Since “The Return of Jezebel James” is only a sitcom, how hard should the reviewer be on it? How critical the critic? After all, it’s only a sitcom, and ripping it to shreds on the grounds of implausibility, strained jokes, overly broad comic acting, and a host of other faults is a bit like complaining that the frozen dinner you brought home from the supermarket last night was a little lacking in culinary subtlety. What did you expect?

On the other hand, judged as a sitcom, “Jezebel,” which makes its premiere Friday on Fox, is not without its pleasures. Written by Amy Sherman-Palladino, the creative force behind “Gilmore Girls,” it stars Parker Posey as Sarah, an amiable and enjoyably ditzy children’s book editor with a great job, a great apartment, a boyfriend — Marcus (Scott Cohen), with whom she enjoys a kind of “Last Tango in Brooklyn” relationship (they know each other professionally but agree not to discuss anything else that might darken a partnership dedicated to “nice dinners, fancy drinks, and sex”) — and the usual motley group of mildly eccentric but lovable co-workers.

She also has a younger sister. That would be Coco (Lauren Ambrose), a redhead with a voice pitched a good octave lower than Sarah’s, a taste for grungy clothing, a soft-butch swagger, and a disdain for anything resembling professional success or even, in fact, a job. At the moment, Coco is crashing on a not-very-friendly friend’s couch along with a sick dog. Her previous accommodation, according to Sarah, was on a shelf above a noodle station inside a Chinese restaurant.

Normally, Sarah and Coco have nothing to do with each other. But Sarah, who is in her late or mid-30s, depending upon whether you believe her or her father, has suddenly become acutely aware of the fact that she would like to have a baby and start an only-child, only-parent family. The problem is that she has just been diagnosed with an inoperable deformation of the uterus that will prevent her from becoming pregnant. Her brilliant idea is to pay her sister to carry a baby to term for her once she secures a donor.

Not that she’ll allow Coco to live her normal life while doing so. “The only condition I would impose,” Sarah tells her during a tense meeting in the kind of New York “diner” that one only finds on sunbaked backlots, is that “you would have to move in to my house for the length of the pregnancy so that I could make sure the baby doesn’t come out with two heads and the words ‘Aged in Oak Barrel’ stamped on it.”

Initially, it looks as if Coco is going to turn this idea down flat, but then Sarah empties her handbag on the table to look for change, and out spills a children’s book titled “The Return of Jezebel James.” Jezebel James, it turns out, was Coco’s imaginary childhood friend and, much to her surprise, Sarah got someone to write a book about her. Coco reads it. Coco is touched. And soon she turns up at Sarah’s office to say she’s ready to cohabit with the sister she barely knows and wait for the sperm donor to arrive.

Forthcoming episodes will see this sibling odd couple argue with each other relentlessly, but ultimately this is one of those feel-good paeans to alternative-family arrangements so beloved in Hollywood. If this one works, it’s because of the casting as much as the writing. All flouncy femininity, Ms. Posey doesn’t act so much as play an actress acting. When she cries, she doesn’t even bother to produce fake tears. And yet her “Breakfast at Tiffany’s” charm holds everything together.

On the other hand, when Coco, in the second episode, jumps on her slacker boyfriend in defiance of the rules she and Sarah have just established during a raucous meeting with a lawyer, her sexuality feels brazen and real. Fed just enough good lines by Ms. Sherman-Palladino, these sisters who don’t look or act like sisters end up convincing us that they are what they claim to be — which, in its modest way, is no small thing.

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The pilot episode of “Unhitched,” the new sitcom written by the Farrelly brothers, also on Fox, was subjected to some fairly savage treatment in the critics’ corner — unjustly, it seems to me. The tale of four newly divorced or separated friends — a woman, a nerdy, vaguely Indian doctor, and two all-American goofballs — “Unhitched” is played purely for laughs and gets quite a few. It celebrates embarrassment, freakishness, and oddity for their own sake, as well as the unalloyed fun of wasting your life while enjoying it thoroughly, which may not be such a waste after all. It has its share of gross-out humor, but at its core it’s as innocent as the Marx Brothers.

There’s been so much high-concept grandiosity on television lately, whether it’s the quasi-religion of “Eli Stone,” the pile-on-the-wealth of “Dirty Sexy Money” and “Gossip Girl,” or the magical realism of “Pushing Daisies,” that watching a bunch of goons bumbling through one idiotic encounter after another is wonderfully liberating. The sequence in the pilot episode in which Shaun Majumder, who plays the naïve “Indian” doctor, gets taken for a ride to the tune of $8,000 by a calculating blond escort who persuades him to celebrate his birthday by taking her to Atlantic City rather than to his favorite place to eat chutney-flavored cheesecake, had more to say about human nature (in this case, men’s willingness to believe whatever women want them to if they think a lifetime of erotic bliss will follow) than hours of so-called “serious” TV.

The same could be said of the horrified look on the face of the sole female in the foursome, played by Rashida Jones, when she discovers that the sexy rock guitarist she was dating was actually an “air” guitarist. Sometimes television is best when it doesn’t take itself, or the world, too seriously.

bbernhard@earthlink.net