But more often, the point of a revival is to deny change, at least creatively. “Will & Grace” acknowledged the new era with a heavy-handed premiere episode about the Trump administration. But the new season was so eerily like the original in its rhythms and tone that you could convince yourself it had never gone off the air (as long as you forgot about the original series ending that the revival Etch-a-Sketched).

At its heart, the appeal of a revival is the appeal of a high school reunion, or a visit to Facebook: What are they doing now? But it can be as unsettling to find your old prime-time favorites unnaturally preserved as to find them changed.

Most sitcoms could theoretically go on for decades. But there’s usually an unspoken expiration date: the point beyond which the characters’ lives would change — making it a different show — or, in remaining the same, they would be less funny than sad. (This is one reason I pray no one ever loads up a big enough Brink’s truck to reunite the cast of “Friends.”)

A reboot, on the other hand, may be successful or disastrous, but it at least offers the possibility, and the requirement, for rethinking and transformation. “Battlestar Galactica,” after 9/11, turned a breezy 1970s space opera into an ambitious story about politics, religion and the ethics of survival in the face of an existential threat.

More recently, when Netflix imagined “One Day at a Time” with a Cuban-American family, it was able to speak to modern questions about immigration and representation, about who defines America and the working class.

All this points to another distinction of reboots: Revivals, which reproduce TV’s past down to the original casting, have tended to be very white, as TV’s history is. But the planned reboot of “Party of Five” will focus on Mexican-American siblings after their parents are deported, and the “Roswell” reboot (also not yet screened for review) will reportedly have an immigration twist alongside its space-alien plot.