Jung describes psychology as moving beyond materialism since it “does not yet see” how to reduce psychical causes to physical ones. I think one can go further and given an in-principle argument for the same thing based on what it would mean for a mental health practitioner to cure someone. Here we go:
Say you establish that everyone who either has no friends or can’t speak with them loses brain chemical F and reports feeling depressed. You then synthesize brain chemical F and give it to patients who in turn report that their depression goes away. Say there are three classes of patients:
1.) Those forced to spend long hours alone for punitive reasons either in solitary confinement cells or like Napoleon on St. Helena.
2.) Those who are alone because of vocation or mission, like a trip to Mars.
3.) Those who have no friends because of clear personality problems that we have every reason to assume they could fix.
We could say they were all treated, but I can’t see calling any of them cured, except for #2. Those in #3 are being positively harmed by the treatment and are worse off than if they never took the pill at all since since they are losing their strongest motive for a good while getting nothing equal or better, and those in #1 are either being being muzzled into accepting injustice or suffering an injustice themselves, depending on what moral estimation one makes of the deprivation.
So if mental states are brain states, then the same mental state is the same brain state. But the consequent is false since in identical brain states one counts as a cure another doesn’t. Another take: it seems that a purely physical process is one where an artificial fix would count as a real cure: if we can’t grip things because of a broken bone in the finger, then an artificial bone will really cure our gripping problems. But not all artificial fixes of brain states are cures of mental states.
the point of this isn’t just to score points against materialism, but to point to a way in which it covers over real psychological healing. Even if a drug could permanently eliminate what everyone agrees are the symptoms of the disease, it doesn’t follow that one is cured. Mental illness differs from physical illness in that eliminating symptoms – even if permanently and with no side effects – does not suffice for a cure.