## 1. What is Functionalism?



Functionalism is the doctrine that what makes something a thought,
desire, pain (or any other type of mental state) depends not on its
internal constitution, but solely on its function, or the role it
plays, in the cognitive system of which it is a part. More precisely,
functionalist theories take the identity of a mental state to be
determined by its causal relations to sensory stimulations, other
mental states, and behavior.



For (an avowedly simplistic) example, a functionalist theory might
characterize *pain* as 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. According to this theory, all and only creatures with
internal states that can meet this condition, or play this role, are
capable of being in pain, and an individual is in pain at time
*t* if and only if they are in a state that is playing this
role at *t*.



Suppose that, in humans, there is some distinctive kind of neural
activity (C-fiber stimulation, for example) that plays this role. If
so, then according to this functionalist theory, humans can be in pain
simply by undergoing C-fiber stimulation. But the theory permits
creatures with very different physical constitutions to have mental
states as well: if there are silicon-based states of hypothetical
Martians or inorganic states of hypothetical androids that also meet
these conditions, then these creatures, too, can be in pain. As
functionalists often put it, pain can be *realized* by
different types of physical states in different kinds of creatures, or
*multiply realized*. (See entry on
 multiple realizability.)
 Indeed, since descriptions that make explicit reference only to a
state's causal relations with stimulations, behavior, and one
another are what have come to be known as "topic-neutral"
(Smart 1959) - that is, as imposing no logical restrictions on
the nature of the items that satisfy the descriptions - then
it's also logically possible for *non*-physical states to
play the relevant roles, and thus realize mental states, in some
systems as well. So functionalism is compatible with the sort of
dualism that takes mental states to cause, and be caused by, physical
states.



Still, though functionalism is officially neutral between materialism
and dualism, it has been particularly attractive to materialists,
since many materialists believe (or argue; see Lewis, 1966) that it is
overwhelmingly likely that any states capable of playing the roles in
question will be physical states. If so, then functionalism can stand
as a materialistic alternative to the Psycho-Physical Identity Thesis
(introduced in Place 1956, Feigl 1958, and Smart 1959, and defended
more recently in Hill 1991, and Polger 2011), which holds that each
type of mental state is identical with a particular type of
*neural* state. This thesis seems to entail that no creatures
with brains unlike ours can share our sensations, beliefs, and
desires, no matter how similar their behavior and internal
organization may be to our own, and thus functionalism, with its claim
that mental states can be multiply realized, has been regarded as
providing a more inclusive, less "(species-) chauvinistic"
(Block 1980b) - theory of the mind that is compatible with
materialism. (More recently, however, some philosophers have contended
that the identity thesis may be more inclusive than functionalists
assume; see Section 6 for further discussion.)



Within this broad characterization of functionalism, however, a number
of distinctions can be made. One of particular importance is the
distinction between theories in which the functional characterizations
of mental states purport to provide analyses of the meanings of our
mental state terms (or otherwise restrict themselves to a priori
information), and theories that permit functional characterizations of
mental states to appeal to information deriving from scientific
experimentation (or speculation). (See Shoemaker 1984c, and Rey 1997,
for further discussion and more fine-grained distinctions.) There are
other important differences among functionalist theories as well.
These (sometimes orthogonal) differences, and the motivations for
them, can best be appreciated by examining the origins of
functionalism and tracing its evolution in response both to explicit
criticisms of the thesis and changing views about the nature of
psychological explanation.


## 2. Antecedents of Functionalism



Although functionalism attained its greatest prominence as a theory of
mental states in the last third of the 20th century, it has
antecedents in both modern and ancient philosophy, as well as in early
theories of computation and artificial intelligence.


### 2.1 Early Antecedents



The earliest view in the Western canon that can be considered an
ancestor of functionalism is Aristotle's theory of the soul (350
BCE). In contrast to Plato's claim that the soul can exist apart
from the body, Aristotle argued (*De Anima* Bk. II, Ch. 1) that
the (human) soul is the *form* of a natural, organized human
body - the set of powers or capacities that enable it to express
its "essential whatness", which for Aristotle is a matter
of fulfilling the function or purpose that defines it as the kind of
thing it is. Just as the form of an axe is whatever enables it to cut,
and the form of an eye is whatever enables it to see, the (human) soul
is to be identified with whichever powers and capacities enable a
natural, organized human body to fulfill its defining function, which,
according to Aristotle, is to survive and flourish as a living,
acting, perceiving, and reasoning being. So, Aristotle argues, the
soul is inseparable from the body, and comprises whichever capacities
are required for a body to live, perceive, reason, and act. (See
Shields, 1990, and Nelson, 1990, for further debate about whether
Aristotle's view can be considered to be a version of
functionalism.)



A second, relatively early, ancestor of contemporary functionalism is
Hobbes's (1651) account of reasoning as a kind of computation
that proceeds by mechanistic principles comparable to the rules of
arithmetic. Reasoning, he argues, is "nothing but
*reckoning*, that is adding and subtracting, of the
consequences of general names agreed upon for the *marking* and
*signifying* of our thoughts." (*Leviathan*, Ch.
5) In addition, Hobbes suggests that reasoning - along with
imagining, sensing, and deliberating about action, all of which
proceed according to mechanistic principles - can be performed
by systems of various physical types. As he puts it in his
Introduction to *Leviathan*, where he likens a commonwealth to
an individual human, "why may we not say that all automata
(engines that move themselves by springs and wheels...) have an
artificial life? For what is the heart but a spring; and the nerves
but so many strings, and the joints but so many wheels...".
It was not until the middle of the 20th century, however, that it
became common to speculate that thinking may be nothing more than
rule-governed computation that can be carried out by creatures of
various physical types.


### 2.2 Thinking Machines and the "Turing Test"



In a seminal paper (Turing 1950), A.M. Turing proposed that the
question, "Can machines think?" can be replaced by the
question, "Is it theoretically possible for a finite state
digital computer, provided with a large but finite table of
instructions, or program, to provide responses to questions that would
fool an unknowing interrogator into thinking it is a human
being?" Now, in deference to its author, this question is most
often expressed as "Is it theoretically possible for a Turing
machine (appropriately programmed) to pass the Turing Test?"
(See the entry on the
 Turing Test.)



In arguing that this question is a legitimate replacement for the
original (and speculating that its answer is "yes"),
Turing identifies thoughts with states of a system defined solely by
their roles in producing further internal states and verbal outputs,
given certain verbal inputs - a view on which, like
Hobbes's and subsequent functionalist theories - many
physically different systems could have internal states that play
these roles. Indeed, Turing's work was explicitly invoked by
many theorists during the beginning stages of 20th century
functionalism, and was the avowed inspiration for a class of theories,
the "machine state" theories most firmly associated with
Hilary Putnam (1960, 1967) that had an important role in the early
development of the doctrine.


### 2.3 Behaviorism



Other important recent antecedents of functionalism are the
behaviorist theories that emerged in the early-to-mid twentieth
century. These include both the "logical" or
"analytical" behaviorism of philosophers such as Malcolm
(1968) and Ryle (1949) (and, arguably, Wittgenstein 1953) and the
empirical psychological theories associated primarily with Watson and
Skinner. 



Logical behaviorism is a thesis about the meanings of our mental state
terms or concepts - in particular, that all statements about
mental states and processes are equivalent in meaning to statements
about behavioral dispositions. So, for (again, an overly simplified)
example, "Henry has a toothache" would be equivalent in
meaning to a statement such as "Henry is disposed (all things
being equal) to cry out or moan and to rub his jaw". And
"Amelia is thirsty" would be equivalent to a statement
such as "If Amelia is offered some water, she will be disposed
(all things being equal) to drink it." These candidate
translations, like all behavioristic statements, eschew reference to
any internal states of the organism, and thus do not threaten to
denote, or otherwise induce commitment to, properties or processes
(directly) observable only by introspection. In addition, logical
behaviorists argued that if statements about mental states were
equivalent in meaning to statements about behavioral dispositions,
there could be an unproblematic account of how mental state terms
could be applied both to oneself and others, and how they could be
taught and learned. 



In contrast, scientific behaviorism is an empirical theory that
attempts to explain the behavior of humans (and other animals) by
appealing solely to behavioral dispositions, that is, to the lawlike
tendencies of organisms to behave in certain ways, given certain
environmental stimulations. Stimulations and behavior, unlike
thoughts, feelings, and other internal states that can be directly
observed only by introspection, are objectively observable, and are
indisputably part of the natural world. Thus behavioral dispositions
seemed to be fit entities to figure centrally in the emerging science
of psychology, allowing for a science of human behavior as objective
and explanatory as other "higher-level" sciences such as
chemistry and biology. Also, behaviorist theories promised to avoid a
potential regress that appeared to threaten psychological explanations
invoking internal representations, namely, that to specify how such
representations produce the behaviors in question, one must appeal to
an internal intelligent agent (a "homunculus") who
interprets the representations, and whose skills would themselves have
to be explained.



Both varieties of behaviorism, however, faced a common problem.



