You’d be forgiven if you didn’t know the exact boundaries between fantasy and science fiction. Fans of one tend to be fans of the other, resulting in a lot of cross-pollination and blurring. It happens so often that they’re common grouped under the umbrella-term “speculative fiction.” Any fan will tell you that science fiction is more than spaceships and crazy gadgets, and fantasy is more than dragons and sorcery. There is a difference between these two genres, but it’s not where you think it is.

Back in 2016, there was a lively discussion on LegendFire about the role of science and magic in fiction. One person claimed that “physics is anathema to magic” while others strongly disagreed, arguing that what’s commonly thought of as magic has (or could one day have) a scientific basis and explanation.

What I took away from this debate, however, wasn’t that one side was right or wrong. The debate showed me that distinguishing science from magic was pointless when it comes to storytelling. These genres aren’t strictly defined by the presence of magic or hard scientific facts.

The true difference lies in the setting’s core assumptions.

Every fictional world is built on a set of core assumptions – axioms about what exists, what doesn’t, and how things work. These assumptions can be similar to or different from the real world. Examining these core assumptions – what they are, how they are presented in the story, and the logic that forms around them – reveal the true difference between fantasy and science fiction.

Science fiction is an open system.

Its core assumptions are drawn from external sources – namely, science as it was understood at the time the story was written. The story often doesn’t spend much time detailing these scientific concepts, though considerate writers do strive to educate their audience when necessary. Instead, most rely on the reader already having a basic understanding of the science involved when they start on page one. Writers can get away with this since there are plenty of resources the reader can turn to in order to gain this basic understanding.

In many cases, the story can be viewed as the writer’s argument and conclusions drawn from these external assumptions. But even the softest science fiction story allows the current (at the time of writing) scientific understanding of the real world to influence and/or form the basis of what occurs in the story. The story’s logic also applies to the real world. This is how science fiction predicts real-life scientific advancements.

Fantasy is a closed system.

Its core assumptions are established internally. In other words, events in the story are used to set precedents for what can and can’t happen. The story relies on these precedents to shape the plot, and good fantasy writers maintain consistency with them.

This reliance on internal precedents explains why fantasy stories are often sprawling epics set during great turning points in the world’s history. It’s just efficient to center the plot on these events since it allows the writer to establish these necessary precedents while weaving an interesting narrative at the same time.

Yet even when these events aren’t the main focus of the plot, the reader can expect to hear a lot of backstory on them. The fantasy writer must assume that the reader doesn’t know anything about the world and its magic, thus it falls on the writer to teach the reader. Unlike science fiction, there are no external resources the reader can reference in order to learn about how magic works in Narnia or Middle Earth. The only way the reader can learn these things is if they read C.S. Lewis and Tolkien.

Relying on internal assumptions also means that the story’s logic doesn’t apply to the real world or any other fictional world. The core assumptions are different. This explains the great diversity of fantasy worlds and magic systems.

Once you move away from surface level differences, from spaceships and dragons, a wide array of settings and aesthetics open up to you. Science fiction doesn’t have to be purely a futuristic genre. You can take an alternate history route and speculate what might have been. The steampunk genre is a vivid example of this. Likewise, fantasy doesn’t have to include mythic beasts and overt magic. You can make the strangeness subtle and the world more modern, like in the sub-genres of magical realism and urban fantasy.

Blurring the lines between genres isn’t a bad thing. Keeping your story grounded as an open or closed system, however, can assure the reader that they’re getting the type of story they want, even if it looks different at first glance.

What do you think? Do you agree or disagree? Leave your thoughts down in the comments below.