Philosophy 4610Philosophy 4610

Philosophy of MindPhilosophy of Mind

Week 5: FunctionalismWeek 5: Functionalism

Theories of Mind: RECAPTheories of Mind: RECAP• DUALISM DUALISM (Descartes): Mind and body (Descartes): Mind and body

are distinct substances. Body is are distinct substances. Body is physical and exists in physical space, physical and exists in physical space, but the mind is non-physical and does but the mind is non-physical and does not exist in physical spacenot exist in physical space

• PHYSICALISMPHYSICALISM: Everything in the world, : Everything in the world, including “minds”, is physical. What including “minds”, is physical. What we talk about when referring to the we talk about when referring to the “mind” is just physical processes and “mind” is just physical processes and events.events.

Theories of Mind: RECAPTheories of Mind: RECAP• PHYSICALISM breaks down into a PHYSICALISM breaks down into a

number of distinct sub-theories:number of distinct sub-theories:– Logical BehaviorismLogical Behaviorism: Mental states are : Mental states are

just ways of behaving, or being disposed just ways of behaving, or being disposed to behave.to behave.

– Identity TheoryIdentity Theory: Mental states (states of : Mental states (states of the mind) are identical with physical the mind) are identical with physical states of the brain.states of the brain.

– FunctionalismFunctionalism: Mental states are : Mental states are functionalfunctional states of the whole organism. states of the whole organism.

FunctionalismFunctionalism• The Functionalist The Functionalist

theory of mind was first theory of mind was first proposed by Putnam proposed by Putnam and a few others in the and a few others in the early 1960searly 1960s

• Though it is usually Though it is usually understood as a understood as a physicalistphysicalist theory, it is theory, it is an alternative to both an alternative to both behaviorismbehaviorism and the and the identity theoryidentity theory..

Multiple realizability: Multiple realizability: An objection to the Identity An objection to the Identity TheoryTheory• According to the Identity Theory, According to the Identity Theory,

every mental state is every mental state is identicalidentical to a to a brain state. brain state.

• For instance, the state of For instance, the state of being in being in painpain might be identical to brain state might be identical to brain state R1R1, a certain rate of neurons firing in , a certain rate of neurons firing in the temporal lobes.the temporal lobes.

Multiple realizability: My pain Multiple realizability: My pain and squid painand squid pain• However, a squid or a However, a squid or a

Martian can also be in a Martian can also be in a state of having pain.state of having pain.

• But the squid’s brain is But the squid’s brain is essentially different from essentially different from mine: although the squid mine: although the squid has pain, it is has pain, it is nevernever in in state R1.state R1.

• It follows that the identity It follows that the identity theory’s identification of theory’s identification of pain with state R1 must pain with state R1 must be incorrectbe incorrect

Functionalism: Multiple Functionalism: Multiple RealizabilityRealizability• ““Consider what the brain-state theorist has Consider what the brain-state theorist has

to do to make good his claims. He has to to do to make good his claims. He has to specify a physical-chemical state such that specify a physical-chemical state such that any organism (not just a mammal) is in any organism (not just a mammal) is in pain if and only if (a) it possesses a brain of pain if and only if (a) it possesses a brain of a suitable physical chemical structure; and a suitable physical chemical structure; and (b) its brain is in that physical-chemical (b) its brain is in that physical-chemical state . . .” (p. 77)state . . .” (p. 77)

• But this is implausible. We need a more But this is implausible. We need a more generalgeneral way of identifying mental states way of identifying mental states with states of the organism (if we still want with states of the organism (if we still want to be physicalists at all) to be physicalists at all)

FunctionalismFunctionalism• These considerations led Putnam to These considerations led Putnam to

suggest the functionalist theory of mind. suggest the functionalist theory of mind. • ““I shall . . . argue that pain is not a brain I shall . . . argue that pain is not a brain

state in the sense of a physical-chemical state in the sense of a physical-chemical state of the brain (or even the whole state of the brain (or even the whole nervous system), but another kind of nervous system), but another kind of state entirely. I propose the hypothesis state entirely. I propose the hypothesis that pain, or the state of being in pain, is that pain, or the state of being in pain, is a functional state of the whole a functional state of the whole organism.” (p. 75)organism.” (p. 75)

What is a functional state?What is a functional state?-A -A functional partfunctional part

of an organism of an organism or system is or system is defined in terms defined in terms of what it of what it does does rather than what rather than what it is composed of it is composed of or what actual or what actual shape it takes.shape it takes.

-Example: Brakes-Example: Brakes

What is a functional state?What is a functional state?• Similarly, a functional state can be Similarly, a functional state can be

defined in terms of defined in terms of what the organism what the organism doesdoes rather than the actual rather than the actual composition of the internal state.composition of the internal state.

• Example: Example: being thirstybeing thirsty. We might . We might define being thirsty in terms of the define being thirsty in terms of the organism’s tendency to move toward organism’s tendency to move toward water, to drink, etc. water, to drink, etc.

Functionalism vs. Identity Functionalism vs. Identity TheoryTheory

• If this is right, then one and the same If this is right, then one and the same functional statefunctional state – e.g. being thirsty – can – e.g. being thirsty – can be identical with a variety of different be identical with a variety of different brain states in different organisms. brain states in different organisms. One One and the same function can be served and the same function can be served by a variety of different brain states.by a variety of different brain states.

