Absolutely! (Perhaps), Wyndhams Theatre, London

Far better than its oafish new title would suggest, Luigi Pirandello's Right You Are If You Think You Are is not only one of the most important plays of the 20th century, it's also extraordinarily prescient. This work about the fragility and mutability of identity was written in 1917 but belongs to the age of Beckett. Though he outraged the proprieties of his time, Pirandello fitted cosily into the absurdism of the Sixties, so much so that for some time he has seemed as dated as they. But, considered anew, he still has a great deal to say to us. With Pirandello, the questions "What is real?" and "What is truth?" are only the first of many.

Signora Frola, an elderly widow, excites the suspicion and concern of her neighbours by living alone, though her daughter and son-in-law have a flat nearby. Her son-in-law visits frequently, but her daughter never comes to see her; indeed, she never leaves her home. Is she ill? Is her husband keeping her a prisoner? Why does he leave his wife alone and spend so much time with his mother-in-law? Is it relevant that they come from a town that was almost entirely destroyed by an earthquake? One by one the participants in this strange drama appear and tell their story. The widow says that her son is mad; her son-in-law's quite different explanation makes her out to be the madwoman. The two are brought face to face, but their stories interweave. The daughter/wife is sent for, but the mystery only grows.

The title is much the worst line in Martin Sherman's fluid adaptation, but putting Pirandello's classical language into colloquial speech is a leap almost as great as using English in place of Italian. What's important here is not the comedy, which this version emphasises, but the poignancy of not knowing who one is, and who others really are.

"What on earth can we ever know about anybody else?" says Laudisi, the commentator, whose determined detachment does not signify a lack of concern but the reverse. For, though we might be motivated by simple curiosity in seeking to penetrate another's persona, what, once we have seen behind the mask, do we do? What is our obligation to those whose disguises we have disturbed? Laudisi's answer asks for something that the bored, voyeuristic characters have not considered and may not be able to provide: "Compassion, love, and silence."

Formal diction, requiring the audience's concentration, would have created a deeper feeling of involvement in the drama, and set up a stronger contrast with the disruptive devices of seating rows of participating spectators on stage and planting an actor in the audience. The superficiality of the humour also plays down the disquieting nature of the piece, which does not simply state that our identities are vulnerable, but asks what our response to this problem should be. In his own life Pirandello was bitterly tested by it - for 16 years he lived with an insane and pathologically jealous wife.

Franco Zeffirelli's direction is ponderous, and his set - a metal screen in front of a garish mosaic of squares and rectangles flanked by mirrors - is as oppressively vulgar metaphorically as it is aesthetically. Raimonda Gaetani's costumes are so dowdy that I kept thinking they were making some point I missed. But Oliver Ford Davies as the gruff, sardonic raisonneur is just right, and Joan Plowright, as Signora Frola - the name is a homonym of the Italian word for "tender" - gives the play the brush of a dove's wing. Gawn Grainger also contributes a sympathetic presence as a neighbour who, unlike his shrill, flippant wife, sees the afflicted family as more than a subject for gossip. Though there is much to laugh at in the conflicting accounts and bewildered characters, what we remember are not the jokes but Pirandello's metaphor of human relationships: ghosts chasing one another in a labyrinth.

To 23 August (020-7369 1736)