Social media for democracy – understanding the causal mechanisms of digital citizenship (SoMe4Dem) Current diagnoses that democracy is in crisis at the beginning of the 21st century share a common argumentative reference point: the (implicit) reference to the dysfunctional constitution of the political public sphere which is currently undergoing structural change. The rise of social media platforms is considered as one of its main constituents. While social media make the public arena more open and thus more responsive, these platforms also lead to new mechanisms of fragmentation and exclusion, an erosion of norms in public debate and a loss of trust in traditional institutions. The project will reconsider the diagnoses of this crisis by (1) providing better empirical evidence for the impact of social media on society with respect to political debates, (2) understanding the main causal mechanisms of this impact and (3) developing tools that improve the capacity of social media to contribute to the functioning of the public arena in a liberal democracy, i.e., deliberation, legitimation and the self-perception of the democratic subject.