At its considerable worst, that is all that newspaper reviewing is: popping it on a postcard - the only difference being that the postcard is sent to thousands of homes and has a fairly classy address at the top. A lot of critics are, after all, powerful only by virtue of their temporary position. So a good rule when you are writing a review is to imagine it anonymously scrawled in Biro on a crumpled scrap of paper picked up from the pavement the next day by a member of the public. Would it still arrest that person with its cogency of argument, vividness of evocation, and lightly worn authority? Or would it be held at arms' length and hastily dropped in a bin?
Theatre reviewing has certain distinctive features that can make it an even trickier and more treacherous business than criticism of the visual arts, cinema and TV. Unlike a painting or a movie, a theatrical production vanishes - the evanescence of the experience beautifully evoked by Ben Jonson who wrote, of one of his masques: "The envy was that it lasted not still, or, now it is past, cannot by imagination, much less description, be recovered to a part of that spirit it had in the gliding by."
By struggling to preserve and analyse the spirit which a production had in the gliding by, theatre criticism attempts to prove that Jonson was being unduly defeatist here.
Of course, any critic who got swollen-headed and made a show of writing for posterity would be behaving not only immodestly but counter-productively. Theatre is inherently a social activity: an energy between actors and audience in a particular space at a particular moment - an image of society facing itself. So the best way a critic can serve posterity is by fulfilling his first duty: to communicate to those of his contemporaries who weren't there what the occasion felt like and what thoughts it provoked.
The advent of video recordings of productions has not destroyed, nor will it, this historical function of the theatre critic. It's not just that - as anyone who has heard a gramophone record of Gielgud's Richard II or the preserved squeaking of Ellen Terry will attest - theatrical fashions date alarmingly quickly and need contextualising. It's that, as evidence, this mechanically reproduced stuff is on the level of old home movie footage of a party nobody living was invited to.
Another distinctive feature of theatre is that a production is a work- in-progress (or regress) for the whole of its life and therefore especially exposed to the interventions of critics. An art or film reviewer may pan a piece of work but, in so doing, they don't risk changing its nature. By contrast, try going to a performance of a stage comedy on the night after bad reviews have appeared. The event is unnaturally skewed as the cast battle to win over an audience prejudiced from the outset. This process can, of course, equally be constructive. Take the case of the much rewritten musical Martin Guerre, now in its third incarnation at the West Yorkshire Playhouse, and all the better for having taken on board the criticisms made of its two West End versions.
Theatre is also a peculiarly embattled medium, constantly having its obituary notice trotted out by fashionable types whose minds are serenely unbiased by any recent research. There is, therefore, the charge that critics are too complicit with the theatrical establishment, overrating things on principle and providing managements with screaming superlatives in order to raise their own diminished profile and to ensure that their particular trade survives (there's a fair bit of this).
Conversely, there's the charge that we are all too professionally jaded to rise to the occasion. It's a no-win scenario, amusingly illustrated by a passage in Alan Bennett's Diaries. Noting that Steven Berkoff had described critics as "worn-out old tarts", Bennett rejoins: "If only they were, the theatre would be in a better state. In fact, critics are more like dizzy girls, out for the evening, just longing to be fucked and happy to be taken in by any plausible rogue who will flatter their silly heads while knowing roughly the whereabouts of their private parts."
Peter Brook in The Empty Space made a similar point more soberly when he wrote that: "A critic is always serving the theatre when he is hounding out incompetents. If he spends most of his time grumbling, he is almost always right." Not that he should be bellyaching into a void. His complaints should be set against "an image of how theatre should be in his community". It's no accident that Shaw and Tynan, the greatest theatre critics in England this century, both began writing in periods when hidebound theatrical institutions cried out for the devastating wit of the constructive iconoclast.
In his fine book on theatre criticism, Irving Wardle quotes a lovely phrase from Charles Marowitz: "The quality of imminence: the tacit assumption that behind the inadequate, the extraordinary is raging to get out," which Marowitz sees as the mark of great reviewing. Not what is, but what could be. In an ideal world, critics would, I suppose, be so eloquent about these sensed possibilities, that the playwrights would be inspired to transform them into living realities.
Meanwhile, in the actual world, reviewing space gets tighter: there's a philistine blurring of criticism and news reporting; and even some supposedly civilised papers now put a coded-for-the-consumer range of stars over a review - a practice seemingly designed to free people from the dreadful burden of actually having to peruse it. But it is not serving the reader to allow theatre criticism to dwindle into mere thumbs-up, thumbs-down tipstering, important though that role is. The reviewers' prime duty is to keep the level of debate surrounding a play or production as high as possible and its manner entertaining. Bad critics try to second-guess the taste of their audience and cravenly pander to it. I know of one broadsheet paper that would not let its reviewer cover productions at the Gate Theatre at a time when that fringe venue was winning every award in sight. Why? "Because our readers don't go the Gate." By that logic, of course, they never will.
A critic needs to break through such circularity of thinking. As James Fenton once put it: "This is the spirit of critical timidity: I can't stand this new piece, but, oh dear, Johnny Public is going to love it, so I'd better watch my words." Above all, you have to guard against both personal and cliqueish complacency. Every theatre reviewer should have pinned over his or her desk the following remarks by Harold Pinter: "There is a definite and amusing resistance on the part of the London critics to a writer doing anything at all different... The critics don't like play `C', but , when play `D' comes along, they point immediately to the virtues that play `C' possessed and regard play `D' as the deviation."
As the past year has demonstrated, fixed ideas about what constitutes drama would bar you from imaginative entry into a lot of new works. An open mind is not the same as an empty one. It's as well to take care, for when the waters of theatrical creativity have gurgled down the plughole of oblivion, the critic's words are the grimy tidemark left round the edges of the bath. Better make sure it's not too unprepossessing a sight.