The paper investigates formal language in persuasive discourse on the r/ChangeMyView subreddit. We collected a corpus of 100 million messages, split into subcorpora based on the user-awarded marker delta, which rewards changing an original poster’s view. Assuming that formality/ informality is potentially an important factor in the persuasiveness of a message, we examine the two subcorpora with respect to formality markers. The results indicate no systematic variation along the formality/informality continuum between persuasive and non-persuasive posts on r/ChangeMyView. The posters use personal pronouns, suasive verbs, emphatics, imperatives, elaborate connectors and WH-questions with similar frequency, and express themselves using vocabulary and syntax of similar complexity. Moreover, keyword lists and n-gram rankings indicate no register difference. A qualitative analysis of concordance lines for persuade and change PRONOUN view paints a picture of a community that values factual, evidence-based discourse and openness to logical persuasion, with a linguistic norm of relatively formal, sophisticated register.