There's a method to staged madness, says PETER CRAWLEY

A young man goes to see a psychiatrist. He takes to the couch rather willingly – he likes to talk. Dressed in black, speaking of the uselessness of the world and toying frequently with the idea of suicide, the guy is clearly depressed.

You note, too, that his father died not long before from mysterious causes, that his widowed mother hastily married his uncle, and that the patient has finished rather melodramatically with his girlfriend. Come to think of it, you should schedule an appointment with her, pronto.

Still, he confides that his recent manic behaviour has actually been an act – which would be more encouraging if he didn’t add that, when the wind is southerly, he knows a hawk from a handsaw. Uh huh . . . By the time you realise that he intends to kill his uncle because a ghost told him to, you’ve tick the boxes marked Oedipus complex, suicidal depression, borderline personality disorder and paranoid schizophrenia. When it comes to Hamlet, it may be too late for Prozac.

Madness in great ones must not unwatched go, of course, but is the theatre really a good source for psychiatric case studies? The pros seem to think so. Derek Russell Davis's book, Scenes of Madness: A Psychiatrist at the Theatre, Ernest Jones's Hamlet and Oedipus, and Bennet Simon's Mind and Madness in Ancient Greeceall suggest that the riddles of mental health are best observed on a stage, rather than from behind a two-way mirror.

You can see their point. Playwrights don’t throw pills at the problem; they put things into context: You get private revelations from Hamlet, but you also get to know his dysfunctional family, all assembled far easier than any group therapy session. Hamlet is a more diagnosed possessor of an Oedipus complex than any other character in drama. Including Oedipus.

Still, it’s asking a lot of playwrights to have an unusually realistic grasp of human psychology. No historian would ever credit Hamlet with an airtight view of 14th-century Danish politics, for instance. But when it comes to the disordered minds of Orestes, King Lear, Macbeth, Blanche Dubois or Mary Tyrone, the doctor will see them now.

Even the under-qualified among us can play along, cast in the role of sympathetic therapist and amateur detective. When Macbeth sees a dagger before him, is he clearly disassociated from reality? In The Gigli Concert, what psychic imbalance prompts the Irishman to visit a quack therapist and demand to sing like an opera singer? And if a young man in 1960s Donegal inhabits the stage with an alter ego that only he can hear (as in Philadelphia, Here I Come!), is that a clever dramatic device or a clear-cut personality disorder?

It's hazardous to diagnose a fiction, though, particularly when the sufferer rarely finds relief. The Abbey accompanied Christ Deliver Us!with talks on "Mental Matters", recognising that a play might not offer a remedy, but can start a useful discussion. Exploring disorders, empathising with them and maybe understanding them can be therapeutic for everyone.

Or, to put it another way, you don’t have to be mad to work in theatre, but it helps.