Computational Functionalism

Motivations A functionalist general purpose input-output device certainly sounds like a computer A functionalist general purpose input-output device certainly sounds like a computer Mind does informational things Mind does informational things A machine implementation of functionalism is natural A machine implementation of functionalism is natural Computational functions are multiply realisable Computational functions are multiply realisable

Turing Machine Turing machines consist of: Turing machines consist of: an infinite tape divided into squares an infinite tape divided into squares a head that reads from and writes to the tape a head that reads from and writes to the tape a finite set of internal states; q 0, …, q n a finite set of internal states; q 0, …, q n a finite alphabet; b 1, …, b m a finite alphabet; b 1, …, b m

Turing Machine # # # # q 0 q0q0q0q0 q1q1q1q1 1 1Rq 0 #Halt + # #Lq 1

Turing Machine # # # # q 0 q0q0q0q0 q1q1q1q1 1 1Rq 0 #Halt + # #Lq 1

Turing Machine # # # # q 0 q0q0q0q0 q1q1q1q1 1 1Rq 0 #Halt + # #Lq 1

Turing Machine # # # # q 0 q0q0q0q0 q1q1q1q1 1 1Rq 0 #Halt + # #Lq 1

Turing Machine # # # # q 0 q0q0q0q0 q1q1q1q1 1 1Rq 0 #Halt + # #Lq 1

Turing Machine # # # # q 0 q0q0q0q0 q1q1q1q1 1 1Rq 0 #Halt + # #Lq 1

Turing Machine # # # # q 0 q0q0q0q0 q1q1q1q1 1 1Rq 0 #Halt + # #Lq 1

Turing Machine # # # # q 1 q0q0q0q0 q1q1q1q1 1 1Rq 0 #Halt + # #Lq 1

Turing Machine # # # # # Halt q0q0q0q0 q1q1q1q1 1 1Rq 0 #Halt + # #Lq 1

Turing Machine # # # # q 0 q0q0q0q0 q1q1q1q1 1 #Rq 1 1Rq 1 +1Halt #

Machine Functionalism The computational functionalist claim is that the mind can be thought of as a TM 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 Mental states of Stephen are to be identified with the internal states of Stephen’s TM

Psychology Instrumentalism Instrumentalism A theory predicts Realism Realism A theory explains

Difficulties Identity Identity What does it means for A to have the same mental state as B? What does it means for A to have the same mental state as B? q 0 is only definable as the triplet: q 0 is only definable as the triplet: {,, } Each state is defined in terms of the other states Each state is defined in terms of the other states Different psychologies can’t even be compared Different psychologies can’t even be compared

Difficulties Simulation Simulation Do we think that a weather simulation program actually has weather going on inside it? 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. 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. 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. Searle thought that the idea that mental states could be identified with computational states was almost demonstrably incorrect.

The Chinese Room Responses Responses System System The room + the man + … understands Reply Reply Let him memorise it all

The Chinese Room Responses Responses Robot Robot Connect the room to the world Reply Reply What is the robot really receiving?

The Chinese Room Responses Responses Simulator Simulator Make the room look like the brain Reply Reply Where’s computation now?

The Chinese Room Searle thinks that only machines can think, ie. brains, but not by computing. Searle thinks that only machines can think, ie. brains, but not by computing.