A curious by-product of our celebrity-crazed culture is the assumption that every time a well-known face on film or television steps on a stage, he or she will make a complete pig's ear of the exercise.
It may well be the case that Keira Knightley, who makes her professional stage debut next week as an American film star celebrity in an updated version of Molière's French classic The Misanthrope, is aiming too high.
You could as easily say, as she's playing a sort-of hyperventilated version of herself, that she's aiming too low. But at 24 years old, she's certainly aiming somewhere, and that's surely admirable.
If she succeeds as the insufferable Jennifer in cutting-edge playwright Martin Crimp's translation, she will acquire no little kudos and the show-business press will applaud her acting chops. If she flops, there will be tears at midnight and the sort of clucking, vengeful "I told you so" backlash that always stems from the ridiculous idea that film acting is easy, a kind of con, and that proving yourself on the stage is what really matters.
The trouble with Knightley is that there is no general agreement about her talent in the first place. Her major film debut in Bend It Like Beckham was a total delight, while her television stab at Boris Pasternak's Lara in Doctor Zhivago was almost embarrassingly unwatchable.
Similarly, she's gorgeous and funny in the Pirates of the Caribbean film series (she's just signed to make the fourth) but looks awkward and blank, with a silly adolescent pout, in the two Joe Wright movies she's made, Pride & Prejudice and Atonement (where Vanessa Redgrave in the last reel showed us what screen acting's all about).
So, can film stars act, anyway? There is a difference between casting celebrity and casting a screen star with stage credentials. Martine McCutcheon was actually outstandingly good as Eliza Doolittle in Cameron Mackintosh's stage production, with the National Theatre, of My Fair Lady (interestingly, he's just signed Knightley for the new film version), but for one reason or another she couldn't sustain the role over many weeks.
Acting on stage takes stamina and discipline, as well as experience. Jude Law has just completed a sell-out season on Broadway in Hamlet, following the London run, no problem. But Law had stage history. A graduate of the National Youth Music Theatre, he's done pre-Hamlet time on the boards at the National and the Young Vic in major roles.
Snobs – and Jonathan Miller, surprisingly – denounced David Tennant playing Hamlet for the Royal Shakespeare Company, unmindful that television's Doctor Who had been an outstanding Berowne in Love's Labour's Lost over a couple of busy seasons with the RSC and an incandescent Jimmy Porter in Look Back in Anger in Edinburgh.
And Anna Friel, currently playing Holly Golightly (not very well, as it happens) at the Theatre Royal, Haymarket, may be best known for a lesbian kiss in Brookside or for hanging out on red carpets and inside West End clubs, but she's served serious time as a brilliant Lulu on stage at the Almeida Theatre in Islington and is clearly no chump in the footlights.
There have been examples of film stars fouling up on the West End stage. But they were invariably senior stars with an eye on the respectability stakes, such as Charlton Heston as a catastrophically dull Thomas More in A Man for All Seasons – he wore three different wigs on top of each other; execution in the Tower must have been a great weight off his mind – or Richard Dreyfuss stuttering painfully through Complicit at the Old Vic earlier this year. And Elizabeth Taylor was likened to a sedate cottage loaf when she appeared in Little Foxes many moons ago.
Usually, though there are no general rules about this, the younger film stars are doing the stage work because they want to prove themselves, not soak up respect, so there's at least a positive dynamic to the process. American playwright Kenneth Lonergan's This Is Our Youth proved a template back in 2002 when a succession of Hollywood young stars found huge popular and critical West End success: Hayden Christensen and Jake Gyllenhaal followed by Matt Damon and Casey Affleck, Anna Paquin by Summer Phoenix. It helped that the play was really good, too.
Martin Crimp's Molière certainly gives Knightley a good platform to bite the hand that feeds her in the celebrity stakes. Molière's updated crowd of showbiz malingerers even includes a vain, posturing, badly dressed critic called Michael Covington with a nasty word for everyone including Andrew Lloyd Webber, Alan Bennett and David Hare. (Surely some mistake here, amalgamating my chic, good-natured self with the smooth, sage theatre guru on The Guardian, Michael Billington... )
When first seen at the Young Vic in 1996, this media-savvy satire starred the low-profile American film actress Elizabeth McGovern, beset by gadflies in a cocoon of moral, bitchy neutrality. Knightley is surrounded with a stellar stage cast including Damian Lewis, Tara Fitzgerald, Dominic Rowan and Chuk Iwuji, the first black actor to play a Shakespearean king for the RSC. And she'll have absorbed years of advice and example from her parents, the excellent actor Will Knightley and the sensitive dramatist Sharman Macdonald.
Her director is Thea Sharrock, who guided Daniel Radcliffe through his very successful stage debut in London and New York last year as the boy who blinds horses in Peter Shaffer's Equus. And Knightley won't have to cope with the further distraction that bugged Radcliffe, that of appearing naked. Not for her, a cry of "I'm a celebrity, get me out of these togs".
One can only wish her well, for the moment at least. She really does start with a clean sheet as far as the critics are concerned, and the news from the previews is not entirely alarming. Still, when the going gets tough, and it will at some stage, Keira can always dash across Leicester Square in the new year to take comfort from another film star, 28-year-old Rupert Friend, making his stage debut at the Garrick Theatre in a play called The Little Dog Laughed; he's her current beau. So maybe they're both going "legitimate" as a seasonal jape and to catch the sales. Nice one.
'The Misanthrope' plays at the Comedy Theatre, London SW1 until 13 March 2010 (0844 579 1940)