This chapter concerns the communicative conditions in the relation between informal practice of sakprosa and informal style in social media communication. By focusing on knowledge and interaction in authorities’ crisis communication, the objective is to discuss whether the public discourse undergoes an informalization within the framework of critical discourse analysis. The aim of this study is to shed light on communicative strategies in authorities’ prose on social media. The data consist of two corpora from the Twitter platform of the Swedish crisis authority—the first from the terror attack in Stockholm in 2017 and the second from an official false alarm for a total number of 1,951 tweets. Methodologically, the data are arranged chronologically and rest on a qualitative approach to style.

A result of this study is that boundaries within the public discourse in social media are not blending, but rather are parallel. When the authority takes the initiative to post informative tweets, they use formal written style. On the contrary, when they write responses to citizens’ tweets, they often use a personal and informal style. Another result is that when the authority does not communicate, it seems to trigger citizens to post informal and sometimes harsh comments.