Lecture 8. Physicalisms (Functionalisms)

General notice: The script is for internal use only, do not quote! I deliberately
make use of other texts and textbooks without always indicating what source it is.

Philosophy of Mind

Lecture 8. Physicalisms (Functionalisms)

1. Functionalisms overview
2. Metaphysical functionalisms
3. sidestep: Turing machines

So far, we studied several positions of physicalism: semantic physicalism, eliminativism, and
the identity theory. Today I am going to discuss functionalism. Functionalism is the position
that really coined philosophy of mind during the last 30 years. However, there are lots of
functionalisms around. Therefore, we have to sort things a bit. Let me first follow some dis-
tinctions Ned Block draw in the early eighties of the last century. (Sounds as if it’s long ago
…):

Types of Functionalism (Block 1980, Vol. I, 171 ff.)

• Functional analysis – is a type of explanation; it relies on a decomposition of a system
into its component parts and explains the working of the system in terms of the capaci-
ties of the parts and the way the parts are integrated with one another.

• Computation-representation functionalism – is a special case of functional explana-
tion as defined above: Our mental life is dissolved by functional analysis of mental
processes to the point where they are seen to be composed of computations as mechani-
cal as the primitive operations of a digital computer; the key notions of functionalism in
this sense are representation and computation. Psychological states are seen as system-
atically representing the world via a language of thought, and psychological processes
are seen as computations involving these representations. (cf. Fodor: “Particularly strik-
ing in retrospect was the widespread failure to distinguish the computational program in
psychology from the functionalist program in metaphysics; the latter being, approxi-
mately, the idea that mental properties have functional essences” (2000, 105 fn.4)).

• Metaphysical functionalism – is a theory of the nature of the mind, rather than a the-
ory of psychological explanation. It is not concerned with how mental states account for
behavior, but rather with what they are: What is there in common to all mental states of
a certain type M, say pain, in virtue of which they are M? Metaphysical functionalists
characterize mental states in terms of their causal roles, particularly, in terms of their
causal relations to sensory stimulations, behavioral outputs, and other mental states.

In more detail, the core idea of metaphysical functionalism is the following:

• mental states are inner causes of behavior (contra behaviorism) that are specified by
three kinds of clauses
o input clauses which say which conditions typically give rise to which mental
states
o output clauses which say which mental states typically give rise to which behav-
ioral responses
o interaction clauses which say how mental states typically interact

Achim Stephan: Philosophy of Mind. Lecture 8. Physicalisms (functionalisms)

Comment. Notice that there is a linkage between metaphysical and epistemological claims.
According to functionalists, mental states are internal states within us, but we identify and
name them by the effect the world has on them, the effect they have on one another, and the
effect they have on the world causing our behavior (cf. Braddon-Mitchell & Jackson 1996,
41). There are many states and entities which are characterized functionally:

Examples. If living beings die after ingesting food, we have the name “poison” for whatever it
is which causes their death. For an organism to be in pain is for it to be in an internal state
caused by bodily damage and that in turn typically causes winces, groans, certain beliefs, and
escape behavior.

Comment on the connections among the functionalist doctrines just enumerated: (i) function-
alism in all the senses described has something to do with the notion of a Turing machine.
Metaphysical functionalism often identifies mental states with Turing machine “table states”.
Computation-representation functionalism sees psychological explanation as something like
providing a computer program for the mind. Its aim is to give a functional analysis of mental
capacities broken down into their component mechanical processes. If these mechanical proc-
esses are algorithmic, as is sometimes assumed then they will be Turing-computable as well.
(ii) Another similarity among functionalisms is their relation to physical characterizations.
The causal structures with which metaphysical functionalism identifies mental states are real-
izable by a vast variety of physical systems. Similarly, the information processing mecha-
nisms postulated by a particular computation-representation functionalist theory could be real-
ized hydraulically, electrically, or even mechanically. (iii) each type of functionalism legiti-
mates at least one notion of functional equivalence; for example, for functional analysis, one
sense of equivalence would be: has capacities that contribute in similar ways to the capacities
of a whole (e.g. amplifier).

In what follows, we are only concerned with metaphysical functionalisms. Till now, we have
been talking on a rather abstract level; thus, it’s time to be a bit more precise; among the vari-
ous versions of functionalism we usually distinguish

• machine functionalism (or computer functionalism) from
• causal-role functionalism (or causal-theoretical functionalism) which is a more general

characterization

Within both versions we can make further distinctions depending on how the causal roles (or
the machine tables) should be specified in detail, i.e.: What theory specifies the details of the
causal roles – folk psychology or (scientific) empirical psychology, or something else? Fur-
ther, it is important to make sure with what we identify mental states, i.e. with causal roles or
with the bearers of the roles! But, let me first come back to machine functionalism. This ver-
sion is a good candidate to introduce functionalism appropriately:

Machine functionalism (see Block 1980, 173)

Some versions of functionalism are couched in terms of the notion of a Turing machine
(named after the logician Alan Turing: 1912-1954). Turing machines are specified by two
functions: one from inputs and states to outputs, and one from inputs and states to states.

{input}×{state} → {output}
{input}×{state} → {state}

2

Achim Stephan: Philosophy of Mind. Lecture 8. Physicalisms (functionalisms)

A Turing machine has a finite number of states, inputs, and outputs, and the two functions
specify a set of conditionals, one for each combination of state and input. The conditionals are
of this form: if the machine is in state S and receives input I, it will then emit output O and go
into next state S’ (where S’ may be the same state as S; see example from Kim).

