Functionalism (philosophy of mind)
From Wikipedia, the free encyclopedia
Functionalism is a theory of the mind in contemporary
philosophy, developed largely as an alternative to both the
identity theory of mind and
behaviorism.
Its core idea is that mental states (beliefs, desires, being in pain,
etc.) are constituted solely by their functional role – that is, they
are causal relations to other mental states, sensory inputs, and
behavioral outputs.
[1] Functionalism is a theoretical level between the physical implementation and behavioral output.
[2] Therefore, it is different from its predecessors of
Cartesian dualism (advocating independent mental and physical substances) and Skinnerian
behaviorism and
physicalism
(declaring only physical substances) because it is only concerned with
the effective functions of the brain, through its organization or its
"software programs".
Since mental states are identified by a functional role, they are
said to be realized on multiple levels; in other words, they are able to
be manifested in various systems, even perhaps computers, so long as
the system performs the appropriate functions. While computers are
physical devices with electronic substrate that perform computations on
inputs to give outputs, so brains are physical devices with neural
substrate that perform computations on inputs which produce behaviors.
While functionalism has its advantages, there have been several
arguments against it, claiming that it is an insufficient account of the
mind.
Multiple realizability
An important part of some accounts of functionalism is the idea of
multiple realizability.
Since, according to standard functionalist theories, mental states are
the corresponding functional role, mental states can be sufficiently
explained without taking into account the underlying physical medium
(e.g. the brain, neurons, etc.) that realizes such states; one need only
take into account the higher-level functions in the cognitive system.
Since mental states are not limited to a particular medium, they can be
realized in multiple ways, including, theoretically, within
non-biological systems, such as computers. In other words, a
silicon-based machine could, in principle, have the same sort of mental
life that a human being has, provided that its cognitive system realized
the proper functional roles. Thus, mental states are individuated much
like a valve; a valve can be made of plastic or metal or whatever
material, as long as it performs the proper function (say, controlling
the flow of liquid through a tube by blocking and unblocking its
pathway).
However, there have been some functionalist theories that combine
with the identity theory of mind, which deny multiple realizability.
Such
Functional Specification Theories (FSTs) (Levin, § 3.4), as they are called, were most notably developed by
David Lewis[3] and
David Malet Armstrong.
[4]
According to FSTs, mental states are the particular "realizers" of the
functional role, not the functional role itself. The mental state of
belief, for example, just is whatever brain or neurological process that
realizes the appropriate belief function. Thus, unlike standard
versions of functionalism (often called
Functional State Identity Theories),
FSTs do not allow for the multiple realizability of mental states,
because the fact that mental states are realized by brain states is
essential. What often drives this view is the belief that if we were to
encounter an alien race with a cognitive system composed of
significantly different material from humans' (e.g., silicon-based) but
performed the same functions as human mental states (e.g., they tend to
yell "Yowzas!" when poked with sharp objects, etc.) then we would say
that their type of mental state is perhaps similar to ours, but too
different to say it's the same. For some, this may be a disadvantage to
FSTs. Indeed, one of
Hilary Putnam's
[5][6]
arguments for his version of functionalism relied on the intuition that
such alien creatures would have the same mental states as humans do,
and that the multiple realizability of standard functionalism makes it a
better theory of mind.
Types of functionalism
Machine-state functionalism
The broad position of "functionalism" can be articulated in many
different varieties. The first formulation of a functionalist theory of
mind was put forth by
Hilary Putnam.
[5][6] This formulation, which is now called
machine-state functionalism, or just
machine functionalism, was inspired by the analogies which Putnam and others noted between the
mind and the theoretical "machines" or computers capable of computing any given
algorithm which were developed by
Alan Turing (called
Universal Turing machines).
In non-technical terms, a Turing machine can be visualized as an
indefinitely and infinitely long tape divided into rectangles (the
memory) with a box-shaped scanning device that sits over and scans one
component of the memory at a time. Each unit is either blank (
B) or has a
1 written on it. These are the inputs to the machine. The possible outputs are:
- Halt: Do nothing.
