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The theory of Einheitspsychosen (literally, the unity of psychoses) was put forth by the German psychiatrist Heinrich Neumann in 1859. The main postulate of the theory was that all psychoses represent a single disorder.

This theory has been much criticised, particularly since the distinction made by Kraepelin between schizophrenia and manic-depressive disorder. In the nineteenth century, people such as Wernicke or Kleist believed that psychoses were a discrete class of disorders, whereas people such as Neumann believed that all psychoses were part of the same nosological category.

Karl Kahlbaum was a fierce opponent of Neumann's view. Kraepelin's contribution can be considered a compromise between the positions of Neumann and Kahlbaum, stating that all psychoses can be fitted into one of two basic categories - dementia praecox (now called schizophrenia) or manic-depressive psychosis.

Although today, many clinicians would dispute this doctrine, holding that one should at least make the distinction between schizophrenia and manic-depressive psychosis proposed by Kraepelin, the theory continues to have some influence. Eysenck (1992a), for example, in describing the trait of psychoticism does so with very similar assumptions to those made by Neumann. Eysenck (1992b) has claimed that a low level of platelet monoamine oxidase may be the biological marker that links all psychoses.

See also: Psychoticism


  • Eysenck, H.J. (1992a). Four ways five factors are not basic. Personality and Individual Differences, 13, 667-676
  • Eysenck, H.J. (1992b). The definition and measurement of psychoticism. Personality and Individual Differences, 13, 757-785
  • Lanczik, M. (1992). Karl Kahlbaum (1828-1899) and the Emergence of Psychopathological and Nosological Research in German psychiatry. History of Psychiatry 3, 53-58
  • Shorter, E. "A History of Psychiatry"
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