Theater folks in England are debating a recent revival of the musical “Falsettos,” asking whether non-Jews should play its Jewish characters.

In an open letter, critics of the casting complain that non-Jewish actors can at best portray only a “secondary understanding” of Jewish mannerisms but have no awareness of the “psychology, geography, culture and history that have framed these outward signifiers of Judaism.”

To this perennial debate, I have a two-word answer:

Rhoda Morgenstern.”

Valerie Harper, who died last week at age 80, starred in “The Mary Tyler Moore Show” as the earthy, wise-cracking, Bronx-born neighbor and best friend of the WASPy, reserved, carefully coiffed TV producer played by Moore.

Harper, a native of Suffern, N.Y., was so convincing in the role that many viewers had a hard time believing that Harper herself was not Jewish. (She was actually a lapsed Catholic of French, English, Irish, Scottish and Welsh extraction.)

“Listen, in my heart, I’m Jewish,” she would tell fans, according to her 2013 memoir, “I, Rhoda.” “And if you go back far enough, we’re all Jewish. The Jews are an ancient people.”

In their long history, Jews have always served as a convenient foil for gentile beliefs and attitudes, a tradition that began with the Gospels and continued on “The Mary Tyler Moore Show,” which debuted in September of 1970.

Rhoda, considered plump only by the body-shaming perspective of a television sitcom, envied Mary’s figure and poise, but also served Mary by helping her shed some of her Midwestern reserve. Her Jewish angst balanced Mary’s gentile insecurity. She said aloud what Mary had a hard time admitting to herself. She threw Mary’s character into high relief, and Mary returned the favor.

“You’re talking about Midwestern love. I’m talking about Bronx love,” Rhoda tells Mary in season 1. “There’s a certain amount of guilt that goes with that. My mother wants the people she loves to feel guilty.”

“The Mary Tyler Moore Show” is remembered as a feminist breakthrough in television, depicting women who were single and career-minded and not defined only by their relationship to the men in their lives.

The Rhoda character was groundbreaking, too: the first Jewish leading TV character, cultural historian and author Neal Gabler reminds us, since Gertrude Berg starred as Molly Goldberg on CBS from 1949 to 1951.

And just as Mary represented a soft feminism, Rhoda represented soft ethnicity: Although her Jewishness was rarely made explicit (except perhaps for that last name, which might be a rebuke of sorts to the ambitious, assimilationist protagonist of Herman Wouk’s 1955 novel “Marjorie Morningstar”), her Jewish signifiers were apparent.

This earned the show’s creators both praise and criticism. Marlene Adler Marks wrote in the Los Angeles Jewish Journal in 1991 that Rhoda proved “there was more to the Jewish woman than the stereotype. She was not a princess. She was not a shrew. Yes, she was an underdog, but not a loser.”

By contrast, a character in a Francine Prose short story, “Electricity,” is described as “assimilated to the point of Jewishlessness, like Valerie Harper playing Rhoda.”

But Rhoda’s Jewishness was nonetheless out there, by the standards of the day, no more so than in the season 2 episode titled “Some of My Best Friends Are Rhoda.” Mary makes a new friend, Joanne, leaving Rhoda feeling snubbed. The friendship sours, however, when Joanne invites Mary to a club that prohibits Jews, and Mary defends Rhoda.

When CBS spun off the character for Harper’s own show, “Rhoda,” some of her recognizably Jewish attitude didn’t survive the transition. Although she gained a stereotypically Jewish mother, Ida (portrayed by the non-Jewish actress Nancy Walker), Rhoda herself sheds some of her Jewish tics (and more than a few pounds) as well as the ethnic burden. Meanwhile, many of the show’s best lines are given to Julie Kavner as her younger sister, Brenda.

When Rhoda marries — more than 50 million viewers tuned in for the episode — the fact that her husband isn’t Jewish is barely treated as a plot point. Maybe that’s why so few Jews objected to this much-hyped portrayal of interfaith marriage, especially compared to the communal conniption fit that greeted the ill-fated “Bridget Loves Bernie.”

Harper was very much aware of how Rhoda’s Jewishness informed her relationship with Mary. Describing her character, she once said in an interview, “All I could do was, not being as pretty, as thin, as accomplished, was: ‘I’m a New Yorker, and I’m going to straighten this shiksa out.’”

It worked the other way, too. In the absence of positive expressions of Judaism — ritual, language and dress — ethnic Jewishness only becomes apparent in the things that we are not: New York, not Minnesota; loud, not reserved; carnal, not buttoned up; wittily self-deprecating, not morbidly self-lacerating. It was how a rapidly assimilating Jewish community began to think of what it meant to be Jewish.

Rhoda wasn’t the first Jewish character to be understood in contradistinction to the non-Jews with whom she shared a stage. But never before was that stage so large, nor the character so delightful.

Andy Silow-Carroll is editor in chief of the JTA global Jewish news source.