A network situation comedy that is genuinely funny doesn’t come along every weeknight at 8:30, or most weeknights at 8:30, and even if the producers passed on the most obvious title—“Post-Modern Family”—their new “Extended Family” has legs. Jokes. Jon Cryer’s scrupulous comedic timing. And a premise that even 20 years ago would have had the old Legion of Decency writhing on the floor: happy divorce.

Does it help that it isn’t so happy? The creation of writer-actor-producer Mike O’Malley starring Mr. Cryer and Abigail Spencer, “Extended Family” is based on two pillars of classical sitcom philosophy—people’s intentions are good and they are not as smart as they think. As we are told by Jim and Julia—directly to the camera, which is how much information is exchanged—their marriage had basically run aground after 17 years and two kids, and they believed, sincerely, that they could engage in a civilized breakup. Share the kids, share the home (in alternating shifts) and be grownups about the whole thing. The amount of hubris involved almost qualifies “Extended Family” as Greek tragedy.