Unitary psychosis (Einheitspsychose) refers to the 19th-century belief prevalent in German psychiatry until the era of Emil Kraepelin that all forms of psychosis were surface variations of a single underlying disease process. According to this model, there were no distinct disease entities in psychiatry but only varieties of a single universal madness and the boundaries between these variants were fluid. The prevalence of the concept in Germany during the mid-19th century can be understood in terms of a general resistance to Cartesian dualism and faculty psychology as expressed in Naturphilosophie and other Romantic doctrines that emphasised the unity of body, mind and spirit.