"You got Sci-fi in my Fantasy! No, you got Fantasy in my Sci-fi!"

I read a lot, as any person interested in writing should. It's primarily fantasy/urban fantasy, but I read some fiction and sci-fi.; I also like to watch sci-fi TV shows and movies (I like Killjoys and Dark Matter). I've been reading Jean Johnson's Theirs Not to Reason Why series (good read, though the MC is a serious Mary Sue), and something about all the alien races made me think: if you wanted to do non-human races in fantasy, you would do worse than thinking of them of them as "aliens". I also started replaying the Mass Effect trilogy a few months back, and that made me think of something else: fantasy and sci-fi are simply two sides of the same coin.

You probably just rolled your eyes and said "well duh" - it's pretty obvious when you think about it, right? Simply put, sci-fi is fantasy writ large. Observe:

Setting: Fantasy generally takes place on a single world; rarely, it can cover a few different locations on different planes. Sci-fi takes place on anything from a single world to an entire galaxy, and sometimes even multiple galaxies. Instead of hopping on a ship and sailing across the sea to the next continent, you hop on a ship and fly to the next star system.

Races: Both genres range from "humans are the lone race" to "the setting is home to several dozen races". As I mentioned earlier, if you want to make your fantasy races really unique, think of them as aliens. This is especially effective if they originate on a different plane or a continent/location that's never seen humans. Aliens don't think like humans - that's why they're aliens. They have a different set of morals, culture, standards of beauty and bravery and whatever. Sure, they can be like humans, but I think it's be better to start with something far away and adjust them to bring them closer to a human viewpoint, rather than vice versa - that way, you can retain a lot of the "alienness" that makes them unique, instead of making them seem like "humans with pointy ears" (or fur, or sharp teeth, or whatever).

Magic: In fantasy, it's magic. In sci-fi, it's psionics. Either way, it's almost a given that you'll have one or the other. Magic is often genetic and sometimes taught at schools/academies, while psionics is also often genetic, but can also be granted through science (genetic alteration, advanced tech, or some powerful alien being/race) and can also be taught/developed. Magic can exist in a sci-fi setting, but that turns the genre more toward cyberpunk, steampunk, or magitech, which I'll discuss in another post.

Religion/gods: As a rule, gods don't exist in sci-fi. You can, however, have god-like beings - creatures or races who are so far advanced that they're beyond the human ken (Clarke's Third Law takes effect here). Religion is pretty well a constant among all intelligent races, though: if you're self-aware, you tend to wonder where you came from, why you're here, and where you're going, and religion is a good way to explain that.

Civilizations: In general terms, sci-fi and fantasy are nearly identical. A nation is still a nation, an empire is still an empire, you still have governmens and trade and laws and customs... but again, sci-fi does it on a grander scale. A nation in fantasy is equivalent to a planet or star system in sci-fi; an empire that spans a continent in fantasy could span an entire galaxy in sci-fi. Both genres feature lost civilizations, old races that turned to dust long before humans came on the scene, and ancient artifacts whose function and purpose have since been lost to the mists of time.

Want to do something fun? Try converting your favorite sci-fi story to fantasy. Or vice versa. Take Star Wars, for example - it just begs to be made into a fantasy story. The Jedi are an order of martial artists who use ki power instead of the Force. They still fight with swords (which are not lightsabers), but these can vary depending on the user, or maybe Jedi can change the sword's form at will. Their role: let's say they're a group that transcends race and nation and works toward peace and harmony. The Sith, obviously, want to do Bad Stuff (tm) - destabilize governments, take over the world, crush the Jedi, etc. Droids could be replaced with clockwork constructs or just non-human races (depends on the tech level). The Death Star is still a massive engine of destruction, but its appearance and makeup could vary widely - anything from a monstrous sea-going ship to a massive land-bound vehicle to a mobile fortress carried on the backs of 10,000 undead slaves. Planets are turned into cities, the Empire becomes smaller (but no less of an Empire), and the Resistance remains as it is - a ragtag group of people fighting the Empire. Hell, file off the serial numbers, make a few alterations, and you've got a full series right there.

On the flip side, you could take, say, Game of Thrones and make it into a space opera spanning worlds or even star systems. Most it's about war and politics - that stuff is universal. The White Walkers become an interstellar threat looming over all (see Jean Johnson's books). The Faceless Men? Easy - that's just advanced tech. The sorceress (her name escapes me now) would need a little tweaking, but she could be a psionic priestess. Since we're not going for an exact conversion, you can play around with it.