The basic tenet of these arguments is
the idea that neurophysiological types must be more coarse grained (that
is, more abstractly understood). By adding the suggestion that
neurophysiological types must also be seen as essentially neurofunctionally
defined, as I do in this paper, I hope to show something about how they
must be more abstractly defined and to what extent.
[2] Philosophers have conceived of bizarre circumstances that seem to
contradict this definition. One can imagine, for example, a possible world
where people are extremely overweight and sedentary, so that chairs must
resemble benches on which two or three persons of our world could sit
side-by-side… One can also imagine a situation in which benches function like
chairs, because no more than one person is permitted to sit on them at one
time… See Paul Elbourne: Meaning: A Slim
Guide to Semantics (Oxford: Oxford University Press, 2012), chap. 1. Nonetheless, in the world where people
are extremely overweight, the chairs are not benches, because they are still
designed to be chairs, that is, to be used by only one person at a time, and in
the second situation, the benches are still designed as benches, even if their
use is limited to just one person at a time. As can be expected, there are
borderline cases, like that of a trunk that happens to have the form of a
chair, and because of this, with some minor changes, is used as a chair and is
also called a chair. And there are extended (non-proper) senses, like the chair
of rock in Victor Hugo’s Les Travailleurs
de la mer, not to mention metaphorical senses. Still, I don’t see why we should conclude that concepts are generally
indefinable merely because there are borderline cases. What is important is
that definitions usually work.
[3] The idea of a neurofunctional
state does not commit us to functionalism, at least insofar as functionalism
tends to confuse our forms of epistemic access to a mental state with the
mental state as such.
[4] Hilary Putnam, ‘The Nature of Mental States’, in Mind,
Language and Reality: Philosophical Papers (Cambridge: Cambridge University
Press, 1975), Vol. 2, p. 436 (my italics).
[5] For a converging approach, see P. M. S. Hacker’s
interpretation of Wittgenstein in his book, Wittgenstein: Meaning and Mind,
part I: Essays (Oxford: Blackwell, 2001), chap. IV.
Nenhum comentário:
Postar um comentário