In Reply.
—Dr Summer's use of the Feighner diagnostic criteria as an authoritative reference to challenge the validity of the borderline personality disorder reflects a common error in scientific reasoning. The Feighner criteria (like the Gunderson criteria for borderline personality disorder) are syndromal definitions—not based on a defined pathophysiology of mental disorder, but on the statistical association of signs, symptoms, and (in some cases) familial patterns. To assume that the Feighner criteria define actual disease entities with mutually exclusive (albeit undetermined) etiologies is somewhat premature. The proper use of the Feighner criteria is for research purposes: to define homogeneous patient samples that are statistically reliable. The true test of validity for these disorders lies not only in a consistent longitudinal course, but also in a defined etiology. We have not yet achieved this level of sophistication for most of our diagnostic entities. The creation of "Briquet's syndrome" is an excellent case in