Diodorus may seem an odd choice of focus for an entire chapter. He is widely known for having taken over long stretches of text from his sources, paraphrasing and summarising, but not adding anything new in terms of historical analysis or interpretation. I have argued my point of view on Diodorus’ source usage in detail elsewhere, but it is necessary to restate my case briefly here before embarking on an analysis of Diodorus’ moralising. It is clear from the sections of Diodorus’ Bibliotheke for which the sources are extant that Diodorus generally stayed close to the text of the source, that is, he rephrased and abbreviated rather than create a new narrative from scratch. This explains why, although Diodorus’ language is similar throughout his work, his narrative style is uneven, being characterised by detached summary in some books in contrast with an emotionally involved mixture of summary and scenes in others: it seems that he often took over the style and tone as well as the content from his sources. In this chapter, we shall examine moralising in the Bibliotheke comprehensively and see that Diodorus seems to have followed this working method also in terms of moralising: he took over moralising passages from his sources, in some cases changing the point slightly, but he does not seem to have written new moralising passages from scratch. However, we shall also see that there is nevertheless a high degree of consistency in the moral lessons offered by the Bibliotheke as a whole. The possible reasons for this surprising finding will be discussed in the conclusion to the chapter.

It has been a favourite sport of scholars to try to surmise which source(s) Diodorus used for each stretch of his narrative. Without entering into the finer points of such Quellenforschung, it will be useful here to give a brief overview of some of the more certain sources used by Diodorus in different parts of the Bibliotheke, as we shall be referring to them time and again throughout this chapter, and return to some of them in Chapters 3 and 7. The sources used by Diodorus in the early books of the Bibliotheke are still much discussed, but something approaching a communis opinio exists for some of the middle and later books.