For decades, Star Wars developed a near cult-like following. Fans treated the original series with reverence, finding inspiration in the original series’ moral dimensions (love and forgiveness vs. hate and anger, the light side vs. the dark side), as well as the idea of a mystical “Force” that bound the universe together and empowered the story’s protagonists. When The Phantom Menace was released, though, it was as if a million voices cried out in horror: George Lucas had pulled the veil back on the “Force,” and it became no more worthy of reverence than any other natural phenomena, such as gravity or inertia.

It didn’t take much. The character of Qui-Gon Jinn described the existence of tiny microorganisms living in the cells of “force-sensitive” people, called “midichlorians.” It was these organisms that made people sensitive to the force. With a single line of dialogue, the entire franchise pivoted away from fantasy towards science fiction. Was it because the force was “demystified”? (We argue no.) Was it because it was “scientized”? (It depends on what we mean by science.) Regardless of the reason for the backlash, it is widely regarded as a major misstep in the franchise.

This example highlights three things: (1) Fantasy and science fiction are different in identifiable ways. (2) Readers and viewers can intuit the difference, even if they can’t always articulate it. (3) The line can be inadvertently crossed by writers who don’t have a good understanding of the differences.

The differences between science fiction and fantasy extend far deeper than merely aesthetic differences (dragons and castles vs. aliens and spaceships). Even when a work of fiction has all the aesthetic trappings of science fiction, it can still be labeled as “science fiction with fantasy elements,” or as “science fantasy” (as was the case with Star Wars). Nor is it that science fiction takes place in the future while fantasy takes place in the past (the reverse can be just as true). Neither is it that science fiction involves plausible extrapolations of known science, while fantasy deals with the impossible — science fiction often deals with the impossible.

Rather, the core distinction is that science fiction assumes a particular kind of universe, while fantasy assumes another. Our argument is that science fiction consists of speculative fiction set in a naturalistic universe, whereas fantasy is a subset of speculative fiction set in a non-naturalistic universe. The rest is just window dressing. In this series, we do not use the terms naturalism and non-naturalism in a colloquial sense, so we will clarify these terms in Parts 2 and 3.

We acknowledge that science fiction and fantasy have been successfully mingled for decades without this distinction clearly laid out. This is because we often intuit far more than we can articulate, and intuitions often serve us well. Understanding these distinctions, however, can help writers more carefully navigate how to mix the genres, how not to mix them, and how to not mix them (when not-mixing is the goal).

For example, introducing a clearly non-naturalistic element into an otherwise science fiction story (and vice versa) affects the entire work, and whether that effect is good or bad depends on how well the author understands the universe he or she is creating. Introducing such an element inadvertently — and, vice versa, turning established fantasy into science fiction without realizing it — can be a good way to sleepwalk your way into a midichlorian-scale disaster.

In addition, understanding these distinctions can help us see new creative avenues for writing and storytelling; they can help us see where unexplored territory might lie. In short, the purpose for exploring these contours is not to limit writers or readers, but to liberate them — to free them from the tyranny of unexpressed assumptions. Assumptions that we are unaware of can bind us (and blind us), whereas assumptions that are open, stated, and understood can free us instead.

In Part 2, we will explore the nature of science fiction, and in Part 3, we will explore the nature of fantasy. In Part 4, we will highlight some examples of this distinction in action. In Part 5, we will discuss how authors signals a work is science fiction, and in Part 6, we will explore how authors signal that a work takes place in a fantasy universe.