'If anything, we choreograph the viewer's gaze." The American choreographer William Forsythe is describing Kammer/Kammer, the dance-theatre piece he's bringing to Sadler's Wells in London.
Forsythe, now 53, is wiry, softly-spoken and voluble. He sits with one leg slung over the arm of his chair, demonstrating gestures or bouncing up and down for emphasis. He launches gleefully into details about his new piece: the plot, the practicalities, theories. In print, and sometimes on stage, his theoretical side can be determinedly dense. In person, he's eager to explain.
Kammer/Kammer is a pair of love stories, "a discussion of love and the tokens of love". The first story comes from Douglas Martin's autobiographical account of his affair with a rock star. The second - this is where it gets theoretical - is from Anne Carson's essay "Irony is not Enough: My Life as Catherine Deneuve". The poet and scholar imagines herself as the French film star, who in this fantasy is a scholar fantasising about one of her students.
It's the fantasies that really interest him. He's staging the piece with dancers and film sequences, which are filmed and edited live - "it's all live performance". As fantasy starts to dominate, "we slowly draw all the action off the stage and onto the screen". The real life on stage is "kind of plain and dumb, but the images look very glamorous, just gorgeously composed."
The balance of drama and dance in Kammer/Kammer makes it "a choreographic piece, not a dance piece". What's the difference? The speaking roles, played by Forsythe dancers, dominate. There are dancers, who support the story "in a filigree kind of way. There's no weight to their presence. They're almost like little moving designs." He says there's hardly any dancing, then adds that "the emotional tension is all done through dance".
Kammer/Kammer will be Forsythe's last work with Ballett Frankfurt, the company he has directed since 1984. His departure has been driven by politics: "It's a very destructive situation." Last May, he discovered that the council of Frankfurt planned to close his company, without discussion and without warning. The city is in financial crisis, and Ballett Frankfurt is subsidised. Yet at home it plays to packed houses. His tours, besides raising the city's cultural profile, have earned Frankfurt around £12 million. "There was no question of them saying, 'Bill, could you work with less money?' I don't need twenty-eight people, I could do it with five."
Forsythe made the closure threat public, and received messages of support from around the world. Faced with international protest, the council backed down. But Forsythe refused to renew his contract. "I can't work for someone who is un-serious, because a lot is expected from us. I'd rather do other kinds of work than continue with this kind of organisation above me."
What will he do instead? He's in demand as a freelance choreographer, but he prefers to work with dancers already experienced in his style. The next step is probably a private Forsythe company. Two German states, Hesse and Saxony, have volunteered funding. Local businessmen are keen to hang on to Forsythe's cultural prestige. "They were appalled at the idea of losing the Frankfurt ballet, and went straight to the state governors."
He hopes to have something agreed this month, but points out that this "doesn't have to be the only solution for us. We're a collective of very independent artists." He and his long-term collaborators will certainly work together again, "We're trying to decide the most interesting form besides a dance. His latest idea is an education project: "It would be an anarchic education."
Whatever direction he chooses, Forsythe is likely to remain controversial. His choreography, especially pure dance pieces such as In the Middle, Somewhat Elevated, is hugely in demand from ballet companies worldwide. Admirers see him as a pioneer, an innovator in a highly traditional art form.
He's best known for how his dancers move, not for the theoretical material he builds into his dances, and certainly not for his response to music. It's a style of extremes: legs go sky-high and torsos are wrenched in different directions. It's fast, off-balance and uses a lot of force.
Fans and critics emphasise the aggressive qualities of his work. So do dancers. In one interview, the Paris Opéra dancer Agnès Letestu said how much she loved his dances. She also described them as brutal.
The word surprises Forsythe. "That's so weird, because it's just the opposite." He guesses that it's the view of someone more used to dancing Swan Lake, and insists: "It doesn't look brutal when you understand the work behind it." He argues that "performers are most beautiful when they are consumed by the act of dancing. So a lot of the choreography is designed to give the dancers no room for acting." He's not alone in wanting dancers just to dance; plenty of choreographers have aimed for an objective style. But it is unusual to use such punishing extremes to achieve it.
He remembers watching one of his dances with the Royal Ballet's Leanne Benjamin, a dancer from a classical company with an acting tradition. "She turned to me and said, 'I feel lazy'. And I said, 'You are. But if you didn't work here, you wouldn't be.' I think that people from classical companies are immured in a faux fantasy of decorum." The treatment of ballet dancers shocks him: "You want brutality? That's brutality, in my opinion. Working conditions are so abominable, anachronistically crude."
Still, there are things he loves about ballet. He's happy to praise the Paris Opéra or the ballerina Alina Cojocaru, to regret how much has been lost in an art where works are passed from dancer to dancer. "We will never ever ever see a real Swan Lake, a real Paquita. Maybe we'll see close, but not the real thing."
It's already happening with his own dances. He saw one of his ballets performed in Australia, "and apparently the third cast had told the fourth cast. I did not recognise a step." He plans to put some of his repertory on DVD, with analysis from experienced Forsythe dancers. "The idea is to document as much as we conceivably can. So they'll get the details and do it really well." These won't be whole ballets: "It's just too much information. But there will be a lot of fragments, hopefully, that will be really great things to dance."
Two years ago, Forsythe was reported as saying that his will would stop his ballets being performed after his death. "Crap. Not true. It's just that I want to prevent my children from plundering. Just securing that they didn't cash in on that situation."
This isn't a joke. Much of the Diaghilev repertoire is now in the hands of choreographers' relatives and - as in the Kirov Ballet's recent staging of Nijinska's Les Noces - they've done some weak productions. The Paris Opéra can go on dancing In the middle, but he means to prevent bad new versions of his ballets.
He also wants to encourage new work. The DVD fragments mean his work will be "there for future dancers, but not in the way of future choreographers." There would be less demand for new dances, he argues, if "some old dead fart like myself was being sold by his children." He catches my eye, and grins. "Sam's the one I'm worried about. I have an entrepreneur in the family."
'Kammer/Kammer' is at Sadler's Wells from 22-25 October (020-7863 8000; www.sadlerswells.org)