Download LECTURE SIX FUNCTIONALISM

LECTURE SIX
FUNCTIONALISM
第六讲 功能主义
WHAT IS FUNCTIONALISM?
 Functionalism in the philosophy of mind is the doctrine
that what makes something a mental state of a particular
type does not depend on its internal constitution, but
rather on the way it functions, or the role it plays, in the
system of which it is a part。
 Functionalism is a theoretical level between the physical
implementation and behavioural output.[2] Therefore, it
is different from its predecessors of
Cartesian dualism (advocating independent mental and
physical substances) and
Skinnerian behaviourism 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’
MACHINE-STATE FUNCTIONALISM

Hilary Whitehall Putnam (born
July 31, 1926) is an American
philosopher,mathematician and
computer scientist, who has been a
central figure in analytic
philosophy since the 1960s, especially
in philosophy of mind, philosophy of
language, philosophy of mathematics,
and philosophy of science.[2] He is
known for his willingness to apply an
equal degree of scrutiny to his own
philosophical positions as to those of
others, subjecting each position to
rigorous analysis until he exposes its
flaws.[3] As a result, he has acquired a
reputation for frequently changing his
own position.[4] Putnam is currently
Cogan University Professor Emeritus
at Harvard University.
THE VERY IDEA OF MACHINE-STATE
FUNCTIONALISM
 The early functionalist theories of Putnam (1960, 1967) can be seen as a
response to the difficulties facing behaviorism as a scientific psychological
theory, and as an endorsement of the (new) computational theories of mind
which were becoming increasingly significant rivals to it. According to
Putnam's machine state functionalism, any creature with a mind can be
regarded as a Turing machine (an idealized finite state digital computer),
whose operation can be fully specified by a set of instructions (a “machine table”
or program) each having the form:
 If the machine is in state Si, and receives input Ij, it will go into state Sk and
produce output Ol (for a finite number of states, inputs and outputs).
 A machine table of this sort describes the operation of
a deterministic automaton, but most machine state functionalists (e.g. Putnam
1967) take the proper model for the mind to be that of
a probabilistic automaton: one in which the program specifies, for each state
and set of inputs, the probability with which the machine will enter some
subsequent state and produce some particular output.
THE VERY IDEA OF TURING MACHINE
 Alan Mathison
Turing, OBE, FRS ( /ˈtjʊərɪŋ
/ TEWR-ing; 23 June 1912 – 7
June 1954), was an
English mathematician, logici
an, cryptanalyst,
and computer scientist. He
was highly influential in the
development of computer
science, providing a
formalisation of the concepts
of "algorithm" and
"computation" with
the Turing machine, which
played a significant role in the
creation of the modern
computer.
THE VERY IDEA OF TURING MACHINE
 A Turing machine is a device that manipulates symbols on a strip of tape
according to a table of rules. Despite its simplicity, a Turing machine can be adapted
to simulate the logic of any computer algorithm, and is particularly useful in
explaining the functions of a CPU inside a computer.
 The "Turing" machine was described by Alan Turing in 1936,[1] who called it an
"a(utomatic)-machine". The Turing machine is not intended as a practical
computing technology, but rather as a hypothetical device representing a computing
machine. Turing machines help computer scientists understand the limits of
mechanical computation.
 Turing gave a succinct definition of the experiment in his 1948 essay, "Intelligent
Machinery". Referring to his 1936 publication, Turing wrote that the Turing
machine, here called a Logical Computing Machine, consisted of:
 ...an infinite memory capacity obtained in the form of an infinite tape marked out
into squares, on each of which a symbol could be printed. At any moment there is
one symbol in the machine; it is called the scanned symbol. The machine can alter
the scanned symbol and its behavior is in part determined by that symbol, but the
symbols on the tape elsewhere do not affect the behaviour of the machine. However,
the tape can be moved back and forth through the machine, this being one of the
elementary operations of the machine. Any symbol on the tape may therefore
eventually have an innings.[2] (Turing 1948, p. 61)
More precisely, a Turing machine consists of:





A tape which is divided into cells, one next to the other. Each cell contains a symbol from some finite alphabet. The
alphabet contains a special blank symbol (here written as 'B') and one or more other symbols. The tape is assumed to be
arbitrarily extendable to the left and to the right, i.e., the Turing machine is always supplied with as much tape as it
needs for its computation. Cells that have not been written to before are assumed to be filled with the blank symbol. In
some models the tape has a left end marked with a special symbol; the tape extends or is indefinitely extensible to the
right.
A head that can read and write symbols on the tape and move the tape left and right one (and only one) cell at a time.
In some models the head moves and the tape is stationary.
A finite table (occasionally called an action table ortransition function) of instructions (usually quintuples [5tuples] : qiaj→qi1aj1dk, but sometimes 4-tuples) that, given thestate(qi) the machine is currently in and the symbol(aj) it
is reading on the tape (symbol currently under the head) tells the machine to do the following in sequence (for the 5tuple models):

Either erase or write a symbol (instead of aj, write aj1),and then

Move the head (which is described by dk and can have values: 'L' for one step left or 'R' for one step rightor 'N' for
staying in the same place), and then

