This article traces the development of how the early Heidegger tried to integrate the structures of social life into phenomenological ontology. Firstly, I argue that Heidegger's analysis of the three elements of the lifeworld—the with-world (Mitwelt), the environing world (Umwelt), and the self-world (Selbstwelt)—is ambiguous, because it shifts between defining sociality as a domain of entities and a mode of appearance. This is untenable because the social as a mode of appearance constantly overflows the definition as a domain by implicating (...) social structures in phenomenological explications of entities that, formally, belong to other domains. Secondly, I argue that Heidegger realized this and subsequently changed his terminology from Mitwelt to Mitsein in order to avoid confusing the mode of appearance with the innerworldly entities. The systematic consequence of this line of argument is that the object of social ontology must be the world as such rather than a particular domain. Lastly, I respond to the common worry that this position is unable to explain the significance of interpersonal encounters by arguing that the world not only makes the appearance of others possible but also that the world is itself at stake in these encounters. (shrink)