Fantasy is right-leaning while SF is left-leaning. Easy peasy.

What was it again in science fiction, hard and soft? Whereas hard is more realistic and soft has more fantasy.

I would argue that science fiction and fantasy are the same thing and the only difference is the explanation for how all the cool stuff works.

Functionally, there's no real difference between a portal that takes the characters to another world using a wormhole and one that does it through through magic. Just like how there's no difference between Vulcans/Klingons/Wookies and Elves/Dwarves/Beastmen. Both are intelligent non-humans.

science fiction is in space and fantasy has castles.

I will take no further questions.

I've been reading stories from the Hatsune Miku rhythm game app, that almost straddles the line between urban fantasy and unexplained sci-fi. The premise is that instances of the vocaloids live in personalized virtual worlds for different (small) groups of humans. The humans can teleport to these worlds by playing a special song on their phone, or the vocaloids can project themselves as holograms from the humans' phones. It's almost sci-fi because it mostly works within constraints of technology. For example, you get booted out of the virtual world if your phone runs out of battery, and if your phone gets shorted out, it can prevent the vocaloids from projecting themselves until the phone is repaired (though if the phone still works otherwise, they can voice chat.) Also the special song can be transferred to different machines and still works. But then what makes it more fantasy is that the song and worlds are created from the humans' feelings (and if they lose the song, a new copy will appear for them,) and it works without internet connection (if one member of a group is stranded and another isn't, they could have a vocaloid relay a message.) And then just recently I read a chapter where some characters were able to access their virtual world through their dreams, without needing the song file in the first place. For me, that's what completely tipped the scale into urban fantasy.

just like IRL trees and computer science trees!

Fantasy evolved out of folk tales in the public domain. It was owned by nobody, and everyone could add to the story. It'd be accepted if people thought the story was good enough. Later, new stories were under copyright, but their heritage was clearly public.

SF grew up when a strong copyright regime was already in place. It was owned by either a single person or a corporation, and only they had the legal right to declare what was canon or not.

Science fiction is used to look down upon society and is often pessimistic. Fantasy look ls up at what could be and is generally optimistic.

Science fiction is based in reality and usually just extrapolates what we know is scientifically possible, just not with current technology. They can usually explain how stuff works because it's based on real science to some degree.

Star Trek is science fiction.

Fantasy really just follows the rule of cool. If it's cool, throw it in. It's based on nothing but what the writer thinks is cool as shit.

Star Wars is future fantasy.

Fantasy is when there's magic, sci-fi is when the magic has specific terminology.

If it's not from the fantasy region of middle earth then it's just sparkling fiction.