The core function of argumentation in a democratic setting must be to constitute a modality for citizens to engage differences of opinion constructively – for the present but also in future exchanges. To enable this function requires acceptance of the basic conditions of public debate: that consensus is often an illusory goal which should be replaced by better mastery of living with dissent and compromise. Furthermore, it calls for an understanding of the complexity of real-life public debate which is an intermixture of claims of fact, definition, value, and policy, each of which calls for an awareness of the greater ‘debate environment’ of which particular deliberative exchanges are part. We introduce a rhetorical meta-norm as an evaluation criterion for public debate. In continuation of previous scholarship concerned with how to create room for differences of opinion and how to foster a sustainable debate culture, we work from a civically oriented conception of rhetoric. This conception is less instrumental and more concerned with the role of communication in public life and the maintenance of the democratic state. A rhetorical meta-norm of public argumentation is useful when evaluating public argumentation – not as the only norm, but integrated with specific norms from rhetoric, pragma-dialectics, and formal logic. We contextualise our claims through an example of authentic contemporary public argumentation: a debate over a biogas generator in rural Denmark.