FILM-RATING systems have long been hopelessly subjective. Simply consider “I know it when I see it”, the statement made in 1964 by Potter Stewart, a Supreme Court justice, when ruling on an obscenity case. The situation hasn’t improved in the decades since. Both the Motion Picture Association of America and the Board of Film Classification in Britain sort films into a handful of age categories depending on whether a film contains violence, swearing, drug abuse, sex or nudity. That may seem straightforward enough, but each board can arrive at different ratings for the same film. The American system, for example, considers long sequences of “action violence” or “frightening images” to be inappropriate for 12-year-olds; the British system feels violence and gore is permissible so long as it is “justified by the context”.

There have been less formal efforts to evaluate films, based on different criteria. To pass the Bechdel test—shorthand for “whether a film is woman-friendly”—a film need only feature two female characters who talk to each other about something other than men. The Internet Movie Database created a site for parents to submit descriptions of films in order to draw attention to scenes that may be unsuitable for children. And Movieguide assesses films based on “biblical principles”. “All Saints” (2017), a story of a salesman-turned-pastor, comes highly recommended, while “3 Generations” (2015), a movie about a teenager transitioning from female to male, was “abhorrent” for its “homosexual, leftist worldview”.

Common Sense Media (CSM), a non-profit organisation based in San Francisco, has been reviewing films and television shows since 2003, with the intention of informing parents about the media their children might consume. It provides the minimum age each film or series is suitable for, along with a five-point rating system indicating the amount of sex, violence, sweary language, binge-drinking or drug-taking featured. After urging from its users, CSM announced in June that they would be developing the system further—to account for representations of gender. CSM argued that parents “want help choosing content that better reflects the world we live in today”, and cited research indicating that negative gender representations on screen “can affect children’s sense of self, relationships and career aspirations”.

In theory, the system is quite simple: a film will be awarded the organisation’s seal of approval if it presents characters that defy gender stereotypes. Films designed for early childhood (between the ages of two and six) should depict boys and girls as friends and equals. By the time of early adolescence (between 11 and 13), films must demonstrate that worth is based on more than just physical beauty. In foregrounding the lazy depictions of men and women on television and in films, the move is being hailed by some as a breakthrough. Geena Davis, an actor and the founder of an organisation dedicated to addressing gender imbalances in the media, told the New York Times that the CSM system increases accountability: “people making these products are sure they’re gender-balanced when they’re profoundly not.”

The system is still in its infancy, but CSM has chosen dozens of films and television shows that offer progressive depictions of gender roles. “Moonlight” gets the thumbs-up for its portrayal of being young, black and gay in America. “Mulan” (1998) makes the list thanks to its “strong female character” that fights the Huns. “Bend it Like Beckham” (2003), a romantic comedy, is also praised for its determined, ambitious, football-loving protagonist, Jess.

But some might argue that these are not unequivocally progressive characters. Mulan can only join the Chinese army by posing as a man—men are, it is repeated, superior to women—and when she is offered a high-ranking job, she turns it down in order to return to the homestead. Jess, too, is an unusual female lead, but one could argue that she relies heavily on the film’s male football coach for guidance and encouragement. These examples rather illustrate the problem: “gender-positive” is hardly a neutral concept.

CSM is aware that the ratings process will not be simple. Betsy Bozdech, the executive editor, says she has already enjoyed a taste of the lively debates that are on the horizon. A recent internal discussion revolved around whether the recent “Beauty and the Beast” film, starring Emma Watson, should be considered a force for good. Some pointed to its strong female lead; others made a case for her suffering from Stockholm syndrome. Ms Watson said that she had helped to make feminist adjustments to the character of Belle, but for some viewers the coercive overtones of her relationship with the Beast remained problematic.

Turning a multifaceted issue into a simple rating is sure to be riddled with difficulties. Not only does “positive gender representation” have a multitude of interpretations; any well-made film has layered characters and plots. Sometimes they may contradict or complicate the picture. Indeed, just as violence and sex can be part of great art, so can a story be a worthy one even if it has traditional gender roles; exploring those roles can be a way to challenge them. So although the research showcased by CSM is worthwhile, reducing it to a binary rating is not. The creators would do well to allow the classification to be as nuanced as the art form.