As many philosophers have pointed out (e.g. Chisholm 1957; Geach
1957), logical behaviorism provides an implausible account of the
meanings of our mental state terms, since, intuitively, a subject can
have the mental states in question without the relevant behavioral
dispositions - and vice versa. For example, Gene may believe
that it's going to rain even if he's not disposed to wear
a raincoat and take an umbrella when leaving the house (or to perform
any other cluster of rain-avoiding behaviors), if Gene doesn't
mind, or actively enjoys, singing in the rain. And subjects with the
requisite motivation can suppress their tendencies to pain behavior
even in the presence of excruciating pain, while skilled actors can
perfect the lawlike disposition to produce pain behavior under certain
conditions, even if they don't actually feel pain. (See e.g.
Putnam 1965) The problem, these philosophers argued, is that no mental
state, by itself, can plausibly be assumed to give rise to any
particular behavior unless one also assumes that the subject possesses
additional mental states of various types. And so, it seemed, it is
not in fact possible to give meaning-preserving translations of
statements invoking pains, beliefs, and desires in purely
behavioristic terms; one needs to include reference to the
subject's other mental states as well. Nonetheless, the idea
that our common sense concepts of mental states reveal an essential
tie between mental states and their typical behavioral expressions is
retained, and elaborated, in contemporary "analytic"
functionalist theories.



Scientific behaviorism faced similar challenges. The theories of
Watson, Skinner, et al had some early successes, especially in the
domain of animal learning, and its principles are still used, at least
for heuristic purposes, in various areas of psychology. But as many
psychologists (and others, e.g. Chomsky 1959) have argued, the
successes of behaviorism seem to depend upon the experimenters'
implicit control of certain variables which, when made explicit,
involve ineliminable reference to organisms' other mental
states. For example, rats are typically placed into an experimental
situation at a certain fraction of their normal body weight -
and thus can be assumed to *feel* *hunger* and to
*want* the food rewards contingent upon behaving in certain
ways. Similarly, it is assumed that humans, in analogous experimental
situations, *want* to cooperate with the experimenters, and
*understand* and know how to follow the instructions. It seemed
to the critics of behaviorism, therefore, that theories that
explicitly appeal to an organism's beliefs, desires, and other
mental states, as well as to stimulations and behavior, would provide
a fuller and more accurate account of why organisms behave as they do.
They could do so, moreover, without compromising the objectivity of
psychology as long as the mental states to which these theories appeal
are introduced as states that *together play a role* in the
production of behavior, rather than states identifiable solely by
introspection. Thus work was begun on a range of
"cognitive" psychological theories which reflected these
presumptions, and an important strain of contemporary functionalism,
"psychofunctionalism" (Fodor 1968, Block and Fodor 1972)
can be seen a philosophical endorsement of these new cognitive
theories of mind.


## 3. Varieties of Functionalism



Given this history, it is helpful to think of functionalist theories
as belonging to one of three major strains - "machine
state functionalism", "analytic functionalism", and
"psychofunctionalism" - and to see them as emerging,
respectively, from early AI theories, empirical behaviorism, and
logical behaviorism. It's important to recognize, however, that
there is at least some overlap in the bloodlines of these different
strains of functionalism, and also that there are functionalist
theories, both earlier and more recent, that fall somewhere in
between. For example, Wilfrid Sellars's (1956) account of mental
states as "theoretical entities" is widely regarded as an
important early version of functionalism, but it takes the proper
characterization of thoughts and experiences to depend partially on
their role in providing a scientific explanation of behavior, and
partly on what he calls the "logic", or the a priori
interrelations, of the relevant concepts. Still, it is instructive to
give separate treatment to the three major strains of the doctrine, as
long as these caveats are kept in mind.


### 3.1 Machine State Functionalism



The early functionalist theories of Putnam (1960, 1967; see also Block
and Fodor 1972) 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. (But see Putnam 1988,
for subsequent doubts about machine functionalism, Chalmers 1996b, for
a response, and Shagrir 2005, for a comprehensive account of the
evolution of Putnam's views on the subject)



According to *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) 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.



On either model, however, the mental states of a creature are to be
identified with such "machine table states"
(*S1*,...,*Sn*). These states
are not mere behavioral dispositions, since they are specified in
terms of their relations not only to inputs and outputs, but also to
the state of the machine at the time. For example, if *believing it
will rain* is regarded as a machine state, it will not be regarded
as a disposition to take one's umbrella after looking at the
weather report, but rather as a disposition to take one's
umbrella if one looks at the weather report *and* is in the
state of wanting to stay dry. So machine state functionalism can avoid
what many have thought to be a fatal difficulty for behaviorism. In
addition, machines of this sort provide at least a simple model of how
internal states whose effects on output occur by means of mechanical
processes can be viewed as *representations* (though the
question of *what*, exactly, they represent has been an ongoing
topic of discussion (see sections 4.4-5). Finally, machine table
states are not tied to any particular physical (or other) realization;
the same program, after all, can be run on different sorts of computer
hardware.



It's easy to see, therefore, why Turing machines provided a
fruitful model for early functionalist theories. And the idea that
mental states are best regarded as computational states appears in
many theories of the mind (see, for example, Rey 1997; but see
Piccinini 2004 for dissent and the entry on the
 computational theory of mind
 for a comprehensive discussion of this question). Nonetheless,
because machine table states are total states of a system, most
contemporary functionalists - both analytic functionalists and
psychofunctionalists - have adopted another way of
characterizing mental states, namely, as states implicitly defined by
the co-called Ramsey-sentence of a psychological theory - either
one that derives from our commonly held beliefs about the causal roles
of mental states in the production of behavior, or from the results of
empirical psychological investigation. This will be the focus of the
next section.


### 3.2 Functional Definitions and Ramsey-sentences



The key feature of this now-canonical method, presented initially by
David Lewis (1972), building on a technique introduced by Frank
Ramsey, is to treat mental state terms as being implicitly defined by
the so-called *Ramsey sentence* of one or another psychological
theory - common sense, scientific, or something in between.
(Analogous steps, of course, can be taken to produce the
Ramsey-sentence of *any* theory, psychological or otherwise).
For (a still simplistic) example, consider the sort of generalizations
about pain introduced before: pain tends to be caused by bodily
injury; pain tends to produce the belief that something is wrong with
the body and the desire to be out of that state; pain tends to produce
anxiety; pain tends to produce wincing or moaning.



To construct the Ramsey-sentence of this "theory", the
first step is to conjoin these generalizations, then to replace all
names of different types of mental states with different variables,
and then to existentially quantify those variables, as follows:



[?]*x*[?]*y*[?]*z*[?]*w*(*x*
tends to be caused by bodily injury & *x* tends to produce
states *y*, *z*, and *w* & *x* tends
to produce wincing or moaning). 



Such a statement is free of any mental state terms. It includes only
*quantifiers* that range over mental states, terms that denote
stimulations and behavior, and terms that specify various causal
relations among them. It can thus be regarded as providing implicit
definitions of the mental state terms of the theory. An individual
will have those mental states just in case it possesses a family of
first-order states that interact in the ways specified by the theory.
(Though functionalists of course acknowledge that the first-order
states that satisfy the functional definitions may vary from species
to species - or even from individual to individual - they
specify that, for each individual, the functional definitions be
*uniquely* satisfied.)



A helpful way to think of the Ramsey sentence of a psychological
theory is to regard it as defining a system's mental states
"all at once" as states that interact with stimulations in
various ways to produce behavior (See Lewis 1972; also see Field 1980
for a more technical elaboration of Lewis's method, and an
account of some crucial differences between this kind of
characterization and the one Lewis initially proposed.) It is also
helpful to view the differences between analytic and
psychofunctionalism as differences in the Ramsey-sentences of our
"commonsense theory of the mind" versus our empirical
psychological theories of the roles of mental states in the production
of other mental states and behavior.


### 3.3 Analytic Functionalism



Like the logical behaviorism from which it emerged, the goal of
analytic functionalism is to provide dispositional, or other
"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 certain causal and transitional relations that
a mental state has to stimulations, behavior, *and other mental
states*. So, for example, 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 any theory - and its Ramsey-sentence
- that is acceptable to analytic functionalists must include
only generalizations about mental states, their environmental causes,
and their joint effects on behavior that are so widely known and
"platitudinous" to count as *analyzing our ordinary
concepts* of the mental states in question. (See Smart 1959,
Armstrong 1968, Shoemaker 1984a,b,c, Lewis 1972, and Braddon-Mitchell
and Jackson 1996/2007.) 



A major question, of course, is whether a theory that limits itself to
such "platitudes" about the causal relations between
stimulations, mental states, and behavior can make the right
distinctions among mental states, or even worse, is so
"liberal" that it can be realized by systems without any
sort of mentality at all, such as the economy of Bolivia (Block,
1980b). However, commonsense psychology has more resources than it may
initially seem. First, (at least arguably) it need not be restricted
to the "platitudes" that can be accessed immediately; it
may take a certain amount of Socratic questioning to prompt us to
recognize certain similarities and differences among the
causal-relational properties of our mental states. The information
accessed by such questioning, however, was always available to us, at
least in principle, and so can count as the deliverances of common
sense, rather than empirical investigation. Moreover - and
contrary to the claims of some theorists (e.g. Churchland, 1981)
- commonsense psychology is not stagnant. It can, over time,
absorb information acquired by exposure to empirical theories, while
nonetheless retaining its platitudinous status. (Not that this is
always a good thing: think, for example, of how Freudian theory and
various now discredited theories about the causes of autism,
depression, and impulsive behavior once seemed to be the deliverances
of common sense.)



