Genre definition 1
Genre is descriptive, a characteristic of a work. A work can belong to more than one genre. It’s a romance. It’s science fiction. It’s a comedy. It’s horror. It’s fantasy. It’s a mystery. It’s a history. It’s a tragedy. It’s a romantic comedy. It’s science fiction horror tragedy. It’s historical alternate history fantasy. It’s a literary science fiction mystery.
Premise or setting is an obvious way to identify genre (in space = science fiction, has vampires = horror). But genres such as tragedy or romance or mystery are identified primarily by story or plot. Sometimes the thing that makes something seem like it belongs in a certain genre is mood and emotional effect, or approach, or theme, or writing style, or character.
Genre identification is not precise or rigid. It’s more of a tendency cluster.
Science fiction tends to be about our relationship with technology, nature, science, and social constructs, and is generally assumed to be about realistic extrapolations and plausible hypothetical scenarios. But sometimes it’s about going out to space and shooting stuff with laser cannons. And sometimes the concept of "realistic" gets a little fuzzy anyway. Realistic in what sense? In the sense of the author having worked out the physics equations to the nth degree? Or realistic in the sense of human behavior? And how realistic does it have to be to still be considered science fiction?
Horror tends to be about being scary. But it’s not always all that scary. In fact, horror that isn’t really all that scary is so popular that we keep inventing new terms to describe it. Dark fantasy: horror by premise and mood, adventure or drama by story. Urban fantasy: horror by premise, mystery or thriller by story. Paranormal romance: horror by premise, romance by story.
Humor is about being funny, right? But a story can be a comedy even if it’s not very funny. Comedy is still the type of story it is. And there’s often plenty of humor in stories that are not fundamentally comedies. And plenty of tragedy in comedy. And so on.
Genre definition 2
Genre is also used in a different sense, where genre is assumed to be a bucket that something gets put into. This idea of genre is much more rigid. Something goes into one bucket and it stays there in that bucket.
This view of genre isn’t new — the Greeks were very particular about what category their plays belonged in and what made something a comedy, tragedy, or satire.
Most arguments about genre come about because people use the term "genre" interchangeably to mean both the Greek bucket model and the descriptive tendency cluster model.
For example: when a literary novelist writes something with a science fictional premise. Reviewers get all confused trying to figure out whether they can call it science fiction or not. Because they’re different buckets! How can there possibly be a thing like literary science fiction or science fiction literature? How? How?
The bucket model exists in the modern world for one reason: marketing. It allows you to have different sections in your bookstore. It allows for different marketing channels — how do you hear about this book? How is it packaged? What publications review it? What organizations are likely to give it awards? What expectations are set up for it in the reader’s mind?
Since most people tend to prefer the contents of particular buckets, this isn’t necessarily a disservice to readers or writers. After all, booksellers, writers, and readers all want the same thing: to put books in the hands of people who are likely to enjoy them enough to pay money for the privilege of reading them. If genre buckets help do that, where’s the problem?
Well, here’s the problem. People act like the different buckets mean something. They act like the buckets are actually very important, little walled castles worth defending from the onslaught of the mongrel hordes. That can’t be science fiction because it’s fantasy! That can’t be horror because it’s romance! That can’t be literary because it’s science fiction!
Worse, they want genre to have a hierarchy. For some genres to be better than others in some inherent, objective way. For literary fiction to be better than science fiction, or hard science fiction to be better than other science fiction, or science fiction to be better than fantasy or fantasy to be better than horror or some horror to be better than other horror. They’ll make ridiculous claims like "science fiction is harder to write than fantasy" and then act like the truth of that should be self-evident.
"Good" is not a genre.
Well-written is not a genre. Interesting, emotionally effective, well-paced, thought-provoking, none of these are genres. A vivid setting is not a genre. Good dialogue and intriguing characters are not genres. Novelty and imagination are not genres. Engaging, satisfying stories are not a genre.
"I like it" is not a genre.
"Awesome" is not a genre.