I. Multiple realizability: A challenge for identity theory & motivation for functionalism

III. Functionalism and the mind/body problem

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PHL103 Lecture 11-Functionalism

2.

I. Multiple realizability: A challenge for identity theory &
motivation for functionalism
II. Machine functionalism
III. Functionalism and the mind/body problem
IV. Some problems for functionalism

3. I. Multiple realizability: A challenge for identity theory & motivation for functionalism

I. Multiple realizability: A challenge for identity theory
& motivation for functionalism

Recall the basic thesis of identity theory
Every mental state is identical to a physical state of the brain.
Identity theory (Type-physicalism): For any mental state M, there
is a brain state B, such that M = B.
The thesis identifies mental types (e.g. anger, pain, belief) with types of
brain state
PAIN = C-FIBER ACTIVATION
VISUAL IMAGE = BRAIN STATE V
BELIEF = BRAIN STATE B
DESIRE = BRAIN STATE D

5.

Recall the basic thesis
Every mental state is identical to a physical state of the brain.
Identity theory (Type-physicalism): For any mental state M, there
is a brain state B, such that M = B.
The thesis identifies mental types (e.g. anger, pain, belief) with types of
brain state
PAIN = C-FIBER ACTIVATION
Implications:
there are no changes in mental life without changes in the physical
states of the brain (supervenience).
An organism is in pain if and only if a certain type of brain state
occurs; C-fiber activation is both necessary and sufficient for the
mental state PAIN.

6.

The success conditions for identity theory
“Consider what the brain-state theorist has to do to make good on his
claims. He has to specify a physical-chemical state such that any organism
(not just a mammal) is in pain if and only if (a) it possesses a brain of
suitable physical-chemical structure; and (b) its brain is in that physicalchemical state. This means that the physical-chemical state in question
must be a possible physical state of a mammalian brain, a reptilian brain, a
mollusc’s brain…etc. At the same time, it must not be a possible (physically
possible) state of the brain of any physically possible creature that cannot
feel pain. Even if such a state can be found, it must be nomologically
certain that it will also be a state of the brain of any extra-terrrestrial life
that may be found that will be capable of feeling pain before we can even
entertain the supposition that it may be pain” (Putnam, ‘The Nature of
Mental States’, 77).

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Some thought experiments
Octopus pain

8.

Some thought experiments
Octopus pain
Martian pain

9.

The problem: success conditions for identity theory
“…the hypothesis becomes even more ambitious when we realize that the
brain-state theorist is not just saying that pain is a brain state; he is, of
course, concerned to maintain that every psychological state is a brain state.
Thus if we can find even one psychological predicate which can clearly be
applied to both a mammal and an octopus…, but whose physical-chemical
‘correlate’ is different in the two cases, the brain-state theory has collapsed”
(Putnam 77).

10.

Chauvinism and the challenge of multiple realizability
Multiple realizability: Mental states can be realized by different
physical processes or structures.
This is what the thought experiments teach us: it is possible for an
octopus, a human, and a Martian to all experience the same type of
mental state (e.g. PAIN) in spite of significant neural differences
(such that they could not be in the same type of brain state).

11.

Chauvinism and the challenge of multiple realizability
Multiple realizability: Mental states can be realized by different
physical processes or structures.
The possibility of multiple realizability sheds significant doubt upon the
ultimate success of identity theory. This worry can be expressed as a:
Conceptual worry: Agents with the same types of mental states but
differing brains are easily conceived. So identity theory looks
unpromising as a metaphysics of mind.
Empirical worry: It seems “overwhelmingly likely” that we will discover
one creature with the same mental state type but distinct neural
structures. So identity theory looks doomed as a science of the mind.

12.

Chauvinism and the challenge of
multiple realizability
This challenge can also be seen as a motivation
for an alternative theory of mind:
Functionalism.
Instead of thinking of mental states as identified
with brain states, we allow that they are
realized by brain states (in humans), and think
about the states themselves in terms of their
causal-functional roles…

13. II. Machine functionalism

14.

Background:
Computational
technology and
the Turing Test

15.

Functionalism and computers
Machine functionalism (and often
functionalism generally) is
sometimes described by a
computational analogy:
the mind is to the brain as
computer software is to computer
hardware
To understand the analogy, we first
have to understand in basic terms
how a software or program relates
to the computer running it.

16.

