“Maggie’s Plan”

Rated R (1:38)

***1/2

Opens today at Dole Cannery Stadium 18 and Kahala 8

Columbia University should give Julianne Moore tenure. In “Still Alice,” for which she deservedly won the best actress Oscar in 2015, Moore was a linguistics professor on the Upper Manhattan campus. And now, in Rebecca Miller’s wily screwball romance “Maggie’s Plan,” the actress — deploying a frighteningly droll Danish accent — is a Columbia anthropologist with her name, Georgette Harding, on the department door.

By comparison, her husband, John, played with a scruffy charm by Ethan Hawke, is but a lowly adjunct at NYU. His specialty is “fictocritical” anthropology, he is the author of the hefty “Rituals of Commodity Fetishism,” and he is about to embark on an affair with a single woman with two master’s degrees and a closet of decidedly unfashionable togs. Penny loafers. Cardigans. Blouses buttoned to the neck.

She is the Maggie of the title, and she is played by Greta Gerwig in the Gerwigian manner people have come to love — or have come to be incredibly annoyed by, depending on your view of the naturally daffy up-from-mumblecore star. (I stand in the former queue — in my book, the star of “Greenberg,” “Frances Ha” and “Mistress America” can almost do no wrong.)

Maggie and John’s relationship begins innocently, with walk-and-talks through Washington Square, but soon he is sharing pages of the novel he is writing, and sharing his frustrations about living with Georgette. (“She is wonderful, but she is kind of destroying my life.”) John and Georgette have two children, who attend a fancy Danish-American school. Dinners are awkward.

One night, John comes running to Maggie’s little apartment, slumps to his knees, and announces, breathlessly, “I’m in love with you.”

It was not Maggie’s plan to fall in love — she had a different agenda, having recruited an artisanal pickle maker in Brooklyn to donate his sperm so she can have a child. The motherhood thing and the John Harding thing dovetail, though, and soon John has left Georgette, and Maggie is learning how to be a mom — and a stepmom, too.

The “plan” of the title comes midway through Miller’s disarmingly shambling comedy. (This is not the rat-a-tat-tat screwball of Howard Hawks or Preston Sturges.) John and Maggie have settled into a life together, but he seems to be taking her for granted. Maggie complains to her friend (Maya Rudolph) who listens and then responds: “Too bad you can’t give him back to his ex-wife.”

A light bulb goes on over Maggie’s head, and soon she is meeting with the frosty Dane (Moore). Wary and watchful, Georgette takes her time warming to the idea, but she does — and the plot thickens.

Although it’s set in the highbrow spheres of academe, “Maggie’s Plan” is really very down-to-earth. Moore goes at the critical Scandinavian-intellectual thing with hilarious results — she’s tightly wound (with a tight bun of a ’do) and just this side of camp. Hawke is comfortably convincing as the bright but busily self-absorbed writer-philosopher. At the center of things, Gerwig stands her ground, making observations that are smart and soul-baring and true.

“Maggie’s Plan,” which filmmaker Miller adapted from a short story by Karen Rinaldi, has some of the spirit, fabric and milieu of Woody Allen’s earlier, more resonant comedies (“Hannah and Her Sisters” comes to mind). But Miller (daughter of playwright Arthur Miller and photographer Inge Morath) understands women in a way Allen probably never will, and she also understands how to move characters along without relying on shtick. (Even the greatest Woody Allen shtick remains shtick.)

There are some great punch lines in “Maggie’s Plan,” though. Fictocritical and funny.