In a serious discussion of this topic, a basic understanding of what an epilogue and prologue are will help. I’ve read quite a few definitions, and in my opinion, Wikipedia has the best. First: “A prologue…is an opening to a story that establishes the context and gives background details, often some earlier story that ties into the main one” https://en.wikipedia.org/wiki/Prologue.
Similarly: “An epilogue or epilog is a piece of writing at the end of a work of literature, usually used to bring closure to the work. It is presented from the perspective of within the story. When the author steps in and speaks directly to the reader, that is more properly considered an afterword.” https://en.wikipedia.org/wiki/Epilogue.
Epilogues and prologues go in and out of fashion. This has been happening for so long, even Shakespeare noted it at the end of his play, As You Like It: “It is not the fashion to see the lady the epilogue; but it is no more unhandsome than to see the lord the prologue.”
It’s actually easier to discuss what an epilogue is not. Not an afterward, not the final chapter. I look at it as tying up possible loose ends from your story, usually from the perspective of distance. Thus, the final scene in the Harry Potter saga, where over a decade has passed and you see the characters able to carry on with their lives, despite all they’ve been through, is an excellent example of an epilogue. (Whether you like it or not is another matter.) The Harry Potter series could have ended without that scene. But the author evidently believed that this final glimpse into the lives of her characters would enhance the readers’ experience, and that’s not a bad benchmark.
In that sense, it’s like a reflection of a prologue. A prologue gives the reader some additional information, usually occurring during a significant time interval before the story. In my Greek hero story, Bellerophon, I showed his birth, since it actually did have bearing on the later tale. Then chapter one opened with my hero as an adult.
One acid test that may be helpful is that it should be possible to enjoy your story without reading the prologue or epilogue. This is important, not just from the standpoint of literary purity, but because many readers skip them. If it’s absolutely necessary to know these events, then it belongs in a chapter at the front or end of your book.
And no matter what you choose to do, expect to suck up some criticism. If you simply rename your prologue Chapter One, someone will complain that it should be a prologue. If you include a passage as an epilogue, somebody will take issue with that as well.
My best advice is that if you must have a prologue or epilogue, keep them as short as possible. : )
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