Turing machines (Alan Turing, 1950)
Turing machines are abstract computational devices, used to clarify
and analyze what can be computed.
The “state machine” involves a set of instructions that determine
how, given any input, the machine changes its internal states and
outputs. This instruction program is called a machine table.
Turing was interested in whether, in principle, any given task could
be computed in this way.
We are interested in the concept of a Turing machine table, and how
it allows us to define inner states in terms of their relations to
inputs and outputs.

17.

Turing machines
A modified example
Imagine a simple computing machine, whose task is to
distribute pop given the appropriate combination of input.
Pop Machine
Suppose the pop machine accepts only nickels (N) and dimes (D) as
input.
The internal states consist only of (0), (5), (10), and (15)
A pop is outputted only when the machine reaches state 15 (a pop
costs 15 cents); otherwise the machine waits.
With these details in hand, we can construct a set of rules for the
operation of the machine.

18.

Turing machines
A modified example
Imagine a simple computing machine, whose task is to
distribute pop given the appropriate combination of input.
Soda Machine
Rules:
If input (N) and in state (0), then enter state (5) and output (wait).
If input (N) and in state (5), then enter state (10) and output (wait).
If input (N) and in state (10), then enter state (0) and output (soda).
If input (D) and in state (0), then enter state (10) and output (wait).
If input (D) and in state (5), then enter state (0) and output (pop).
If input (D) and in state (10), then enter state (5) and output (pop)
Note that these rules insure task completion and continued
functioning of the machine.

19.

Turing machines.
Soda Machine
Rules:
If
If
If
If
If
If
input (N) and in state (0), then enter state (5) and output (wait).
input (N) and in state (5), then enter state (10) and output (wait).
input (N) and in state (10), then enter state (0) and output (soda).
input (D) and in state (0), then enter state (10) and output (wait).
input (D) and in state (5), then enter state (0) and output (pop).
input (D) and in state (10), then enter state (5) and output (pop)
Machine table:
INPUTS
INTERNAL
STATES
0
N
5/wait
D
10/wait
5
10/wait
0/pop
10
0/pop
5/pop

20.

Turing machines.
Soda Machine
Machine table:
INTERNAL
STATES
INPUTS
0
N
5/wait
D
10/wait
5
10/wait
0/pop
10
0/pop
5/pop
Using this machine table, the inner states of the machine can be
defined in terms of the input-output relations. Thus:
Inner state 5 = the state that is caused by inputting (N) when the machine is in
state (0) and by inputting (D) when the machine is in state (10); that causes an
output of (wait) when input is (N) and an output of (pop) when input is (D); and
that makes the machine enter into state (10) when input is (N) and enter into state
(0) when input is (D).

21.

Turing machines.
Soda Machine
Inner state 5 = (i) the state that is caused by inputting (N) when the machine is in
state (0) and by inputting (D) when the machine is in state (10); (ii) that causes an
output of (wait) when input is (N) and an output of (pop) when input is (D); and
(iii) that makes the machine enter into state (10) when input is (N) and enter into
state (0) when input is (D).
Note that ‘inner state 5’ is thus defined by three types of clause:
(i) the inputs that typically cause it
(ii) the outputs it typically causes
(iii) the inner state changes it typically causes.
All the internal states of the machine can be defined accordingly: in
terms of the causal-functional role in the system.

22.

Turing machines.
Soda Machine
Machine table:
INTERNAL
STATES
INPUTS
0
N
5/wait
D
10/wait
5
10/wait
0/pop
10
0/pop
5/pop
Understanding our pop machine in terms of a machine table makes it
multiply realizable: the only requirement is that it has internal states
that can play the above functional roles.
Our pop machine can thus be understood as a program which can be run
by (realized by) any “computer” with the appropriate causal powers.
Machine functionalism understands the mind analogously: mind is to
brain as computer software (program) is to computer hardware.

23.

Machine functionalism
Mental states can similarly be defined in terms of causal-functional
role; in terms of input-output relations specified by a machine
table.
A toy theory of pain
Suppose we have
two inner states: pain (P) and relief (R)
two inputs: smashing finger with hammer and taking aspirin
two outputs: saying ‘Ouch!’ and saying ‘Ahhh’.
INPUTS
INTERNAL
STATES
Hammer smash
finger
Take aspirin
P
P/ ‘Ouch!’
R/ ‘Ahhh’
R
P/ ‘Ouch!’
R/ ‘Ahhh’

24.

