What's the Difference Between Sci-Fi and Fantasy?

Science Fiction and Fantasy Are Both Speculative Fiction

What's the difference between science fiction and fantasy? Some would say that there is very little difference between the two forms, that both are speculative fiction. They take a premise of "What if..." and expand it into a story.  However, others would make a distinction between the two genres, with science fiction extrapolating on current knowledge for future possibilities, while fantasy creates impossible scenarios that have never and will never exist.

Illusory Differences Between Science Fiction and Fantasy

Science fiction and fantasy both explore other realities than our own. And in the sense that either way what really matters is human nature, the difference is one of setting and environment.  Orson Scott Card, an award-winning novelist in both genres, has said that the difference is illusory. "Half joking, I was writing to Ben [Bova] about this very subject, and I said, look, fantasy has trees, and science fiction has rivets," Card said in a 1989 interview. "That's it, that's all the difference there is, the difference of feel, perception."

Aspiration vs. Transcendence

But there is a fundamental difference between science fiction and fantasy, one of aspiration. Humanity can look forward to the kinds of achievements postulated in science fiction, or look in horror at the consequences the result in a future dystopia. In fantasy another part of our brains dream of the impossibilities that can be conjured.

Science fiction expands our world; fantasy transcends it.

Possibility vs. Impossibility

Science fiction takes current knowledge and uses it as a springboard to imagine how it will continue to develop in the future, and what the consequences may be. It imagines things that are possible, however improbable.

Fantasy does not require an underpinning of science, and it may involve magic and supernatural beings and effects. It doesn't care whether these are impossible and does not justify them with science. For example, in a science fiction story, there may be a spacecraft that travels faster than light speed. While this is currently not possible, the author justifies the craft with a technology and scientific theory that allows it to operate within the story. In a fantasy story, a human character may suddenly develop the ability to fly, but there is no technological explanation.

Following the Rules

Both science fiction and fantasy worlds operate according to internal rules. Just because impossible things happen in fantasy doesn't mean they happen randomly. The author lays out the parameters of the story and the characters and events follow the rules as assigned. The same is done in science fiction, although more of the rules are likely to based on current scientific knowledge. In both fantasy and science fiction the author determines what the rules are by which their stories will operate. In the case of the faster-than-light spaceship, it will operate according the rules laid out by the author.

In the fantasy story, the human who could suddenly fly has this ability explained by supernatural means, perhaps by using magic or a wish granted by a supernatural being.

Of course, there is the saying by author Arthur C. Clarke that all sufficiently advanced technology is indistinguishable from magic. This is where authors can blend and shade science fiction into fantasy, sometimes revealing in a fantasy story that the impossible occurrences actually stem from technology.