In research into the origin of schizophrenia discrepancies repeatedly arise through the habit of treating schizophrenia as an entity. If independent subforms are differentiated, many ambiguities can be cleared up. A special form of catatonia (periodic catatonia) seems to be transmitted by dominant inheritance, a special paraphrenia (affective paraphrenia) recessively. In a large group of schizophrenias (systematic schizophrenias) with a poor outcome family histories of psychosis were rarely found, but examination of twins suggested a psychosocial origin for the disorder. In cycloid psychoses with a benign outcome family histories of psychosis were also seldom found. Only by diagnostic separations can the discrepancies in the field of schizophrenia be solved.