If rooms reflect their inhabitants, Peter Brook's apartment in Paris seems an especially accurate mirror of its owner. It is a surprisingly quiet oasis, just at the edge of the hurly-burly of the Place de la Bastille, on a Friday evening. And it is simple, uncluttered and calmly elegant. These are also the qualities that have made Brook the most influential theatre director of the past 40 years. His theatre occupies a space very close to the chaos and disorder of the contemporary world. It tries at the same time to fill that space with a hard-won simplicity.

The chaos, of course, is encroaching. As we speak, the aftershocks of the terrorist attacks on New York and Washington DC are still in the air. Does he feel that the imaginative territory once occupied by artists is being filled by the much darker imagination of those who can turn atrocity into a spectacle?

He thinks for a long time before answering. One of the reasons he does few interviews is that he has a horror of repeating himself. Unable to reel off stock answers, he needs to think hard. He is unhappy, for a start, with being called an artist. "I don't think that anyone has much right to call themselves an artist, but I think you can say that one is working in a field called art. Once you enter into this field, like in any field, you have a responsibility."

That responsibility he sums up in one word: honesty. "Your responsibility is, within your own limitations, to be as honest as you can. Being honest means, on the one hand, opening your eyes totally to the world as it is and, on the other, not trying to give a lying view of the world to other people."

His objection to Hollywood and to theatre that is conducted as a purely commercial enterprise is that they tell lies, "reassuring people that something is lovely when it isn't. The responsibility of anyone in the arts is to look, which is much more difficult, for the other side of every coin. The moment that you see a black side, your obligation is to look for the luminous side. The surface, more and more, of what we see doesn't allow anything luminous to penetrate. The role of the arts is to see what more there is behind the surface".

For examples, he looks to Greek tragedy, to Shakespeare and to Samuel Beckett, whose Happy Days is one of the few conventional contemporary plays he has directed. Each, he believes, asked the audience to confront "the pitiless nature of human existence in a way that made you at the end very positive, full of courage, in a sense stronger than when you came in".

This, he insists, has little in common with the relentless negativity of much fashionable art. It is "very, very far from what has become more and more a contemporary approach to the arts, where you say: 'The world is made of shit, so we paint with shit, we show everything in shit colours and we rub everyone's noses in the shit.' That to me is not honest, it's semi-honest. It's showing one side and shirking the responsibility, which is to show that and the rest".

This is where his sense of theatre lies after a journey that has taken him from being the enfant terrible of English theatre in the 1950s, through the communal quest of the 1960s and on to the artistic homeland of his International Centre for Theatre Research in Paris. Though that journey has been documented with extraordinary elegance in his books - the hugely influential The Empty Space, the essays collected as The Shifting Point and the recent autobiography Threads of Time - it has never followed a straight path. That the highlights of his career, from the acclaimed Theatre of Cruelty season in London in 1964 to the legendary Midsummer Night's Dream for the RSC in 1970 to the epic Mahabharata of 1985 suggest an imagination torn between a recogniti on of horror and a deep desire for transcendence, the impression is entirely appropriate.

The apparent contradictions make sense when you recall that he sees theatre as a kind of medicine. The theatre artist, like the doctor, must be able to look deeply into a wound before producing an act of healing. "Theatre in its origin," he says, "was conceived as a healing instrument for the city. The city always needs healing. The theatre has the advantage over the rest of society in that it can do something radical for one hour. Something can be done for an hour that we can't believe can be done for a long time.

"We can create an image in which racism, cultural and social barriers can be transcended by a group of people working together in very concentrated conditions for a very short space of time. On a limited scale it is possible, and it gives a taste of what might be possible on the bigger scale."

That ability to combine an unflinching view of human cruelty with a faith in the possibility of overcoming barriers is less mysterious when you remember that Brook comes from a culture that knows both the horrors of obliteration and the joys of moving across boundaries. His name, properly speaking, is not Peter Brook but Peter Bryk. His parents were Russian-speaking Jews from Latvia, his father a Menshevik agitator who fled from prison to Paris, his mother a brilliant student who gave up her desire to be a doctor to follow him into a chemistry course at the Sorbonne.

Though this Russian-Jewish background left the young Peter open to a degree of persecution in middle-class England, he did not, he recalls, have any hang-ups about his complex identity. It gave him, instead, a sense of freedom and independence.

"I've had the great, great pleasure, great privilege rather, of being less bamboozled by imposed identities. On the first day at school, when the schoolmaster said, 'You must believe in your house, you must be proud of your school,' inside me something said: 'Fuck you.' I think as an Irishman you will understand this: one just isn't taken in by that stuff."

Likewise, though he enjoyed his time at Oxford University, "somehow I didn't believe in the myth of Oxford. I could just take it as it was, for its extraordinary traditions, while being bored stiff by many aspects of it".

He approached his early encounters with the English and French theatres in the same way, taking what was good without falling for the self-aggrandising myths. This ability has become a consistent part of his aesthetic. "If one is both open and not fooled, then one gradually discovers that nothing is to be rejected, nothing is as good as it thinks it is and nothing is the final answer."

What makes Brook almost unique among the major figures in modern culture, however, is that he has applied this dictum to himself. In an era when the director is expected to be an intellectual dictator, shaping both play and cast to his or her will, Brook has gone against the grain.

"I learned very early on that you have to come to conclusions by the first day of rehearsal, but by the second you have to recognise that those conclusions, that very clear vision, are not true. It's just something that's already going out of date."

This openness to experience and to the ideas of his collaborators comes not from shyness or evasion, but from a different kind of confidence. He has the supreme confidence to follow the instinct that tells him that self-revelation bores him.

"I don't find it interesting when I pick up the Daily Mail and I read all these revelations of the sex lives of somebody or the hang-ups of somebody else. Equally, I don't find a projection of my own ideas as interesting as the process of discovery. I don't take credit for this, and I'm not trying to be modest, either. This is just a fact.

"When my children were small and I told them stories, the exciting thing was to get into the sort of bind in the story where, as I'm telling it, I'm thinking: 'How is he going to get out of this trap, what is going to happen next?' Then it's interesting to tell a story, because you yourself don't know what's going to happen."

This extreme openness is at the heart of his view both of the world and of the theatre. Part of what Brook does is scientific: testing what dramatic causes will have what effects on an audience. Part of it is almost magical, an attempt to transform this hard discipline into something that touches the spirit. These impulses, he says, are not contradictory.

"From very, very young I just couldn't believe that religious experience, artistic experience and science could be contradictions, but just partial views of the whole which encompassed them all. Every conflict can be contained by something that encompasses the contradictions and makes them part of a whole.

That's why I've always believed that the theatre is a meeting point between the wish for perfection and the inevitable imperfection of the world."

Peter Brook is directing Le Costume for ThΘΓtre des Bouffes du Nord, as part of the Eircom Dublin Theatre Festival; it runs at the Tivoli Theatre from Wednesday to Saturday, with a preview tomorrow. There is also a matinee on Saturday (bookings at 01-6772600)

Peter Brook will be taking part in a public interview, conducted by Fintan O'Toole, in Liberty Hall, Dublin, on Wednesday at noon (free tickets from 01-6772600), in association with the Critical Voices programme