THE CLASSIFICATION of personality disorders is one of the most difficult challenges in the field of psychiatry. A fundamental question is whether they are best classified dimensionally or categorically and, more specifically, whether they are qualitatively distinct from normal personality traits.^1,2 The study by Livesley et al¹ is among the most informative and sophisticated efforts to empirically address this issue, and provides a tough standard against which future research in personality disorders will be measured (whether it is categorical or dimensional in nature).

The major finding of this study is perhaps the remarkable congruency of the domains of normal and abnormal personality functioning. It is indeed quite striking that an extensive history of research to develop a dimensional model of normal personality functioning that has been confined to community populations³ is so closely congruent with a model that was derived from an analysis confined to personality disorder symptoms. This is a "coincidence" that is difficult to ignore. The emotional dysregulation, dissocial, inhibition, and compulsivity factors of Livesley et al⁴ correspond closely to the neuroticism, antagonism, introversion, and conscientiousness factors of the 5-factor model (FFM) of normal personality functioning. There are some differences, perhaps even a few minor inconsistencies, but the breadth and depth of the convergence is far more compelling. Personality disorders are not qualitatively distinct from normal personality functioning, they are simply maladaptive, extreme variants of common personality traits.