Creepy beyond belief, “Hereditary” is one of those movies you shouldn’t describe in detail, because if you do, it will not only ruin surprises but make the listener wonder if you saw the film or dreamed it. The movie sustains a throb of dread throughout its first 90 minutes, and its final 30 are off-the-rails in the best way. Writer/director Ari Aster structures the tale in such a way that you can never be sure if the uncanny events you’re witnessing are real or figments of the imaginations of the Graham family, a clan cursed both by Biblical bad luck and a genetic disposition towards various types of mental illness. Toni Collette stars as Annie Graham, an artist and mother who’s coping with the death of her mother while trying to finish an exhibition of dioramas that appear to depict her own family’s life and Annie’s internal state. Alex Wolff is Annie’s oldest child, Peter, a sad-eyed pothead drifting through life. Milly Shapiro plays Charlie, Peter’s younger sister, a disturbed 13-year-old with the dead stare of a statue. Gabriel Byrne plays Annie’s stoic, kindhearted husband Steve, who just wants the family to be happy and struggles to make peace between the others. All are reeling from the death of the family matriarch, who we learn was anything but cuddly. The family is uncomfortable with frank displays of emotion, and with anything that might reveal the truth of their emotional interiors to one another. Annie tells her husband that she’s going off to the movies when she’s really attending a grief management circle that meets in a church basement. Peter anesthetizes himself with marijuana. Charlie draws obsessively in a small notebook, and … Well, maybe I shouldn’t tell you about the things I was just about to tell you about. Maybe it’s better if you just experience the story on your own. The deeper that “Hereditary” pulled me in, the more grateful I was that I didn’t know much about it before setting foot in the theater—including what relationship, if any, the plot has to the movie’s one word title, which refers simultaneously to the mental illness handed down through the generations, the family lore and lies that are also handed down, and the social, religious, philosophical and psychological concepts that carry from one generation to the next, whether they’re illuminating or destructive. Unspeakably horrible things happen to the family throughout. Every time they experience new trauma, it cracks their controlling facades a bit more, exposes emotional fissures in the family as a whole, and makes you wonder if perhaps the social institutions surrounding us and the intricate practices of language, science, and literature aren’t just elaborate means of holding back fear of death and random misfortune. It’s not often that a horror movie so dedicated to the low art of the jump scare seems genuinely interested in the wider issues that it raises, but “Hereditary” is that kind of movie. “Hereditary” is also a terrific entry in the sub-genre of psychodramas about repressed families. The regular eruptions of weirdness, surrealism and nightmare spectacle live in the spaces where family arguments and breakdowns might occur in a realistic movie. The parents and children speak to each other in the language of considerate individuals, but very soon you learn how to spot the passive-aggressive digs, the excuses and deflections, the knife-twists disguised as statements of concern. When something bloody, bizarre or merely unsettling happens, it seems to be in response to whatever the characters are refusing to really address. There are images of mangled, burned and mutilated flesh, uncanny behavior by reflections and beams of light, and sound effects that seem to be happening inside your head. There’s actual, shocking physical violence in this film, but ultimately not as much as you might falsely remember when you talk about it later. And yet if somebody were to ask me how violent “Hereditary” is, I’d say it’s one of the most violent films I’ve ever seen, because the emotional damage inflicted on the Grahams by life and by one another is so profound, and because the entire thing is perched right on the edge of catastrophe, and the smaller shocks are so effective that you really don’t want to see what will happen when the movie finally tips over into the abyss (and yet, at the same time, you do; that’s horror). Aster and the cast make you care very deeply about these disturbed people and fear what they might do to one another, to themselves and to strangers, and when something awful invariably does happen, you feel sadness as well as shock, because now it’s going to be even harder for the Grahams to climb out of the pit of sadness that the grandmother’s death cast them into, and finally address all the past traumas that they’ve been ignoring or covering up. Film literate in the extreme, “Hereditary” seems inspired by a wide array of classic sources both inside and outside of the horror genre, everything from “Rosemary’s Baby,” “The Exorcist,” “The Amityville Horror” and “The Texas Chainsaw Massacre” to Asian horror touchstones like “The Grudge” and “The Eye.” But the film owes just as much to the intense family psychodramas of Mike Leigh and John Cassavetes, which place strong-willed but deeply damaged people in close proximity and look on as they suffer barely-concealed torment from sitting on their rage, then finally lash out against each other in displays of emotional violence that are every bit as intense, in their own way, as the bloodletting and surrealism. Aster keeps intimating that something horrible could occur at any moment (notice how every sharp object used for any reason gets its own, ominous close-up), but when something horrible does happen, it’s usually far worse than whatever you envisioned, not just because of the incidents themselves, but because “Hereditary” is a rare horror movie that pays proper real-world attention to how individuals deal with trauma. We see the Grahams lying in bed, depressed to the point of paralysis. We see them nipping and snapping at each other, hiding inside themselves, hurting themselves and others. There are scenes in this film that brought me to the edge of tears because of how brutally people speak to each other, saying profoundly hurtful things that are as petty and self-serving as they are true, inflicting damage that can never be undone, all because they’re in such pain that they need to see someone else hurting even worse. At times, Aster’s film seems to be attacking rationality itself, scraping and scratching and tearing at the thought structures and language we’ve developed over the millennia in order to live in the world, with the ultimate goal of plunging us backwards in time so that we reconnect with the superstitious cave-mind that looked up at the sky when it started to rain and wondered what the tribe had done to anger the gods. The movie’s final act raises questions about the verifiable reality of anything you’ve just seen, but it seems appropriate considering all the attention that the script paid to the idea of curses, spirits and the inexplicable. Aster, his cinematographer Pawel Pogorzelski, the camera and lighting crew, and the entire sound department deserve special recognition for coming up with creepy moments so specifically imagined that you truly can say you’ve never seen them before. It’s been a while since I looked over my shoulder during a movie, to make sure something sinister wasn’t lurking beyond my sightline, but this film made me do it.