Fifty years ago, when Alfred Hitchcock's North By Northwest opened, it was received with gratitude, appreciation and nearly complete misunderstanding. After all, said the wise judges of 1959, the world is not like this - its schemes of espionage do not turn on men as frivolous and charming as Cary Grant's character in the film. Those people boarding the American railway system cannot expect to meet femmes as fatale as Eva Marie Saint (behaving in a very unsaintly manner). And it was absurdity - albeit a killer joke - to have a bus stop on a bare midwest prairie, where a plane might hunt a man. All of those ingredients, it was said, were at the convenience of the movie, the essence of its movieness. But you'd never find them in life.

That's exactly correct, Hitchcock might have said: I have made a movie - something you see in the dark. I am not in the business of making life. Indeed, I know very little about life, and have less interest. But I know a great deal about film. What Hitchcock didn't say was that cinema is about cinema - it is a field of play where someone makes shapes and sounds on a screen, and we feel some intense motion. It may be delight. It may be dread (don't forget that North By Northwest fell between Vertigo and Psycho, alarmist works filled with anxiety that a movie may be a wounding thing to witness).

Nor did Hitchcock say: "Just wait 50 years." He wasn't interested in that kind of future, for he knew he would not be there. But from our vantage, we can behold a travesty: that North By Northwest (which was not nominated for the best picture Oscar) is as alive, beautiful and complex as ever it was, while most of the pictures that were nominated - Ben-Hur, The Diary of Anne Frank, The Nun's Story, Room at the Top - are nearly impossible to sit through because of their leaden attempt to resemble life and teach us a useful lesson (for example, it was a bad thing that Anne Frank was killed). There is no lesson in North By Northwest except for this: in the great and continuing crisis of life, try to behave with wit and style. The humour in North By Northwest is not just "silliness" and fanciful situations, one after another. It is an exhilarating escape from the earnest hopes for salvation in Ben-Hur and The Nun's Story. It is, to quote Henri Bergson, to know that "the comic demands something like a momentary anaesthesia of the heart. Its appeal is to the intelligence, pure and simple." Hitchcock believed in that intelligence, because it was cold and clear and because it reduced every decision in film-making to a question of style. In other words, nothing happened or really existed in a movie until his very sharp, idiosyncratic eye saw it - and style in his movies was how he chose to show something.

You need an example: 40 or so minutes into Psycho, Marion Crane (Janet Leigh) enters the shower in the bathroom at cabin one of the Bates motel. The story content of what follows is this: an intruder, a tall woman, draws back the curtain and stabs Marion to death. You could film that content in one unbroken shot, from outside the shower, at a fixed distance, so that we saw exactly what happened - it would be gruesome and sickening because in one fixed shot you could only show such a murder by actually hacking a naked woman to pieces. It is still the case that bloodletting - think of Sam Peckinpah - can only be handled on film if the victims are clothed so that sachets of red vegetable dye can be exploded (inside the actors' clothes) giving the effect of blood and fragments of flesh bursting free in the impact. You couldn't show a naked person being knifed in a single shot without ... well, without committing murder.

Hitchcock elected to use 70 separate shots in the murder. In part, that was to get off the hook of making a snuff movie. But it was also to escape the restrictions of censorship as they existed in 1960. So Hitch was very proud of never showing pubic hair or a nipple, and never showing a knife pierce skin - those things would have had to be cut. The black undertone that was vital to his style rested in this weird balance of outrage and propriety.

Instead, by shooting always within the shower stall, he gave an intense impression of the knife thrusts falling on us, as well as Marion. He conveyed the terror, the claustrophobia, the nightmarish intrusion on intimacy. On top of all this, he made it "beautiful", because he was a connoisseur of framing, editing and harnessing the musical accompaniment (by the great Bernard Herrmann) to make the whole scene both a savage sensation and a filmic tour de force. And make no mistake, in 1960 or so, the impact of Psycho was rooted in that apparently paradoxical marriage of order and disorder.

That is a first lesson in what "style" means, and how stylists can forget that they're making a murder - they think they are making a film. Style exists in framing, lighting and editing and how those areas of choice make us feel. It is a matter of electing to make any scene a montage of different shots and camera angles, or a fluid, moving coverage in one unbroken shot. I spell out these extremes because Hitchcock tried both. There was a period in his life, in the late 40s, when he suddenly fell in love with this kind of fluent coverage - call it the sequence shot, or the 10-minute take, the label applied to Rope, in which there are only eight shots in the entire film. But in the rest of his career, Hitch believed in short shots cut together to give us an impression of action.

Why talk so much about style? For this reason: at the moment of North By Northwest (1959) even the commercial system of film-making was crowded with a number of remarkable stylists - not just Hitchcock, but Howard Hawks, Anthony Mann, Nicholas Ray, Vincente Minnelli, Samuel Fuller and Otto Preminger. In the way these directors composed shots, edited, moved the camera, a trained viewer could discern not only style, but the identity of authorship. In including Preminger, I refer back to those nominated films of 1959 where I omitted one intriguing choice, Preminger's Anatomy of a Murder, a fairly routine trial picture, except that Preminger frames and watches the action in such a way that we do not know whom to trust. If I can contrast this with Ben-Hur or The Diary of Anne Frank, those pictures are so embedded in the idea that their title characters are Good that the moral imperative has eclipsed style - or perhaps eliminated the need for it.

At a wider level, the same description of personal style could be applied to Jean Renoir, Yasujir¯o Ozu, Max Ophuls, Fritz Lang, Orson Welles, Kenji Mizoguchi, Carl Dreyer, DW Griffith, and so on. To everyone? No, not quite. There was, in Hollywood and elsewhere, what I call a certain house style in terms of shooting - modest, efficient, withdrawn, covering action without grand movements - that applies to a lot of Hawks, as well as to other major figures such as Preston Sturges, Billy Wilder, and Ernst Lubitsch. But with those modest masters, style might be apparent in other ways - in the flavour of dialogue, in the casting that carried the talk. You know it's Hawks, because only Cary Grant talks as fast as His Girl Friday. You know it's Wilder, because no one gets bittersweet the way Double Indemnity does.

And where has this stylishness gone? As I think about the present range of film-makers I can see very few where one might reliably recognise their work simply from the way it looks - Michael Mann, Martin Scorsese, Paul Thomas Anderson. But who could say there has ever been an evident personal style in Steven Soderbergh, Ron Howard, George Clooney, the Coen Bothers, or even George Lucas, Francis Ford Coppola, Oliver Stone, Barry Levinson, Stephen Frears or Milos Forman?

It's not that those people aren't considerable directors. These may rely on modesty (Howard), a sense of overriding efficiency (Levinson), or a wish not to show off (Frears) or an eclecticism that can do all styles (the Coens). It may be a lack of authorial character or ambition (Lucas). But you can't tell their style, in the way you could with Antonioni, Bergman, Godard or Fassbinder.

Are we weary of the great authors who signalled themselves with point of view? Has the era of personal passion gone out of film-making? Or are there yet other reasons? Fifty years ago, there were great critical battles fought over "authorship" in film. So style mattered then. Is it possible now that the innate impersonality of film (a mechanical means of reproduction) has become dominant? Think of it this way: a paragraph of Hemingway, Dickens, Dostoevsky, Joyce, Nabokov or Faulkner could likely be identified by any well-read person. So why are so many films nowadays so anonymous? Is that something film-makers have settled for, or is it our wish?

• North By Northwest is at the BFI Southbank, London, and in selected cities from 19 June