Aristotle turns his attention to epic poetry. While the mimesis of tragedy is in actions told in a dramatic form, the mimesis of epic poetry is in verse told in a narrative form. Aristotle notes that there are a number of similarities between tragedy and epic poetry.
First, epic poetry must maintain the unity of plot. In this it is allied with tragedy against history. History tells us all that happened during a certain time period or to certain people, and as such it is often somewhat disconnected. Epic poetry should focus on one particular story that remains an organic whole. Homer is an excellent example of such an epic poet, as he tells a particular, connected story in the Iliad rather than trying to narrate everything that happened during the Trojan War.
Second, epic poetry must share many of the elements of tragedy. Like tragedy, it should be either simple or complex, and it should deal primarily either with a character or with suffering. Aside from spectacle and melody, the six parts of tragedy are all present in epic poetry, and epic poetry can also feature peripeteia and anagnorisis.
There are also two notable dissimilarities between epic poetry and tragedy. The first is the length: an epic poem can reasonably last as long as a whole series of tragedies, provided it can be presented in one hearing. The plot of an epic poem can be far more expansive because it is not limited by the stage. Epic poetry can jump back and forth between events happening at the same time in different places in a way that would be impossible on stage. Second, epic poetry should be narrated in heroic meter, while tragedy is normally spoken in iambic meter.
Aristotle is clearly an admirer of Homer's, as almost all his examples of good epic poetry are drawn from Homer. He praises Homer for reducing his own voice in the narrative and letting the actions and the characters tell the story themselves. He uses Homer to show how epic poetry can recount exaggerated events in a believable manner. A tragedy could never get away with such marvels, since they are less credible when we see them performed. Having said this, he remarks that no plot should ever hinge on improbable events but praises Homer for managing through his art to make this flaw in the Odyssey seem insignificant. He also praises Homer as a master of using paralogisms (conclusions resulting from faulty or illogical arguments) to make lies seem believable.
Aristotle cautions against an overenthusiastic use of elaborate diction. While it is pleasing when there is no action to recount, and no character or thought to reveal, ornate diction can often obscure these more important elements when they are found together.
Aristotle seems to treat tragedy and epic poetry as largely similar. They are both meant to be imitations of great deeds, noble heroes, and tragic suffering, the main difference being that tragedy conveys all this by means of action, while epic poetry does so by means of language alone. They deal in the same genre, so the only differences are determined by the different limitations imposed by the different media of expression. A tragedy, for instance, cannot be as long as an epic, nor can it portray so many different happenings or get away with as many fantastic events. On the other hand, tragedy is more focused, and epic poetry cannot make use of the music or spectacle of stage performances.
Tragedy, it seems, is a more realistic medium. Because we see everything in a tragedy happening before our eyes, the action is limited to the realm of human possibility. Admittedly, Greek stagecraft became increasingly complex, allowing actors to fly about suspended from cranes, and so on, but too much of this would be absurd. Indeed, Aristophanes, the great comic poet, made good comic use of such devices.
Epic poetry, on the other hand, is a purely narrative medium and as such is limited only by the imagination of the poet and listener. Because we have no help in visualizing events, the epic poet can more easily recount the improbable without disturbing us. Aristotle refers to the episode in the Iliad where Achilles chases Hector three times around the walls of Troy. Homer makes no mention of the rest of the Greek army, which presumably must have been sitting idly by, watching the chase. Such a picture would immediately seem ridiculous if presented on stage, but because Homer can focus exclusively on the characters of Achilles and Hector, we are liable not to notice this absurdity.
The larger-than-life qualities of epic poetry are also brought about by the heroic meter. This contrived and elevated meter further removes the characters in the story from realistic portrayal, their extraordinary speech meshing well with their extraordinary deeds. By contrast, tragedy employs an iambic meter that closely resembles the rhythms of everyday speech.
In spite of these differences, Aristotle seems to think that epic poetry and tragedy can be judged according to similar criteria. Most important to both is that they maintain unity of plot. Epic poetry, by virtue of its length, is more suited to episode and digression, but these digressions must be tied to the plot as tightly as the fewer digressions found in tragic poetry. Similar requirements regarding character presumably apply to the epic hero as to the tragic hero. In spite of the differences in genre, it would seem that the basic criteria for judging quality remain the same.