I know this essay is very popular here, but I’ve always disagreed with it.
In practice, people often define science fiction as “you know, lasers and robots and space ships and shit”. Obviously, Star Wars meets this criteria. But a more useful criteria for science fiction probably entails stories that are in some way actually about how some hypothetical future technology or development affects people and society. Stuff like Contact or Blade Runner are obviously sci-fi under that definition, as are movies like the Matrix or Terminator. These movies are actually about how some new technology or future condition affects people and society. This definition is not a binary thing either - there’s obviously a “sci-fi spectrum” here, and a movie can be both sci-fi and other genres simultaneously.
Some might prefer an even stricter definition or criteria for sci-fi. Under this stricter definition, a movie’s themes should not be reducible to conventional themes, i.e. the movie can’t simply use sci-fi elements as window dressing to tell a conventional, non-sci-fi story. For example, arguably something like Terminator 2 has prominent themes about motherhood, fatherhood, and determinism/fate. The movie doesn’t necessarily need science fiction elements to explore those themes. It could be reimagined as a story with the same themes and overall plot structure but with the sci-fi elements removed. For example, it could just be about a delinquent teenage orphan on the run from something while an unconventional father-like figure protects him. You don’t necessarily need killer time-traveling cyborgs to explore those themes - but they do make the movie a lot cooler. On the other hand, a movie like 2001 - A Space Odyssey is irreducibly science fiction, because the sci-fi elements are absolutely required in order to explore the themes the movie wants to explore, like space exploration, AI and the long-term evolution of the human race. But this stricter definition is pretty impractical, because few people use the term “sci-fi” in such a narrow way.
Anyway, I think Star Wars - at least A New Hope - is actually science fiction using either of these definitions (even the stricter one!). Most people are likely to describe A New Hope as a “hero’s journey” or a fantasy about a young farmboy who meets a space wizard and goes on a fantastical adventure. But the main plot is also very much about a new technological super-weapon, and how it affects society as a political game-changer, making an absolute technocratic dictatorship possible and stable over the long-term without any accompanying bureaucracy or democracy. There are also themes of “man vs. machine”, spirituality vs. technology, etc., all of which are themes that are not reducible to non-science-fiction themes.
Moreover, the “Star Wars is fantasy not sci-fi” argument is often used defensively in the context of discussions about obvious absurdities, like Han Solo walking around inside an asteroid, exposed to the vacuum of space, with no protective suit and a magical source of artificial gravity. Fans (and Irvin Kershner himself) often hand-wave away such criticisms with arguments about the artistic merits of Star Wars viewed as surrealism or expressionism. Star Wars certainly has elements of surrealism and expressionism, but the films also anchor many sequences around objective rules based on technological systems - e.g. we can’t penetrate the deflector shield so we need to blow up the shield generator.
Fundamentally, the boundaries between sci-fi and surrealism or fantasy are often arbitrary, based mostly on the experiences and expectations of the average person living today. If I complain that Han Solo shouldn’t survive in the vacuum of space, somebody might respond by telling me “Star Wars isn’t supposed to be science fiction.” J.J. Abrams said exactly that (“Star Wars is not a science lesson”) when fans complained that the bright red Starkiller beam in Force Awakens shouldn’t be visible in the sky.
But why exactly do we accept this? Probably because most humans have never been to outer space, so the average person doesn’t have the experience or mental model to develop expectations about how outer space works. Thus, they’re okay if a movie ignores the reality of physical conditions imposed in outer space if doing so increases drama or spectacle. Okay, but what if there was a scene where Han Solo dives into a river, and then just starts walking around underwater for hours, with no breathing apparatus? If no explanation is provided, the audience would be like “WTF? How is he not dead from lack of oxygen?” It’s doubtful anybody would respond with “Who cares! Star Wars is fantasy, not sci-fi!”. Because of course, the average person in the 21st century has the experience to understand intuitively that humans can’t breathe underwater. If a movie violates this intuition, the audience gets frustrated.
Even pure fantasy, like Lord of the Rings, generally adheres to the audiences’ base-line expectations about physics on a human scale. If Frodo Baggins falls off a tall cliff we expect he will die when he hits the ground. If he falls into a river and can’t swim, we expect him to drown. If these expectations are violated and no explanation is provided, the audience becomes frustrated. Pure surrealism or expressionism, on the other hand, doesn’t even necessarily require this minimal adherence to some baseline set of expectations rooted in the common shared experiences of being human. So I’ve always felt that labeling Star Wars as surrealism, expressionism, or pure fantasy - often defensively - to be pretty arbitrary, based mostly on our current, average experiences of reality, which change rapidly with each passing year as humanity collectively experiences new things and learns more about the Universe.
I don’t expect Star Wars to ever be hard sci-fi, nor do I want it to. It relies extensively on fantasy conceits like the Force, FTL travel, and space dog-fights. But that doesn’t mean we should pretend it’s entirely expressionist, as if objective, physical rules should always be a secondary concern, or that it doesn’t incorporate themes that are irreducibly science fiction.