Stamenflicker, there are several issues here. Are the descriptions in the DSM accurate reflections of inner states that people experience (i.e., can we differentiate using these criteria)? And if they are, can they be detected in physiological ways? You say that you don't believe in either, yet this whole conversation started because you claimed
here that:
I also believe that how we "feel" affects our health. Now I can't "sunshine sing" my way into a new arm, but certainly I can better fight off a cold by staying upbeat, positive, and active. That God does or does not play a role in that upbeat feeling, is hardly my concern.
And then I pointed out that "positive thinking" plays a more complicated role in human immunology than commonly supposed, and that your assertion was much of an overstatement.
Could you please explain how mood could affect us physiologically, yet mood disorders wouldn't? We don't test for depression by monitoring the immune system, just because too many things also affect the immune system, and because we have much easier ways to find out. And that's the list of criteria offered by the DSM. Yes, they can always be argued over and refined, but the truth is, they're useful.
Perhaps you have heard that women are more afflicted with depression. Latest research shows that men suffer from it more commonly than supposed. It's just that men tend to "cover up" the sadness more, especially with anger. But if you get that person into therapy, and start figuring out what's behind the anger, you'll find the same feelings of sadness, helplessness, hopelessness... The DSM doesn't need to change the criteria for depression to say "In men, excessive feelings of anger are common, etc." That's because it's not part of the underlying disorder, but merely one expression of it (and the DSM does make such a note in the section on "Specific Culture, Age, and Gender Features"), which not all men exhibit, and which women can also exhibit.
As for your objection that one can have people with, say, the same level of serotonin in their brains, one of whom is depressed and one of whom is not - well, of course. That's because neurotransmitters play multiple roles in the organism, and are affected by multiple factors. So one person may be more able to compensate for the lack than the other, same as how people with identical levels of sugar in their blood may have their health in different states (say, one already has nerve damage, and the other one doesn't), because diabetes
does not affect the same organs at the same speed in all people, but we know which structures tend to break down first in diabetes, and can use that knowledge in diagnosing. Mental disorders have been shown to affect everything from brain structure to blood flow, just as physical diseases do, like my hypothyroidism example and Blutoski's much more extensive list. If medical disorders are often just as vague as psychological disorders in their symptoms, then how can you insist that one describes something real, and the other doesn't?
At one point you say:
And while high blood pressure is a measurable symptom, fatigue is not.
Stamenflicker, I have had the misfortune of suffering from several diseases, both physical and mental. Curiously enough, for most of my physical illnesses, the first and most noticeable symptom was fatigue. Of course, each time, I would at first dismiss it as due to stress, overwork, what have you, until such a point as I could not ignore it anymore. The doctor would then have to run a large battery of tests, because fatigue can indeed be a symptom of many, many diseases, including mental ones, and no disease at all. I was fortunate enough to have my problems identified relatively quickly, instead of being dismissed as a neurotic, but many people are not as fortunate, and suffer for years before being diagnosed properly by medical doctors. Does that make their experience any less real? By contrast, anxiety which is strong enough to make my whole body shake at the mere thought of doing the feared thing - that's rather noticeable and unmistakable.
I could go on, but the point is this - the measure of a disease, whether physical or mental, is often simply how much it disrupts the person's life. Some people don't wear glasses despite strong near-sightedness, simply because they can get along well enough without. Some people neglect their blood pressure or high blood sugar, despite all the tests showing them to be extremely high, simply because they can't feel the effects. Some people don't take their psych meds for the same reason. None of this means that they don't have a serious problem, one which will, in all probability, come back to bite them.
I can also point at my head when it hurts, but so what? I am not pointing at the actual pain I'm experiencing. I can similarly point to my chest when it tightens during a panic attack.
As for the example of Little Susie and her grandma - you're again ignoring the fact that there's a matter of degree involved. Little Susie is playing - she imagines hearing the voices, but she doesn't "actually" hear them, nor are they disrupting her life, or insisting that something terrible will happen if she does not give her dolls tea right now. If that happened, she'd have childhood schizophrenia, as one of my cousins does.
Finally, Katana and Blutoski also make the very good point that mental disorders respond to medication, while religious feelings don't. Of course, there are a few threads on this forum about the new mushroom that will induce such experiences for you (curiously enough, not in all people who try it, and not in the same way), but we yet know of nothing that would take them away (and we do know of other substances that induce mental disorders. Alcohol, for instance.) I'm restating what they said, because it bears repeating.