Language is widely held to underpin cumulative technology and social institutions. We argue that central to this power of language is one under-acknowledged feature: namely, the reflexivity of language. Language can be used to refer to itself. We first define reflexivity in language, and explicate some of the aspects of language that are made possible by it, including names, reported speech, paraphrase, tense, and pronouns. We then argue that the reflexive property of language has had at least three revolutionary consequences for our species: first, reflexivity enables quoted speech, crucial for reach and reputation management; second, reflexivity enables the building of texts, such as the narratives that build common sense-making as well as legal texts that create social realities; third, reflexivity of language enables social accountability, which is indispensable for the creation of social realities—anything grounded in rights and duties, from ownership to political authority. In the final section, we discuss an apparent paradox arising from the claim that metalanguage is a prerequisite for language, and we speculate that practices of repair in interaction (e.g., saying “Huh?” when one person hasn’t understood what another is doing) may constitute a path by which metalanguage precedes language.