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Functionalism (philosophy of mind)
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Functionalism is a theory of the mind in contemporary philosophy, developed largely as an alternative to both the identity theory of mind and behaviourism. 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. 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.
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Functionalism is a theory of the mind in contemporary philosophy, developed largely as an alternative to both the identity theory of mind and behaviourism. 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. 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 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 (1980) and David Malet Armstrong (1968). 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 "Ouch!" 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 (1960, 1967) 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
Functionalism can be hashed out in many different varieties. The first formulation of a functionalist theory of mind was put forth by Hilary Putnam (1960, 1967). 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 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 is specified by the following machine table:
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 behaviourist 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 behavioural 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 behaviour 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. 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 a indefinite sub-critical tensor is caused by sitting on a tack (for example) and causes one to bemoan the collapse of the quantum wavefunction. 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 with each one carrying out the functional or causal role that would normally be ascribed to the mental states of an individual mind, for example, 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 M and the set of mental facts that occur at the lower-level M1. Given the transitivity of supervenience, if M supervenes on M1 and M1 supervenes on P (physical base), then M and M1 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 as 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 inorganic 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 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
The Chinese room
The Chinese room argument by John Searle (1980) 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.
In "Troubles with Functionalism" (1980b), Ned Block poses several problems for functionalism. The first of these is known as the "Chinese nation" (or China brain) thought experiment. The 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.
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 (1980b). 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 red, 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 cannot sufficiently account for all mental states.
Chalmers (1996) tries to show 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 (1975b), 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 seems hard to swallow. 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 (1972) 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).
See also
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