1. The Mind-Brain Type Identity Theory
Michael Lacewing
© Michael Lacewing

2. Substance and properties
A substance is an entity, a thing, that does not depend on another entity for its continued existence.
It has ‘ontological independence’.
Substances are what possess properties.
Properties can’t exist without substances
They depend on substances to exist.
Substances persist through changes in properties.

3. Dualism and materialism
Dualism: there are two sorts of substance, mind (or soul) and matter
Minds can exist independent of bodies
Mental properties are properties of a mental substance
Materialism: there is just one sort of thing, matter
Mental properties are properties of a material substance (a brain or person)

4. Type identity theory Substances can have different sorts of properties
Swan: bird (biological), white (colour)
Are mental properties a sort of physical property?
Type identity theory: mental properties just are physical properties
E.g. Thinking a thought is exactly the same thing as certain neurones firing

5. Type identity theory Identity is not correlation
Hearts and kidneys; size and shape
Neuroscience can only establish correlations
Philosophy: Appeal to Ockham’s razor: don’t multiply entities beyond necessity
‘Type’ identity
Mental types of thing are actually physical types of thing
They don’t seem the same because we have different ways of knowing about them

6. Reduction
Ontological reduction: the things in one domain (e.g. mental things) are identical with some of the things in another domain.
There is nothing more to a mental property than being a particular physical property
This is not conceptual or ‘analytic’ reduction
The claim is not that ‘pain’ means ‘the firing of nociceptors’
But that two distinct concepts pick out just one property

7. Multiple realizability
Putnam: Mental properties are not identical to physical properties because the same mental property can be ‘realized by’ different physical properties
e.g. the brain states that relate to pain are different in different species, but pain is the same mental state.

8. Multiple realizability
A priori form:
It is conceivable, and therefore possible, for a being with quite a different physical constitution from us to have the same thoughts or sensations.
But it is inconceivable, and therefore impossible, for something both to have and not have a certain property.
Therefore, mental properties can’t be the same as physical properties.

9. The location problem
If mental states are identical to brain states, then they must share all their properties in common. (Leibniz’s Law)
Brain states have a precise spatial location, and stand in spatial relations to both other spatial locations and other physical objects.
Mental states are not located in space, at least in the same way.
Therefore, mental states are not brain states.

10. Smart’s response
It is odd to say that mental states have spatial location, but this is an empirical matter. If they are brain states, then they do.
Obj: it makes no sense to say they have spatial location
Ryle: it is a category mistake
Reply: this is a matter of linguistic convention