  We do not know any of the other books from the same series of summaries based on the lectures of Zeno, who was evidently the source and model of Philodemus’s ideas about how to run an Epicurean school. They are often thought to have included On Conversation (PHerc. 873, apparently Book 2, according to the final title), and On Gratitude (PHerc. 1414) because those topics also relate to conduct and relations among school members; the titles of these two bookrolls, however, evidently lacked any indication that they belonged to a larger work; the final title of PHerc. 873 is in the same hand as the front and back titles added to the uniform edition of the books of On Vices which may indicate that the book belonged rather to that series.