The dichotomy between “dementia praecox” and “manic-depressive insanity” by Emil Kraepelin is one of the milestones of nosology in psychiatry [1].

This dichotomy reflects the necessity – particularly in the absence of effective treatment in Kraepelin's time – to differentiate (and to predict) the functional outcome of individual patients. Since Kraepelin's original division particularly the influence of Kurt Schneider has led to a full acknowledgment of the dichotomy in both ICD and DSM.

While this division has proven to be clinically useful, alternatives have been proposed covering a large spectrum from the idea of unitary psychosis as in Wilhelm Griesinger and Klaus Conrad to further subdivisions as in Karl Leonhard. Recent research in neuroscience suggests the presence of an overlap between schizophrenia and other psychiatric disorders [2–4].