Nonetheless, many functionalists argue that commonsense theories do
not have sufficient resources to capture the causal roles of the
internal states that differentiate us from other cognitive (and
non-cognitive) systems. They look instead to a more empirically
informed, and presumably more restrictive, theory of mental states and
their effects on behavior - psychofunctionalism - that
derives primarily from reflection upon the goals and methodology of
the "cognitive" psychological theories that are the
descendants of scientific behaviorism.


### 3.4 Psychofunctionalism



In contrast to the scientific 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, 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.



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, and thus to have
autonomy from lower-level sciences such as neurophysiology: 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.



Psychofunctionalism, therefore, can be seen as straightforwardly
adopting the methodology of cognitive psychology in its
characterization of mental states and processes as entities defined by
their role in a cognitive psychological theory. What distinguishes it
from analytic functionalism is that the information used in the
functional characterization of mental states and processes
needn't be restricted to what is considered common knowledge or
common sense, but can include information available only by careful
empirical observation and experimentation. For example, a
psychofunctional theory might be able to distinguish phenomena such as
depression from sadness or listlessness even though the distinctive
causes and effects of these syndromes are difficult to untangle solely
by consulting intuitions or appealing to common sense. And
psychofunctional theories will not include characterizations of mental
states for which there is no scientific evidence, such as
buyer's regret or hysteria, even if the existence and efficacy
of such states is something that common sense affirms.



This may seem to be an unmitigated advantage, since psychofunctional
theories can avail themselves of all the tools of inquiry available to
scientific psychology, and will presumably make all, and only, the
distinctions that are scientifically sound. This methodology, however,
leaves psychofunctionalism open to the charge that it, like the
Psycho-Physical Identity Thesis, may be overly
"chauvinistic" (Block 1980b), since creatures whose
internal states share the rough, but not fine-grained, causal patterns
of ours wouldn't count as sharing our mental states. Many
psychofunctionalists, however, may not regard this as an unhappy
consequence, and argue that it's appropriate to treat only those
who are psychologically similar as having the same mental states.



But there is another serious worry about the thesis, namely, that if
the laws of the best empirical psychological theories diverge from
even the broad contours of our "folk psychology" -
that is, our common sense beliefs about the causal roles of our
thoughts, sensations, and perceptions - it will be hard to take
psychofunctional theories as providing an account of our mental
states, rather than merely changing the subject (Loar 1981, Stich
1983, Greenwood 1991, Braddon-Mitchell and Jackson 1996/2007). Many
theorists, however (Horgan and Woodward 1985), argue that it's
likely that future psychological theories will be recognizably close
to "folk psychology", though this question has been the
subject of debate (Churchland 1981).



Yet another reason that some prefer analytic functionalism derives
from a debate that occurred in the early days of the Psycho-Physical
Identity Theory, the thesis that each type of mental state can be
identified with some type of brain state or neural activity. For
example, early identity theorists (e.g. Smart 1959) argued that it
makes perfect sense (and may well be true) to identify *pain*
with *C-fiber stimulation*. The terms 'pain' and
'C-fiber stimulation', they acknowledged, do not have the
same *meaning*, but nonetheless they can denote the same state;
the fact that an identity statement is not a priori, they argued, does
not mean that it is not true. And just because I need not consult some
sort of brain scanner when reporting that I'm in pain
doesn't mean that the pain I report is not a neural state that a
brain scanner could (in principle) detect.



An important - and enduring - objection to this argument,
however, was raised early on by Max Black (reported in Smart 1959).
Black argued, following Frege (1892), that the only way that terms
with different meanings can denote the same state is to express (or
connote) different properties, or "modes of presentation",
of that state. But this implies, he argued, that if terms like
'pain', 'thought' and 'desire' are
not equivalent in meaning to any physicalistic descriptions, they can
denote physical states only by expressing *irreducibly mental*
*properties* of them. This argument has come to be known as the
"Distinct Property Argument", and was taken by its
proponents to undermine a thorough-going materialistic theory of the
mind. 



In response, Smart (1959) and later, Armstrong (1968) countered that
there could be relational, "topic-neutral" terms that are
equivalent in meaning to terms such as 'pain',
'thought', and 'desire', and if so, then there
are properties distinct from physical properties by virtue of which
mental state terms can denote brain states, yet are not irreducibly
mental. However, Smart's and Armstrong's suggestions were
widely regarded as inadequate. The appeal of meaning-preserving
functional characterizations, therefore, derives from their promise to
provide more plausible topic-neutral equivalents of our mental state
terms and concepts and thereby blunt the anti-materialistic force of
the Distinct Property Argument. (See Lewis 1966).



Still, though many regard functional characterizations as an
improvement on the earlier attempts by Smart and Armstrong, there is a
dispute about whether any relational characterizations of our mental
states, especially sensations, could fully preserve the meanings of
our mental state terms. On the other hand, there is a dispute about
how seriously to take the Distinct Property objection. (See White 1986
and 2007, for more recent versions of this objection, and Block 2007,
and Levin, 2020, for a response; these questions will be addressed
more fully in Section 5.5.)



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" (or "filler") functionalism
(McLaughlin 2006).


### 3.5 Role-functionalism and Realizer-functionalism



To see the difference between role-functionalism and
realizer-functionalism, consider - once again - the
(avowedly simplistic) example of a functional theory of pain
introduced in the first section.



*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?



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).



Some of the earliest versions of analytic functionalism (Lewis 1966,
Armstrong 1968 - but see Lewis 1980, for a modification) were
presented as functional specification theories, as topic-neutral
"translations" of mental state terms that could pave the
way for a psycho-physical identity theory by defusing the Distinct
Property Argument (see section 3.3). However, if there are differences
in the physical states that satisfy the functional definitions in
different (actual or hypothetical) creatures, such theories -
like most versions of the identity theory - would violate a key
motivation for functionalism, namely, that creatures with states that
play the same role in the production of other mental states and
behavior possess, literally, the same mental states.



It may be that there are some important, more general, physical
similarities between the neural states of seemingly disparate
creatures that satisfy a given functional characterization. (This
issue will be discussed further in Section 6.) However, even if this
is so, it is unlikely that these similarities hold of *all* the
creatures, including Martians and other hypothetical beings, who could
share our functional organization, and thus our theory of mental
states would remain, in Block's (1980) terms, overly
"chauvinistic". One could counter the charge of
chauvinism, of course, by suggesting that all creatures with
lower-level states that satisfy a given functional characterization
possess a common (lower-level) *disjunctive* state or property.
Or one could suggest that, even if all creatures possessing states
that occupy (for example) the pain role are not literally in the same
mental state, they nonetheless share a closely related higher-level
property (call it, following Lewis 1966 (note 6), "the attribute
of having pain"). But neither alternative, for many
functionalists, goes far enough to preserve the basic functionalist
intuition that functional commonality outweighs physical diversity in
determining whether creatures can possess the same mental states. Thus
many functionalists - both analytic and empirical -
advocate role functionalism, which, in addition to avoiding
chauvinism, permits mental state terms to be rigid designators (Kripke
1972), denoting the same items - those higher-level
"role" properties - in all possible worlds.



On the other hand, some functionalists - here, too, both
analytic and empirical - consider realizer functionalism to be
in a better position than role functionalism to explain the causal
efficacy of the mental. If I stub my toe and wince, we believe that my
toe stubbing causes my pain, which in turn causes my wincing. But,
some have argued (Malcolm 1968; Kim 1989, 1998) that if pain is
realized in me by some neural event-type, then insofar as there are
purely physical law-like generalizations linking events of that type
with wincings, one can give a complete causal explanation of my
wincing by citing the occurrence of that neural event (and the
properties by virtue of which it figures in those laws). And thus it
seems that the higher-level role properties of that event are causally
irrelevant. This is known as the "causal exclusion
problem", which is claimed to arise not just for functional role
properties, but for dispositional properties in general (Prior,
Pargetter, and Jackson 1982) - and indeed for any sort of mental
states or properties not type-identical to those invoked in physical
laws. This problem will be discussed further in Section 5.2.


## 4. Constructing Plausible Functional Theories



So far, the discussion of how to provide functional characterizations
of individual mental states has been vague, and the examples avowedly
simplistic. Is it possible to do better, and, if so, which version of
functionalism is likely to have the greatest success? These questions
will be the focus of this section, and separate treatment will be
given to experiential (often called 'qualitative' or
'phenomenal') states, such as perceptual experiences and
bodily sensations, which have a distinctive qualitative character or
"feel", and intentional states, such as thoughts, beliefs,
and desires, which purport to represent the world in various ways To
be sure, there is increasing consensus that experiential states have
representational contents and intentional states have qualitative
character and thus that these two groups may not be mutually exclusive
(see Horgan and Tienson, 2002). Nonetheless I will discuss them
separately to focus on what all agree to be the distinctive features
of each.


