theory admits that it is possible that brains may not function in
exactly the same way to produce mental states. So, suppose that
it is not possible to identify certain types of mental activity
– such as seeing a red bus or feeling angry – with a
certain type of brain state. Also suppose that it is possible that
different people who are in the same mental state have different
brain states. Even if all these things are true, it does not mean
that identity theory is false.
possibility. Even though when I have a similar mental experience
to you my brain state is very different to yours, it may still be
true that my mental experience is identical with my brain state.
This is called the type-token theory. In this view, although the
brain is still responsible for my mental states, it simply achieves
them in a different way. This may lead to a difference between how
individuals’ brain states correspond to the same mental states,
but also a the same mental state in the same individual may produce
different brain states at different times.
with this view is that it is even more open to the benchmark argument
than the type identity theory – in fact, there is no benchmark
at all, because your brain activity is unique. If I compare what
your brain does when you are celebrating a goal and what my brain
does – or even what my brain does at different times - there
may be very little similarity. This leaves us with an odd picture
where similar types of behaviour do not seem to correspond to any
particular mental state. Even if it can be argued that each mental
state would be slightly different and therefore each brain state
will be, it is still a problem for the identity theorists.
The last refuge
of identity theory is the token-token theory. This supposes that
an individual thought is identical only with the individual brain
state which it corresponds to. However, this leaves us with the
problem that no brain activity need correspond to any sort of mental
state or behaviour whatsoever. This cannot even be tested for, since
it may be argued that we can never have the same thought twice –
and therefore never the same brain state. Even though this does
not disprove the theory, it means that there is nothing to suggest
beyond doubt that brain states are mental states.