Science-Fiction versus Fantasy

Genres. What I have discovered on my trek to getting published is that the "industry" likes to categorize things. Makes sense. We all categorize. But what leaves me somewhat confused is the blurred edge between many of the literary genres. For instance, Fantasy and Science-Fiction.

On the surface the distinction seems simple. You've got wizards, dragons, fairies? You're Fantasy.

Got robots, spaceships, Jedi? You're Science-Fiction.

I once heard the distinction stated as "science-fiction is what is probable and fantasy is improbable."

Wait. What? One is real and one is not? Not all science-fiction that I've read (or seen) is in any way probable. Are you telling me the Force is probable? No. That's why some consider Star Wars a Fantasy. But it has robots! And spaceships! So what, exactly, is the true definition? Is all Science-Fiction hard Science-Fiction? Relying on scientific fact and/or scientific probability? Or is there some deeper reasoning?

I ask because my YA novel is currently being categorized as Science-Fiction. But there's not really any science. Sure, it's in space. But it's a fun adventure in space and I didn't spend 5 years researching the physics of space travel. And I'm positive it's not in any way probable. So what is it...Fantasy? Since there's no vampires, witches, magic or swordplay then I bet the "industry" would balk at that title. Space Opera? Not widely accepted, I think. And so far, to stand out you need to fit in a box.

But what if we started having robots in the Middle Ages alongside wizards, and dragons in the future on spaceships? Would heads explode?

(Sigh). I shall have to do more research. Let the genre wars begin.