The ongoing interpretation of the debates between Jules Dupuit and the French liberals of the nineteenth century on intellectual property rights is mainly based on the opposition between justice (the French liberals) and utility (Dupuit). In this article, I argue that they rather derive from a different interpretation of the relationship between utility and justice. While the French liberals assume that justice conforms to utility, Dupuit states that utility conforms to justice. Unlike the traditional reading of these debates, this has two consequences. First, the French liberal School does not only used moral arguments to legitimize intellectual property rights, and more generally property rights, but also economic arguments which are an integral part of their mode of reasoning. Second, Dupuit’s justification of intellectual property rights is not independent of his conception of justice.