Mental illnesses are really syndromes. That is, they are constellations of symptoms that appear to correlate. Beyond that, we move into the world of inference. Mental illnesses as things per se are culturally constructed (as is everything else. I would point to the now nonexistent diagnoses of hysteria and neuraesthenia), but these constructions are useful in some cases. At the end of the day, what matters is that some people find themselves tortured by their own mental states and also find treatment to be helpful.
I am not so sure if humans can do this if it is a chemical imbalance. >>
A couple points.
1. The totality of subjective experience is neurochemical in basis. From this perspective, life is a chemical soup.
2. Non-chemical treatments have been shown to affect neurochemistry. Chemical disorder does not necessitate chemical treatment.
>>For most mental illnesses, I think they fall somewhere in the middle. Some illnesses, in theory, could be tested for, like an X-ray. Others seem to be the result of conditioning gone wrong, or the body reacting badly to some stressful event. I don't think these could be tested for.>>
Once again, non-chemical factors can have chemical consequences/manifestations.
>>The current theory, and I ascribe to this, is that illnesses such as depression, anxiety, and schizophrenia have to do with neurochemicals in our brains. Unfortunately there are no specific tests at this time that can tell us what chemicals are out of sync. There are genetic components, social and environmental factors that can contribute to the manifestation of these illnesses. There are a wide range of mental illnesses that need different types of treatment. They can be treated with medications alone and in the case of some illnesses counseling alone can be effective, but in general a combination medications and counseling.>>
This is fairly nuanced. Cool.
My main hesitation with simplistic theories of mental illness, such as the serotonin hypothesis for depression, is that the supporting evidence is insufficient. Basically, we found that particular drugs work for depression, and that these drugs increase intercellular serotonin, and then argued that depression is thus caused by a serotonin deficiency. This conclusion does not follow. If I am tired and amphetamine makes me wakeful, it does not mean that I have a monoamine deficiency (amphetamine stimulates monoamine release).
>>Which is doubly true given that psychiatry isn't a science at all.>>
Nor is pedantry.
>>To some degree we have some PET scan data showing difference in activity due to some severe mental illnesses.>>
It's the "to some degree" part that gives me hesitations. These differences in activity are reliable central tendencies of groups, but are NOWHERE near reliable enough to diagnose individuals.