The Mind-Brain Type
Identity Theory
Michael Lacewing
enquiries@alevelphilosophy.co.uk
© Michael Lacewing
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.
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)
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
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
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
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.
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.
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.
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