Copernicus’s De revolutionibus and Girolamo Fracastoro’s Homocentrica were both addressed to Pope Paul III. Their dedicatory letters represent a rhetorical exercise in advocating an astronomical reform and an attempt to obtain the papal favour. Following on from studies carried out by Westman and Barker & Goldstein, this paper deals with cultural, intellectual and scientific motives of both texts, and aims at underlining possible relations between them, such as that Copernicus knew of Fracastoro’s Homocentrica, and that at least part of the (...) rhetorical strategy laid out in De revolutionibus’s dedicatory letter can be read as a sophisticated response to Fracastoro’s arguments.Keywords: Copernicus; Fracastoro; Paul III; History of astronomy; Patronage. (shrink)