Robert Altman's re-released Nashville, the centrepiece of a two-month NFT season of Sixties/Seventies American cinema, still looks bracingly unruly 30 years after it was made - a manic, all-embracing pageant that is to Seventies America what Frith's painting Derby Day is to Victorian Britain. But Nashville has endured less as a statement specifically about mid-Seventies America than as a radical experiment in open-form cinema, an attempt to see how fiction film-making might attain a more complex and immediate purchase on the world.
One thing Nashville can't claim to be, however, is a film about country music, any more than a film set in Los Angeles is necessarily about movies: it's just that showbusiness has so totally annexed the two cities that their non-industry populations risk being ignored, relegated to "civilian" status. In fact, Altman's Nashville is less a microcosm of America than a mirror image of Hollywood. There are established stars, more or less venerated royalty, like spangle-suited patriarch Haven Hamilton (Henry Gibson) and fragile princess Barbara Jean (Ronee Blakley). There is a whole ancillary population of industry support - management, lawyers, chauffeurs - and there are the dreamers, such as Gwen Welles's hopeless singer, cruelly co-opted into stripping. (Music, Altman implies, is crueller than the movies: at least in film you can get away with never opening your mouth and so exposing your lack of talent.)
Then there are the opportunistic visitors: Michael Murphy's political aide, trying to raise support for a third-party "people's candidate"; Shelley Duvall, at her most Martian, as a man-hungry West Coast waif.
Other characters move between worlds, like attorney's wife Linnea (Lily Tomlin, in the film's most nuanced performance), who moonlights with a gospel choir and is pursued by Keith Carradine's vain, predatory folk singer.
Altman's characters don't just vie for space, but compete to be heard: his famous overlapping dialogue is at its most dizzying and demanding in Nashville. At moments, you catch what sounds like a hugely significant line and realise that it's been mutttered in passing by a walk-on player, as if picked up on the soundtrack by accident. This is, in fact, a film about sound, the music industry providing a model of a world in which people listen to each other, or fail to: the film begins with its unseen "Replacement Party" candidate driving round in a van, his Tannoy haranguing empty streets. The 24 characters correspond to 24-track recording technology, with Altman deciding who gets heard and who gets drowned out, and who surfaces for a brief solo before sinking back into the mix. Significantly, the clearest communication is between Tomlin's character and her two profoundly deaf children.
Nashville effectively founded the school of American improv-ensemble cinema, with its actors given free rein to improvise, work on their characters, diverge from Joan Tewkesbury's script. Many of the cast wrote or co-wrote the songs, and although a few really do sound like the "redneck ... crapola" derided by Murphy's character, many are strongly crafted and nearly all are dead-on pastiche without being caricature.
Invariably, certain actors' strength of personality means that some characters end up bigger than the fiction they inhabit.
Nashville's most irrepressibly oversized figure - sometimes but not always to the film's advantage - is Geraldine Chaplin's monstrous Opal, a self-absorbed babbler supposedly making a documentary for the "British Broadcasting Company". Opal's improvised running commentary surely figures as Altman's warning about the futility of trying to impose coherent meaning on the film's frenzied circus, of trying to reduce it all to neat allegory.
Nashville's reputation as a political allegory partly rests on its ending with an (unexplained) assassination, and not the one we expect. Especially with hindsight, we can see Altman's finale as a chilling exposure of the American culture of denial, of what these days is routinely referred to as the nation's need to "move on", to "find closure". No sooner is the victim bundled out of sight than a communal sing-song is organised and it's as if nothing has ever happened: the song, appropriately, is called "It Don't Worry Me". It's surely as much to Nashville as to the murders of John F Kennedy and John Lennon that we owe our sense that in America sudden death is just a specialised branch of showbusiness.