### 4.1 Characterizing Experiential States



The common strategy in the most successful treatments of perceptual
experiences and bodily sensations (Shoemaker 1984a, Clark 1993;
adumbrated in Sellars 1956) is to individuate experiences of various
general types (color experiences, experiences of sounds, feelings of
temperature) in part by appeal to their positions in the
"quality spaces" associated with the relevant sense
modalities - that is, the (perhaps multidimensional) matrices
determined by judgments about the relative similarities and
differences among the experiences in question. So, for example, the
experience of a very reddish-orange could be (partially) characterized
as the state produced by the viewing of a color swatch within some
particular range, which tends to produce the judgment or belief that
the state just experienced is more similar to the experience of red
than of orange. (Analogous characterizations, of course, will have to
be given of these other color experiences.) The judgments or beliefs
in question will themselves be (partially) characterized in terms of
their tendencies to produce sorting or categorization behavior of
certain specified kinds.



This strategy may seem fatal to analytic functionalism, which
restricts itself to the use of a priori (or platitudinous) information
to distinguish among mental states, since it's not clear that
the information needed to distinguish among experiences such as color
perceptions is available to commonsense. However, this problem may not
be as dire as it seems. For example, if sensations and perceptual
experiences are characterized in terms of their places in a
"quality space" determined by a person's
pre-theoretical judgments of similarity and dissimilarity (and perhaps
also in terms of their tendencies to produce various emotional
effects), then these characterizations may qualify as platitudinous,
even though they would have to be elicited by a kind of
"Socratic questioning".



There are limits to this strategy, however (see Section 5.5.1 on the
"inverted spectrum" problem), which seem to leave two
options for analytic functionalists: fight - that is, deny that
it's coherent to suppose that there exist the distinctions that
the critics suggest, or switch - that is, embrace another
version of functionalism in which the characterizations of mental
states, though not platitudinous, can provide information rich enough
to individuate the states in question. To switch, however, would be to
give up the benefits (if any) of a theory that offers
meaning-preserving translations of our mental state terms.



There has been significant skepticism, however, about whether
*any* functionalist theory - analytic or empirical
- can capture what seems to be the distinctive qualitative
character of experiential states such as color perceptions, pains, and
other bodily sensations; these questions will be addressed in section
5.5 below.


### 4.2 Characterizing Intentional States



On the other hand, intentional states such as beliefs, thoughts, and
desires (sometimes called "propositional attitudes") have
often been thought to be easier to characterize functionally than
experiential states such as pains and color experiences (but not
always: see Searle 1992, G. Strawson 1994, Horgan and Tienson 2002,
Kriegel 2003, Pitt 2008, and Mendelovici, 2018) who suggest that
intentional states have qualitative character as well). We can begin
by characterizing beliefs as (among other things) states produced in
certain ways by sense-perception or inference from other beliefs, and
desires as states with certain causal or counterfactual relations to
the system's goals and needs, and specify further how (according
to the relevant commonsense or empirical theory) beliefs and desires
tend to interact with one another, and other mental states, to produce
behavior.



Once again, this characterization is crude, and needs more detail.
Moreover, there are some further questions about characterizing
intentional states - particularly belief - that have
emerged in recent discussions. Once is whether a subject should be
regarded as believing that p if there is a mismatch between her
avowals that p and the characteristic behaviors associated with
believing that p in standard circumstances: do avowals outweigh
behaviors, or vice versa - or are there pragmatic factors that
determine what the answer should be in different contexts? (See
Gendler, 2008, and Schwitzgebel, 2010). Another question is whether
the states that interact with desires (and other mental states) to
produce behavior are best regarded as "full on" or
"outright" beliefs, or rather as representations of the
world for which individuals have varying degrees of confidence. (See
Staffel, 2013, 2019, and the many contributions to Huber and
Schmidt-Petri, 2009, and Ebert and Smith, 2012, for further
discussion. Functionalism, at least arguably, can accommodate a number
of different answers to these questions, but the project of
characterizing beliefs may not be straightforward.



Independently of these questions, functionalists need to say more
(outright or not) about what makes a state a particular belief
(outright or not) or desire, for example, the belief - or desire
- that it will snow tomorrow. Most functional theories describe
such states as different relations (or "attitudes") toward
the same state of affairs or proposition (and to describe the belief
that it will snow tomorrow and the belief that it will rain tomorrow
as the same attitude toward different propositions). This permits
differences and similarities in the contents of intentional states to
be construed as differences and similarities in the propositions to
which these states are related. But what makes a mental state a
relation to, or attitude toward, some proposition P? And can these
relations be captured solely by appeal to the functional roles of the
states in question?



The development of conceptual role semantics may seem to provide an
answer to these questions: what it is for Julian to believe that P is
for Julian to be in a state that has causal and counterfactual
relations to other beliefs and desires that mirror certain
inferential, evidential, and practical (action-directed) relations
among propositions with those formal structures (Field 1980; Loar
1981; Block 1986). This proposal raises a number of important
questions. One is whether states capable of entering into such
interrelations can (must?) be construed as being, or including
elements of, a "language of thought" (Fodor 1975; Harman
1973; Field 1980; Loar 1981). Another is whether idiosyncrasies in the
inferential or practical proclivities of different individuals make
for differences in (or incommensurabilities between) their intentional
states. (This question springs from a more general worry about the
*holism* of functional specification, which will be discussed
more generally in Section 5.1.)



Yet another challenge for functionalism are the widespread intuitions
that support "externalism", the thesis that what mental
states represent, or are about, cannot be characterized without appeal
to certain features of the environments in which those individuals are
embedded. Thus, if one individual's environment differs from
another's, they may count as having different intentional
states, even though they reason in the same ways, and have exactly the
same "take" on those environments from their own points of
view.



The "Twin Earth" scenarios introduced by Putnam (1975) are
often invoked to support an externalist individuation of beliefs about
natural kinds such as water, gold, or tigers. Twin Earth, as Putnam
presents it, is a (hypothetical) planet on which things look, taste,
smell, and feel exactly the way they do on Earth, but which have
different underlying microscopic structures; for example, the stuff
that fills the streams and comes out of the faucets, though it looks
and tastes like water, has molecular structure XYZ rather than
H2O. Many theorists find it intuitive to think that we
thereby *mean* something different by our term
'water' than our Twin Earth counterparts mean by theirs,
and thus that the beliefs we describe as beliefs about water are
different from those that our Twin Earth counterparts would describe
in the same way. Similar conclusions, they contend, can be drawn for
all cases of belief (and other intentional states) regarding natural
kinds.



The same problem, moreover, appears to arise for other sorts of belief
as well. Tyler Burge (1979) presents cases in which it seems intuitive
that a person, Oscar, and his functionally equivalent counterpart have
different beliefs about various syndromes (such as arthritis) and
artifacts (such as sofas) because the usage of these terms by their
linguistic communities differ. For example, in Oscar's
community, the term 'arthritis' is used as we use it,
whereas in his counterpart's community 'arthritis'
denotes inflammation of the joints and also various maladies of the
thigh. Burge's contention is that even if Oscar and his
counterpart both complain about the 'arthritis' in their
thighs and make exactly the same inferences involving
'arthritis', they mean different things by their terms and
must be regarded as having different beliefs. If these cases are
convincing, then there are differences among types of intentional
states that can only be captured by characterizations of these states
that make reference to the practices of an individual's
linguistic community. These, along with the Twin Earth cases, suggest
that if functionalist theories cannot make reference to an
individual's environment, then capturing the representational
content of (at least some) intentional states is beyond the scope of
functionalism. (See Searle, 1980, for related arguments against
"computational" theories of intentional states.)



On the other hand, the externalist individuation of intentional states
may fail to capture some important psychological commonalities between
ourselves and our counterparts that are relevant to the explanation of
behavior. If my Twin Earth counterpart and I have both come in from a
long hike, declare that we're thirsty, say "I want some
water" and head to the kitchen, it seems that our behavior can
be explained by citing a common desire and belief. Some theorists,
therefore, have suggested that functional theories should attempt
merely to capture what has been called the "narrow
content" of beliefs and desires - that is, whichever
representational features individuals share with their various Twin
Earth counterparts. There is no consensus, however, about just how
functionalist theories should treat these "narrow"
representational features (Block 1986; Loar 1987, Yli-Vakkuti and
Hawthorne, 2018), and some philosophers have expressed skepticism
about whether such features should be construed as representations at
all (Fodor 1994; also see the entry on
 narrow mental content).
 Even if a generally acceptable account of narrow representational
content can be developed, however, if the intuitions inspired by
"Twin Earth" scenarios remain stable, then one must
conclude that the full representational content of intentional states
cannot be captured by "narrow" functional
characterizations alone (and this will be true as well for certain
sorts of qualitative states, e.g. color experiences, if they too have
representational content).


### 4.3 Characterizing the Inputs and Outputs of a System



Considerations about whether certain sorts of beliefs are to be
externally individuated raise the related question about how best to
characterize the stimulations and behaviors that serve as *inputs
and outputs* to a system. Should they be construed as events
involving objects in a system's environment (such as fire
trucks, water and lemons), or rather as events in that system's
sensory and motor systems? Theories of the first type are often called
"long-arm" functional theories (Block 1990), since they
characterize inputs and outputs - and consequently the states
they are produced by and produce - by reaching out into the
world. Adopting a "long-arm" theory would prevent our Twin
Earth counterparts from sharing our beliefs and desires, and may thus
honor intuitions that support an externalist individuation of
intentional states (though further questions may remain about what
Quine has called the "inscrutability of reference"; see
Putnam 1988).



