The Identity Theory The Identity Theory says that mental states are physical states of the brain Cf Property dualism which says they are nonphysical states of the brain Clarification The Identity Theory says that ID: 311517
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Slide1
The Identity TheorySlide2
The Identity Theory
The Identity Theory says that mental states are physical states of the brain.
Cf. Property dualism, which says they are non-physical states of the brain.Slide3
Clarification
The Identity Theory says that
all
mental states are brain states.
It does
not
say that all brain states are mental states.
We might characterize it:
certain
brain states are mental states.Slide4
Mental States
Brain StatesSlide5
More Specific Claims
Conscious visual perception = high levels of neural activity in V1.
Experience of pain = C-fibers firing.
Type of mental state = type of brain state.Slide6
J. J. C. Smart
J. J. C. Smart is one of the best-known 20
th
Century identity theorists.
At the beginning of his career he was a behaviorist, but later defended the Identity Theory.Slide7
Smart’s Analogy
For Smart, the claim
Mental states are brain states.
w
as a lot like the claims:
Water is H
2
O.
Lightining is an electrical discharge.Slide8
Smart’s Analogy
These identities are:
Not obvious
Not easily discovered
Not part of the meanings of the words
(Compare “Bachelors are unmarried men,” or “Hens are female chickens.”)Slide9
Type vs. TokenSlide10
Type vs. TokenSlide11
Examples
“Scientists have discovered a 10,000 year old fish.”
“Dinosaurs are extinct.”
“I have hundreds of foreign coins.”Slide12
Types and Properties
Standardly, types and properties are considered to be the same thing. The type dog = the property of being a dog.
Tokens of a type are specific instances: things that have those properties.Slide13
Type Identity Theory
Type identity theory claims that mental properties (mental states) are identical to properties of brains (brain states).
The property of being water = the property of being H2O.
The property of being a mental state = the property of being (certain) brain states.Slide14
Token Identity Theory
(Token identity theory is more difficult to understand. We’ll talk about it next time.)Slide15
Arguments for the identity theorySlide16
1. MSs Caused by States of the World
According to the Identity Theorist, the fact that mental states are caused by states of the world is the same fact as the fact that brain states are caused by states of the world.Slide17Slide18Slide19Slide20Slide21
2. Some MSs Cause Actions
For the Identity Theorist, this is the same as the claim that certain brain states cause actions. Again, the evidence for this is very strong.Slide22Slide23
Some MSs Cause Other MSs
(In Reason-Respecting Ways)
We can tell from what we’ve already seen that brain states cause other brain states.
But can the identity theorist explain why these processes are rational/ logical? Slide24
Evidence from deficit studiesSlide25
Phineas GageSlide26Slide27
From RavenscroftSlide28
While he was recovering, his family says he amused his nieces and nephews by making up fun stories.
A doctor did say he was changed– while he was recovering. But he said he was fine afterward.
He did lose his job– because his old employer wouldn’t take him back when he was better.Slide29
Later in his life a doctor said Gage experienced ‘no impairment whatsoever.’
Gage did die early– but that’s because he experienced severe brain trauma.
No credible report says that he was an alcoholic or irresponsible.Slide30Slide31
Expressive Aphasia
Broca’s
aphasia (expressive aphasia) results from damage to
Broca’s
area. Here, patients can understand language perfectly, but can’t produce it. Here’s one patient explaining why he was at the hospital:
“Yes... ah... Monday...
er
... Dad and Peter H... (his own name), and Dad.... er
... hospital... and ah... Wednesday... Wednesday, nine o'clock... and oh... Thursday... ten o'clock, ah doctors... two... and doctors... and er... teeth... yah
.
”Slide32
Video Time!
http://
www.youtube.com/watch?v=1aplTvEQ6ew
Slide33
Arguments against the identity theorySlide34
Leibniz’s Law
Also known as “the indiscernibility of
identicals
”
If X = Y, then X and Y have all the same properties.
[Converse] If X and Y
don’t
have all the same properties, then X ≠ Y.Slide35
Example
Property: drives a motorcycle
Sally = the tallest person in the room.
Sally drives a motorcycle.
Therefore, the tallest person in the room drives a motorcycle.Slide36
Example
Property: being red
My car is red (has the property of being red.
That car is not red (does not have the property
).
Since my car and that car don’t have all the same properties, that car is not my car.Slide37
Type Example
Property: boils at 100 degrees Celsius.
Water = H2O.
Water boils at 100 degrees Celsius.
Therefore, H2O boils at 100 degrees Celsius.Slide38
Schema of Objection to Identity Theory
Mental state S has property P.
No brain state has property P.
Therefore mental state S is not a brain state.Slide39
Objection 1
My pain [a mental state] is in my foot.
No brain state is in my foot.
Therefore, my pain is not any brain state.Slide40
Response
You have no pain in your foot.
You have a brain state that registers or represents a state of your foot.
This is why you can feel a pain in your foot even when you have no foot (phantom pain).Slide41
Objection 2
Activity in V1 has a frequency.
My visual sensation of red does not have a frequency.
Therefore, activity in V1 is not my visual sensation of red. Slide42
Neuronal FrequencySlide43
Response
How do you know that?
Science has discovered that your sensation of red does have a frequency.
Science discovers new and interesting things all the time.Slide44
Final LL Objection
My pain hurts.
My brain don’t hurt.
Therefore, pain
ain’t
brain.Slide45
“Multiple Realizability
”Slide46
Mental Multiple RealizabilitySlide47
Argument from M.R.
If souls, squid, aliens, and robots can all feel pain, then pain can’t be a brain state, because these things don’t have brains.
Maybe all human pains are brain states, but being a mental state type is not the same thing as being a brain state type.Slide48
Dualism Doesn’t Follow
Mental states are multiply realizable, and so can’t be type-identified with brain states. Does that mean that the mind is not the brain?
No. Having $5 is multiply realizable, and can’t be identified with having a coin like this one in my pocket. But right now the coin in my pocket
is
the $5 I have.Slide49
Reductive &
Nonreductive
Physicalism
One way to maintain
physicalism
is to say that whenever you have a mental state, it is in fact (token identical) to a physical state.
BUT, there’s no particular physical state a thing has to have to be that mental state. And maybe even a non-physical thing could have that mental state (there just aren’t any such things).Slide50
summarySlide51
The Identity Theory says that mental states and certain brain states are type-identical.
The theory is consistent with physics and explains the causal interactions between mind and world (maybe not rationality).
A principal objection to the theory is the apparent multiple
realizability
of mental states.Slide52
Functionalism
What does a token-identity
physicalist
theory look like? We’ll find out next time!