It is here argued that 'culture' is a universal in the philosophical sense of the term: it expresses a general property. It is not a singular term naming an abstract entity, but rather a singular predicate the intension of which is 'cultureness.' Popper's view of the ontology of mathematics is used as an analogous example in the light of which the ontology of culture is analyzed. Cultures do not have an independent existence (realism), they are not mere names (Nominalism), and neither do they exist as fixed entities in the mind (conceptualism). Cultures are abstractions made by the mind, which yet are not reducible to the mind. They exist in the form of certain mental operations creating a new level of reality. Scientific study of culture involves both explaining how cultural phenomena are constructed in minds and how these constructions function in cognition and communication.