A corollary of the fact that good books almost always make bad films (and that successful adaptations should be taken as no more than freaks or flukes - No Country For Old Men being a case in point after last night's Oscars) is that many of the best films come from inferior source material.

What's frustrating for anyone who's a lover of both is that the worlds of books and films are so similar, yet so stubbornly irreconcilable; they tell the same stories, and the broad commercial (and largely repetitive) Hollywood movie relates to the marginalized art house film in much the same way as the commercial blockbuster does to the literary novel. But there is something so different about the experiences of watching a good film and reading a good book (I imagine it's something to do with the differing speeds at which we take in information in the different media) that the disciplines of being a successful artist in either medium seem to be completely separate. So, talented filmmakers often stay away from great books, and seek projects whose source material doesn't challenge them as artists. And perhaps that's why there's such an amazingly low number of people who have been both - I run out after the very different Pier Paolo Pasolini, Neil Jordan and Stephen Fry. Stephen King's one film as director was a notorious flop and, purely on personal taste, I thought William Boyd's The Trench was a badly acted compendium of First World War cliches.

As mentioned by William Nicholson on the Today Programme last week, probably the most famous great film made from a poor book is The Godfather, a film whose every element (tone, pace, photography, performance) is judged and overseen by Francis Ford Coppola with the skill of a great novelist. The book remains successful, but I can't remember anyone ever saying to me that it's much cop as a novel. Goodfellas is not dissimilar, although it's from a non-fiction book. To me, Henry Hill's account of his mob days reads like a list of scams, murder, bullying and opportunism not entirely redeemed by his confession of them, or the skill of Nicholas Pileggi's writing. Scorsese's film is a rush of style and brilliance, and carved itself a place in the culture that I don't think the book had, or would otherwise have, achieved.

It seems it's always been this way - the first great narrative film, D.W. Griffiths's Birth of a Nation, was based on not just a bad novel, but an extremely politically repugnant one. The Clansman (1905) by Thomas F. Dixon, Jr., might as might as well be called Fanfare for the Common Racist. The film climaxes with the rounding up of black men who are trying to vote by the heroically photographed Ku Klux Klan, in a sequence which is almost as thrilling to watch as it is appalling (which makes it weirdly compelling, like Leni Riefenstahl's Triumph of the Will: the thing about the bad guys is that they're not supposed to be able to make good art). But the film's impossible to ignore, because besides making the first genuinely exciting action sequence, The Birth of a Nation invented the grammar of cinema: the combination of the same events filmed in wideshot, midshot and close-up edited together for emotional emphasis, which remains unchanged more than ninety years on. Film hadn't come anywhere near being an art form before this moment. (Griffiths realised he'd made a bit of a faux pas on the racism front and followed it up with Intolerance, a film with a contrary message, but, purely as a narrative, an identical viewing experience: two hours of epic tedium followed by some of the most amazing film making you've ever seen.)

Perhaps it's attitude - the challenge of bringing lasting class to a shoddy product. That's probably partly what drew Hitchcock to Psycho, a decidedly silly, slim and over-the-top shocker by Robert Bloch. All of those adjectives could be used to describe the film, but then Bloch wasn't able to marshal his prose in the way that Hitchcock was his images, with absolute, manipulative precision. By 1960 Hitch's silhouette was on screens all over the world on the TV show Alfred Hitchcock Presents, and he had chosen to be come publicly identified with his films (to 'star' in them from behind the camera) in a totally new way for a film director. Therefore it suited his purposes to use material as schlocky as possible to play with audiences' expectations in the cruel, almost surgical way which was his particular talent. That's why it's not his best film, but it's his most characteristic one - you can practically hear him giggling with glee as the camera tracks up the stairs with the detective, Arbogast, both audience and detective tensing for what they feel will be something horrible.

Then there's another approach - actual antagonism towards the material. When we discuss the projects which a director chooses, we often don't consider the actual day-to-day business side of film financing, whereby most directors who want to remain in work have to make do with the projects offered them by producers. (Coppola's The Godfather would fit into this group. He tried to turn it down several times.) Robert Altman was offered one such in 1971, a Western novel called McCabe, which he thought was clichéd rubbish - exactly the sort of mythologizing old fashioned story he had no interest in. But it was a project. So he took the title and little else, and turned it into McCabe & Mrs Miller with Warren Beatty and Julie Christie, a film which works exactly because it goes against obfuscating mythology of the Old West. Instead he tried to imagine what it might have actually been like to live there, and came up with a funny, sad and sublime film with credible portrayals of ordinary people, where normally our gun-toting hero and whore-with-a-heart-of-gold would be.

An even better approach is shown in the hoary old anecdote about Howard Hawks and Ernest Hemingway lounging on a yacht, and Hawks betting the future Nobel winner that he could make a movie out of one of his stories that would improve on it. Of course Hemingway took the bet. The result was To Have and Have Not, from one of Hemingway's lesser novels - Hawks was blessed with the pairing of Bogart and Bacall on screen for the first time (and in love), and the film is atmospheric, moving, erotic and timeless. This is the only instance I know of where the author was actually told beforehand that a director was going at their book because it could be improved upon. And in the way the story was told to me, Hemingway paid out on the bet.

Previously in this series: Adaptation 1: short stories on film.