The Identity Theory

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.

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.

Mental States

Brain States

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.

J. J. C. Smart

J. J. C. Smart is one of the best-known 20th Century identity theorists.

At the beginning of his career he was a behaviorist, but later defended the Identity Theory.

Smart’s Analogy

For Smart, the claim

Mental states are brain states.

was a lot like the claims:

Water is H2O.Lightining is an electrical discharge.

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.”)

Type vs. Token

Type vs. Token

Examples

• “Scientists have discovered a 10,000 year old fish.”

• “Dinosaurs are extinct.”• “I have hundreds of foreign coins.”

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.

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.

Token Identity Theory

(Token identity theory is more difficult to understand. We’ll talk about it next time.)

ARGUMENTS FOR THE IDENTITY THEORY

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.

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.

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?

EVIDENCE FROM DEFICIT STUDIES

Phineas Gage

From Ravenscroft

• 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.

• 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.

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.”

Video Time!

http://www.youtube.com/watch?v=1aplTvEQ6ew

ARGUMENTS AGAINST THE IDENTITY THEORY

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.

Example

Property: drives a motorcycle

1. Sally = the tallest person in the room.2. Sally drives a motorcycle.3. Therefore, the tallest person in the room

drives a motorcycle.

Example

Property: being red

1. My car is red (has the property of being red.2. That car is not red (does not have the

property).3. Since my car and that car don’t have all the

same properties, that car is not my car.

Type Example

Property: boils at 100 degrees Celsius.

1. Water = H2O.2. Water boils at 100 degrees Celsius.3. Therefore, H2O boils at 100 degrees Celsius.

Schema of Objection to Identity Theory

1. Mental state S has property P.2. No brain state has property P.3. Therefore mental state S is not a brain state.

Objection 1

1. My pain [a mental state] is in my foot.2. No brain state is in my foot.3. Therefore, my pain is not any brain state.

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).

Objection 2

1. Activity in V1 has a frequency.2. My visual sensation of red does not have a

frequency.3. Therefore, activity in V1 is not my visual

sensation of red.

Neuronal Frequency

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.

Final LL Objection

1. My pain hurts.2. My brain don’t hurt.3. Therefore, pain ain’t brain.

“Multiple Realizability”

Mental Multiple Realizability

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.

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.

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).

SUMMARY

• 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.

Functionalism

What does a token-identity physicalist theory look like? We’ll find out next time!