This study investigates the potential of a rhetorical theory of knowledge to expand beyond its own domain and into political theory, specifically theories of deliberative democracy. Despite the increasing interest in communication in democratic theory in the last decades, the majority of theorists have not turned their interest towards rhetorical science. On the contrary, theorists often regard rhetoric as dangerous and incompatible with the deliberative ideal of reason. The aim of this study is therefore to defend rhetorical science by investigating how the rhetorical theory of knowledge – as it is presented by Chaïm Perelman and Oldbrecht Tyteca, and further developed by Mats Rosengren and Maria Wolrath Söderberg – can contribute to the understanding of deliberative democracy. The study is in part a comparison between the rhetorical theory of knowledge and the academic debate about the epistemic dimension of deliberation.  The rhetorical view on knowledge provides an argument that supports the deliberative model without the need of a procedure-independent standard to measure the quality of outcomes. By using Maria Wolrath Söderberg’s understanding of topos as knowledge-producing the study shows that the rhetorical emphasis on language can contribute with a new understanding of why the deliberative ideal is preferable to other models of democracy.