In listening to the following philosophy of mind lecture by John Searle, and he mentions in passing the following argument against materialism (starting around 43 minutes into to the lecture):
- Beliefs have the property of being either TRUE or FALSE.
- Material brain states don't have that property, a neural configuration/brain state doesn't really change depending on whether it corresponds to a TRUE fact or a false fact.
- Some mental states, namely beliefs, therefore have different properties than material brain states.
- By Leibniz's law, since Beliefs and Mental states don't have the same properties, they can't be identical.
Searle then goes on to state that he isn't really convinced by the argument, but he doesn't elaborate any further.
How can one refute the argument? Using computer states or written language or painting or some other human artifact (i.e. some form of functionalism) as a counter example doesn't seem to work, because they ultimately derive their truth value (TRUE or FALSE) from the belief of whichever person created the artifact, so ultimately there has to be a purely mental phenomena at the source of the truth value of the physical representation.
What is wrong with this proof? How is it different from Kripke's modal logic argument and Chalmer's Zombie argument (I find it more convincing than those two, but it seems somehow related to them nonetheless)? Why does Searle not find it convincing?