Public Reason 10 (2) - Public Reason 11 (1): 11-26 © 2019 by Public Reason Te contestation of credibility and the deliberative model of democracy Matheson Russell University of Auckland Abstract: Political discourse is ofen dominated by atacks on credibility at the expense of discussions about policy proposals. Such atacks can exacerbate political division and undermine atempts to discuss difcult policy questions in the public sphere. While this is true, it is argued in this article that it is a mistake to simply dismiss all such atacks as irrational and illegitimate deviations from the norms of deliberative argumentation. Resolving questions about whom to trust is vital to our lives as social knowers. Furthermore, the infuence enjoyed by speakers (individuals and organizations) is not always warranted and deserves to be challenged. Even though it strains the norms of civility, equality, and inclusion promoted by the deliberative model of democracy, the public contestation of credibility can serve epistemically and socially valuable ends. Tus, the contestation of credibility is a profoundly ambivalent phenomenon. Nonetheless, it has a central role to play in the social rationality of public discourse and merits greater atention by democratic theorists. Key words: deliberative democracy, trust, credibility, power, ad hominem argumentation. Political discourse is ofen dominated by atacks on credibility at the expense of discussions about policy proposals. Politicians seek to score points against their opponents, and journalists try to trip up public fgures with embarrassing ‘gotcha’ questions. Tese tactics are widely criticised, and it is not hard to see why. Tey can be exasperating for observers, distressing or hurtful to public fgures, and counterproductive from the point of view of policy debate. But if such tactics strain the norms of civility and hinder atempts to discuss difcult policy questions in the public sphere, why are they so ubiquitous? Escalating political polarisation has no doubt led to an increase in the prevalence and intensity of these tactics. Likewise, ‘takedowns’ are rewarded by atention in the mainstream media and by likes and shares on social media. But neither of these factors explains the existence of the phenomenon in the frst place. In this article, I examine some instances of credibility atacks. I provide an analysis of what motivates them and consider how they should be conceptualised from the point of view of democratic theory. Drawing on observations about the social structure of our epistemic lives, I show why the contestation of credibility has a central role to play in the social rationality of public discourse and why it cannot simply be dismissed as an illegitimate deviation from the norms of civility and deliberative rationality. I. THE CONTESTATION OF CREDIBILITY On the 14 th of February 2018, a 19-year-old gunman shot and killed 17 people, including 14 students, at Marjory Stoneman Douglas High School in Parkland, Florida. What made this school shooting diferent from so many other similar tragedies in the