- R: move one square to the right.
- L: move one square to the left.
- B: erase whatever is on the square.
- 1: erase whatever is on the square and print a '1.
An extremely simple example of a Turing machine which writes out the
sequence '111' after scanning three blank squares and then stops as
specified by the following machine table:
|
State One |
State Two |
State Three |
| B |
write 1; stay in state 1 |
write 1; stay in state 2 |
write 1; stay in state 3 |
| 1 |
go right; go to state 2 |
go right; go to state 3 |
[halt] |
This table states that if the machine is in state one and scans a blank square (
B), it will print a
1 and remain in state one. If it is in state one and reads a
1, it will move one square to the right and also go into state two. If it is in state two and reads a
B, it will print a
1 and stay in state two. If it is in state two and reads a
1, it will move one square to the right and go into state three. If it is in state three and reads a
B, it prints a
1 and remains in state three. Finally, if it is in state three and reads a
1, then it will stay in state three.
The essential point to consider here is the
nature of the states
of the Turing machine. Each state can be defined exclusively in terms
of its relations to the other states as well as inputs and outputs.
State one, for example, is simply the state in which the machine, if it
reads a
B, writes a
1 and stays in that state, and in which, if it reads a
1,
it moves one square to the right and goes into a different state. This
is the functional definition of state one; it is its causal role in the
overall system. The details of how it accomplishes what it accomplishes
and of its material constitution are completely irrelevant.
According to machine-state functionalism, the nature of a mental
state is just like the nature of the automaton states described above.
Just as
state one simply is the state in which, given an input
B,
such and such happens, so being in pain is the state which disposes one
to cry "ouch", become distracted, wonder what the cause is, and so
forth.
Psychofunctionalism
A second form of functionalism is based on the rejection of
behaviorist
theories in psychology and their replacement with empirical cognitive
models of the mind. This view is most closely associated with
Jerry Fodor and
Zenon Pylyshyn and has been labeled
psychofunctionalism.
The fundamental idea of psychofunctionalism is that psychology is an
irreducibly complex science and that the terms that we use to describe
the entities and properties of the mind in our best psychological
theories cannot be redefined in terms of simple behavioral dispositions,
and further, that such a redefinition would not be desirable or salient
were it achievable. Psychofunctionalists view psychology as employing
the same sorts of irreducibly
teleological
or purposive explanations as the biological sciences. Thus, for
example, the function or role of the heart is to pump blood, that of the
kidney is to filter it and to maintain certain chemical balances and so
on—this is what accounts for the purposes of scientific explanation and
taxonomy. There may be an infinite variety of physical realizations for
all of the mechanisms, but what is important is only their role in the
overall biological theory. In an analogous manner, the role of mental
states, such as belief and desire, is determined by the functional or
causal role that is designated for them within our best
scientific psychological theory. If some mental state which is postulated by
folk psychology
(e.g. hysteria) is determined not to have any fundamental role in
cognitive psychological explanation, then that particular state may be
considered not to exist . On the other hand, if it turns out that there
are states which theoretical cognitive psychology posits as necessary
for explanation of human behavior but which are not foreseen by ordinary
folk psychological language, then these entities or states exist.
Analytic functionalism
A third form of functionalism is concerned with the meanings of
theoretical terms in general. This view is most closely associated with
David Lewis and is often referred to as
analytic functionalism or
conceptual functionalism.
The basic idea of analytic functionalism is that theoretical terms are
implicitly defined by the theories in whose formulation they occur and
not by intrinsic properties of the phonemes they comprise. In the case
of ordinary language terms, such as "belief", "desire", or "hunger", the
idea is that such terms get their meanings from our common-sense "folk
psychological" theories about them, but that such conceptualizations are
not sufficient to withstand the rigor imposed by materialistic theories
of reality and causality. Such terms are subject to conceptual analyses
which take something like the following form:
- Mental state M is the state that is preconceived by P and causes Q.
