Sam Shepard has returned to the territory of 'Paris, Texas' for his latest movie

Sam Shepard used obsessively to write down conversations he overheard. I wonder if snippets from our interview end up in one of the Pulitzer-Prize-winner's plays. "We're not having a dialogue, this is question and answers," he replies curtly, in his Midwestern drawl. "Dialogue is like jazz. Dialogue is creative."

The analogy is significant. Music, in one form or another, has always been a part of Shepard's life. He lived with Charles Mingus Jr in New York in the Sixties, had a tempestuous affair with the rock poet Patti Smith (they co-authored and performed the play Cowboy Mouth), and played drums with the acid-fuelled rock outfit Holy Modal Rounders. Even Shepard's early experimental plays were like jazz compositions. "My tendency," he told the biographer Don Shewey, "was to jam... The lonious-Monk-style." Inspired by the likes of Jack Kerouac, Alan Ginsberg and Bob Dylan, he eschewed traditional structure and employed explosive language' he blended the absurd with the surreal and the achingly real, confounding many critics. By the age of 26, Shepard had written 20 plays and won numerous Obie awards from The Village Voice. By the 1980s, he was the most produced playwright in America after Tennessee Williams. However, it is not Shepard's prolific theatrical output that I have come to discuss, but rather his second collaborative effort with the German film-maker Wim Wenders. Their first film, Paris, Texas, was a highlight of the American independent cinema of the 1980s. Written by Shepard and starring Harry Dean Stanton, it was a haunting and elegiac road movie reflecting the author's fascination with the post-war American family, a theme which, on the stage, achieved its greatest expression in the powerful trilogy Curse of the Starving Class, Buried Child and True West.

The new film Don't Come Knocking is a humorous and, dare one say it, even upbeat riff on Paris, Texas. It even ends with a road-sign showing the distances to two destinations: "Wisdom" and "Divide". Has Shepard grown older, wiser and lighter in the intervening years? "I don't know about older and wiser," he laughs, his blue eyes hidden behind sunglasses, "but you see the necessity for keeping a sense of humour. You have to, or it just becomes so grim."

Whereas Travis (Stanton), in Paris, Texas, emerged from the desert and embarked on a search for the family he lost, now Howard Spence (Shepard), a disillusioned star of cowboy films, runs away from the set of his latest movie - an artistically arid Western - and takes refuge with the mother he has not seen in 30 years. Afteryears of making movies, and leading a tabloid lifestyle of sex, drugs and booze, he is, at 60, like a child.

"The film business caters to the weakest parts of yourself," he says, "and everybody has tasted that who has done film. They give you your trailer, more stupid food, more things you don't need, limousines. But it's like dessert: if you eat it all the time you're going to throw up, you know? You have to have some food. This is essentially the point that Howard has arrived at when Don't Come Knocking starts. He runs away, and there's a collision with real life as he escapes this one that he sees has no core."

For people like Spence, who have nothing else in their life, leaving the cocoon of the movies can be a shock. "I think it's absolutely true that if you live in the little structure of the movies you're not, I don't think, quite alive," says Shepard. This is why, despite receiving an Oscar nomination for his performance as Chuck Yeager in The Right Stuff, he has preferred to dip in and out of the film industry. "You can't live in it. If you do, you're dead."

Reality smacks Spence in the face with the news that he has a son. The search for his offspring takes him to the Hopper esque town of Butte, Montana, where he also runs into the young man's mother. The father-figure is a recurring element in Shepard's oeuvre, and critics consider much of his work to be an attempt to come to terms through art with the alcoholic father who violently abused him as a child. Shepard has always been reticent to elaborate on the subject, and today is no different. "They say that writers are always turning over the same thing, and that's the material of my life: the thing of the father, the family and the son. I've been doing it for, I don't know, 40 years." But why this particular theme? "It's part of my life," he says impatiently. "It's what I grew up with. It's my father in me. It was part of my existence. It doesn't come from the clouds."

Shepard ran away from home and joined a theatre company. His men characters are often lost and searching - for what is not always clear - or escaping. In his own life, though, he has found a kind of peace and stability with Lange, whom he met making the film Frances (1982), and with whom he has two children, Hanna and Walker. (He also has a son from his marriage to O-Lan Jones.)

As for his creative partnership with Wenders, he says it works because the director understands and accommodates his writing process. Rather than following a rigid plot, Shepard creates a character and then lets him go where he may. In the case of Don't Come Knocking, it was Wenders who originally came up with a character. Shepard, however, did not like the Howard-Hughes-type figure. "I said, 'I don't relate to the big business thing, the city thing", and he said, 'Well, what about this character seen in that light but a different person?' So I suggested a different character, retaining the name Howard, because it's sort of weak, and he went with it. That's the beautiful thing about him. He's very open to trying things." Shepard also gave Lange a great emotional outburst to essay, during which she goes through a whole range of different emotions.

Shepard considers play wrighting to be a "particularly solo pursuit", and says he prefers to work with Wenders on screenplays. "The great thing with Wim is you can go down many different tracks with a screenplay and he will question it: 'Why do we want to go there? Why do we want to do that?' On my own I probably wouldn't question it as deeply. So it's good to have someone to bounce off of."

Only Wenders will let him work this way, he insists. So are there no other independent film-makers he would like to collaborate with? Shepard laughs. "Independent film-makers? Where are they? I'd love to find them. They call themselves 'independent', but who are they making the films for? They're always making films for somebody else. Trying to please somebody else." As for filmmakers working inside the system, "they're too worried about the studio, too worried about the money, too worried about pleasing other people. We only have to please ourselves."

In any case, film is not Shepard's priority. He admits to sometimes taking roles just so he can afford to write, or, in the case of last year's so-so action movie Stealth, to visit new places. "Stealth allowed me to go to Australia," he smiles. "I had never been there in my life. I got to go to the outback, I got to spend some time with the Aborigines' I couldn't have done that if it hadn't been for the film. And then the labour of it - going to the studio, being inside the studio dealing with the machines and the computers and all that stuff - it's work. So I mainly did it because I wanted to go to Australia, sad to say."

Some of his favourite destinations are in America, and he keeps being drawn back to such mythic places as South Dakota's Badlands. "They're very haunting," he says wistfully, "and I return to them over and over because they have a deep past." He is compiling a journal from his notebooks, but it is a big task, he says, because he has so many of them.

It is tempting to look at these journeys as a quest for continuity and permanence in a world that is rapidly changing for the worse. Indeed, things are getting so bad in America that two years ago Shepard wrote his most overtly political play to date, a coruscating "take-off on Republican fascism" called The God of Hell, which included references to torture, beheadings, contamination, and the toxic brand of bumper-sticker patriotism that has emerged since September 11.

"America's gotten more dangerous, more polarised, more insane," he spits. "Right now it's very, very dangerous. It's volatile. It's ready to explode." And, with that, Sam Shepard stands up, tugs at the cuffs of his shiny, black leather, jacket, and leaves.