The conceptual pair of own-world and common world constitutes an archaic pair, originally introduced by Heraclitus. More than two millennia after its introduction, Binswanger picked up this conceptual pair in the attempt to understand existence and mental disorder. Ever since, this conceptual pair has been part of the conceptualization of schizophrenia in phenomenological psychopathology. However, the concepts of ídios kósmos and koinós kósmos have seldomly been elaborated and expanded upon, and certain unclarities rest within the literature. This paper resolves some (...) of these unclarities and contributes to a theory of anthropological proportions, which furthers our understanding of ídios kósmos and koinós kósmos. The paper begins with an exploration of the theoretical underpinnings of this conceptual pair, i.e., it discusses the concept of world, what is understood by common world, and what it means to live in an own-world. This theoretical exploration segues into an in-depth analysis of the alterations of experiential life in schizophrenia, which can be illuminated via this conceptual pair. It is further argued that this conceptual pair contributes to an understanding of the puzzling phenomenon of double bookkeeping. Finally, the paper concludes in a discussion of clinical implications of this conceptual pair, stressing the importance of a mindfulness of the alterations to the ídios kósmos and koinós kósmos in schizophrenia. (shrink)