 Another major source of Kuhn’s idea of the incommensurability of scientific theories is Gestalt psychology (Kuhn 1962, vi). Wolfgang Köhler, for example, had emphasized the active role of organization in perception and argued that in psychology one begins with Gestalten (organized, segregated wholes such as the objects of human perception or identifiable human behaviours) and then proceeds to discover their natural parts (and not vice versa, like in particle physics). In the opening sentences of the condensed English version of Köhler’s investigation of the relationship between the mental concepts of psychology and the material concepts of physics, Köhler wrote: “In order to orient itself in the company of natural sciences, psychology must discover connections wherever it can between its own phenomena and those of other disciplines. If this search fails, then psychology must recognize that its categories and those of natural science are incommensurable” (1938 [1920], 17).