Stories must have a beginning, a middle and an end. Aristotle wrote that some years ago, and it’s been true ever since. While individual television episodes follow that philosophy, TV shows — particularly successful ones — tend to rattle on forever, or at least until they go into syndication. Whatever comes first.

American broadcasters are particularly guilty of this transgression. With some exceptions, British series tend to end sooner, often before their audiences tire of them. Compare Ricky Gervais’ version of the “Office” — done after two seasons and a Christmas special — with NBC’s adaptation, which at times seemed destined to endure until Jim and Pam entered a retirement home. To our relief, NBC has finally announced that the next season, its ninth, will be its last.

Not to give too much away, but “Episodes” (8:30 p.m. Sunday, Showtime) ends its second season in a manner that makes the prospects of a third pretty darn remote. That’s what I call going out with a bang.

For the uninitiated, “Episodes” concerns two married British television writers (Tamsin Greig and Stephen Mangan) who come to Hollywood to oversee the American adaptation of their genteel series, only to see it shoehorned into a comeback vehicle for Matt LeBlanc (as himself) of “Friends” fame. LeBlanc is in fine form playing a rather crude version of Joey Tribbiani.

”Episodes” offers a witty meditation on the differences between American and British TV and popular culture while showcasing the best and worst of both. If you haven’t yet seen this on Showtime, you owe it to yourself to catch up on DVD.

Sunday’s other highlights

• The New York Jets host the Carolina Panthers in preseason NFL action (7 p.m., NBC).

• Emma throws her hat into the ring on “Once Upon a Time” (7 p.m., ABC).

• “America’s Choice 2012: Countdown to the Republican National Convention” (7 p.m., CNN) sets the stage for those who just can’t wait.

• Nate sets out to solve a lingering mystery on “Leverage” (8 p.m., TNT).

• Cullen tries to keep a lid on chaos on “Hell on Wheels” (8 p.m., AMC).

• Eric makes one last stab at rebellion on “True Blood” (8 p.m., HBO).

• Walt takes charge on “Breaking Bad” (9 p.m., AMC).

• Corcoran’s efforts to protect an exploited minor put him in harm’s way on “Copper” (9 p.m., BBC America).

• A meeting with the owner (Jane Fonda) gets heated on “The Newsroom” (9 p.m., HBO).