One of the first things you hear in “On the Basis of Sex” is the song “Ten Thousand Men of Harvard.” And that is more or less what you see on-screen: a parade of mostly pale males in dark suits marching through Cambridge. In their midst is Ruth Bader Ginsburg (Felicity Jones), a first-year law student and one of only nine women (out of nearly 500 students) in her class.

At a dinner party, she and the others are asked by Erwin Griswold, dean of the law school (Sam Waterston), why they think they have the right be there instead of the men who might have been admitted instead. The answers range from fumbling to diplomatic, but the intent of the question could not be clearer. Harvard, like nearly every other institution where power is concentrated and influence is transmitted, is no place for a woman.

That was in 1956. Ginsburg is now one of three women on the nine-member Supreme Court, and not even her most dogged ideological enemies would question her right to be there. (The Senate vote for her confirmation in 1993 was 96-3). “On the Basis of Sex,” directed by Mimi Leder from a screenplay by Daniel Stiepleman (Ginsburg’s nephew), is interested in Ginsburg’s role in bringing about this change. Rather than trace the full arc of her career, it focuses on the first sex-discrimination case she argued in federal court in the early 1970s, and on the development of a legal strategy to challenge injustices so deeply ingrained as to seem perfectly natural.

This is, almost literally, the story of how Ginsburg found her voice. The real Ginsburg has said that the only thing the movie gets factually wrong is that it portrays her at a momentary loss for words as she addresses the court for the first time. It’s not only the character’s self-confidence that falters there, but also the filmmakers’. Admiring as they are of their heroine’s courage and brilliance in challenging tradition and convention, they can’t help but enshroud her in biopic clichés.

That’s not entirely a bad thing. “On the Basis of Sex” does a brisk, coherent job of articulating what Ginsburg accomplished and why it mattered, dramatizing both her personal stake in feminist legal activism and the intellectual discipline with which she approached it. Her experience of sexism in the legal profession starts at Harvard and continues after she graduates (from Columbia, where she transferred after two years) and tries to find work, taking a teaching job at Rutgers when no firm will hire her.

One place where gender inequality doesn’t affect her is at home. “On the Basis of Sex” is both the narrative of an important legal crusade and the portrait of an extraordinary marriage. Marty Ginsburg (Armie Hammer), who started at Harvard Law School a year before she did — they had met as undergraduates at Cornell — is an ideal partner and helpmeet, unfailingly supportive and solicitous of his wife. He cooks meals, runs interference with their adolescent daughter, Jane (Cailee Spaeny), and most important, declines to make his own ego or ambition the center of the family’s life.

Their partnership is a lovely thing to witness. Jones is brisk and decorous, smart and sensitive, though she sometimes leans too heavily into the Brooklyn accent. Hammer is to “On the Basis of Sex” what she was to “The Theory of Everything,” and he has never looked happier. Unlike that drab homage to Stephen Hawking, which ran about as far from actual science as a movie about a scientist could, Leder’s film trusts the audience’s willingness to handle ideas and debates.

Once she takes up her breakthrough case — representing Charles Moritz (Chris Mulkey), a Colorado man denied a tax benefit routinely given to women caring for family members — the movie becomes a series of arguments about gender, society and the law. Some of these happen between Ruth and Jane, whose feminism is more intuitive and confrontational than her mother’s. Others unfold between Ruth and Mel Wulf of the American Civil Liberties Union (Justin Theroux), who backs the litigation but proves to be (as we might say now) a problematic ally.

“On the Basis of Sex” shows how she succeeded, which is an accomplishment. That the movie may leave you wanting more — more history, more personality, more complicated emotion, more ideological contention — doesn’t necessarily count against it. Historical narratives are best when they pique curiosity as well as satisfy it, and this one is too conscientious to proclaim its own comprehensiveness. It knows that it’s a piece of a larger story, one that is very much unfinished.

“ON THE BASIS OF SEX”

***

(PG-13, 2;00)