Conceptual and historical evolution of psychiatric nosology.

Psychiatric taxonomies exist within conceptual frameworks which presuppose certain conceptions of psychiatric distress and offer guiding principles. This article provides an overview of the historical development of psychiatric classifications with an emphasis on their methodological assumptions. After identifying roots of scientific psychiatric classifications in the works of Sydenham and Linnaeus and discussing early classification systems, our survey focuses on the Kahlbaum-Hecker-Kraepelin paradigm (with its emphasis on longitudinal course of illness), the Wernicke-Kleist-Leonhard tradition (with its emphasis on neural systems), the development of the ICD and the DSM classifications (with their roots in medical statistics, their pragmatic nature, and their emphasis on descriptive and operationalized criteria), psychodynamic and idiographic perspectives (e.g. the Psychodynamic Diagnostic Manual), and transdiagnostic approaches (e.g. Research Domain Criteria). The central philosophical questions of nosology (descriptive vs aetiological, symptoms vs course of illness, idiographic vs nomothetic, categorical vs dimensional, etc.) have appeared and reappeared throughout this evolution. Ongoing controversies reflect the epistemological and ontological difficulties inherent in defining and classifying mental illness. It may be that no single taxonomy can satisfy all clinical, research, and administrative needs, and that, echoing the ideas of Aubrey Lewis, multiple systems may be required to serve different needs.