For example, the state of
pain is
caused by sitting on a tack and
causes
loud cries, and higher order mental states of anger and resentment
directed at the careless person who left a tack lying around. These
sorts of functional definitions in terms of causal roles are claimed to
be
analytic and
a priori
truths about the submental states and the (largely fictitious)
propositional attitudes they describe.
Hence, its proponents are known
as
analytic or
conceptual functionalists. The essential
difference between analytic and psychofunctionalism is that the latter
emphasizes the importance of laboratory observation and experimentation
in the determination of which mental state terms and concepts are
genuine and which functional identifications may be considered to be
genuinely
contingent and
a posteriori identities. The former, on the other hand, claims that such identities are
necessary and not subject to empirical scientific investigation.
Homuncular functionalism
Homuncular functionalism was developed largely by
Daniel Dennett and has been advocated by
William Lycan. It arose in response to the challenges that
Ned Block's
China Brain (a.k.a. Chinese nation) and
John Searle's
Chinese room
thought experiments presented for the more traditional forms of
functionalism (see below under "Criticism"). In attempting to overcome
the conceptual difficulties that arose from the idea of a nation full of
Chinese people wired together, each person working as a single neuron
to produce in the wired-together whole the functional mental states of
an individual mind, many functionalists simply bit the bullet, so to
speak, and argued that such a Chinese nation would indeed possess all of
the qualitative and intentional properties of a mind; i.e. it would
become a sort of systemic or collective mind with propositional
attitudes and other mental characteristics.
Whatever the worth of this
latter hypothesis, it was immediately objected that it
entailed an unacceptable sort of mind-mind supervenience: the
systemic
mind which somehow emerged at the higher-level must necessarily
supervene on the individual minds of each individual member of the
Chinese nation, to stick to Block's formulation. But this would seem to
put into serious doubt, if not directly contradict, the fundamental idea
of the supervenience thesis: there can be no change in the mental realm
without some change in the underlying physical substratum. This can be
easily seen if we label the set of
mental facts that occur at the higher-level
M1 and the set of mental facts that occur at the lower-level
M2. Given the transitivity of supervenience, if
M1 supervenes on
M2, and
M2 supervenes on
P (physical base), then
M1 and
M2 both supervene on
P, even though they are (allegedly) totally different sets of mental facts.
Since mind-mind supervenience seemed to have become acceptable in
functionalist circles, it seemed to some that the only way to resolve
the puzzle was to postulate the existence of an entire hierarchical
series of mind levels (analogous to
homunculi)
which became less and less sophisticated in terms of functional
organization and physical composition all the way down to the level of
the physico-mechanical neuron or group of neurons. The homunculi at each
level, on this view, have authentic mental properties but become
simpler and less intelligent as one works one's way down the hierarchy.
Functionalism and physicalism
There is much confusion about the sort of relationship that is
claimed to exist (or not exist) between the general thesis of
functionalism and
physicalism. It has often been claimed that functionalism somehow "disproves" or falsifies physicalism
tout court
(i.e. without further explanation or description). On the other hand,
most philosophers of mind who are functionalists claim to be
physicalists—indeed, some of them, such as David Lewis, have claimed to
be strict reductionist-type physicalists.
Functionalism is fundamentally what Ned Block has called a broadly metaphysical thesis as opposed to a narrowly
ontological one. That is, functionalism is not so much concerned with
what there is
than with what it is that characterizes a certain type of mental state,
e.g. pain, as the type of state that it is. Previous attempts to answer
the mind-body problem have all tried to resolve it by answering
both
questions: dualism says there are two substances and that mental states
are characterized by their immateriality; behaviorism claimed that
there was one substance and that mental states were behavioral
disposition; physicalism asserted the existence of just one substance
and characterized the mental states as physical states (as in "pain =
C-fiber firings").
On this understanding,
type physicalism can be seen as
incompatible with functionalism, since it claims that what characterizes
mental states (e.g. pain) is that they are physical in nature, while
functionalism says that what characterizes pain is its functional/causal
role and its relationship with yelling "ouch", etc. However, any weaker
sort of physicalism which makes the simple ontological claim that
everything that exists is made up of physical matter is perfectly
compatible with functionalism. Moreover, most functionalists who are
physicalists require that the properties that are quantified over in
functional definitions be physical properties. Hence, they
are physicalists, even though the general thesis of functionalism itself does not commit them to being so.
