6.       The Identity Theory

Identity theory: Every mental state is identical to some brain state

But doesn’t imply that the Mind the brain.

1.                    Not all brain states are mental states

2.                    it’s a theory of mental states, not of the mind.

Origins of the Theory

Modelled on scientific identities for heat, lightning, , …

Occam’s Razor

Occam’s Razor: Don’t multiply entities beyond necessity

Lightning always occurs with electric discharge. First assumption is that they are the same thing.

Pain occurs with C-fibre firings, so assume they are the same thing.

                But this assumption is wrong.

The situation is:

1.                    pain = occupant of causal role R

2.                    occupant of R = brain state B

3.                    pain = B

So only need transitivity of identity, not Occam’s razor.

The Identity Theory and Functionalism

Functionalism, physicalism, identity theory

IT is a type of functionalism where the role occupants of mental states are brain states.

Since they are physical brain states that occupy the relevant roles, IT is a type of physicalism

Descartes

Note that Descartes was a dualist because he thought no physical states could play the proper roles. There is a lack of flexibility, freedom, etc.

Some Early Objections to the Identity Theory

1.                    Why did it take so long to realise this?

It takes time to establish scientific facts

2.                    Why aren’t we immediately and always aware of this

For the same reason as with other identities – e.g. water = H₂O

First-person third-person asymmetry

Why is my knowledge of my own mental state different from my knowledge of others’?

a.             Mental states are internal brain states. I can’t have knowledge of your mental states in the same way because yours aren’t internal to me.

b.             We are aware of brain states not as such but through high level relational features.

Leibniz’s Law

Mental states and brain states have very different properties; so by LL they can’t be the same states.

e.g. brain states have temperatures, but mental states don’t.

The denial of mental objects

Distinguish between mental states and mental objects: ‘I have a pain’ is not like ‘I have a hat’ but is more like ‘I have a limp.’ There are no objects called ‘limps’ to be had. Nor are there ‘pains.’

So there are no mental objects whose properties may be contrasted with physical objects.’

Similarly with beliefs – distinguish the state of believing from the thing believed, the proposition.

Token-Token versus Type-Type Identity Theories

The type/token distinction

Particular things are tokens of a type or class to which they belong. This table is a token of the type ‘table.’

Scientific identities are type-type

Is the IT identifying mental tokens with physical tokens, or types with types?

(Note that an identity of the latter kind implies an identity of the former kind.)

Scientific theories always make type-type identities. So does the IT.

Functionalism and type-type identities

Functionalist theories also make type-type identifications, so, if we want to see IT as a F-ist theory of mind, we’ll prefer it to be understood as a type-type theory.

Multiple realizability and type-type identity

Or maybe not! It may be that the assumption of multiple realizability makes type-type identities impossible. Different types of B state might play the functional role of any M state in different creatures. ‘D-fibres’ in a dolphin do what C-fibres do for us. But as pain = pain, that would imply that D-fibres = C-fibres, which is wrong.

A token-token theory, on the other hand, only says that any token of pain in a dolphin is a token of D-fibring, etc. The psychological type pain is, however, defined as being in the state playing the functional role of pain.

Restricted identities

A different response. Keep the type-type identities, but restrict them.

Compare: money is functionally defined. Any physical kinds could be role players for money; but in any society there are specific physical kinds that actually do play the roles.

So: IT could say, ‘pain-in-dolphins = D-fibres, whereas pain-in-humans = C-fibres.’

Mental types are causes

This is better, because then pain can be a cause of behaviour, insofar, that is, as a type can be a cause of a type. (Of course, it’s actually tokens that have causal powers.)

Role state versus realizer state

A realizer state is the state that occupies the functional role.

A role state is the state of having the role occupied.

E.g. cyanide and strychnine are realizer states for poisoning you, and being poisoned is the role state.

So, a functionalist can say pain is the realizer state or the role state, and the M-B IT claims the former, so mental states can be causally effective.

*Essentialism about Psychological States

It’s not an essential feature of a B-state that it has the functional role it does; therefore it isn’t essential to a M-state that it is the M-state that it is.

E.g. C-fibres firing might not have been pain in people.

Contingent identities

So, there’s a difference between identities in M-B IT and identities in science.

The former are contingent, but the latter are probably necessary. Water is necessarily H₂O, even though we only know that a posteriori.

What are contingent in those identities are the statements of identity.