Creative writing teachers are fond of sweeping generalizations:

“Never use adverbs.”

“Never begin a story with the word the.”

“There’s only one plot: the shift from innocence to experience.”

A friend of mine in Louisiana had a writing teacher who enjoyed proclaiming, “The king dies and the queen dies. That’s not a story. The king dies and the queen dies of grief. Now that’s a story.” I’m not sure what that’s supposed to mean, nor what any of these sayings are supposed to do for young writers. Probably make all but the most dedicated break down and get a real job.

But recently I heard a good one: “There are only two plots: a stranger comes to town and someone goes on a journey.” This aphorism helped distill an idea I’ve developed over years of reading and writing science fiction and fantasy, resulting in my own sweeping generalization: “There are only two kinds of fantastic story: the Alternate World and the Trespass.”

What do I mean by this? Allow me to define my terms.

In “Alternate World” stories, the reader goes on a journey to another era, another planet, a world that follows different rules. Alternative histories, stories of the far future, and tales of elves and magic fall into this category. In their own way, Lord of the Rings, 1984, and Star Wars are all Alternate World stories.

In “Trespass” stories, a stranger comes to town. Something fantastic—whether The X-Files’ aliens or Anne Rice’s vampires—invades our familiar world of credit cards and disposable razors. Reality is shown  …