What is sci-fi? Science fiction's dirty little secret is that sci-fi is in the eye of the beholder. That said, there are certain guidelines that will help anyone genuinely interested in determining whether a work of fiction is science-y enough to qualify as science fiction. So, some guidelines:

Sci-Fi vs. Fantasy

Science fiction and fantasy both answer the question, "What if?" Works of fantasy imagine worlds and situations that could not possibly occur. "The Lord of the Rings" is a classic example of fantasy literature and movies. Maybe hobbits and dragons could someday be genetically engineered…but Gandalf’s magic isn’t based on science. If it’s magic, it’s fantasy. And, generally, if it’s magic, that means it’s not sci-fi.

Some works, like the comic book "Saga," combine elements of both. The same is true of "The Avengers," which features a high-tech robotic combat suit and a Norse god. Generally, such works are considered to employ sci-fi elements, but some critics won’t consider them works of pure, straight-up science fiction. So, what is?

Science fiction takes our current understanding of how the universe works and imagines worlds, ideas, and technologies that we haven't seen yet, but still, could fit within that understanding. It's fiction that expands on what we know about science, and scientific potential, operating within known or hypothesized scientific principles.

Spaceflight, for example, is something that exists today. Once upon a time, any work that included space flight qualified as sci-fi. Today, it’s less clear.

Some works of science fiction imagine new ways of crossing the universe that may seem impossible to us now but still operate according to scientific principles extended from what we know now. Others imagine the discovery of scientific principles currently unimagined. "Jurassic Park" is science fiction because we don’t currently have the technology to produce genetically modified dinosaurs. But that technology is a lot closer and more imaginable than building a Death Star. And if we ever do acquire that technology, "Jurassic Park" may not feel like science fiction anymore. For an example in the more familiar milieu of space, consider "Gravity." Is that sci-fi the same way "Interstellar" is? How far removed must the technology be from our own to qualify? Your light-year mileage may vary.

Take "Star Wars." The Force seems a lot like magic. But the Force eventually got a pseudo-scientific fig leaf with the introduction of midichlorians (don’t ask). This cemented "Star Wars" as a pure sci-fi work — if the rabid love of millions of sci-fi fans hadn’t already (the gravitational pull of "Star Wars" fandom is literally sufficient to change the sci-fi genre’s orbit). Of course, explanatory patchworks like midichlorians may end up making the difference between the good or even classic sci-fi…and hokey sci-fi.

What Films are Considered Sci-Fi?