This month sees the re-release of Ai No Corrida (In The Realm Of The Senses), Nagisa Oshima's controversial Japanese arthouse film from 1976, which divided critics then, and still does today. Top of most people's agenda is the question of how sexually explicit it is and whether we should be bothered by art that verges on porn? James Ferman, director of the British Board of Film Classification in the 70s and 80s took a hard line on it, but was the sex gratuitous, elevating it to good old pornographic status, or integral, justified and arthouse?

Perhaps the BBFC just thought that we'd enjoy it all too much, slapped a big X across it and sliced it up to within an inch of its newly anodyne life. Clearly back then the position was that even art films pushed too many of the wrong (right) buttons, but these days what is considered porn and what is considered art have become more blurred. Playboy thought it was high time to examine other infamous flicks of this century and the last to see which way they swung.

Ai No Corrida (1976) broke boundaries in the 1970s, a decade that reaped the benefits of a countercultural revolution in the west, well before the video nasties era of the 1980s. It was particularly explicit having originated from Japan, a country that had garnered a reputation for servile rigidity and repression that sometimes manifested itself in explicitly graphic sex and violence on-screen. To circumvent Japanese censorship laws the film was listed as a French production, developed and edited in the more relaxed environs of Paris, yet it still encountered classification problems and was refused a video release until the 1990s. Is it porn? It certainly has un-simulated sex including penetration and oral sex in a number of different settings, so a big thumbs up there, but no one seems to be enjoying themselves which means it doesn't really feel sexual or sensual, and its tragic ending consigns it firmly to the art bin, unfortunately.

A couple of years earlier, the incomparable Marlon Brando was up to his old 'method' tricks, this time with Maria Schneider in Last Tango in Paris (1973). Of course, the controversy once again stemmed from the explicit sex scenes, but with a back-story of grief and isolation, it was into art territory from the off. Then the ‘butter scene’ (where Brando uses a table spread to lube Schneider’s anus) came along, and things were back in the balance. Both principal actors claimed to have been lied to and exploited by director Bernardo Bertolucci but the film’s journey into infamy was complete. Verdict: porn masquerading as art.

9 songs (2004) was not the first time Michael Winterbottom had thrown an artistic curveball, and being a director who always erred on the side of experimentation with his films (24 Hour Party People, Welcome to Sarajevo), it represented yet another first for Winterbottom, as it featured not only more un-simulated sex but also the first uncut ejaculation in a UK mainstream cinema film. But was it just for the sake of it? Based around a boring year-long relationship between two young lovers who attend various gigs at the Brixton Academy, it was critically panned on release, and the paucity of storyline (and awful acting), make this particular addition to the canon an entry with all the hallmarks of a porn film.

The middle of this decade saw several films pushing the art/porn envelope, and Shortbus (2006) was no exception. Centred on a disparate group of boho New Yorkers, the film attempts to tie together several story strands with sex scenes of varying explicitness, and despite the fact that the main thing people were discussing prior to release was Sook-Yin Lee's 'performances', its countless film festival awards and half-decent narrative mean this is firmly in the art masquerading as porn court.