If functional characterizations of intentional states are intended to
capture their "narrow contents", however, then the inputs
and outputs of the system will have to be specified in a way that
permits individuals in different environments to be in the same
intentional state. On this view inputs and outputs may be better
characterized as activity in specific sensory receptors and motor
neurons. But this ("short-arm") option also restricts the
range of individuals that can share our beliefs and desires, since
creatures with different neural structures will be prevented from
sharing our mental states, even if they share all our behavioral and
inferential dispositions. (In addition, this option would not be open
to analytic functionalist theories, since generalizations that link
mental states to neurally specified inputs and outputs would not,
presumably, have the status of platitudes.)



Perhaps there is a way to specify sensory stimulations that abstracts
from the specifics of human neural structure enough to include any
possible creature that intuitively seems to share our mental states,
but is sufficiently concrete to rule out entities that are clearly not
cognitive systems (such as the economy of Bolivia; see Block 1980b).
If there is no such formulation, however, then functionalists will
either have to dispel intuitions to the effect that certain systems
can't have beliefs and desires, or concede that their theories
may be more "chauvinistic" than initially hoped.



Clearly, the issues here mirror the issues regarding the individuation
of intentional states discussed in the previous section. More work is
needed to develop the "long-arm" and
"short-arm" alternatives, and to assess the merits and
deficiencies of both.


## 5. Objections to Functionalism



The previous sections were by and large devoted to the presentation of
the different varieties of functionalism and the evaluation of their
relative strengths and weaknesses. There have been many objections to
functionalism, however, that apply to all versions of the theory. Some
of these have already been introduced in earlier discussions, but
they, and many others, will be addressed in more detail here.


### 5.1 Functionalism and Holism



One difficulty for every version of the theory is that functional
characterization is *holistic*. Functionalists hold that mental
states are to be characterized in terms of their roles in a
psychological theory - be it common sense, scientific, or
something in between - but all such theories incorporate
information about a large number and variety of mental states. Thus if
pain is interdefined with certain highly articulated beliefs and
desires, then animals who don't have internal states that play
the roles of our articulated beliefs and desires can't share our
pains, and humans without the capacity to feel pain can't share
certain (or perhaps any) of our beliefs and desires. In addition,
differences in the ways people reason, the ways their beliefs are
fixed, or the ways their desires affect their beliefs - due
either to cultural or individual idiosyncrasies - might make it
impossible for them to share the same mental states. These are
regarded as serious worries for all versions of functionalism (see
Stich 1983, Putnam 1988).



Some functionalists, however (e.g. Lewis, 1972; Shoemaker 1984c), have
suggested that if a creature has states that *approximately*
realize our functional theories, or realize some more specific
*defining* subset of the theory particularly relevant to the
specification of those states, then they can qualify as being mental
states of the same types as our own. The problem, of course, is to
specify more precisely what it is to be an approximate realization of
a theory, or what exactly a "defining" subset of a theory
is intended to include, and these are not easy questions. (They have
particular bite, moreover, for *analytic* functionalist
theories, since specifying what belongs inside and outside the
"defining" subset of a functional characterization raises
the question of what are the conceptually essential, and what the
merely collateral, features of a mental state, and thus raise serious
questions about the feasibility of (something like) an
analytic-synthetic distinction. (Quine 1953, Rey 1997)).


### 5.2 Functionalism and Mental Causation



Another worry for functionalism is the "causal exclusion
problem", introduced in Section 3.4: the worry about whether
role functionalism can account for what we take to be the causal
efficacy of our mental states (Malcolm 1968, Kim 1989, 1998). For
example, if pain is realized in me by some neural state-type, then
insofar as there are purely physical law-like generalizations linking
states of that type with pain behavior, one can give a complete causal
explanation of my behavior by citing the occurrence of that neural
state (and the properties by virtue of which it figures in those
laws). And thus, some have argued, the higher-level role properties of
that state - its being a pain - are causally
irrelevant.



There have been a number of different responses to this problem. Some
(e.g. Loewer 2002, 2007, Antony and Levine 1997, Burge 1997, Baker
1997) suggest that it arises from an overly restrictive account of
causation, in which a cause must "generate" or
"produce" its effect, a view which would count the
macroscopic properties of other special sciences as causally
irrelevant as well. Instead, some argue, causation should be regarded
as a special sort of counterfactual dependence between states of
certain types (Loewer 2002, 2007, Fodor 1990, Block 1997), or as a
special sort of regularity that holds between them (Melnyk 2003). If
this is correct, then functional role properties (along with the other
macroscopic properties of the special sciences) could count as
causally efficacious (but see Ney 2012 for dissent). However, the
plausibility of these accounts of causation depends on their prospects
for distinguishing bona-fide causal relations from those that are
clearly epiphenomenal, and some have expressed skepticism about
whether they can do the job, among them Crane 1995, Kim 2007, Jackson
1995, Ludwig 1998, and McLaughlin 2006, 2015. (On the other hand, see
Lyons (2006) for an argument that if functional properties are
causally inefficacious, this can be viewed as a *benefit* of
the theory.)



Yet other philosophers argue that causation is best regarded as a
relation between types of events that must be invoked to provide
sufficiently general explanations of behavior (Antony and Levine 1997,
Burge 1997, Baker 1997). Though many who are moved by the exclusion
problem (e.g. Kim, Jackson) maintain that there is a difference
between generalizations that are truly causal and those that
contribute in some other (merely epistemic) way to our understanding
of the world, theorists who advocate this response to the problem
charge that this objection, once again, depends on a restrictive view
of causation that would rule out too much.



Another problem with views like the ones sketched above, some argue
(Kim 1989, 1998), is that mental and physical causes would thereby
*overdetermine* their effects, since each would be causally
sufficient for their production. And, though some theorists argue that
overdetermination is widespread and unproblematic (see Loewer 2002,
and also Shaffer, 2003, and Sider 2003, for a more general discussion
of overdetermination), others contend that there is a special relation
between role and realizer that provides an intuitive explanation of
how both can be causally efficacious *without* counting as
overdetermining causes. For example, Yablo (1992), suggests that
mental and physical properties stand in the relation of determinable
and determinate (just as red stands to scarlet), and argues that our
conviction that a cause should be *commensurate* with its
effects permits us to take the determinable, rather than the
determinate, property to count as causally efficacious in
psychological explanation. Bennett (2003) suggests, alternatively,
that the realizer properties *metaphysically necessitate* the
role properties in a way that prevents them from satisfying the
conditions for overdetermination. Yet another suggestion (Wilson,
1999, 2011, and Shoemaker, 2001) is that the causal powers of mental
properties are included among (or are proper subsets of) the causal
powers of the physical properties that realize them. (See also
Macdonald and Macdonald 1995, Witmer, 2003, Yates, 2012, and Strevens,
2012, for related views.)



There has been substantial recent work on the causal exclusion
problem, which, as noted earlier, arises for any non-reductive theory
of mental states. (See the entry on
 mental causation,
 as well as Bennett 2007, and Funkhouser 2007, for further discussion
and extensive bibliographies.) But it is worth discussing a related
worry about causation that arises exclusively for role-functionalism
(and other dispositional theories), namely, the problem of
"metaphysically necessitated effects" (Rupert 2006,
Bennett 2007). If *pain* is functionally defined (either by an
analytic *or* an empirical theory) as the state of being in
some lower-level state or other that, in certain circumstances causes
wincing, then it seems that the generalization that pain causes
wincing (in those circumstances) is at best uninformative, since the
state in question would not *be* pain if it didn't. And,
on the Humean view of causation as a contingent relation, the causal
claim would be false. Davidson (1980b) once responded to a similar
argument by noting that even if a mental state *M* is defined
in terms of its production of an action *A*, it can often be
redescribed in other terms *P* such that '*P*
caused *A*' is not a logical truth. But it's
unclear whether any such redescriptions are available to role (vs.
realizer) functionalists.



Some theorists (e.g. Antony and Levine 1997) have responded by
suggesting that, though mental states may be defined in terms of some
of their effects, they have *other* effects that do not follow
from those definitions which can figure into causal generalizations
that are contingent, informative, and true. For example, even if it
follows from a functional definition that pain causes wincing (and
thus that the relation between pain and wincing cannot be truly
causal), psychologists may discover, say, that pain produces
resilience (or submissive behavior) in human beings. One might worry,
nonetheless, that functional definitions threaten to leave too many
commonly cited generalizations outside the realm of contingency, and
thus causal explanation: surely, we may think, we want to affirm
claims such as "pain causes wincing". Such claims could be
affirmed, however, if (as seems likely) the most plausible functional
theories define sensations such as pain in terms of a small subset of
their distinctive *psychological*, rather than behavioral,
effects (see section 4.2).



A different line of response to this worry (Shoemaker 1984d, 2001) is
to deny the Humean account of causation altogether, and contend that
causal relations are themselves metaphysically necessary, but this
remains a minority view. (See also Bird, 2002, and Latham, 2011, for
further discussion.)


### 5.3 Functionalism and Introspective Belief



Another important question concerns the beliefs that we have about our
own "occurrent" (as opposed to dispositional) mental
states such as thoughts, sensations, and perceptions. We seem to have
immediately available, non-inferential beliefs about these states, and
the question is how this is to be explained if mental states are
identical with functional properties.



