第六讲 功能主义 LECTURE SIX FUNCTIONALISM. WHAT IS FUNCTIONALISM? Functionalism in the philosophy of mind is the doctrine that what makes something a mental.

第六讲 功能主义

LECTURE SIX FUNCTIONALISM

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, logician, 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 [5-tuples] : 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 5-tuple 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

State table for 3 state, 2 symbol busy beaver

Tape symb

ol

Current state A Current state B Current state C

Write symbol

Move tape

Next state

Write symbol

Move tape

Next state

Write symbol

Move tape

Next state

0 1 R B 1 L A 1 L B

1 1 L C 1 R B 1 RHALT

[edit]Additional details required to visualize or implement Turing machines

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 Realizer-functionalism

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 higher-level 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 higher-level “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 )

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FURTHER READING

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