The set of conditionals that specifies a Turing machine is often expressed in the form
of a machine table. Any (real) system that has a set of inputs, outputs, and states related in the
way specified by the machine table is described by the machine table and is a realization of
the abstract automaton specified by the machine table.

One very simple version of machine functionalism states that each system that has
mental states is described by at least one Turing machine table of a certain specifiable sort; it
also states that each type of mental state of the system is identical to one of the machine table
states specified in the machine table. Consider, for example, the Turing machine described in
the following “Coke machine” machine table:

1 EURO input S1 S2
50 CENT input
Emit a Coke Emit a Coke and 50 CENT
Stay in S1 Go to S1
Emit no output Emit a Coke
Go to S2 Go to S1

Each cell of this table stands for a behavioral law which specifies what the Coke machine will
do (output) if you put a certain coin in (input) depending on which of its two possible states it
is in.

(1) If the Coke machine is in state S1 and we put in 1 EURO it will emit a Coke and stay
in S1

(2) If the Coke machine is in state S1 and we put in 50 CENT it goes to state S2
(3) If the Coke machine is in state S2 and we put in 1 EURO it will emit a Coke and 50

CENT, and it goes to state S1
(4) If the Coke machine is in state S2 and we put in 50 CENT it will emit a Coke and go to

state S1

Now, what is decisive is that states S1 and S2 are characterized solely by the causal roles given
by the corresponding 4 behavioral laws.

One can get a crude picture of the simple version of machine functionalism described above
by considering the claim that S1 = 1-EURO-desire, and S2 = 50-CENT-desire. Of course, no
functionalist would claim that s Coke machine desires anything. Rather, the simple version of
machine functionalism described so far makes an analogous claim with respect to a much
more complex machine table.

Machine versions of functionalism are useful for many purposes, but they do not provide the
most general characterization of functionalism. One can achieve more generality by character-
izing functionalism as the view that what makes a mental state what it is (e.g., a pain a pain) is
its having a certain causal role. But this formulation buys generality at the prize of vagueness.
However, a more precise formulation can be introduced as follows. It goes back to David
Lewis (1972) who used the idea of so-called Ramsey-sentence of a theory.

3

Achim Stephan: Philosophy of Mind. Lecture 8. Physicalisms (functionalisms)

First, we have to combine the four laws that make up a complete theory of the Coke machine
to one single sentence. We do this by introducing “and”s:

If the Coke machine is in state S1 and we put in 1 EURO it will emit a Coke and stay in
S1; and if the Coke machine is in state S1 and we put in 50 CENT it goes to state S2; and if
the Coke machine is in state S2 and we put in 1 EURO it will emit a Coke and 50 CENT,
and it goes to state S1; and if the Coke machine is in state S2 and we put in 50 CENT it
will emit a Coke and go to state S1.

In the following this sentence will be represented by the abbreviation TCM(CM, S1, S2). Here
the expressions “CM”, “S1”, and “S2” indicate that they denote the Coke machine and its two
functional states, respectively.

Second, we replace in TCM(CM, S1, S2) the expressions “CM”, “S1”, and “S2” by the variables
“x”, “x1”, and “x2” getting herewith the open sentence

TCM(x, x1, x2).

Eventually and third, we get the Ramsey-sentence of TCM(CM, S1, S2) if we bind the variables
“x1” and “x2” by existential quantifiers. Thus we get the sentences

∃x1∃x2TCM(x, x1, x2).

And this sentences claims nothing else than that there exist two states x1 and x2 that have ex-
actly the causal roles of states S1 and S2.

Now, the important thing is that you can use the Ramsey-sentence – which still has the free
variable x and thus is an open sentence – to define both the concept of a Coke machine and
the functional states S1 and S2:

(CM) A system x is a Coke machine of type CM iff ∃x1∃x2TCM(x, x1, x2).

(S1) A system x is in functional state S1 iff ∃x1∃x2(TCM(x, x1, x2) and x is in state x1).

(S2) A system x is in functional state S2 iff ∃x1∃x2(TCM(x, x1, x2) and x is in state x2).

Explicitly, the last clause says that a system x is in functional state S2 iff the system can have
two states that have the causal roles as described by the open sentence ∃x1∃x2(TCM(x, x1, x2)
and x is in the second of the two states.

Comment. It is important to keep two varieties of functionalism here apart: (i) functionalists
who identify a mental state, say pain, with a causal role, (ii) functionalists who identify a
mental state, say pain, with the bearer of that role (Ansgar Beckermann only discusses the
first type of functionalism). Or, in other words:

“from a functionalist perspective, there are two options concerning the metaphysics of
psychological properties. Functionalism says that x is in pain iff x is in a state playing
the pain role, but this thesis about truth conditions for being in pain is compatible with
holding, qua metaphysical thesis, either that pain is the realizer state or that it is the
role state” (Braddon-Mitchell & Jackson 1996, 101).

4

Achim Stephan: Philosophy of Mind. Lecture 8. Physicalisms (functionalisms)

References

Block, Ned (1980) Introduction: What is Functionalism? In: N. Block (ed.) Readings in Phi-
losophy of Psychology. Vol. I. Cambridge, MA: Harvard University Press, 171-184.

Braddon-Mitchell, David & Frank Jackson (1996) Philosophy of Mind and Cognition. Ox-
ford: Blackwell.

Fodor, Jerry (2000) The Mind Doesn’t Work that Way. Cambridge MA: MIT Press.
Kim, Jaegwon (1996) Philosophy of Mind. Boulder: Westview Press.
Lewis, David (1972) Psychophysical and Theoretical Identifications. Australasian Journal of

Philosophy 50, 249-258.

5