This article studies the friendship between Françoise de Graffigny and François-Antoine Devaux through the lens of fraternal correction. During a fascinating two-year span of their long acquaintance, August 1752 through December 1753, the principal cause of Graffigny’s complaint against Devaux was his enactment and defence of fainéantise, or idleness. Graffigny criticized him and his actions in an effort to make her friend a better person; it is in this sense that she engaged in fraternal correction, a practice that follows from the broader eighteenth-century belief in human perfectibility. Approaching the friendship from the angle of fraternal correction helps to explain the survival of the relation-ship despite two years of harsh criticism. Graffigny’s correspondence illuminates the intricacies of eighteenth-century friendship, particularly between the sexes, and presages a literary tradition of women as moral guides to men.