The answer depends on what one takes these introspective beliefs to
involve. Broadly speaking, there are two dominant views of the matter
(but see Peacocke 1999, Ch. 5 for further alternatives). One popular
account of introspection - the "inner sense" model
on which introspection is taken to be a kind of "internal
scanning" of the contents of one's mind (Armstrong 1968)
- has been taken to be unfriendly to functionalism, on the
grounds that it's hard to see how the objects of such scanning
could be second-order relational properties of one's neural
states (Goldman 1993). Some theorists, however, have maintained that
functionalism can accommodate the special features of introspective
belief on the "inner sense" model, since it would be only
one of many domains in which it's plausible to think that we
have immediate, non-inferential knowledge of causal or dispositional
properties (Armstrong 1993; Kobes 1993; Sterelney 1993). A full
discussion of these questions goes beyond the scope of this entry, but
the articles cited above are just three among many helpful pieces in
the Open Peer Commentary following Goldman (1993), which provides a
good introduction to the debate about this issue.



Another account of introspection, identified most closely with
Shoemaker (1996a,b,c,d), is that the immediacy of introspective belief
follows from the fact that occurrent mental states and our
introspective beliefs about them are functionally interdefined. For
example, one satisfies the definition of being in pain only if one is
in a state that tends to cause (in creatures with the requisite
concepts who are considering the question) the belief that one is in
pain, and one believes that one is in pain only if one is in a state
that plays the belief role, and is caused directly by the pain itself.
On this account of introspection, the immediacy and non-inferential
nature of introspective belief is not merely compatible with
functionalism, but required by it.



But there is an objection, most recently expressed by George Bealer
(1997; see also Hill 1993), that, on this model an introspective
belief can only be defined in one of two unsatisfactory ways: either
as a belief produced by a (second-order) functional state specified
(in part) by its tendency to produce that very type of belief -
which would be circular - or as a belief about the first-order
*realization* of the functional state, rather than that state
itself. Functionalists have suggested, however (Shoemaker 2001,
McCullagh 2000, Tooley 2001), that there is a way of understanding the
conditions under which beliefs can be caused by, and thus be about,
one's second-order functional states that permits mental states
and introspective beliefs about them to be non-circularly defined (but
see Bealer 2001, for a skeptical response). A full treatment of this
objection involves the more general question of whether second-order
properties can have causal efficacy, and is thus beyond the scope of
this discussion (see section 5.2 and the
 mental causation
 entry). But even if this objection can ultimately be deflected, it
suggests that special attention must be paid to the functional
characterizations of "self-directed" mental states.


### 5.4 Functionalism and the Norms of Reason



Yet another objection to functionalist theories of any sort is that
they do not capture the interrelations that we take to be definitive
of beliefs, desires, and other intentional states. Whereas even
analytic functionalists hold that mental states - and also their
contents - are implicitly defined in terms of their (causal or
probabilistic) roles in *producing* behavior, these critics
understand intentional states to be implicitly defined in terms of
their roles in *rationalizing*, or *making sense of*,
behavior. This is a different enterprise, they claim, since
rationalization, unlike causal explanation, requires showing how an
individual's beliefs, desires, and behavior conform, or at least
approximate, to certain a priori *norms* or *ideals* of
theoretical and practical reasoning - prescriptions about which
beliefs and desires we *should* have, how we *should*
reason, or what, given our beliefs and desires, we *ought* to
do. (See Davidson 1980c, Dennett 1978, and McDowell 1985 for classic
expressions of this view.) Thus the defining
("constitutive") normative or rational relations among
intentional states expressed by these principles cannot be expected to
correspond to causal and probabilistic relations among our internal
states, sensory stimulations and behavior, since they constitute a
kind of explanation that has sources of evidence and standards for
correctness that are different from those of empirical theories
(Davidson 1980c). One can't, that is, extract facts from
values.



Thus, although attributions of mental states can in some sense explain
behavior by permitting an observer to "interpret" it as
making sense, they should not be expected to denote entities that
figure in empirical generalizations, either common sense or
scientific. (This is not to say, these theorists stress, that there
are no causes, or empirical laws of, behavior. These, however, will be
expressible only in the vocabularies of the neurosciences, or other
lower-level sciences, and not as relations among beliefs, desires and
behavior.)



Functionalists have replied to these worries in different ways. Many
just deny the intuition behind the objection, and maintain that even
the strictest conceptual analyses of our intentional terms and
concepts purport to define them in terms of their bona-fide causal
roles, and that any norms they reflect are explanatory rather than
prescriptive. They argue, that is, that if these generalizations are
idealizations, they are the sort of idealizations that occur in any
scientific theory: just as Boyle's Law depicts the relations
between the temperature, pressure, and volume of a gas under certain
ideal experimental conditions, our a priori theory of the mind
consists of descriptions of what normal humans *would* do under
(physically specifiable) ideal conditions, not prescriptions as to
what they *should*, or are *rationally required*, to
do.



Other functionalists agree that we may advert to various norms of
inference and action in attributing beliefs and desires to others, but
deny that there is any in principle incompatibility between normative
and empirical explanations. They argue that if there are causal
relations among beliefs, desires, and behavior that even approximately
mirror the norms of rationality, then the attributions of intentional
states can be empirically confirmed (Fodor 1990; Rey 1997). In
addition, many who hold this view suggest that the principles of
rationality that intentional states must meet are quite minimal, and
comprise at most a weak set of constraints on the contours of our
theory of mind, such as that people can't, in general, hold
(obviously) contradictory beliefs, or act against their (sincerely
avowed) strongest desires (Loar 1981). Still others suggest that the
intuition that we attribute beliefs and desires to others according to
rational norms is based on a fundamental mistake; these states are
attributed not on the basis of whether they rationalize the behavior
in question, but whether those subjects can be seen as using
principles of inference and action sufficiently like our own -
be they rational, like Modus Ponens, or irrational, like the
Gambler's Fallacy or the now familiar instances of
"predictable irrationality" documented in Kahneman, 2011.
(See Stich 1981, and Levin 1988, for discussion of this question, and
for a more general debate about the compatibility of normative and
psychological principles, see Rey, 2007, and Wedgwood, 2007. See also
Gluer and Wikforss, 2009, 2013, and for further discussion, the
entry on the
 normativity of meaning and content.)



Nonetheless, although many functionalists argue that the
considerations discussed above show that there is no in principle bar
to a functionalist theory that has empirical force, these worries
about the normativity of intentional ascription continue to fuel
skepticism about functionalism (and, for that matter, any scientific
theory of the mind that uses intentional notions).



In addition to these general worries about functionalism, there are
particular questions that arise for functional characterizations of
experiential or phenomenal states. These questions will be discussed
in the following section.


### 5.5 Functionalism and the Problem of Qualia



Functionalist theories of all varieties - whether analytic or
empirical, role or realizer - attempt to characterize mental
states exclusively in relational, specifically causal, terms. A common
and persistent objection, however, is that no such characterizations
can capture the phenomenal character, or "qualia", of
experiential states such as perceptions, emotions, and bodily
sensations, since they would leave out certain essential properties of
those experiential states, namely, "what it's like"
(Nagel 1974) to have them. The next three sections will present the
most serious worries about the ability of functionalist theories to
give an adequate characterization of these states. (These worries, of
course, will extend to intentional states, if, as some philosophers
argue, "what it's like" to have them is among their
essential properties as well. (See Searle 1992, G. Strawson, 1986,
Horgan and Tienson, 2002, Kriegel 2003, Pitt 2008, Mendelovici, 2018,
for presentations of this view, and see Bayne and Montague, 2011, and
Smithies, 2013a and 2013b for more general discussions of whether
intentional states possess phenomenal character - often called
"cognitive phenomenology" - and if so, what, more
precisely, it is.)


#### 5.5.1 Inverted and Absent Qualia



The first to be considered are the "absent" and
"inverted" qualia objections most closely associated with
Ned Block (1980b; see also Block and Fodor 1972). The "inverted
qualia" objection to functionalism maintains that there could be
an individual who (for example) is in a state that satisfies the
functional definition of our experience of red, but is experiencing
green instead - and similarly for all the colors in the
spectrum. It is a descendant of the claim, discussed by philosophers
from Locke to Wittgenstein, that there could be an individual with an
"inverted spectrum" who is behaviorally indistinguishable
from someone with normal color vision; both objections trade on the
contention that the purely relational characterizations in question
cannot make distinctions among distinct experiences with isomorphic
causal patterns. (Nida-Rumelin, 1996, argues that the science of
color vision leaves open the possibility that there could be
functionally equivalent red-green "inverts", but even if
inverted qualia are not really an empirical possibility for human
beings, given certain asymmetries in our "quality space"
for color, and differences in the relations of color experiences to
other mental states such as emotions (Hardin 1988), it seems possible
that there are creatures with perfectly symmetrical color quality
spaces for whom a purely functional characterization of color
experience would fail.)



