This is a well interesting discussion! As for Star Wars - well, isn't the force something of fantasy? Now I'm not a Star Wars fan and I've only seen eps 1 and 3 (the modern ones, not the original) and that was a lot time ago, so perhaps I've missed something, wouldn't be surprised, but the way I've always understand "the force" is that it's some sort of energy that gives you power/strength to fight and turn you good or evil. Sounds like magic with a cooler name really. For me, sci-fi is anything that's space related, Star Wars, Battlestar, Firefly, Star Trek... Whereas like Naussica, Laputa, Hunger Games, even Doraemon (lol) I've never actually categorised in my head, but it's actually probably my favourite types, this sorta mix of real and fantastical elements explained in quite loose ways that makes it non-magic, but without the tech for it to lose its charm. What about magical realism? People who write magical realism often like to "correct" you if you say it's fantasy. But as far as I understand magical realism, it's simply magic set in the real world, like Potter, right? (and how is that different to urban fantasy?)
The thing with The Force is that it's kind of scientifically explained in the story--which basically means it stops being something magical. If I'm not mistaken, something magical is something that is supernatural or mysterious in that no one has been able to explain how it works. So, I think we could say that The Force is science fiction. Think about it. If we didn't understand how fire works, we'd think that a lighter was a magical artifact. But because we DO understand it, it's just science. Having said that, we'd have to say that Harry Potter is partially science fiction as well. I mean, if only certain people are born wizards--which I believe is tied to their DNA--then we have a scientific explanation for these people being able to use magic. It would be due to some mutation that occurred at some point, creating a subspecies of human: wizards/witches. However, I don't believe the nature of magic itself is ever explained in the world of Harry Potter, which leaves it in the realm of the supernatural or magical. At the end of the day, and this is just my opinion, we should just realize that there are things people will recognize as science fiction and things that they'll recognize as fantasy. You show them aliens and space ships, it's science fiction. They see wizards and dragons, it's fantasy. You put wizards in space, its science fiction AND fantasy. Trying to split hairs about this can be entertaining, but it's not going to change much.
If you want my example of a good novel series that merges magic with science, I highly recommend Philip Pullman's His Dark Materials trilogy. It describes a world with steampunk, witchery, paranormal elements, parallel worlds, etc. One can argue as to how convincingly Pullman tied the two together, but I think it shows it can be done, with some generous suspension of disbelief on behalf of the reader.
That would be episode 1 in my world, then, because I only acknowledge the first 3 films made to be true Star Wars films We do seem to be using the terminology differently. Take out the magical powers and you have the evil powerful person, the old sage and the farm boy going to rescue the princess. That could be written in an entirely naturalistic way (Anne Brontë's The Tenant of Wildfell Hall, perhaps?). Would you still class it as fantasy then? Or is it the "magic" in Star Wars? Well, it's not presented as magic; there is a "scientific" explanation (the Force). Yes, the Force is very much a hand-wave, so it's very much soft sci-fi, but I wouldn't see that as making it cross the line into fantasy (and there's no subversion or blurring of the line). I think this just makes me more convinced that Kyix's original question wasn't clearly enough posed for anybody to give a meaningful answer.
My take on it is that "science" fiction suggests technology. Fantasy, in terms of a story, suggests lore that is amazing or incredible compared to reality. In terms of traditional stereotypes, science fiction seems to include ships, guns, lazers, aliens, etc. Fantasy, in terms of Dungeons and Dragons, Lord of the Rings, countless role-playing video game titles, etc. have usually been stereotyped with bronze- or iron-age technology reminiscent of sword-and-shield and magic. The difference I find between the stereotypes is the idea of mysticism. Fantasy typically champions the use of magic, which is shrouded in a mysterious lore, whereas science fiction unveils the mystery and explains how the magic works--almost insomuch as introducing it as a technology. I think Star Wars was a good example of a fusion, combining the stereotype of Fantasy sword fights, strange beasts, and the mystical Force. To answer your question, you can combine them if you do it convincingly. Creating your own lore is a challenge, because people already have a collection of lore from other stories they have invested in and have emotional ties to. You need to convince readers to want to be attached to your lore--should you create it. I think a lot of people tend to rely on the traditional foundations (e.g. Lord of the Rings: orcs, dwarves, goblins, etc.) because it is easily understood by readers; however, you don't necessarily have to restrict yourself to the foundations that have been laid in the past. A lot of Japanese story designers for video games and Manga have come up with fantastical science fiction--take, for example, the Final Fantasy series. The only thing that you must establish is lore that makes sense and that is alluring.
In magical realism, the fantastical aspect isn't as important as it is in fantasy. The fantastical element is introduced and then taken for granted in a way. Take a look at Gabriel Garcia Marquez's short story "A Very Old Man with Enormous Wings." The wings on the old man (the fantastical element) aren't important. Rather, it's the other characters' reactions that are the key to understanding the story. Sometimes it can seem like an arbitrary distinction, but the more you read magical realism, the easier it'll be to differentiate it from fantasy.
That reminds me. I'm not a big Star Wars fan but I've known a few people who were. They told me they were greatly disappointed at George Lucas's explanation of "The Force" in Episode I as micro cell organisms. Making magic seem (scientifically) real can be frustrating for some.
