According to the philosopher Gilbert Ryle in The Concept of Mind, one commits a category-mistake when one "represents . . . facts . . . as if they belonged to one logical type or category (or range of types or categories), when they actually belong to another."
A case in point is in today's New York Times Magazine, in the article "The Therapeutic Mind Scan" by Paul Raeburn, who laments that most psychiatrists diagnose mental illnesses without examining their patients' brains, but reports hopefully on one exception, Daniel G. Amen, who uses single photon emission computed tomography to scan the brains of his patients. Raeburn is the author of Acquainted With the Night, which the Times says is "a memoir of raising children who have depression and bipolar disorder."
"If scanners could uncover the signs of distinct mental illnesses in the soft folds of the brain, the way X-rays can reveal a tumor, and monitor treatment effectiveness, they would revolutionize psychiatry."