Kraepelin, biological psychiatry, and beyond.

One of Kraepelin's major contributions has been the introduction of the nosological principle in psychiatry. Mental pathology, he presumed, is subdividable in discrete entities each based on a specific pathophysiology. Kraepelin provided the diagnostic process in psychiatry with a solid infrastructure. It has been used in biological psychiatric research until this very day. Searching for the biological determinants of categorical entities has been its major goal. The yield of those efforts has been meagre, in that none of the biological findings reported so far seemed to be specific for a particular nosological entity. The question thus arises: is nosology the right model to classify mental disorders. It is suggested that it is not. The disease categories presently delineated are utterly heterogeneous, and therefore cannot be expected to have a well-defined pathophysiology. The nosological system cannot be rejected (as yet), but it has to be upgraded by incorporation of a strong dynamic-functional component. The functional components should become the focus of biological psychiatric research. The question whether an alternative classificatory model, such as the reaction form model, has to be preferred in biological psychiatry should become a matter of serious discussion.