Political and social theories, contemporary as well as historical, rest on explicit and implicit notions of social life. Even if the subject matter of these theories is not ontology as such, notions about social life inevitably give rise to some kind of ontology that is social for the simple reason that it concerns social phenomena. My aim here is to discover the sort of fundamental elements that social life rests on in the political theory of Johannes Althusius (1557–1638). The analysis shows that besides the human will, which has an important role in the existence of social life, social life is also a product of nature and the will of God. These three forces are also in play in the ontology of consociatio, i.e. an association or union, that is the main locus and mode of social life and the fundamental building block of society understood as an aggregation of multiple consociationes. This is because the existence of consociatio depends on its order-giving ‘symbiotic right’, which is a product of nature, God, and human effort. Further analysis of symbiotic right reveals that the ontology of consociatio is set in a framework of a ‘substantial’ ontology of reality, but that it also manifests ‘relational’ and even ‘processual’ dimensions to an extent that is surprising if pre- and early modern social and political theories are thought to rest firmly on an Aristotelian ontology of substance.