Political interviews are interactionally organized media events in which the co-participants employ argumentative sequences to present themselves and their standpoints as reasonable to an audience and to each other. Against this background, an investigation of the communicative functions of appeals to reasonableness is carried out, with special reference given to how this fundamental premise of argumentation is accessed and controlled. The contribution adapts Habermas's conception of argumentation as a form of conversation based on differences of opinion to the contextual constraints and requirements of a political interview. Contrary to the conception of argumentation as a source of knowledge, argumentation in political interviews is not primarily employed as a means of finding or proving the validity of an argument, but rather as a means of persuading the audience. In a micro-analysis the linguistic representation and distribution of references to reasonableness is examined. Here, the interactional organization of reasonableness follows standard procedure, viz. it is assigned a presuppositional status. In critical situations, however, references to reasonableness are exploited to trigger a conversational implicature which signifies that the co-participant's performance has not been reasonable. Thus, appeals to reasonableness primarily occur in negotiation-of-validity sequences in which the validity of one or more political positions and their presuppositions is at stake. © 2007 Elsevier B.V. All rights reserved.