Assume the same or a new state as prescribed (go to state qi1).
In the 4-tuple models, erase or write a symbol (aj1) and move the head left or right (dk) are specified as separate
instructions. Specifically, the table tells the machine to (ia) erase or write a symbol or (ib) move the head left or
right, and then (ii) assume the same or a new state as prescribed, but not both actions (ia) and (ib) in the same
instruction. In some models, if there is no entry in the table for the current combination of symbol and state then the
machine will halt; other models require all entries to be filled.
A state register that stores the state of the Turing machine, one of finitely many. There is one specialstart state with
which the state register is initialized. These states, writes Turing, replace the "state of mind" a person performing
computations would ordinarily be in.
THIS IS A MACHINE TABLE
[edit]Additional
details required to visualize or implement Turing machines
State table for 3 state, 2 symbol busy beaver
Current state A
Current state B
Current state C
Tape
symbo Write Move
symbo
l
tape
l
Next
state
Write
Move
symbo
tape
l
Next
state
Write
Move
symbo
tape
l
Next
state
0
1
R
B
1
L
A
1
L
B
1
1
L
C
1
R
B
1
R
HAL
T
Multiple realizability多重可实现性
 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).
Psycho-Functionalism
 A second strain of functionalism, psycho-functionalism,
derives primarily from reflection upon the goals and
methodology of “cognitive” psychological theories. In contrast
to the behaviorists‘ insistence that the laws of psychology
appeal only to behavioral dispositions, cognitive psychologists
argue that the best empirical theories of behavior take it to be
the result of a complex of mental states and processes,
introduced and individuated in terms of the roles they play in
producing the behavior to be explained. For example (Fodor’s,
in his 1968, Ch. 3), a psychologist may begin to construct a
theory of memory by postulating the existence of “memory
trace” decay(记忆痕迹之衰变), a process whose occurrence or
absence is responsible for effects such as memory loss and
retention, and which is affected by stress or emotion in certain
distinctive ways.
MOREOVER,
 On a theory of this sort, what makes some neural process an
instance of memory trace decay is a matter of how it
functions, or the role it plays, in a cognitive system; its
neural or chemical properties are relevant only insofar as
they enable that process to do what trace decay is
hypothesized to do. And similarly for all mental states and
processes invoked by cognitive psychological theories.
Cognitive psychology, that is, is intended by its proponents
to be a “higher-level” science like biology: just as, in
biology, physically disparate entities can all be hearts as
long as they function to circulate blood in a living
organism, and physically disparate entities can all be eyes
as long as they enable an organism to see, disparate
physical structures or processes can be instances of memory
trace decay — or more familiar phenomena such as thoughts,
sensations, and desires — as long as they play the roles
described by the relevant cognitive theory.
Analytic Functionalism
 Like the logical behaviorism from which it emerged, the goal of
analytic functionalism is to provide “topic-neutral” translations, or
analyses, of our ordinary mental state terms or concepts. Analytic
functionalism, of course, has richer resources than logical
behaviorism for such translations, since it permits reference to the
causal relations that a mental state has to stimulations,
behavior, and other mental states. Thus the statement “Blanca
wants some coffee” need not be rendered, as logical behaviorism
requires, in terms such as “Blanca is disposed to order coffee when
it is offered”, but rather as “Blanca is disposed to order coffee when
it is offered, if she has no stronger desire to avoid coffee”. But this
requires any functional “theory” acceptable to analytic functionalists
to include only generalizations about mental states, their
environmental causes, and their joint effects on behavior that are so
widely known and “platitudinous” as to count as analyzing our
ordinary concepts of the mental states in question.
FOR INSTANCE
 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 orconceptual 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.
Role-functionalism and Realizerfunctionalism
 There is yet another distinction between kinds of
functional theory — one that crosscuts the
distinctions described so far — that is important to
note. This is the distinction between what has come
to be known as “role” functionalism and “realizer”
functionalism.
The (avowedly simplistic)
example of a functional theory of pain
 Pain is the state that tends to be caused by bodily injury, to
produce the belief that something is wrong with the body and
the desire to be out of that state, to produce anxiety, and, in
the absence of any stronger, conflicting desires, to cause
wincing or moaning.
 As noted earlier, if in humans this functional role is played by
C-fiber stimulation, then, according to this functionalist
theory, humans can be in pain simply by undergoing C-fiber
stimulation. But there is a further question to be answered,
namely, what is the property of pain itself? Is it the higherlevel relational property of being in some state or other that
plays the “pain role”in the theory, or the C-fiber stimulation
that actually plays this role?
THE DIFFERENCE BETWEEN THEM
 Role functionalists identify pain with that higher-level
relational property. Realizer functionalists,however, take a
functional theory merely to provide definite descriptions of
whichever lower-level properties satisfy the functional
characterizations. On these views (also called “functional
specification” theories), if the property that occupies the
causal role of pain in human beings is C-fiber stimulation,
then pain (or at least pain-in-humans) would be C-fiber
stimulation, rather than the higher-level property of having
some lower-level state that plays the relevant role. (This is not
to suggest that there is a difference in kind between higherlevel “role” properties and the lower-level “realizations” of
those roles, since it may be that, relative to even lower-level
descriptions, those realizations can be characterized as
functional states themselves (Lycan 1987 )
FURTHER READING
HTTP://PLATO.STANFORD.EDU/ENTRIES/FUN
CTIONALISM/#MACSTAFUN
THE END