That (“All Things Must End”) was the tagline for the final season of the HBO series Six Feet Under. Used in that context, the old saw cut brilliantly in two directions: In its fifth season, the show itself was coming to an end; and the show, throughout its run, treated death as its core theme. A family drama in which the family home doubled as a funeral home, it began each of its episodes by introducing viewers to a character—and then killing the character off before the opening titles rolled.

Human lives come to a stop, eventually, and so do mere TV shows. That the producers of Six Feet Under knew its endpoint—and could plan its concluding sequence of episodes on their own terms—was vital element of the show’s ultimate artistic success. The series finale, in which flash-forwarded scenes reveal what happens to every member of the Fisher clan before they reach their expiration date, won an immediate spot in the episodic-television Hall of Fame. It offered “closure” on a grand scale, and gave the whole series a certain novelistic solidity. The creators of other standout TV series have not been so wise, or so lucky.

Yesterday, the New York Times reported that the producers of Lost (a show that I’ve never watched, although a smart friend has strongly recommended that I give it a look) will terminate the series three seasons from now. They have wisdom on their side, apparently, along with the good fortune of retaining some leverage with their network gatekeepers.

ABC announced on Monday that it would broadcast three more seasons of its hit castaway mystery, “Lost,” ending the show in 2010 after a run of six seasons.

The announcement has been expected since January, when the creators of the show told a group of television writers that they wanted the network to set a definitive end date for the series.

Such a date was necessary, they said, so that they could begin planning how to unravel the multiple mysteries that beset the fictional survivors of Oceanic Air Flight 815, which crashed on an uncharted island en route from Sydney, Australia, to Los Angeles in September 2004.

But the move by ABC is nevertheless unusual because networks usually try to milk profits from their successful series as long as possible, a strategy that often results in convoluted story lines, shake-ups among production staff and dwindling fan bases.

That is exactly the situation that Damon Lindelof and Carlton Cuse, two of the show’s executive producers, said early this year that they wanted to avoid. When they announced their desire to set a specific end date to the series at a January meeting of the Television Critics Association in Pasadena, Calif., they surprised even the ABC executives who were attending.

“We have always envisioned ‘Lost’ as a show with a beginning, middle and end,” Mr. Lindelof and Mr. Cuse said in a statement, which was released over the weekend to The Hollywood Reporter and to the rest of the news media on Monday. “By officially announcing exactly when that ending will be, the audience will now have the security of knowing that the story will play out as we’ve intended.”

In other words, if the the Lost crew are going to “jump the shark” in the choppy waters near their uncharted island, they’ll be doing it on their own schedule.

Too often, good shows plug along well past the completion in their natural story arc, or else they have the plug pulled on them while that arc is still under construction. Twin Peaks, the early 1990s series that foreshadowed our current golden age of episodic TV, remains the classic example of a show that outlasted its reason for being. By early in the second season, we knew who had killed Laura Palmer (or did we?), and yet Special Agent Dale Cooper kept doggedly at his business, week after week. David Lynch, the show’s creator, had the small-screen equivalent of a Victorian double-decker gothic novel on his hands, but he let it become a shapeless shaggy-dog story. Leap ahead to our own time, and you’ll hear complaints that The Sopranos—now in its final season—may have gone past its proper life span.

Two of my favorite HBO series, Deadwood and Carnivale, suffered the opposite problem of seeing their narrative lives cut short before their time. David Milch, the writer-producer of Deadwood, had a four-season story arc in mind for the show; HBO told him that it would pay for three seasons only. Carnivale stops after two seasons, at a cliffhanger that its creators clearly meant to split the show’s epic saga in two—but HBO had no money to keep the story going. (The immense cost of producing another series, Rome, reportedly drained the network’s coffers.)

Executive decisions of that kind validate the idea that a TV show can never be a work of art; it can only be “product,” to be made and sold according to demand. For a defining attribute of any artwork is that it ends. Only by ending can it become a self-contained whole, and only in that way can it attain the cohesive shape—and the sense of creative intentionality—that art exists in large measure to provide.

A work of art must end not only because the exigencies of storytelling (or of space, in visual art) entail a practical respect for boundaries, but also because all art concerns itself fundamentally with death—with finality. All things do pass, particularly things that we care about (starting, perhaps, with our own dear existence), and a principal goal of art is to reconcile us to that melancholy fact. Artists can pursue that goal overtly or implicitly, wittingly or unwittingly. But if they don’t pursue it at all, if let their work go on and on, they’re cheating.

The term “closure” bears the taint of daffy psychobabble. Which is too bad, since it’s as good a word as any for an indispensable concept. In fact, the problem with the word may be that it belongs in the field not of psychology but of aesthetics. In actual life—the life of our thoughts and emotions—we never truly experience closure. There’s forgetting, there’s sublimation, there’s “moving on.” But while we move on, our trials and traumas really don’t; they stay with us, and they don’t reach “closing time” until we do. Art, meanwhile, gives us precisely the sort of closure that our minds cannot.

(Over at the Atlantic Monthly site, two blogging whippersnappers have posted entries on the same Times article. Their comments match my own, more ponderous musings.)

TV makes you stupid. It’s not an original insight, but back in 1980 the writer George W.S. Trow wrote an essay in the New Yorker that cast a particularly cold and waspish eye on the subject. Television, he suggested, had settled on the land like a slow, soft apocalypse, laying waste to every force in American culture that had formerly supported independence of judgment—and, indeed, the very possibility of adulthood. Trow died in obscurity late last year. Reading a retrospective “appreciation” of him in the New York Sun (via James Wolcott) led me to take a look at his essay, published in book form as The Context of No Context.

The work of television is to establish false contexts and to chronicle the unraveling of existing contexts; finally, to establish the context of no context and to chronicle it.

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The important moment in the history of television was when a man named Richard Dawson, the “host” of program called Family Feud, asked contestants to guess what a poll of a hundred people had guessed would be the average American woman. Guess what they’ve guessed. Guess what they’ve guess the average is . . .

“You said . . .”

“Our survey said . . .”