In general, there are two kinds of horror movies: the ones with artistic value, like The Exorcist and The Silence of the Lambs, and pretty much everything else.

This is about that second group.

Specifically, this is about my favorites of “the unkillable” genre — the movies whose villains cheerfully weather shooting, burning, drowning, electrocution, disintegration and decapitation all while brutally murdering the barely dressed, inexplicably college-aged teenagers who are making dangerous decisions, probably by a haunted lake.

First, a note about my criteria. I omitted any series with less than five installments because, frankly, you’d be surprised how little it takes to get to four sequels (Saw is halfway there).

I also have not considered the following long-running horror institutions for reasons I will list immediately after this colon: Silent Night, Deadly Night, Leprachuan, Children of the Corn and Hellraiser because I couldn’t sit through anything after the third sequel without wanting to throw my TV off a bridge and race it to the ground headfirst; Child’s Play and Puppet Master because no one over the age of five thinks killer dolls are interesting; and The Texas Chainsaw Massacre because the first one was great and the rest of the run, which includes two sequels, two remakes and a prequel to a remake, would be awful if it wasn’t so ridiculous.

This leaves three landmark series, termed “the unholy trinity” by horror buffs (read: those older than 30 who live with their parents, wear lots of black and think group suicide would make a fun Friday night).

They are: Halloween, Friday the 13th and A Nightmare on Elm Street. Between them, they account for 26 incredible movies — 27 if you double count the latter two’s crossover sequel Freddy Vs. Jason, but that would just be silly.

Because it came first, is a legitimately terrific film and features a killer in a heavily made-up William Shatner mask, Halloween undoubtedly has the best initial installment. Second place goes to Wes Craven’s Nightmare for its dream imagery and for introducing the world to Johnny Depp shortly before he is disemboweled in his own waterbed by undead ethereal child rapist Freddy Krueger. Known for his burnt face, poor fashion sense and razorblade nails, Freddy is the only one of the three villains who talks, a trait notable in the sequels, where he massacres victims with horrible puns.

There’s no shame in the bronze medal for Ft13 — its pioneering use of onscreen beheadings and exploitation of its characters paved the way for pretty much every horror movie of the next decade. Importantly, the hockey mask-clad Jason Voorhees, who apparently possesses an internal GPS for finding couples making out in the woods (or, in later chapters, Manhattan sewers and 25th-century space), does not emerge from the glorious green waters of Camp Crystal Lake until the first sequel, the original killer having been his slightly overprotective mother (before she ended up negotiating with the wrong end of an axe).

Because Ft13 and Halloween both feature masked, stoic, knife-wielding killers with supernatural strength, they’re easily confused. The dead giveaway is the pace of the killers. Jason prefers a brisk power walk, while Michael enjoys a leisurely stroll, indicative of his attitude of “I’ll get them eventually, if not in this movie then perhaps in the next seven sequels.”

While the Halloweens suffered the most over time (due to the absence of original director and true genius John Carpenter), Friday the 13th enjoyed the little niche it carved out in the bottom of the horror barrel, and Nightmare on Elm Street actually improved with its second and sixth sequels, the latter (directed by Craven) turning the series on its head through a movie-within-a-movie conceit.

Even if they don’t always scare us, these films fulfill one of the oldest functions of cinema — to put a couple of strangers together in a dark room and bore the hell out of them. Not only are movies good for America, they’re great for America. Forget Barack, Romney or Hillary — how about Freddy, Jason and Michael? They’re uniters, not dividers. In this mixed up world we live in, maybe a little mass murder could do us good.