In the case of David Lewis, there is a distinction in the concepts of "having pain" (a
rigid designator
true of the same things in all possible worlds) and just "pain" (a
non-rigid designator). Pain, for Lewis, stands for something like the
definite description "the state with the causal role x". The referent of
the description in humans is a type of brain state to be determined by
science. The referent among silicon-based life forms is something else.
The referent of the description among angels is some immaterial,
non-physical state. For Lewis, therefore,
local type-physical reductions are possible and compatible with conceptual functionalism. (See also Lewis's
Mad pain and Martian pain.) There seems to be some confusion between types and tokens that needs to be cleared up in the functionalist analysis.
Criticism
China brain
Ned Block
[7] argues against the functionalist proposal of
multiple realizability,
where hardware implementation is irrelevant because only the functional
level is important. The "China brain" or "Chinese nation" thought
experiment involves supposing that the entire nation of China
systematically organizes itself to operate just like a brain, with each
individual acting as a neuron (forming what has come to be called a
"Blockhead"). According to functionalism, so long as the people are
performing the proper functional roles, with the proper causal relations
between inputs and outputs, the system will be a real mind, with mental
states, consciousness, and so on. However, Block argues, this is
patently absurd, so there must be something wrong with the thesis of
functionalism since it would allow this to be a legitimate description
of a mind.
Some functionalists believe China would have qualia but that due to the size it is impossible to imagine China being conscious.
[8] Indeed, it may be the case that we are constrained by our
theory of mind[9]
and will never be able to understand what Chinese-nation consciousness
is like. Therefore, if functionalism is true either qualia will exist
across all hardware or will not exist at all but are illusory.
[10]
The Chinese room
The
Chinese room argument by
John Searle[11]
is a direct attack on the claim that thought can be represented as a
set of functions. The thought experiment asserts that it is possible to
mimic intelligent action without any interpretation or understanding
through the use of a purely functional system. In short, Searle
describes a person who only speaks English who is in a room with only
Chinese symbols in baskets and a rule book in English for moving the
symbols around. The person is then ordered by people outside of the room
to follow the rule book for sending certain symbols out of the room
when given certain symbols. Further suppose that the people outside of
the room are Chinese speakers and are communicating with the person
inside via the Chinese symbols. According to Searle, it would be absurd
to claim that the English speaker inside knows Chinese simply based on
these syntactic processes. This thought experiment attempts to show that
systems which operate merely on syntactic processes (inputs and
outputs, based on algorithms) cannot realize any semantics (meaning) or
intentionality (aboutness). Thus, Searle attacks the idea that thought
can be equated with following a set of syntactic rules; that is,
functionalism is an insufficient theory of the mind.
As noted above, in connection with Block's Chinese nation, many functionalists responded to Searle's
thought experiment
by suggesting that there was a form of mental activity going on at a
higher level than the man in the Chinese room could comprehend (the
so-called "system reply"); that is, the system does know Chinese. Of
course, Searle responds that there is nothing more than syntax going on
at the higher-level as well, so this reply is subject to the same
initial problems. Furthermore, Searle suggests the man in the room could
simply memorize the rules and symbol relations. Again, though he would
convincingly mimic communication, he would be aware only of the symbols
and rules, not of the meaning behind them.
Inverted spectrum
Another main criticism of functionalism is the
inverted spectrum or inverted
qualia scenario, most specifically proposed as an objection to functionalism by Ned Block.
[7][12]
This thought experiment involves supposing that there is a person, call
her Jane, that is born with a condition which makes her see the
opposite spectrum of light that is normally perceived. Unlike "normal"
people, Jane sees the color violet as yellow, orange as blue, and so
forth. So, suppose, for example, that you and Jane are looking at the
same orange. While you perceive the fruit as colored orange, Jane sees
it as colored blue. However, when asked what color the piece of fruit
is, both you and Jane will report "orange". In fact, one can see that
all of your behavioral as well as functional relations to colors will be
the same. Jane will, for example, properly obey traffic signs just as
any other person would, even though this involves the color perception.
