Thomas Sutcliffe: No chemistry lesson with Cate

The only thing wrong with Notes On A Scandal, I realised the other day, is that it didn't make me want to sleep with a 15-year-old boy. In the grand scheme of things - Academy Award electoral politics among them - I don't suppose this is a huge problem. Voters tend to shy away from works that inadvertently propagandise for predatory sexual experimentation. And to be honest I can live with the shortcoming pretty easily myself, never having felt that this was a gap in my life experience that needed to be filled. Indeed, to describe this failure as a shortcoming at all may be off the mark, since Richard Eyre has clearly framed the critical relationship in the story as an inexplicable folly rather than an understandable one. In an interview, he explained the casting of Bill Nighy as a deliberate strategy, designed to deprive Cate Blanchett's art teacher Sheba of one obvious alibi (marital dissatisfaction) for succumbing to the clumsy seductions of her teenage pupil. You are meant to sit there thinking "What is she doing?"

And yet there was something about the flustered embraces between Blanchett and her young co-star that felt disconnected and underpowered as you watched - a sudden drop in intensity that would conventionally be explained away as a failure of screen chemistry. I can perhaps best explain what I mean by citing another scene in the film which undeniably delivers that galvanic charge of personal connection, although the end result is very different. Barbara, the embittered older teacher played by Judi Dench, has been exploiting her knowledge of Sheba's folly to get closer to her and at one point she suggests that she should console the younger women by stroking her arm. It's a moment at which her longing emerges into the open and it unnerves Sheba, who, after submitting for a few moments, recoils. And as a member of the audience you understand both sides of this exchange with an almost physical immediacy. You know why Barbara longs to touch Sheba and why Sheba doesn't want to be touched - though in both cases "feel" would be a better word than "know". The reactions are conveyed through your own bodily instincts.

That's the thing about screen chemistry, which is so often discussed as if it is a matter of simple binary mixtures - add Star A to Star B and wait to see whether there's a sudden surge in temperature and an unexpected fizzing. In truth, we are always part of the compound too - our own sexual prejudices and assumptions stirred in as an essential but unpredictable catalyst. To put it another way, you might say that all sexual encounters in the cinema are threesomes (at the very least). They simply won't work unless we interpose ourselves between the principals and (whatever our day-to-day predilections) look appraisingly in both directions.

And what's missing from Sheba's urgent tumbles with Steven is that rush of blood. I never sat there thinking: "If I was a bored bohemian woman with a sense that life owes me a bit of transgression I would definitely have a bit of that." The other half of the catalysing reaction was a lot easier, of course - yes, I find Cate Blanchett attractive - but then who wants to go to the cinema only to feel like themselves?

This expectation of intimate participation may be a burden only the cinema has to bear. Certainly the novel has no similar problem, since it can confine Sheba's indiscretion to the safe enclosure of the second-hand account. On screen, though, there is only first-hand witness - and, whether it's good for the film or not, you're likely to find yourself identifying with those you can see - and feeling the lack when identification goes missing. Paradoxically, if you want to feel like a detached spectator you need a medium which doesn't show you pictures.

(A confession: while musing about this piece I went out and bought Antonia Quirke's new book, Madame Depardieu and the Beautiful Strangers, in the somewhat ignoble hope that its account of an emotional life lived in the reflected light of a cinema screen might piggyback me to some conclusions of my own. I didn't get my free ride, as it happened, because Quirke's book is far too singular and autobiographical to provide easy building bricks for general theorising. It is a terrific read, though, and contains some of the best writing about actors I've encountered since David Thomson's book The Whole Equation. I should have put it aside as unsuitable for my purposes after just 15 minutes but kept giving myself a few more pages, and then a few more, instead of getting down to work. So, if the above strikes you as hastily unfinished, blame her.)