  For the most part it is unclear how all these works were organized. In some cases (e.g., On Poems I-II and On Rhetoric I-III), Philodemus has plotted the course of more than one book at once, but we do not know if an overall plan was present from the beginning, or if books at first composed separately were later added to the set. The most complex problems arise with regard to the multi-volume work On Vices, which is discussed below. Understanding the organization of such works would give us a clearer picture of Philodemus’ methods and philosophical aims.