DJ Taylor: Kate Winslet doesn't need to read Iris Murdoch to be her

For some reason – let us be charitable and put it down to administrative error – I wasn't among the happy crowd of literary folk invited to last month's preview of Iris, Richard Eyre's forthcoming biopic of the late Dame Iris Murdoch. Thankfully, this slight hasn't diminished my eagerness to see the film when it opens next week.

Neither, curiously, have any of the hilarious advance puffs written about it ("Her performance has the rarest quality known to art," Martin Amis has remarked of Dame Judi Dench, "that of inevitability.") Nor, even, has Kate Winslet's recent revelation – she plays the young Iris – that she has scarcely read a line of Murdoch's considerable oeuvre.

One can envisage a literary purist, and even a certain kind of cinematic purist, turning rather hot under the collar over this admission, marking it down as further evidence of cultural debasement or, at the very least, homework not done. In fact, Ms Winslet's inability to get to grips with, say, the Victorian undercurrents of The Sea, The Sea or construe the existential skits of A Severed Head is on a par with the attitude of the average actor or actress towards their work.

It hardly seems possible, for example, that Helena Bonham Carter should have ploughed her way through Henry James's The Wings of the Dove before appearing in the film of that name. In much the same way, flitting around the fringes of a BBC production of Vanity Fair a few years back, I wasn't particularly shocked to discover that the actress cast as Becky Sharp was under the impression that the film had something to do with an American style magazine.

No, I am not making this up. I am not even suggesting that it is necessarily a bad thing, although occasionally one does see a film in which an actor's unfamiliarity with "the text" seems rather marked when compared to the expertise of the rest of the cast: watching Keith Allen in Martin Chuzzlewit some years ago, marooned amid a crowd of seasoned Dickensians, it was clear that, shall we say, certain resonances had perhaps escaped him.

Actors, after all, are paid to read scripts, not books, to work from instinct, not from a template drawn from what in any case is a different medium. Large numbers of them, one suspects, are able to bring conviction and meaning to dialogue without travelling more than half-way to its core.

Set against some of these evasions, which rarely make any difference to the actor's ability to act, Ms Winslet's ignorance of that groaning cast of fictional library haunters with names like Effingham Cooper and Tallis Browne seems a pretty minor failing. At the same time, together with the rest of the media feeding frenzy accompanying Iris, it is symptomatic of a hulking tendency in contemporary artistic life: the gap that exists between different cultural artefacts even when they stem from the same source.

The mythologizing process that picked up Iris Murdoch in its claws – a process that has claimed many another modern British writer, from George Orwell to Graham Greene – began well before her death. No sooner had she died, or rather before this cut-off point, as her husband John Bayley's books on her Alzheimer's twilight had the effect of publicly embalming her, than it blossomed forth in unimaginable shapes and hues.

Not long after this explosion I picked up a tabloid "Great Lovers of our Time" supplement featuring pictures of Posh and Becks, Taylor and Burton and so on, at whose extreme bottom margin lurked a portrait of what looked like a couple of garden gnomes. Murdoch and Bayley, of course, an Oxford don and a highbrow writer, secretive, self-absorbed and fey, come to join the throng of diamond geezers and their babes. That, whether one likes it or not, is mass culture for you.

And in many ways one rather likes it. Despite the alarm bells set off by Martin Amis's encomium ("a story saturated with oddity, quiddity, exceptionality" etc) you have a suspicion that Iris will turn out to be rather a good film. Conspicuous cinematic merit notwithstanding, you imagine that it will struggle to convey the essential point about Murdoch, which is her ability to write books (apparently Ms Winslet has to do a great deal of frowning in the scenes pegged to Murdoch's professional life).

More or less the same effect was realised by a markedly inferior artefact, last year's film of Captain Corelli's Mandolin – a pretty spectacle, which delighted the Greek tourist board (just as owners of the Southwold beach huts are preening themselves over Iris), not a bad film in its way, but nothing much to do with a novel by Louis de Bernières.

A book and a film are two different things, my wife reassured me as I left a showing of The Fellowship of the Ring, a touch querulously, last week. She was bang right, of course, but there are times when one wants this effervescing cross-cultural tide traced back to its source: that solitary, impassioned mind, bent eternally above the page.