Therefore, the argument goes, since there can be two people who are
functionally identical, yet have different mental states (differing in
their qualitative or phenomenological aspects), functionalism is not
robust enough to explain individual differences in qualia.
[13]
David Chalmers tries to show
[14] that even though mental content cannot be fully accounted for in functional terms, there is nevertheless a
nomological correlation
between mental states and functional states in this world. A
silicon-based robot, for example, whose functional profile matched our
own, would
have to be fully conscious. His argument for this claim takes the form of a
reductio ad absurdum.
The general idea is that since it would be very unlikely for a
conscious human being to experience a change in its qualia which it
utterly fails to notice, mental content and functional profile appear to
be inextricably bound together, at least in the human case. If the
subject's qualia were to change, we would expect the subject to notice,
and therefore his functional profile to follow suit. A similar argument
is applied to the notion of
absent qualia.
In this case, Chalmers argues that it would be very unlikely for a
subject to experience a fading of his qualia which he fails to notice
and respond to. This, coupled with the independent assertion that a
conscious being's functional profile just could be maintained,
irrespective of its experiential state, leads to the conclusion that the
subject of these experiments would remain fully conscious. The problem
with this argument, however, as Brian G. Crabb (2005) has observed, is
that it begs the central question: How could Chalmers
know that
functional profile can be preserved, for example while the conscious
subject's brain is being supplanted with a silicon substitute, unless he
already assumes that the subject's possibly changing qualia would not
be a determining factor? And while changing or fading qualia in a
conscious subject might force changes in its functional profile, this
tells us nothing about the case of a permanently inverted or unconscious
robot. A subject with inverted qualia from birth would have nothing to
notice or adjust to. Similarly, an unconscious functional simulacrum of
ourselves (a zombie) would have no experiential changes to notice or
adjust to. Consequently, Crabb argues, Chalmers' "fading qualia" and
"dancing qualia" arguments fail to establish that cases of permanently
inverted or absent qualia are nomologically impossible.
A related critique of the inverted spectrum argument is that it
assumes that mental states (differing in their qualitative or
phenomenological aspects) can be independent of the functional relations
in the brain. Thus, it
begs the question
of functional mental states: its assumption denies the possibility of
functionalism itself, without offering any independent justification for
doing so. (Functionalism says that mental states are produced by the
functional relations in the brain.) This same type of problem—that there
is no argument, just an antithetical assumption at their base—can also
be said of both the Chinese room and the Chinese nation arguments.
Notice, however, that Crabb's response to Chalmers does not commit this
fallacy: His point is the more restricted observation that
even if
inverted or absent qualia turn out to be nomologically impossible, and
it is perfectly possible that we might subsequently discover this fact
by other means, Chalmers' argument fails to demonstrate that they are
impossible.
Twin Earth
The
Twin Earth thought experiment, introduced by Hilary Putnam,
[15]
is responsible for one of the main arguments used against
functionalism, although it was originally intended as an argument
against
semantic internalism.
The thought experiment is simple and runs as follows. Imagine a Twin
Earth which is identical to Earth in every way but one: water does not
have the chemical structure H₂O, but rather some other structure, say
XYZ. It is critical, however, to note that XYZ on Twin Earth is still
called "water" and exhibits all the same macro-level properties that H₂O
exhibits on Earth (i.e., XYZ is also a clear drinkable liquid that is
in lakes, rivers, and so on). Since these worlds are identical in every
way except in the underlying chemical structure of water, you and your
Twin Earth
doppelgänger
see exactly the same things, meet exactly the same people, have exactly
the same jobs, behave exactly the same way, and so on. In other words,
since you share the same inputs, outputs, and relations between other
mental states, you are functional duplicates. So, for example, you both
believe that water is wet. However, the content of your mental state of
believing that water is wet differs from your duplicate's because your
belief is of H₂O, while your duplicate's is of XYZ.
