This article analyses how written culture influenced the relationship between kings and subjects during the seventeenth century by examining the use of political oaths. The use of political oaths dwindled in Europe at this time and researchers have placed the polemic scholarly debate on oaths in England at the centre of change. This article challenges this singular narrative by focusing on the peripheral state of Sweden and shows how underlying societal changes contributed to undermine oath-swearing. It argues that the performative nature of oaths was decisive in their usage. Oaths were aimed at guaranteeing coherence between actions and statements. The speech act’s objective was to establish trust between king and subjects. As such, oaths were adapted to an oral culture characterised by presence and spoken promises. During the seventeenth century, the emerging literate culture promoted written statements that enabled control that became diametrically opposed to such trust. Consequently, oaths lost their performative force to instill trust.