Why Hoffman hopped the train

You know the face. Maybe you can't quite put a name to it yet, but you know the face. Philip Seymour Hoffman (The Talented Mr Ripley, Magnolia, Almost Famous) has an enviable reputation.

He doesn't usually play the lead, but he's often the best thing in the movie - the one they talk about, the one you are always eager to see because his work is so interesting, so fresh and original. Yet, like many actors who work in the cinema, he feels the need to go back to the theatre to nourish himself.

Seven years ago, he teamed up with another New York actor, the amiable, gentle John Ortiz and his group, LAByrinth Theatre. He is currently directing John and the company in the play Jesus Hopped the "A" Train at the Donmar Warehouse as part of an American theatre season. The play, although the work of Stephen Adly Guirgis, had its origins in a series of improvisational workshops.

The venture immediately sparked my interest. About a year ago, I finished a film called Dancing at the Blue Iguana. It was also an improvisation project, this time about a strip club in Los Angeles, and it was a radical departure from my other work. I had come to this method because I love working with actors and wanted to see what could be achieved by creating characters before you work on the story.

I have often felt that the actor's desire to rush back to the theatre at the slightest opportunity is about the fact that, in film, they do not feel in control of what they are doing. Cinema is a director's medium. But in the theatre, as in movies, you can play symphonies and you can play jazz. You can piece together carefully constructed screenplays or you can improvise. The only thing is, to improvise, you need great musicians. And the opportunity to do this kind of thing comes rarely in the cinema. Only the bravest of producers will give you the money to make a film that has no story.

I found Hoffman and Ortiz just after rehearsals in Kilburn, tucking into hamburger and chips. I wanted to ask them about the group experience, how the play came about, how it served their needs as actors.

Was it to do with a desire to flee the cinema? "Not at all," says Hoffman, animatedly. "I never thought of myself as a movie actor when I started. When I became an actor it was to do theatre. The movies were something that other people did."

Did he have to adjust his technique? He stares for a moment at the half-eaten burger. "It's over more quickly. One day and the scene is gone. Film is like a 40-yard dash, and theatre is like a marathon.

"I try to be as interesting as I can, whatever it takes, and often you don't know where inspiration comes from. That's OK in the movies, because tomorrow you're on to something new. In the theatre, you have to recall where you found it, work on it and make it deeper and stronger so you can do it three months from now."

And if they had that chance in the cinema? They both stare at me. "That'd be something. That'd be totally different." From my experience on Blue Iguana, I knew all about the power of intense collaboration over a period of time, in which all the participants - director, writer and actors - achieve a degree of unimaginable trust and lack of self-consciousness. But you need some focus.