Therefore, so the
argument goes, since two people can be functionally identical, yet have
different mental states, functionalism cannot sufficiently account for
all mental states.
Most defenders of functionalism initially responded to this argument
by attempting to maintain a sharp distinction between internal and
external content. The internal contents of propositional attitudes, for
example, would consist exclusively in those aspects of them which have
no relation with the external world
and which bear the necessary
functional/causal properties that allow for relations with other
internal mental states. Since no one has yet been able to formulate a
clear basis or justification for the existence of such a distinction in
mental contents, however, this idea has generally been abandoned in
favor of externalist
causal theories of mental contents (also known as
informational semantics). Such a position is represented, for example, by
Jerry Fodor's
account of an "asymmetric causal theory" of mental content. This view
simply entails the modification of functionalism to include within its
scope a very broad interpretation of input and outputs to include the
objects that are the causes of mental representations in the external
world.
The twin earth argument hinges on the assumption that experience with
an imitation water would cause a different mental state than experience
with natural water. However, since no one would notice the difference
between the two waters, this assumption is likely false. Further, this
basic assumption is directly antithetical to functionalism; and,
thereby, the twin earth argument does not constitute a genuine argument:
as this assumption entails a flat denial of functionalism itself (which
would say that the two waters would not produce different mental
states, because the functional relationships would remain unchanged).
Meaning holism
Another common criticism of functionalism is that it implies a radical form of
semantic holism. Block and Fodor
[12] referred to this as the
damn/darn problem.
The difference between saying "damn" or "darn" when one smashes one's
finger with a hammer can be mentally significant. But since these
outputs are, according to functionalism, related to many (if not all)
internal mental states, two people who experience the same pain and
react with different outputs must share little (perhaps nothing) in
common in any of their mental states. But this is counter-intuitive; it
seems clear that two people share something significant in their mental
states of being in pain if they both smash their finger with a hammer,
whether or not they utter the same word when they cry out in pain.
Another possible solution to this problem is to adopt a moderate (or
molecularist) form of holism. But even if this succeeds in the case of
pain, in the case of beliefs and meaning, it faces the difficulty of
formulating a distinction between relevant and non-relevant contents
(which can be difficult to do without invoking an analytic-synthetic
distinction, as many seek to avoid).
Triviality arguments
Hilary Putnam,
[16] John Searle,
[17] and others
[18][19]
have offered arguments that functionalism is trivial, i.e. that the
internal structures functionalism tries to discuss turn out to be
present everywhere, so that either functionalism turns out to reduce to
behaviorism, or to complete triviality and therefore a form of
panpsychism.
These arguments typically use the assumption that physics leads to a
progression of unique states, and that functionalist realization is
present whenever there is a mapping from the proposed set of mental
states to physical states of the system. Given that the states of a
physical system are always at least slightly unique, such a mapping will
always exist, so any system is a mind. Formulations of functionalism
which stipulate absolute requirements on interaction with external
objects (external to the functional account, meaning not defined
functionally) are reduced to behaviorism instead of absolute triviality,
because the input-output behavior is still required.
Peter Godfrey-Smith has argued further
[20]
that such formulations can still be reduced to triviality if they
accept a somewhat innocent-seeming additional assumption. The assumption
is that adding a
transducer layer, that is, an input-output
system, to an object should not change whether that object has mental
states. The transducer layer is restricted to producing behavior
according to a simple mapping, such as a lookup table, from inputs to
actions on the system, and from the state of the system to outputs.
However, since the system will be in unique states at each moment and at
each possible input, such a mapping will always exist so there will be a
transducer layer which will produce whatever physical behavior is
desired.
Godfrey-Smith believes that these problems can be addressed using
causality,
but that it may be necessary to posit a continuum between objects being
minds and not being minds rather than an absolute distinction.
Furthermore, constraining the mappings seems to require either
consideration of the external behavior as in behaviorism, or discussion
of the internal structure of the realization as in identity theory; and
though multiple realizability does not seem to be lost, the
functionalist claim of the autonomy of high-level functional description
becomes questionable.
[20]
