Computational Functionalism
Motivations




A functionalist general purpose input-output
device certainly sounds like a computer
Mind does informational things
A machine implementation of functionalism is
natural
Computational functions are multiply realisable
Turing Machine

Turing machines consist
of:




an infinite tape divided
into squares
a head that reads from
and writes to the tape
a finite set of internal
states; q0, …, qn
a finite alphabet; b1, …, bm
Turing Machine
1
q0
q1
1Rq0
#Halt
+
1Rq0
#
#Lq1
# # 1 1 1
q0
+
1 1 # #
Turing Machine
1
q0
q1
1Rq0
#Halt
+
1Rq0
#
#Lq1
# # 1 1 1
q0
+
1 1 # #
Turing Machine
1
q0
q1
1Rq0
#Halt
+
1Rq0
#
#Lq1
# # 1 1 1
q0
+
1 1 # #
Turing Machine
1
q0
q1
1Rq0
#Halt
+
1Rq0
#
#Lq1
# # 1 1 1
+
q0
1 1 # #
Turing Machine
q0
q1
1
1Rq0
#Halt
+
1Rq0
#
#Lq1
# # 1 1 1 1 1 1 # #
q0
Turing Machine
q0
q1
1
1Rq0
#Halt
+
1Rq0
#
#Lq1
# # 1 1 1 1 1 1 # #
q0
Turing Machine
q0
q1
1
1Rq0
#Halt
+
1Rq0
#
#Lq1
# # 1 1 1 1 1 1 # #
q0
Turing Machine
q0
q1
1
1Rq0
#Halt
+
1Rq0
#
#Lq1
# # 1 1 1 1 1 1 # #
q1
Turing Machine
q0
q1
1
1Rq0
#Halt
+
1Rq0
#
#Lq1
# # 1 1 1 1 1 # # #
Halt
Turing Machine
1
+
#
q0
q1
#Rq1
1Rq1
1Halt
# # 1 1 1 + 1 1 # #
q0
Machine Functionalism

The computational functionalist claim is that the
mind can be thought of as a TM

Mental states of Stephen are to be identified
with the internal states of Stephen’s TM
Psychology

Instrumentalism
A theory predicts

Realism
A theory explains
Difficulties

Identity
What does it means for A to have the same mental
state as B?
 q0 is only definable as the triplet:
{<1, 1Rq0>, <+, 1Rq0>, <#, #Lq1>}
 Each state is defined in terms of the other states
 Different psychologies can’t even be compared

Difficulties

Simulation

Do we think that a weather simulation program
actually has weather going on inside it?
Turing Test

If a machine passes a test that we think could
only be passed by a thinking thing then we have
no grounds to deny that the machine is thinking.

Have a conversation with A and B, one of them
a machine, the other a person. If you can’t tell
which is the machine then both are thinking.
The Chinese Room

Searle thought that the idea that mental states
could be identified with computational states
was almost demonstrably incorrect.
The Chinese Room

Responses

System
The room + the man + … understands

Reply
Let him memorise it all
The Chinese Room

Responses

Robot
Connect the room to the world

Reply
What is the robot really receiving?
The Chinese Room

Responses

Simulator
Make the room look like the brain

Reply
Where’s computation now?
The Chinese Room

Searle thinks that only machines can think, ie.
brains, but not by computing.