Identity Theory Leads to Skepticism Concerning Necessary Truths
This is my first argument: an attempt to establish the immateriality of the mind.
P1. Identity theorists maintain that mental events are brain events—that a particular mental event is identical to a particular brain event.
P2. The mental event n of a belief in a necessary truth is identical with a particular brain event b (1).
P3. Necessary truths are true in all possible worlds, and contingent truths are only true in some possible worlds.
P4. Thus belief in a particular necessary truth nt is a contingent fact, since biological facts are contingent and not true in all possible worlds (2) (3).
P5. Thus, there are some possible worlds in which brain state bn is a false belief concerning necessary truth xnt (2) (4).
P6. Contingent biological facts cannot guarantee an accurate belief in necessary truths (5).C1. Therefore, identity theory leads to skepticism with regard to necessary truths (5) (6).