According to many philosophers and scientists, human sociality is explained by our unique capacity to “share” attitudes with others. The conditions under which mental states are shared have been widely debated in the past two decades, focusing especially on the issue of their reducibility to individual intentionality and the place of collective intentions in the natural realm. It is not clear, however, to what extent these two issues are related and what methodologies of investigation are appropriate in each case. In (...) this article, I propose a solution that distinguishes between epistemic and ontological interpretations of the demand for the conditions of reduction of collective intentionality. While the philosophical debate has contributed important insights into the former, recent advances in the cognitive sciences offer novel resources to tackle the latter. Drawing on Michael Tomasello’s research in the ontogeny of shared intentionality in early instances of interaction based on joint attention, I propose an empirically informed argument of what it would take to address the ontological question of irreducibility, thus making a step forward in the naturalization of collective intentionality. (shrink)