 Kraepelin worked from an assumption of underlying brain pathology, but also promoted a distinction between endogenous (internally caused) and exogenous (externally caused) types.German psychiatrist Kurt Schneider coined the terms "endogenous depression" and "reactive depression" in 1920, the latter referring to reactivity in mood and not "reaction" to outside events, and therefore frequently misinterpreted.The division was challenged in 1926 by Edward Mapother who found no clear distinction between the types.