I am a fan of “The Simpsons” in the way the severely mentally ill are fans of anti-psychotics. Which is to say, it’s less a TV show than the thing that keeps the bad voices at bay for me.

All this week they’re doing “Classic Simpsons Week” at Splitsider, and it’s a perfect excuse for me to indulge my neurosis.

Even though “The Simpsons” has gone downhill in the past decade or so, I still keep injecting the episodes through my eyeballs into my brain. And there are bright spots that cause me to actually Laugh Out Loud, as opposed to just typing the acronym.

But if there’s a moment the show jumped the sharkif I had to name just one — I’d go with “The Principal and The Pauper.” The second episode of Season Nine, it was the first Simpsons ep to crumple all the accumulated love and goodwill of the show and toss it in the trash for the sake of a not-very-funny joke.

Harry Shearer, who voices Seymour Skinner (and many other characters), has said he didn’t know what the hell the writers were thinking when they decided Skinner wasn’t actually Skinner, but someone named Armin Tamzerian. Many fans agree. Showrunners Bill Oakley and Josh Weinstein defended the episode as “an experiment,” and have said that it’s not really meant to be taken as canon.

There’s an argument to be made about what constitutes the “real” continuity of the fictional lives of a bunch of cartoon characters, but frankly, it’s the effect on the franchise itself that’s more interesting to me.

Todd VanDerWerff of the Onion has a great essay on the two types of sitcoms: the anything-for-a-laugh sitcom, which uses the characters as joke delivery vehicles, with little or no concern for their long-term development; and the character-driven sitcom, which tries for laughs based on the people and the stories rising from their cramped little worlds. Think of it like this: Type 1 is “30 Rock.” Type 2 is “Community.” (That’s at the high end, of course.)

Up until “Principal, “The Simpsons” was a Type 2 sitcom. Even as surreal as it could get — the man falling off the bridge while in line for Itchy and Scratchy: The Movie who screams “I regret nothing!” on his way down  — I’d argue its core was always the interactions between the family members. This provided some of the best laughs, but also the genuinely touching moments.

Then, with “Principal,” the show shifted gears into a Type 1 show with such a lurch that its transmission was left in pieces all over the asphalt.

Whatever the intention behind the episode, it broke the show. After “Principal,” the series was a Type 1 sitcom — and that’s something that just does not have the same kind of vital, beating heart as character-based fiction to me. Any interplay between Homer, Marge, Bart, Lisa and Maggie is just another gimmick now. It’s nothing that arises from a sense of them as a family. It’s simply what needs to be done to wrap up the plots and jokes in time for the credits.

You can go from a Type 2 to a Type 1 sitcom; it happened after too many seasons on “Cheers.” But once you break the heart of the story like that, you cannot go back to being Type 2. It would be like Charlie Sheen’s character suddenly asking his mother why she never loved him on Two and a Half Men.

I watch Type 1 sitcoms the same way I read plot-driven novels or watch special-effects tentpole movies — to see what happens. I rarely ever watch them again, because once that question is answered, there’s no reason to go back for more.

But with shows like “Firefly,” “Sports Night” and “Venture Bros.,” I replay them again and again, and not just because I missed some of the jokes while I was laughing. I catch new stuff, see scenes in new ways and discover little hidden meanings in the margins.

Yeah. I need to get out more.

But look back to “The Simpsons” 100th episode and you’ll see what I mean. Another Skinner-centric story, “Sweet Seymour Skinner’s Baadasssss Song” — written by Oakley and Weinstein, by the way — shows the principal getting fired from his job due to Bart’s dog getting loose in the school’s ventilation system. He and Bart actually become friends in the outside world. Of course, everything has to go back to normal at the end of the ep, but it’s not done in the ham-fisted, meta-commentary way of “Principal.” Instead, Bart places a “kick me” sign on Skinner’s back when the two hug after Skinner resumes his job. And Skinner puts a sign on Bart that says “teach me.” It’s an undeniably sweet moment.

And it’s one that the show could never pull off today.

I still love “The Simpsons.” But it’s never going to feel like that again.