Misery is another puzzler, since the Horror of it is really more in the mind. No doubt being kidnapped and hobbled is scarier than hell, but there are no supernatural elements, no one defies death, nor do any other Horror tropes make an appearance. Drama or Horror? I don't really care, and it makes a good discussion (which I enjoy because I've learned a lot from this thread alone!), but I could definitely see where anyone might choose one or the other (Drama or Horror). In the book, the hobbling is a bit more severe, taking it from a creepy drama about the dark side of fame directly into Horror territory. And, IIRC (and I may well be wrong, sorry), ol' Annie, our nummmmmberrr whan fannnn, takes a few to the chest and keeps on ticking.
Book=Horror, no doubt; movie=???
To be fair to other posters, without the gore, Carrie would have been sci-fi. Without the gore and stalking, I Spit on Your Grave would have been a Drama instead of a revenge flick. Sorry, I love horror and even run a blog on stuff just like this, so I'm enjoying the conversation. I apologize if I hijacked it or got OT.
Horror does not require a supernatural element, at all, and for my money
Misery is 100% horror. It's not a thriller - it's not about the pursuit of the killer, for example (c.f.
Silence of the Lambs). A psychotic fan capturing and torturing her favourite author to force him to write the book she wants...that's a brilliant horror premise, and in being told mainly from the perspective of the terrified, all but helpless victim, has a classic horror construction.
I really don't understand labeling a film based as horror or not because it might have sci-elements, or western elements, or whatever. Is a principal aim of the film to scare or horrify you?
Alien is unquestionably a horror film, as is
A Quiet Place.
Carrie doesn't need the gore to be horror, it's horror because of the plot. Its principal aim isn't to explore the implications of telekinesis (which might have made it soft sci-fi) but to explore the horrifying consequences of Carrie's trauma on everyone around her. The telekinesis is just there to give her a means to externalize her hurt. The blood adds shock value, true, which is one element of horror, but the principle horror of Carrie's existence is set out in the opening scene of both book and film, and it's not about telekinesis, it's about being relentlessly bullied at school and at home (also, the initial body horror of menstruation, particularly for a sheltered girl who doesn't understand what is happening, is a brilliant cold open from King that establishes the theme right up front).
A film is horror if its principal aim is to scare, repulse, unsettle you. To horrify you. That can be combined with other genre, so you can have horror set in outer space, or the old west, or on a ship, etc. but if it is primarily designed to provoke fear, then it's horror. Horror is a product of story structure, not setting.
Some blended films can be harder to categorize, since they are appealing to very different audience responses.
Ghostbusters is not a horror film, despite being built around a supernatural premise; when you break down the story beats, it is clearly a buddy comedy. Similarly,
Ghost might have a supernatural premise, but it is obviously a romance, not horror.
Evil Dead 2 is horror, though often a very funny one, but
Army of Darkness is fantasy.