A related objection, the "absent qualia" objection,
maintains that there could be creatures functionally equivalent to
normal humans whose mental states have no qualitative character at
all. In his well-known "Chinese nation"
thought-experiment, Block (1980b) invites us to imagine that the
population of China (chosen because its size approximates the number
of neurons in a typical human brain) is recruited to duplicate his
functional organization for a period of time, receiving the equivalent
of sensory input from an artificial body and passing messages back and
forth via satellite. Block argues that such a
"homunculi-headed" system would not have mental states
with any qualitative character (other than the qualia possessed by the
individuals themselves), and thus that there could be states
functionally equivalent to sensations or perceptions that lack their
characteristic "feels". Conversely, some argue that
functional role is not *necessary* for qualitative character:
for example, it seems that one could have mild, but distinctive,
twinges that have no typical causes or characteristic effects.



All these objections purport to have characterized a creature with the
functional organization of normal human beings, but without any, or
the right sort, of qualia (or vice versa), and thus to have produced a
counterexample to functional theories of experiential states. One line
of response, initially advanced by Sydney Shoemaker (1994b), is that
although functional duplicates of ourselves with inverted qualia may
be possible, duplicates with absent qualia are not, since their
possibility leads to untenable skepticism about the qualitative
character of one's own mental states. This argument has been
challenged, however (Block 1980b; but see Shoemaker's response
in 1994d, and Balog, 1999, for a related view), and the more common
response to these objections - particularly to the absent qualia
objection - is to question whether scenarios involving creatures
such as Block's Chinese nation provide genuine counterexamples
to functionalist theories of experiential states.



For example, some theorists (Dennett 1978; Levin 1985; Van Gulick
1989) argue that these scenarios provide clear-cut counterexamples
only to *crude* functional theories, and that attention to the
subtleties of more sophisticated characterizations will undermine the
intuition that functional duplicates of ourselves with absent qualia
are possible (or, conversely, that there are qualitative states
without distinctive functional roles). The plausibility of this line
of defense is often questioned, however, since there is tension
between the goal of increasing the sophistication (and thus the
individuative powers) of the functional definitions, and the goal (for
analytic functionalists) of keeping these definitions within the
bounds of the platitudinous (though see Section 4.2), or (for
psychofunctionalists) broad enough to be instantiable by creatures
other than human beings. A related suggestion is that absent qualia
seem possible only because of our imaginative shortcomings, in
particular, that it is hard for us to attend, at any one time, to all
the relevant features of even the simplest functional characterization
of experiential states; another is that the intuition that these
creatures lack qualia is based on prejudice - against creatures
with unfamiliar shapes and extended reaction times (Dennett 1978), or
creatures with parts widely distributed in space (Lycan, 1981,
Schwitzgebel 2015 and commentary).



There are other responses to analogous absent qualia arguments that
are prominent in the literature, but the target of those arguments is
broader. Block's argument was initially presented as a challenge
exclusively to functionalist theories, both analytic and empirical,
and not generally to physicalistic theories of experiential states;
the main concern was that the purely relational resources of
functional description were incapable of capturing the intrinsic
qualitative character of states such as feeling pain, or seeing red.
(Indeed, in Block's 1980b, p. 291, he suggests that qualitative
states may best be construed as "composite state[s] whose
components are a *quale* and a [functional state]," and
adds, in an endnote (note 22) that the *quale* "might be
identified with a physico-chemical state".) But there are
similar objections that have been raised against all physicalistic
theories of experiential states that are important to consider in
evaluating the prospects for functionalism. These will be discussed in
the next two sections.


#### 5.5.2 Functionalism, Zombies, and the "Explanatory Gap"



One important objection, advanced by (among others) Kripke (1972) and
Chalmers (1996a), derives from Descartes's well-known argument
in the *Sixth Meditation* (1641) that since he can clearly and
distinctly conceive of himself existing apart from his body (and vice
versa), and since the ability to clearly and distinctly conceive of
things as existing apart guarantees that they are in fact distinct, he
is in fact distinct from his body.



Chalmers's version of the argument (1996a, 2002), known as the
"Zombie Argument", has been particularly influential. The
first premise of this argument is that it is *conceivable*, in
a special, robust, "positive" sense, that there are
molecule-for-molecule duplicates of oneself with no qualia (call them
"zombies", following Chalmers 1996a). The second premise
is that scenarios that are "positively" conceivable in
this way represent real, metaphysical, possibilities. Thus, he
concludes, zombies are possible, and functionalism - or, more
broadly, physicalism - is false. The force of the Zombie
Argument is due in large part to the way Chalmers defends its two
premises; he provides a detailed account of just what is required for
zombies to be conceivable, and also an argument as to why the
conceivability of zombies entails their possibility (see also Chalmers
2002, 2006, 2010, Ch. 6, and Chalmers and Jackson 2002). This account,
based on a more comprehensive theory of how we can evaluate claims
about possibility and necessity known as "two-dimensional
semantics", reflects an increasingly popular way of thinking
about these matters, but remains controversial. (For alternative ways
of explaining conceivability, see Kripke (1986), Hart (1988); for
criticism of the argument from two-dimensional semantics, see Yablo
2000, 2002, Bealer 2002, Stalnaker 2002, Soames 2004, Byrne and Prior
2006; but see also Chalmers 2006.)



In a related challenge, Joseph Levine (1983, 1993, 2001) argues that,
even if the conceivability of zombies doesn't entail that
functionalism (or more broadly, physicalism) is false, it opens an
"explanatory gap" not encountered in other cases of
inter-theoretical reduction, since the qualitative character of an
experience cannot be deduced from any physical or functional
description of it. Such attempts thus pose, at very least, a unique
epistemological problem for functionalist (or physicalist) reductions
of qualitative states.



In response to these objections, analytic functionalists contend, as
they did with the inverted and absent qualia objections, that
sufficient attention to what is required for a creature to duplicate
our functional organization would reveal that zombies are not really
conceivable, and thus there is no threat to functionalism and no
explanatory gap. A related suggestion is that, while zombies may
*now* seem conceivable, we will eventually find them
inconceivable, given the growth of empirical knowledge, just as we now
find it inconceivable that there could be H2O without water
(Yablo 1999). Alternatively, some suggest that the inconceivability of
zombies awaits the development of new *concepts* that can
provide a link between our current phenomenal and physical concepts
(Nagel 1975, 2000), while others (McGinn 1989) agree, but deny that
humans are capable of forming such concepts.



None of these responses, however, would be an effective defense of
Psychofunctionalism, which does not attempt to provide analyses of
experiential concepts (or suggest that there would, or could, be any
to come). But there is an increasingly popular strategy for defending
physicalism against these objections that could be used to defend
Psychofunctionalism, namely, to concede that there can be no
conceptual analyses of qualitative concepts (such as *what
it's like to see red* or *what it's like to feel
pain)* in purely functional terms, and focus instead on developing
arguments to show that the conceivability of zombies neither implies
that such creatures are possible nor opens up an explanatory gap.



One line of argument (Block and Stalnaker 1999; Yablo 2000) contends
that the conceivability of (alleged) counterexamples to
psycho-physical or psycho-functional identity statements, such as
zombies, has analogues in other cases of successful inter-theoretical
reduction, in which the lack of conceptual analyses of the terms to be
reduced makes it conceivable, though not possible, that the identities
are false. However, the argument continues, if these cases routinely
occur in what are generally regarded as successful reductions in the
sciences, then it's reasonable to conclude that the
conceivability of a situation does not entail its possibility.



A different line of argument (Horgan 1984; Loar 1990; Lycan 1990; Hill
1997, Hill and McLaughlin 1999, Balog 1999, Levin 2018) maintains
that, while generally the conceivability of a scenario entails its
possibility, scenarios involving zombies stand as important
exceptions. The difference is that the phenomenal, or "what
it's like", concepts used to describe the properties of
experience that we conceive zombies to lack are significantly
different from the third-personal, discursive concepts of our common
sense and scientific theories such as *mass, force* or
*charge*; they comprise a special class of non-discursive,
first-personal, perspectival representations of those properties.
Whereas conceptually independent third-personal concepts *x*
and *y* may reasonably be taken to express metaphysically
independent properties, or modes of presentation, no such metaphysical
conclusions can be drawn when one of the concepts in question is
third-personal and the other is *phenomenal*, since these
concepts may merely be picking out the same properties in different
ways. Thus, the conceivability of zombies, dependent as it is on our
use of phenomenal concepts, provides no evidence of their metaphysical
possibility.



Key to this line of defense is the claim that these special phenomenal
concepts can denote functional (or physical) properties without
expressing some irreducibly qualitative modes of presentation of them,
for otherwise it couldn't be held that these concepts do in fact
apply to our functional (or physical) duplicates, even though
it's conceivable that they don't. This, not surprisingly,
has been disputed, and there is currently much discussion in the
literature about the plausibility of this claim. If this line of
defense is successful, however, it can also provide a response to the
"Distinct Property Argument", discussed in section 3.3.
(See Chalmers 1999, Holman 2013 for criticism of this view, but see
the responses of Loar 1999, Hill & McLaughlin 1999, Balog 2012,
Levin 2008, 2018, Diaz-Leon, 2010, 2014; see also see Levin 2002,
2008, and Schroer 2010, for the presentation, if not endorsement, of a
hybrid view.)


