Diegesis is a technical term literature can do without. Mimesis we should keep—but not in the sense as diegesis’s “counterpart,” where it isn’t particularly useful as well.
“Diegesis” is related to one of my favorite topics, namely Show, Don’t Tell and the reservations I entertain with regard to the latter as being inferior to the former. There’s a rather lengthy article on diegesis on Wikipedia, but most of it is related to movies, theater, and role-playing games. So let’s start with The Glossary of Literary Terms.
Nothing! But of course Abrams has a substantial entry for “mimesis”, of which “diegesis” is said to be antagonistic to. But let’s retreat and regroup and check out Wikipedia’s entry for diegesis:
Diegesis (Greek διήγησις) and mimesis (Greek μίμησις) have been contrasted since Plato’s and Aristotle’s times. Mimesis shows rather than tells, by means of action that is enacted. Diegesis, however, is the telling of the story by a narrator. The narrator may speak as a particular character or may be the invisible narrator or even the all-knowing narrator who speaks from above in the form of commenting on the action or the characters.
For both Plato and Aristotle, “diegesis” reports rather than represent, narrates rather than embodies, tells rather than shows. But in contrast to other theoretical constructs Aristotle developed about poetry, I think “diegesis” should be scrapped as a diagnostic tool for literary texts. There are other fields where it makes a lot of sense, like movies or video games, and there diegesis shouldn’t be scrapped as a diagnostic tool at all, far from it, and I’ll come back to that further below.
Even in the context of Greek tragedy, the term “diegesis” doesn’t make much sense, really. Greek tragedies had much less “show” elements than “tell” elements compared to contemporary theater. It’s not that they didn’t have “show” elements at all, but that didn’t turn Greek Tragedies into Michael Bay movies. Everything is related either by the chorus or through dialogue, and differentiating between diegesis vs. mimesis doesn’t make any sense for either of them. Plus, you have to add parabasis and quite a few other very odd things, and the best that could be said about contrasting mimesis with diegesis in this context would be that they mark two fuzzily defined positions connected by an unreliable slider bar.
Now, among literature’s most defining characteristics is its ability to engage the reader directly with the characters’ thoughts, what’s going on in their minds—there you can’t show, you just have to tell. And that’s exactly what movies can’t. Unlike literature, movies don’t have the power to directly “tell” what’s going on in the mind of a character; if they want to do that, they have to use VO, i.e., voice over narration, and similar techniques—for which we have a technical term, and that term is—diegesis!
And that’s what all this boils down to.
Using diegesis as a tool, particularly in the context of differentiating between diegesis and mimesis, makes a lot of sense when analyzing movies (or video games). But when analyzing texts, this tool isn’t productive or helpful at all.