Five years, 17 countries, four continents, countless conversations. The two-part documentary by the New York-based film-maker Jennifer Fox, Flying - Confessions of a Free Woman, which screens on BBC Four next week, is a modern epic. It follows Fox's quest to establish common ground between women the world over, and at the same time, by following her own story over those five years, examining what it means to be a “modern woman”.

She and her subjects, from outcast widows in India to prostitutes in Cambodia, as well as her “girlfriends” in Berlin, London, Johannesberg and elsewhere, pass the camera between them as they talk, always over food, about sex (mostly), their freedoms, their restrictions. Fox isn't afraid to ask embarrassing questions (the widows become hysterical with laughter when she explains the concept of masturbation), sometimes acting as a “cultural bulldozer” to establish where the boundaries lie. But everywhere she goes, regardless of religion or culture, the intimate way women talk together is the same.

The documentary language is ingenious but as another single, affluent, middle-class, Western, “modern” woman, for me it is Fox's own journey that struck a chord.At the start of the film Fox has two boyfriends: a married lover, Kai (a pseudonym), and Patrick. The first is a forbidden romance - she describes Kai, when we speak, as having been her “artistic muse” and says that neither ever wrote so much as when they were together. If the nauseating text message he sends her during the film is anything to go by then they're better off apart. The second is a slow-burn friendship that matures into something more, much to Fox's continuing surprise. As her friends fight in divorce courts, marry, have babies, Fox realises how much she wants children, and must come to terms with the possibility that she may have left it too late (she was 42 when filming began). She learns to understand her mother and grandmother, whose domestic way of life she has rejected, and see them in the context of their own era. None of this constitutes a huge revelation, though it becomes clear, as she notes, that “to be a single woman, and not be the focus of people's pity, you have to be a very strong person”.

At the end of the film, Fox says that the project has meant that she is no longer afraid to think of herself as a woman. What the hell does that mean? To Fox, it's to do with not denying that you belong to what she describes it as “my tribe”. When you're young, she says, “you decide that everybody is gender equal. I know that, for me, survival depended on not acknowledging differences. The only way to get out of the trap of being a woman was to pretend that there were no gender differences. At 15 I could go cross-country on a bus and it would be safe because I was equal to a man, and of course that was a complete lie! I had to put those blinders on to become equal. But it isn't true.”

As far as I'm concerned safety isn't the issue. But she's right about the difficulty of allying yourself with one side: “The minute you define gender, men look askance at you.” Not just men, I'm afraid, but also people like me, who label as shrill the “wimmin” who define themselves by their sisterhood.

When I ask Fox why she embarked on the film, her answer sounds familiar. “Even though I'm a so-called free woman,” she says, “the men come and go, but it began to dawn on me that the women didn't come and go, that the women were rocks in my life over many years and that it was these talks that knitted my life together.”

As Fox says, she is “a child of psychology. I've had a lot of therapy”, and the film does have the slightly grating whiff of New York angst. I hestitate to call it

“required viewing for every woman”, as the Sex & the City author Candace Bushnell did. It makes me squirm. But Flying is a powerful film. To think that women are “free” yet is simple self-delusion. “We are free-er,” Fox says, “and I appreciate that tremendously, but the film is also about the price - I don't have children. If I were truly free I would have children and work but that is not the world I live in. We are on the path and we're at a very early stage, I mean we're the first 50 years out of the gate! Women have been the property of men for thousands of years. It's the first time in history that we're not, as a mass movement.” She's right. But thank goodness we're free to sit around the kitchen table and talk about it.

Storyville: Flying - Confessions of a Free Woman, Aug 13 & 20, BBC Four, 10pm

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