Machine functionalism
A toy theory of pain
INTERNAL
STATES
INPUTS
Hammer smash
finger (HS)
Take aspirin
(TA)
P
P/ ‘Ouch!’
R/ ‘Ahhh’
R
P/ ‘Ouch!’
R/ ‘Ahhh’
Just as we did with the internal states of Pop machine, we can define
these mental states (on this simple theory of pain) by inputoutput relations.
Mental state P = (i) the state that that is caused by input (HS) when one is in state
(P) and caused by input (HS) when one is in state (R); (ii) that causes output
“Ouch!” when one is in state (P) and input is (HS) and that causes output “Ahhh”
when one is in P and input is (TA); and that causes the system to enter into state
(P) when input is (HS) and enter into state (R) when input is (TA).

25.

Machine functionalism
A toy theory of pain
INPUTS
INTERNAL
STATES
Hammer smash
finger (HS)
Take aspirin
(TA)
P
P/ ‘Ouch!’
R/ ‘Ahhh’
R
P/ ‘Ouch!’
R/ ‘Ahhh’
Mental state P = (i) the state that that is caused by input (HS) when one is in state
(P) and caused by input (HS) when one is in state (R); (ii) that causes output
“Ouch!” when one is in state (P) and input is (HS) and that causes output “Ahhh”
when one is in P and input is (TA); and that causes the system to enter into state
(P) when input is (HS) and enter into state (R) when input is (TA).
Note again that the internal states are defined by 3 types of clause:
(i) the inputs that typically cause it
(ii) the outputs it typically causes
(iii) the inner state changes it typically causes.

26.

Machine functionalism and
computational theory of mind
Thus early functionalism theorized
the mind as an (admittedly
complex) computer, where
mental states are understood in
terms of their computational
role.

27.

Machine functionalism and computational theory of mind
The computational analogy is a powerful one: to think of minds in
terms of mental operations (a la computational operations) is to
abstract from the material realization (the hardware) of those
operations and focus on the operations themselves, in terms of
their functional roles.
Minds can thus be understood in terms of these higher level
properties, not in terms of lower level physical properties (e.g.
brains or computer chips).
Machine functionalism accommodates multiple realizability:
computers are multiply realizable
if minds are computers, then minds will be multiply realizable

28.

Functionalism-The basic idea
Mental states are internal states of a system, identified with the
causal-functional role they play in that system.
For any state Φ, these roles are defined in terms of 3 types of
clause:
(i) Input clause: the inputs that typically cause Φ
(ii) Output clause: the outputs Φ typically causes
(iii) Internal mediation clause: the inner state changes Φ typically
causes.
Mental states are thus identified with a job description:
The state PAIN is identified with…
The state VISUAL IMAGE is identified with…
The state BELIEF is identified with…
…

29.

Arguments and motivation
Inference to the best explanation
“I contend…that this hypothesis, in spite of it admitted vagueness, is far
less vague than the ‘physical-chemical’ state hypothesis is today, and far
more susceptible to investigation of both a mathematical and an
empirical kind. Indeed, to investigate this hypothesis is just to attempt
to produce ‘mechanical’ models of organisms—and isn’t this, in a sense,
just what psychology is about?” (Putnam 76).
“I shall now compare the hypothesis just advanced with (a) the hypothesis
that pain is a brain state, and (b) the hypothesis that pain is a behavior
disposition” (Putnam 76).
The implication, once identity theory and other materialist theories
are considered, is that by inference to the best explanation,
functionalism is the best theory.
…What does it better explain?

30.

Arguments and motivation
Multiple realizability

31.

Arguments and motivation
Explanation without theoretical commitment re. substance of the
mind

32.

Arguments and motivation
Accommodation of causal role of mental
Substance Dualism

33.

Arguments and motivation
Inference to the best explanation
Insofar as functionalism provides the best explanation with respect
to these and other features of the mind, we have good abductive
evidence that it is the correct theory.

34. III. Functionalism and the mind/body problem

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38.

The mind/body problem
The logical problem
Inconsistent tetrad:
(1) The human body is a material thing.
(2) The human mind is a spiritual thing.
(3) Mind and body causally interact.
(4) Spirit and matter do not causally interact.
Possible solutions:
Functionalism can remain non-committal on which proposition
to deny: it requires only that mental states are casualfunctional roles.
And since causal-functional roles are multiply realizable, the
mind could be material OR immaterial.
Functionalism?

39.

The mind/body problem
The logical problem
Inconsistent tetrad:
(1) The human body is a material thing.
(2) The human mind is a spiritual thing.
(3) Mind and body causally interact.
(4) Spirit and matter do not causally interact.
Possible solutions:
So although functionalists tend to be materialists: functionalism
as such provides an explanation of mental states without
committing to the substantial nature of the mind.
Functionalism?

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