Chapter 4 and 5 of Preface to Plato are a continuation of understanding Plato's rejection of epic and dramatic poetry. Chapter 4 addresses a particular scene from the Iliad, in which the Achaean (Greek) army is at camp taking inventory of their spoils after defeating the Trojans. The amount of lessons in the story make this as much a didactic (educational) tale as a purely dramatic one. The audience is shown common mores exemplified both by men and gods, the proper rituals for a sacrifice, and a variety of other examples of proper Greek citizenship. Chapter 5 then expounds upon this by discussing the dual role of Homeric poetry as both an "encyclopedia" and a drama by identifying the integration of the "social apparatus" into Homer's storytelling, to the point that it cannot be considered a product of pure poetic invention, or art.
Plato's opposition, after these chapters, becomes far more clear. These poets, and Homer in particular, bear a considerable amount of weight in the educational power of their poetry. Despite this, the "knowledge" that is contained within these poems is only approximate and is not actually useful in teaching in Plato's conception of the word. In other words, a Greek citizen would not consult the Iliad for guidance on mores nor the proper way to sail because while they describe both, it is better likened to an impression than a manual. This realization is particularly disturbing for Plato, as he understands Homer and other poets are the de facto educators of the Athenian populace.