Best way into this whole can of worms is to look at some debatable “mental illnesses“. Homosexuality, pedophilia. Are these, or are these not, mental illnesses?
And once you ask that question, you’re led on to further questions, one of which is trifling, but troubling. Are “mental illnesses” misnamed in the first place? A bodily illness is usually (but not always) something like a virus getting into your body and replicating. You can classify the illness by its cause, it has defined phases, and you can relate it to biology — you can see it under a microscope. Many (but not all) mental illnesses, in contrast — you don’t classify by cause, but by symptoms; there aren’t defined phases; and you can’t relate purely to biology, but have to also talk about behaviour, society, environment and even things like feelings and thoughts.
So, there’s reason to think that “mental illness” or ” mental disease” are often misleading terms. “Mental condition” might be improvement, but, ironically, doesn’t cut it when the condition is in fact more process-like, like a bodily disease.
Anyway, that’s by the by. Yes, there might be problems with language, but most people would probably agree that there is something here that we need to talk about — that, for practical purposes, we can’t get by without a theory of mind and a theory of broken minds. So, onto the next question — what’s in and what’s out? What counts as a mental illness, and what doesn’t?
The instinctive response is to appeal to what’s normal. If it’s not normal, then it’s a disease. But then: (a) some abnormal behaviours/conditions are regarded as good, not bad — like virtuoso ability at piano; (b) some abnormal behaviours/conditions are regarded as neither good nor bad, like a love for fixing old grandfather clocks.
So, if you can’t appeal to normality to define disease, maybe you can appeal to good functioning. If you’re not functioning properly, there’s something wrong with you, and if it ain’t bodily, then it’s mental.
But how to define good functioning?
If you presume to define it according to some standard like “human nature”, then there’s plenty of people who will quibble with you. Any time you make a claim about what’s natural and what isn’t, people are going to argue with you. Human beings are multifaceted, evolving, adaptable.
But if, on the other hand, you define good functioning in terms of how the individual wants to function, then it seems disagreeably subjective — like anything could be “mental illness”. If the individual wants to kill people, but has feelings of empathy that inhibit this, are these feelings an “illness”? (The example is not that unrealistic: German soldiers were advised in WWII to ignore their emotions and do what they intellectually knew was right.)
So what counts and what doesn’t count as mental illness? Seems irreducibly subjective at the end of the day; it’s not pure science, it’s values and agreement.
And all these problems pertain to bodily “disease” as well…