According to a new government-sponsored survey, most Americans qualify for a psychiatric diagnosis at some point in their lives. Trying to explain how so many of us became mentally ill, The New York Times offered a history lesson that reminded me of an old "Saturday Night Live" sketch.

 In the sketch, Steve Martin plays Theodoric of York, a medieval barber with a patient whose condition has not improved despite a bloodletting, a sheep's-urine-and-staghorn poultice, and a night buried in the marsh up to her neck. "Medicine is not an exact science," Theodoric tells the girl's mother, "but we are learning all the time. Why, just 50 years ago, they thought a disease like your daughter's was caused by demonic possession or witchcraft. But nowadays we know that Isabelle is suffering from an imbalance of bodily humors, perhaps caused by a toad or a small dwarf living in her stomach."

 To provide context for the government's mental health survey, the Times told a similarly inspiring story of science replacing superstition. In the old days, it explained, "gamblers and drinkers, the excessively impulsive or rebellious, [and] the sexually promiscuous . . . were considered sinners, deviants or possessed," while "those who denied themselves food or comfort, or who prayed or performed ritual cleansing repeatedly, often struck others as especially pious."

 But "as science gradually displaced religion," the Times continued, "such behavior was increasingly seen in secular, diagnostic terms." Hence "excessive fasting became anorexia," and "ritualized behavior was understood as compulsive, or obsessive-compulsive."

 This is the sort of progress that might impress Theodoric of York, but does it bring us any closer to the truth? If anything, the claim that mental illness causes someone's bad or odd behavior obfuscates the issue even more than the claim that the devil made him do it.

 As the psychiatric iconoclast Thomas Szasz has been arguing for many years, mental illness is a literalized metaphor that conceals more than it reveals. Although their training and billing practices suggest that psychiatrists deal with medical problems, it seems unlikely that many of them truly believe all the myriad sins and foibles listed in their Diagnostic and Statistical Manual of Mental Disorders (DSM) are in fact brain diseases.

 If they did, why would they cling to the deliberately ambiguous term "mental disorder"? Why would the diagnostic criteria for so many psychiatric conditions include ruling out, as opposed to confirming, an organic cause? And how could psychiatry be justified as a discipline distinct from neurology?

 Judging from the way psychiatrists respond to Szasz's critique, most of them believe schizophrenia and perhaps a few other conditions described in the DSM are diseases of the brain in the same sense as Alzheimer's or multiple sclerosis, albeit with etiologies that are not yet clear. But when it comes to habits and traits such as smoking, gambling, gluttony, shyness, impulsiveness, inattentiveness, dishonesty, and nastiness -- not to mention diagnoses that have fallen out of psychiatric fashion, such as homosexuality and multiple personality disorder -- even psychiatrists recognize the arbitrariness of their taxonomy. Continued...