• Thus, the functionalist avoids the problem Thus, the functionalist avoids the problem of of multiple realizabilitymultiple realizability that made that made trouble for the identity theoristtrouble for the identity theorist

Functionalism vs. Functionalism vs. BehaviorismBehaviorism• For the functionalist, mental states are For the functionalist, mental states are

recognizedrecognized by the behavior they cause: “… by the behavior they cause: “…let us begin with the fact that we identify let us begin with the fact that we identify organisms as in pain, or hungry, or angry, or organisms as in pain, or hungry, or angry, or in heat, etc., on the basis of their behavior” in heat, etc., on the basis of their behavior” (p. 77)(p. 77)

• But they are not But they are not identicalidentical with these with these behaviors (as the logical behaviorist would behaviors (as the logical behaviorist would hold). Rather, the functional state is hold). Rather, the functional state is whatever underlying state whatever underlying state causescauses the the behavior, without being identical with it. behavior, without being identical with it.

Functionalism:Functionalism: The Computer Model of Mind The Computer Model of Mind

• Another important Another important influence on Putnam, influence on Putnam, and on functionalism in and on functionalism in general, is the analogy general, is the analogy between between mindsminds and and computerscomputers. .

• Like minds, computers Like minds, computers can be defined can be defined purely purely functionallyfunctionally without without reference to the actual reference to the actual physical parts that physical parts that make them up.make them up.

The computer model of The computer model of mindmind

• When Putnam wrote When Putnam wrote in the early 1960s, in the early 1960s, computer technology computer technology was still at an early was still at an early stage. Computers stage. Computers took up a lot of took up a lot of space, and weren’t space, and weren’t very fast.very fast.

• Today computers Today computers have advanced a have advanced a great deal and come great deal and come to be a part of almost to be a part of almost every aspect of our every aspect of our daily lives.daily lives.

Functional analysisFunctional analysis• The computer model of mind holds that The computer model of mind holds that

minds, like computers, are simply minds, like computers, are simply complex complex information-processing information-processing systems systems that can be analyzed in that can be analyzed in functional terms.functional terms.

• To give a functional analysis, we begin To give a functional analysis, we begin by thinking about what the system or by thinking about what the system or organism organism doesdoes as a whole. as a whole.

• Then we start thinking about Then we start thinking about whatwhat functionally described and related parts functionally described and related parts are needed to accomplish this.are needed to accomplish this.

Functional analysisFunctional analysis• Example: human face-recognitionExample: human face-recognition

• We can give a general functional description We can give a general functional description in terms of information flow in terms of information flow without without knowing anything about the actual knowing anything about the actual physical make-up of the systemphysical make-up of the system that is that is carrying out these functions.carrying out these functions.

• If the computer model is right, then it is the If the computer model is right, then it is the job of cognitive science to give such a job of cognitive science to give such a description or analysis, without worrying description or analysis, without worrying about the specific material basis of the parts about the specific material basis of the parts described. described.

The computer model: The computer model: Turing MachinesTuring Machines

• In the late 1940s – before there even In the late 1940s – before there even were computers at all – Alan Turing were computers at all – Alan Turing gave a general functional model that gave a general functional model that actually works as a description of all actually works as a description of all actual computers, and more actual computers, and more generally generally allall information-processing information-processing systems.systems.

Turing machinesTuring machines

Turing machinesTuring machines• The Turing machine is a kind of The Turing machine is a kind of

general functional architecture for general functional architecture for any computer or any information-any computer or any information-processing system whatsoever. processing system whatsoever.

• Turing machines are also Turing machines are also multiply multiply realizablerealizable – we can build them out of – we can build them out of whatever materials we like. In fact, whatever materials we like. In fact, the description of the Turing machine the description of the Turing machine “program” has nothing to do with the “program” has nothing to do with the physics or chemistry of the actual physics or chemistry of the actual underlying states. underlying states.

The computer model and The computer model and cognitive sciencecognitive science

• The idea of functional description and the The idea of functional description and the computer model gave scientists access to a computer model gave scientists access to a very general and abstract way of talking about very general and abstract way of talking about mind in terms of what they do.mind in terms of what they do.

• This allowed researchers in artificial intelligence, This allowed researchers in artificial intelligence, computer science, psychology, engineering, and computer science, psychology, engineering, and many other fields to address a unified subject-many other fields to address a unified subject-matter: the matter: the science of information-processingscience of information-processing (whatever the material basis or substrate). (whatever the material basis or substrate).

• This is what came to be called “cognitive This is what came to be called “cognitive science.” It brings together research in all these science.” It brings together research in all these different fields into a unified field of study of different fields into a unified field of study of information-processing systems, defined in information-processing systems, defined in functional terms.functional terms.

Functionalism and the Functionalism and the computer model: Summarycomputer model: Summary

• Functionalists are (usually) physicalists, but instead of Functionalists are (usually) physicalists, but instead of identifying mental states with identifying mental states with behaviorbehavior or with or with physical brain statesphysical brain states, they identify them with , they identify them with functionally described states of the whole organism.functionally described states of the whole organism.

• This allows them to identify and describe mental This allows them to identify and describe mental states that can be shared even by organisms or states that can be shared even by organisms or systems with very different material substrates.systems with very different material substrates.

• Functional analysis treats the mind as an information-Functional analysis treats the mind as an information-processing system – on the level of functional processing system – on the level of functional description, essentially the same as a computer.description, essentially the same as a computer.

• By allowing researchers in different areas of By allowing researchers in different areas of psychology and engineering to communicate, this psychology and engineering to communicate, this model of mind has proved deeply influential in the model of mind has proved deeply influential in the development and growth of “cognitive science” from development and growth of “cognitive science” from the 1960s to today. the 1960s to today.