#### 5.5.3 Functionalism and the Knowledge Argument



In another important, related, challenge to functionalism (and, more
generally, physicalism), Thomas Nagel (1974) and Frank Jackson (1982)
argue that a person could know all the physical and functional facts
about a certain type of experience and still not "know what
it's like" to have it. This is known as the
"Knowledge Argument", and its conclusion is that there are
certain properties of experiences - the "what it's
like" to see red, feel pain, or sense the world through
echolocation - which cannot be identified with functional (or
physical) properties. Though neither Nagel (2000) nor Jackson (1998)
now endorse this argument, many philosophers contend that it raises
special problems for any physicalistic view (see Alter 2007, and, in
response, Jackson 2007).



An early line of defense against these arguments, endorsed primarily
but not exclusively by a priori functionalists, is known as the
"Ability Hypothesis". (Nemirow 1990, 2007, Lewis 1990,
Levin 1986). "Ability" theorists suggest that knowing what
it's like to see red or feel pain is merely a sort of
*practical* knowledge, a "knowing how" (to imagine,
remember, or re-identify, a certain type of experience) rather than a
knowledge of propositions or facts. (See Tye 2000, for a summary of
the pros and cons of this position; for further discussion, see the
essays in Ludlow, Nagasawa, and Stoljar 2004.) An alternative view
among contemporary functionalists is that coming to know what
it's like to see red or feel pain is indeed to acquire
propositional knowledge uniquely afforded by experience, expressed in
terms of first-personal concepts of those experiences. But, the
argument continues, this provides no problem for functionalism (or
physicalism), since these special first-personal concepts need not
denote, or introduce as "modes of presentation", any
irreducibly qualitative properties. This view, of course, shares the
strengths and weaknesses of the analogous response to the
conceivability arguments discussed above. If it is plausible, however,
it can also challenge the argument of some philosophers (e.g.,
Chalmers, 2002, Stoljar, 2001, and Alter, 2016) that maintains that no
physicalistic theory, not even fundamental physics, can provide
anything but a relational characterization of the items in their
domains - their structure and dynamics - and concludes
that no physicalistic theory can capture what seems, from the inside,
to be the intrinsic, non-relational properties of our experiential
states. (See the essays in Alter and Nagasawa, 2015, Part III, for
further discussion.)



There is one final strategy for defending a functionalist account of
qualitative states against all of these objections, namely,
eliminativism (Dennett 1988; Rey 1997, Pereboom 2011, Frankish 2016).
One can, that is, deny that there are any such things as irreducible
*qualia*, and maintain that the conviction that such things do,
or perhaps even *could*, exist is due to illusion - or
confusion.


## 6. The Future of Functionalism



In the last part of the 20th century, functionalism stood as the
dominant theory of mental states. Like behaviorism, functionalism
takes mental states out of the realm of the "private" or
subjective, and gives them status as entities open to scientific
investigation. But, in contrast to behaviorism, functionalism's
characterization of mental states in terms of their roles in the
production of behavior grants them the causal efficacy that common
sense takes them to have. Moreover, functionalism, in contrast to the
psychophysical identity thesis, seems to offer an account of mental
states that is friendly to materialism without limiting the class of
those with minds to creatures with brains like ours.



More recently, however, there has been a resurgence of interest in the
psycho-physical (type-) identity thesis. This is fueled in part by the
observation that in the actual practice of neuroscience, neural states
are type-individuated more coarsely than early identity theorists such
as Place, Feigl, and Smart assumed, and the contention that, contrary
to the claims of early defenders of functionalism (e.g. Putnam), there
are relatively few extant creatures that are physically unlike humans
but share our functional organization. If this is so, then it may well
be that many of our genuine functional equivalents that differ from us
in their fine-grained neurophysiological make-up can nonetheless share
our neural, as well as mental, states, and thus that the
psycho-physical identity thesis can claim some of the scope once
thought to be exclusive to functionalism. (See Bechtel 2012, Bickle
2012, McCauley 2012, Shapiro & Polger 2012, and Polger &
Shapiro 2016.)



The plausibility of this thesis, of course, depends on whether or not
these underlying similarities would in fact be (coarse grained)
*neural* similarities, and not (fine-grained) psycho-functional
similarities. In addition, functionalists can argue that there are
*possible* creatures, both biological and (especially)
non-biological, that are functionally equivalent to us but do not
possess even our coarse-grained neural properties. If so, and if these
creatures can plausibly be regarded as sharing our mental states
- to be sure, a controversial thesis - then even if neural
states can be individuated more coarsely, some variety of
functionalism will retain its claim to greater universality than the
identity thesis.



Another source of skepticism about the relative universality of
functionalist (versus type-identity) theories derives from the
suggestion that - at least in humans - the properties that
could play the relevant roles in our functional architecture are not
exclusively electrical impulses of our neurons, but a combination of
these impulses *plus* other features of the brain and body,
including the endocrine system. (See Cao 2022 and Damasio 1999.) If
this is so, then there may be fewer extant examples of creatures that
are functional, but not physical, duplicates of humans, and it may be
less likely that such creatures are even nomologically possible. They
may, of course, be metaphysically possible, existing in fairly distant
possible worlds, but there is debate about whether this is plausible,
and if so, whether it would seriously undermine the psycho-physical
identity theory.



On the other hand, some critics of the psycho-physical identity theory
contend that only a theory that characterizes mental states as
higher-order properties, with causal powers not possessed by the
states or properties that realize them, can preserve the explanatory
hierarchy modeled on the relations between biology and chemistry, and
chemistry and physics. The identification of mental states with
functional roles would do the trick, whether or not our mental states
are in fact multiply realized. (See Gillett 2002, Aizawa and Gillett
2007, 2009, and the essays in DeJoong and Shouten 2007 for further
discussion; see also the entry on
 multiple realizability.)
 These questions remain the subject of active debate.



Yet another question is whether Role Functionalism, by itself, is as
friendly to materialism as its initial advocates had suggested -
even if the functional roles to be identified with mental states are
realized exclusively by physical states. It is generally agreed that
the mere supervenience of the mental on the physical - that is,
the impossibility of there being a mental difference without some
physical difference - leaves open the possibility that mental
properties are emergent properties with additional causal powers,
whereas the realization of mental states by physical states eliminates
this possibility. However, some say, while others deny, that
materialism requires something more, namely, an explanation of how (or
why) those physical properties can occupy the relevant functional
roles. This too is a contentious question. (See, for further
discussion, Endicott 2016 and Shaffer 2021).



There remain other substantive questions about functionalism. One is
whether it can provide an adequate account of all mental states. Most
discussions of the prospects for functionalism focus on its adequacy
as an account of familiar experiential states such as sensational and
perceptual experiences, and familiar intentional states such as
beliefs and desires. But what about emotions - and moods?
Although there is some discussion of these states in the functionalism
literature, (e.g. Rey 1990, Nussbaum 2003, deHooge, et al. 2011)
there is increasing interest in these questions, and more work needs
to be done. In addition, there is increasing interest in determining
whether there can be plausible functional characterizations of
non-standard perceptual experiences, such as synesthesia, and various
sorts of altered states of consciousness that can arise from the
ingestion of drugs, natural hallucinogenic substances, or focused
meditation. (See Gray et al. 2002, 2004, and Deroy 2017, for
discussions of synesthesia. For general discussions of altered states
of consciousness, see Velmans and Schneider (eds.) 2007, and
Thompson 2015.)



Another question is whether functional theories can accommodate
non-standard views about the location of mental states, such as the
hypothesis of extended cognition, which maintains that certain mental
states such as memories - and not just their representational
contents - can reside outside the head. This question has
implications not only for the viability of a functionalist
characterization of memory, but also of beliefs, emotions,
hallucinations, and moods. (See Clark and Chalmers 2002, Clark, 2008,
Adams and Aizawa 2008, Rupert 2009, Sprevack 2009, Byrne and Manzotti
2022, and the essays in Menary 2010, for further discussion.)



Yet another question of increasing interest to philosophers is whether
groups of individuals, or entire communities, can possess mental
states (e.g. beliefs, desires, intentions, moods, and emotions) that
cannot be reduced to the mental states of the individuals in those
communities. (See Gilbert 2013.) Is it merely metaphorical to say
that a community (and not just the individuals in it) is optimistic,
or conservative, or believes that human activities cause climate
change, or remembers the 60s? Or can claims like this be literally
true - and if so, how; does it matter how many members of the
community in question individually possess the belief, intention, or
emotion in question? It is easy to see, moreover, that answers to
these questions would have implications not only for theories of the
nature of mental states, but also for theories of self-knowledge and
knowledge of other minds. They would also have implications for
theories of moral evaluation: Desires and intentions lead to actions,
and if a community intends to help resettle new immigrants or block
access to a public beach, then whom (or what) can we legitimately
praise and blame for these actions, and to whom (or what) do we have
moral obligations?



In general, the sophistication of functionalist theories has increased
since their introduction, but so has the sophistication of the
objections to functionalism, especially to functionalist accounts of
mental causation 
 (section 5.2), 
 introspective knowledge 
 (Section 5.3),
 and the qualitative character of experiential states 
 (Section 5.5).
For those unconvinced of the plausibility of dualism, however, and
unwilling to restrict mental states to creatures physically like
ourselves, the initial attractions of functionalism remain. The
primary challenge for future functionalists, therefore, will be to
meet these objections to the doctrine, either by articulating a
functionalist theory in increasingly convincing detail, or by showing
how the intuitions that fuel these objections can be explained
away.