Whereas former research on academic discourse has paid a great deal of attention to writing and its hedging strategies, this paper aims to show that a complementary and equally important feature of academic spoken discourse is the use of modal certainty. An examination of modal selections in two American Dissertation Defenses additionally reveals that the choices are purposeful and can be related to the speakers' role in the discourse, their commitment to propositions and their aims in such discourse events. On a more speculative level this paper aims to demonstrate that interpersonal meanings structure texts just as much as ideational ones and that modalities contribute to coherence in important ways. Finally, it is argued that a productive analysis of modality in the discourse of dissertation defenses should be based on the view that modal selections in a strict sense are closely related to other choices indicating the speakers' stance in relation to propositions.