Gerwig has long been interested in how women fight. “Frances Ha” (2013), the film she made with her partner, Noah Baumbach, begins with two best friends sparring gleefully in Washington Square Park. Over the course of the film, they fall out in the usual way — very slowly and then all at once — but by the end are back in each other’s lives, casually, at arm’s length. In “Mistress America” (2015), which Gerwig and Baumbach also made together, a major act of betrayal leads to the severing of a bond between two women. In “Lady Bird” the fights between mother and daughter are constant — at once background noise and main event. Every situation is pretext for a confrontation: underdone eggs, a pile of rumpled clothes, a hand reaching too quickly for the radio. The question on the surface might be What did you do? but the feeling underneath is Who are you and why don’t you know how to love me?

The visual style of “Lady Bird” is intentionally unshowy — most shots are framed and still, so that attention is focused on the actors and the dialogue. Language is what matters. There was no improvisation on the set, and the movie matches the shooting script “probably 95 percent.” The writer and director Lena Dunham told me that what she often admires about Gerwig’s dialogue is the contrast between erudition and naturalism — “In one breath she’ll be referencing a superobscure book and also utilizing the awkward parlance of our times.” “Lady Bird” does that, too. Gerwig expects her audience to be well read enough to get what’s funny about a nun referencing Kierkegaard’s “love story” (Kierkegaard broke off his engagement) but also to laugh when Lady Bird tells her friend that they’re done with “the learning portion of high school.” The rhythm is very quick, and much of the humor lies in the way that characters respond to or undercut one another. My favorite joke of the movie is when Lady Bird, after passing her driver’s test, profusely thanks the guy from the D.M.V. “It’s not a thanking situation,” he says. “You either pass or you don’t.”

The plot is structured according to the “rituals” of senior year — homecoming, prom — which Gerwig has said she imagined “unfolding in a series of placed scenes like Stations of the Cross.” Emotional drama presents itself in the form of Lady Bird’s two boyfriends, Danny and Kyle, and a rough patch with her best friend, Julie, but the big narrative question is where Lady Bird will go to college. She longs to go to a private East Coast (i.e., outrageously expensive) college; her family expects her to stay in state. As it is, they’re barely keeping it together, moneywise. Marion works double shifts as a psychiatric nurse, and Lady Bird’s father, played by Tracy Letts, has lost his job. They live in a shabby, cramped house that is literally on the wrong side of the railroad tracks. (Marion and Lady Bird’s favorite Sunday-afternoon activity is dropping in at real estate open houses and admiring what they cannot have.) But “those East Coast schools” carry complex symbolic weight for Lady Bird: They mean possibility, and glamour, and leaving home, and something like self-worth. The movie doesn’t totally endorse her fantasy, but it is a little unsettling, in this moment, to witness a narrative triumph that hinges on a teenager’s assumption of a lifetime of student debt.

Gerwig wrote “Lady Bird” partly as a response to films about boys growing up. At the New York Film Festival, she asked the crowd: “What is ‘Boyhood,’ but for a girl? What is ‘The 400 Blows,’ but for a girl? What is personhood for young women?” In most films, girls exist to be looked at. Sometimes they help a male protagonist come to a realization about himself. Sometimes they die. Gerwig makes Lady Bird the one who looks: at boys but also houses, magazines, books, clothes and at the city of Sacramento. She also takes the wind out of a particular kind of male self-seriousness around cultural objects. Toward the end of the movie, a very drunk Lady Bird is in her dorm room with a boy — the kind of boy who would invite you to see “The 400 Blows” on a first date — who is flipping through her CD case. He scoffs that her taste in music sucks: All she has are greatest-hits albums. “But they’re the greatest,” she says. They immediately start making out.

As in “Boyhood,” “Lady Bird” is remarkable for what doesn’t happen. No one dies. No one overdoses. Conflicts are reconciled. The film is ostensibly about a young girl’s ambition, but the mood is one of poignant loss. “There is a certain vividness in worlds that are coming to an end,” Gerwig wrote in the production notes. “It is something beautiful that you never appreciated and ends just as you come to understand it.” Her characters are always preternaturally nostalgic, able to look back on recent hurts with the bittersweet regard that it takes more rancorous humans a lifetime to achieve. She loves Mike Leigh and Éric Rohmer, but the movie moment that will always stay with her is the end of “Annie Hall”: “When they leave each other, and he says it’s just nice knowing her, and you’re like, ugh! That’s life!”