"Horror has a funny reputation," the film's writer-director Ari Aster says. "Most horror films are considered guilty until proven innocent as far as quality is concerned. For me too! So many are made so cynically – there is a built-in audience and the risk-reward algorithm works in the favour of producing as many as cheaply as you can."

Aster admits his own motives were less than pure; he had written nine scripts before Hereditary but, as a first-time filmmaker, he couldn't raise the money to make them. "So I figured it would be easier to get a horror film financed, a suspicion that was actually validated."

What he discovered within the genre was a surprising degree of freedom. "I wanted to make a film about grief and trauma that showed the corrosive effect they could have on a family, as opposed to showing a family going through loss, suffering and ultimately being strengthened," Aster says.

He pulls a face; he wanted to show the family that went through hell and never came back. "If you make that film as a drama, suddenly you have a very limited audience," he says. "But what serves as a deterrent to the audience in one genre is a virtue in another one."

Genre also provides a reliable framework of recognisable tropes, precedents and role models. Like zombie films or vampire films, horror films conventionally refer back to predecessors that sailed under the same flag.

So it is that critics have compared Hereditary to Hitchcock's Psycho (1960) and William Friedkin's The Exorcist (1973). Aster admits to studying the former but not the latter. Never mind: he'll take it. "This is a film that definitely tries to honour certain traditions while also trying to subvert them," he says. "One reason I make films is because I love films and I want to have a dialogue with them."

One film he did think about a great deal was Nicholas Roeg's terrifying Don't Look Now (1973), which was also about debilitating grief for a lost child. It's a film that tends to be overlooked by online list-makers, in part because (like Hereditary, perhaps) it wasn't "proper horror" and in part because it came out the same year as The Exorcist, which included everything a horror was supposed to have: a crazily possessed child, ominous weather, marauding demons and a defeated priest.

There are plenty of theories linking genre peaks with social upheaval. Sometimes, as with George Romero's zombie films, those links are explicitly made by the filmmakers themselves; other times, it takes the critic to see the convulsions of Watergate and its aftermath working through those 1970s masterpieces. Torture porn (Saw and its much lesser imitators, for instance) is seen to be expressing the brutality of the new world order.

"But this happens all the time," Aster says. "Even when The Exorcist or Rosemary's Baby came out, B-movies were happening, like we also had schlocky horror movies. I feel there have always been exceptions to the rule."

New technology, used inventively, can be a game changer: witness The Blair Witch Project (1999), supposedly spliced together from found footage, which gave rise to a sub-genre of its own.

"There has been a healthy number of exceptions recently, but South Korean genre films have been exciting for a long time; the juggling of tones and genres there has been really forward-thinking," Aster says. "For 10 years I've been watching South Korean films, feeling I belong in South Korea."

Now, however, he says he'll be making one more horror movie and then drawing a line under the genre. At least for a while. Another moment may be around the corner.

Hereditary is on general release