The rise of populism and post-truth politics, the process of digitalization and new methods of political partizipation are changing public debate. Populist rhetoric, fake news, and adverse incentive structures in traditional and social media challenge and perhaps even threaten the ideal of democratic deliberation. In recent years, but especially in the light of these changes in the political and media landscape, it has become clear that the deliberative ideal of rational and cooperative debate between equals - exemplified by Jürgen Habermas' "ideal speech situation" - is limited in its practicability. It is time to take seriously Habermas' own demand for uniting the philosophical approach to public debate with the empirical social sciences. This project aims to establish the *normative* grounds of public debate, but it will do so in close collaboration with psychology, political science, as well as media and communication studies.

Public debate is a series of forums in which people's opinions, interests, and expectations are expressed on an issue that concerns (a part of) society. Of course, every participant ties different goals to public debate. But even from a theoretical point of view, it is anything but clear what its goal should be. Should it primarily legitimize the democratic decision-making process? Should it actually improve it? Should it make people engage with politics? Should it help to reduce power abuse? Should it enable mutual understanding? Should it foster epistemic goals such as opinion formation, truth, and knowledge? Should it facilitate consensus? Should it do all of this at once?

Democratic theory has discussed these questions at great length. Only recently, they have become also the focus of empirical research. The aim of this project is a "theory of middle range": Its main purpose is to identify the goals and to establish and justify the normative rules of public debate with respect to specific forums. In particular, its focus will be the goals and normative rules of (the contributions to) political debates in talkshows (such as *Hart aber fair* or *Anne Will*), in social media (such as *Facebook* or *Twitter*), in regular newspapers (such as *Die Zeit* or *Bild*), on open online debate websites (such as *kialo.com* or *reddit.com/changemyview*), and on expert online debate websites (such as *causa.tagesspiegel.de* oder *sagwas.de*).

This project tries to answer what normative rules constitute and guide these different forums of public debate and how these rules can be justified. Its objective is a normative theory of public debate that is both philosophically grounded and practically applicable.