Scholars have long been aware of striking similarities between a crucial passage in Book II of Plato’s Republic and the longest papyrus fragment surviving from Antiphon’s On Truth. Previous scholarship has identified some views common to both texts but has not explained how these views hang together in a unified and coherent ethical outlook. A deeper investigation into these two texts turns up a blueprint for Greek immoralist arguments, a finding which should be of considerable interest to scholars of ancient (...) Greek ethics and political philosophy. The paper argues that both texts include an argument whose demonstrandum is that it is by nature good or advantageous to commit injustice when one can do so undetected; that this argument in each case involves a set of background premises that constitute a blueprint for immoralist arguments in Classical Athens; and that the immoralist ethical theory of Republic II is an outline distilled from several more detailed theories, including the one belonging to On Truth. (shrink)