This chapter concerns a striking paradox: on the one hand, Alain Badiou has emerged as one of the most influential public intellectuals of recent decades; on the other, he is known for insisting that philosophy is subservient to truths produced by politics, science, art and love. The chapter argues that the paradox can be unravelled by attending to how the philosophical categories and choice of mathematical models in Being and Event aim to, and fall short of, imposing limits on theoretical authority. These difficulties highlight the problematic nature of Badiou’s attempt to revive Althusser’s rationalist programme of the 1960s while avoiding that project’s theoreticist excesses. The final section reflects on how these unresolved tensions can help make sense of the charges of Stalinism levelled against Badiou after the Arab Spring.