It may not have seemed very likely back in March, but when CBS announced its fall prime-time schedule this week, "Two and a Half Men" was on it. As anyone who cares about this kind of thing knows, Ashton Kutcher will introduce a new character that will replace the one played by Charlie Sheen, who was asked to leave the show after publically engaging in behaviors that suggested to some that he may have lost his mind.

I like "Two and a Half Men." It’s an old-school sitcom that doesn’t require a lot of attention to be enjoyed. I watch "Mad Men" with the lights turned off; I watch "Two and a Half Men" while balancing my checkbook.

The entire ensemble cast, Sheen included, consistently delivered amusing performances, and the writers provided stories with a raunchy sophistication. After eight seasons, however, the show was getting a little long in the tooth.

The problem with a lot of American television isn’t an issue of quality, but of quantity. Many shows that started out very strong--"Happy Days" and "L.A. Law" come immediately to mind--ended up by staying too long at the fair.

The economics of American TV dictate that the longer a show runs, the more it can earn in syndicated reruns. As long as the show is delivering a reasonably large audience, it’s in everybody’s best interest to keep it going, even if it has exhausted its artistic possibilities. It would be like telling Beethoven, after he’d completed his fifth symphony: “That was great---can you give us four more movements?”

But even before Charlie Sheen’s notorious “meltdown,” one began to get the sense that "Two and a Half Men" had said what it had to say; that it had exhausted the character relationships upon which it was based. A new leading character, therefore, may be just what the series needed. The writers, one might think, should be happy to have a whole new set of relationships to mine when Kutcher’s character is introduced next season.

It should be remembered that one of the longest-running fictional television series in the medium’s history, "Law & Order," had frequent turnover in its principal cast. "M*A*S*H" and "Cheers," two of the biggest hits of the ‘70s and ‘80s, thrived in spite of (and maybe partly because of) major casting changes.

Ashton Kutcher is a funny guy, and he knows the ropes of the American sitcom. And, as we’re constantly reminded, he’s also one of the most-followed denizens of Twitterdom and has the potential of bringing a core of fans to "Two and a Half Men" who may never have watched it before.

The hiring of Kutcher may not save the show—and history tells us that with a series this old it probably won’t---but some variation in the character gene pool does have the possibility of refreshing a program that was slouching toward its dotage.

Robert J. Thompson is the founding director of the Bleier Center for Television and Popular Culture at Syracuse University, where he is also a Trustee Professor of Television and Popular Culture at the S.I. Newhouse School of Public Communications. He was a visiting professor for six summers at Cornell University and served for nine years as professor and director of the N.H.S.I. Television and Film Institute at Northwestern University.