This chapter explores the exceptional role of private conversations in the trial of Jean Fontanier, who stood accused of having written and taught from a text seeking to convert its readers to Judaism. Unlike most authors of the libertine canon, Fontanier invited his would-be students across the public/private threshold into the privacy of his own home, where he was able not only to supervise their readership of his text, but also to invite them to join him as co-authors through dictation. In blending literary studies with legal history, Horsley highlights the role of private conversations in Fontanier’s case from the point of view of the author, his readers, and his judges.