Conceptualization of schizophrenia: the symptom-oriented approach.

E. Bleuler proposed to establish the diagnosis of schizophrenia on the basis of fundamental symptoms which he presumed to be particularly linked with the primary deficiency. K. Schneider, on the other hand, based his diagnosis on the presence of symptoms recognizable without difficulty. Modern classifications include both Bleuler's fundamental and Schneider's first-rank symptoms in their diagnostic criteria. This may lead to erroneous attributions in view of the possibility that most first-rank and some of the symptoms Bleuler suspected to be fundamental may be unspecific reactions to different basic disturbances. It can therefore be expected that research on symptoms is better suited for aetiopathogenetic investigations than research based on diagnoses. Strategies to select those symptoms on which research should focus are described and recent findings of symptom-oriented studies are discussed.