“The Last Jedi” is set in large part in a green, mountainous landscape inhabited by Luke Skywalker (Mark Hamill) — an old, grizzled dude with flowing robes and mysterious powers. The plot involves talk of royal bloodlines, astral projection, swords that choose their wielders, and an epic battle between light and a twisted, all-seeing Sauron-like darkness. The film also includes cute Disney-like snow cats and owl-critters, and it opens with the words, "A long time ago in a galaxy far, far away," which sure sounds like a variation on the classic "Once upon a time."

"The Last Jedi" is built around magic and mysticism and backwards-looking nostalgia for a time of knights and royal houses. Those are tropes of fantasy, not of future-obsessed science fiction.

Or is it? To figure out whether Star Wars is science fiction, you first need to figure out how to define the term — which is harder than you might think. Genres are notoriously difficult to pin down, which is why they spark so many arguments. Some country fans protested loudly when Beyoncé appeared at the Country Music Awards because she (supposedly) was not a country artist. Some critics similarly argued that Bob Dylan's lyrics are not literature, though the Nobel committee disagreed.

Genre is a marker of quality and belonging, of seriousness and community. Science fiction in particular is often seen as more important or serious than fantasy, so it's no wonder that there's been some struggle over how to place the films. George Lucas himself declared that "Star Wars isn't a science-fiction film, it's a fantasy film and a space opera" in 2015. Others have also waded in over the years; Annalee Newitz included Star Wars in a list of 10 science-fiction works that are really fantasy at io9, while author Brian Clegg says Star Wars is only "low-grade science-fiction" — it's not quite real science-fiction, so it's not high quality.

Not your average hiker. The Walt Disney Studios

All of this begs the question: What is science-fiction, anyway? Sci-fi godfather Isaac Asimov offered one popular definition of science-fiction in 1951. According to Asimov, science fiction is the "branch of literature which is concerned with the impact of scientific advance upon human beings."

But despite the high-tech gadgets, Star Wars is supposedly set in the past, not the future. While it includes space ships and blasters, it barely speculates on how they'd affect the future beyond positing that space battles would be really cool. So by Asimov's definition, Star Wars clearly isn't science fiction.

But Asimov's definition of science fiction is flawed — as you can see by comparing it to any number of iconic works from the genre. Mary Shelley's “Frankenstein,” often cited as the first science-fiction novel, isn't concerned with realistic scientific-advances or their effect on society. It's a meditation on whether nature or nurture makes us human, with vaguely articulated references to alchemical processes tacked on for atmosphere. Similarly, H. G. Wells' “The War of the Worlds” isn't about the effect of scientific advances. It's a reverse colonial nightmare, imagining what would happen if alien invaders did to the British what the British did to their colonies.

Similarly, a contemporary sci-fi/horror show like "Stranger Things" doesn't care about scientific advances — it, like Star Wars, is set in the past. Asimov's definition blatantly excludes both foundational works in the genre and famous contemporary examples of the form. It's useless.

So, if definitions aren't working, how can we decide if Star Wars is science fiction? Literary scholar John Rieder has argued that we might see genre as a "web of resemblances." To decide whether Star Wars qualifies as science fiction, you could look at other iconic works of science fiction and see whether it resembles them or not. “The War of the Worlds” has spaceships and aliens; Star Wars has spaceships and aliens. Star Trek has warp speed; Star Wars has hyperdrive. The John Carter science fiction novels had epic fantasy elements in a space setting and were called science fiction. So is it science fiction

Of course, by its nature, the "web of resemblances" test is going to be vague and subjective. It also can go both ways. Star Wars has a battle between light and dark and sword fights and wizards. In this respect, it resembles Tolkien. Why not call it fantasy?

Flying high. Walt Disney Pictures

Jason Mittell in his book “Comics and Television” suggests another approach to genre. He argues that genres are simply those things that are socially agreed upon as genres. In other words, “Stranger Things” is science fiction because critics and fans and even non-fans have loosely agreed that it's science fiction — as a Google search confirms.

In contrast, consider NBC's “The Good Place.” The show is a sit-com about the afterlife created by angels and devils. It includes a robot servant (who doesn't like to be called a robot). It uses a concept of multidimensional space and parallel worlds that is not so far removed from the one that anchors “Stranger Things.” It has sci-fi elements, just like Star Wars.

But “The Good Place” is basically never referred to as science fiction — and so it isn't. Definitions and resemblances influence how people decide what is science fiction and what is not, perhaps. But there's no one true definition; Genres are ultimately crowd-sourced.

From that perspective, Star Wars is probably the single most famous science-fiction film, and science-fiction franchise, in the world. Anything associated with Star Wars is going to be thought of as science fiction by just about everybody.

Indeed, the Star Wars franchise is science fiction in part because science fiction has been defined by Star Wars. Today, vast swaths of science fiction bear the Star Wars franchise's stamp: “Guardians of the Galaxy;” recent Star Trek films; Ann Leckie's Imperial Radch novels; Syfy's “KillJoys.” They all are sweeping space adventures in which the tech is basically treated like magic — a source of wonder and fun that doesn't need to be explained. "The Last Jedi" demonstrates that a movie about a mystic order of wizards and their sacred texts can be science fiction, if you call it Star Wars. Though it can be fantasy too, if you want it to be.

Noah Berlatsky is a freelance writer. He edits the online comics-and-culture website The Hooded Utilitarian and is the author of the book "Wonder Woman: Bondage and Feminism in the Marston/Peter Comics, 1941-1948."

CORRECTION (Dec. 20, 2017, 5:30 p.m. ET): An earlier version of this piece misstated the name of Jason Mittell's book. It is called "Genre and Television," not "Comics and Television."