The Unity of the Brethren in the Public Sphere of the Polish–Lithuanian Commonwealth in the Early Eighteenth Century: A Study through Correspondence

This article examines Jürgen Habermas’s public sphere model through a case study of the Unity of the Brethren (lat. Unitas Fratrum), a Protestant minority church in early modern Poland. In contrast to research examining the public sphere through the activity of the printing press, this study investigates the phenomenon through the lens of David Cassius’s (1673–1734) handwritten correspondence. As a senior of Unity of the Brethren, Cassius played a key role in the church’s communication and opinion-making processes. The paper demonstrates that Cassius, despite being deprived of political rights, actively participated in politics, defending the church and exerting political agency. The study reveals that, although the Unitas Fratrum was on the margins of the Polish–Lithuanian Commonwealth’s public sphere, it sought to articulate its demands, which were ultimately rejected by the dominant noble public.