What Changes by Genre

Two stories can share almost the same plot — someone discovers a hidden threat and has to stop it — and still feel like they belong to entirely different shelves in a bookstore. One reads as fantasy, one as mystery, one as science fiction, one as realistic fiction. What actually changes between them isn't the events. It's the promises the story makes to a reader from the very first page about what kind of explanation they're going to get.

The promise each genre makes

A mystery promises that every strange detail will eventually make sense through reasoning — a reader is implicitly invited to guess along, which means clues have to be fair, not withheld from the story until convenient. Fantasy and science fiction promise that the world runs on rules different from our own, and that those rules will be shown clearly enough that a reader can tell what's actually surprising within them, rather than the writer inventing a new one every time a character needs saving. Realistic fiction promises that nothing will happen that couldn't plausibly happen to someone in the world as it actually is.

This is why genre matters even in a first draft, not just as a marketing label at the end. If you're writing fantasy and a character escapes danger using a power that was never mentioned before that exact moment, you haven't just surprised your reader — you've broken the specific promise fantasy makes, that the rules were knowable in advance. The same twist in a story that had established that kind of power earlier would land as satisfying instead of like cheating.

Trying on a genre, then, isn't really about choosing a setting. It's about choosing which promise you're making to your reader, and then writing carefully enough to actually keep it.