Portrait of the artist as a young man

Sometime in the late 1960s, the painter Philip Guston had a kind of aesthetic breakdown. The Abstract Expressionist style in which he'd been painting (highly successfully) for nearly two decades had lost all potency for him. It had come to seem inadequate to deal with the dramas of contemporary American life. "I was feeling split, schizophrenic," he told an interviewer. "What kind of man am I, sitting at home, reading magazines, going into a frustrated fury about everything - and then going into my studio to adjust a red to a blue?" And so, in one of the more striking U-turns of contemporary art, Guston returned to representation, producing the confrontational, cartoon-ish paintings which marked his final years. The reaction to his apostasy was a mixture of embarrassment and fury; "I felt like I'd been excommunicated", Guston said later, although the critical cold shoulder didn't deter him.

It's a dramatic story and it gives the Royal Academy's current retrospective of Guston's work what Hollywood executives would call a strong narrative arc. First you get Guston's youthful work (precocious pastiches of Picasso and Ben Shahn) and then you get what one critic calls his "abstract impressionism" (canvases filled with Monet-like cross-hatched brush-strokes) and then finally the "funnies" - canvases filed with stogie-smoking Ku Klux Klanners, Mickey Mouse hands, and dangling light bulbs. What's more, the storyline here has a twist. Whereas in many retrospectives the first room comes across as the "false start" room - the conventional beginnings that genius eventually sheds - here it is hard not to read it as a clue to the core of Guston. You can find most of the motifs of his later career - bin-lids as shields, nooses, men in hoods.

It's irresistibly tempting, in fact, to read this exhibition as a cautionary tale of a talent that temporarily abandons its genuine calling in the interests of fashion and aesthetic orthodoxy, and then finds itself again. That's a temptation that retrospectives almost always offer. Take the big Donald Judd show now at Tate Modern, which begins with four of his paintings and then turns you round a corner to the artist's future - a free-standing work made out of two sheets of wood and an angled drainpipe he found in a local hardware store. The story isn't complicated here either - and it's underlined by the catalogue essays. Judd begins with work that clearly relates to contemporary artists such as Frank Stella and Barnett Newman - and then he strikes out for a new frontier of his own. There are clues in the first room to the direction he's taking - a shiny baking tin embedded in a charcoal grey canvas, a bright yellow Perspex letter at the centre of a brilliant red one - and because these works come first they inevitably reinforce the exhibition's implicit storyline, which tells of an artist dedicated to refining the artist out of the equation. Judd stops applying colour with a brush and starts using commercial materials in which the colour is integral. He stops making the work himself and gets fabricators to do it in factories. The result is art free of expressive fingerprints - and as metaphor-proof as he can make it.

Neither of these stories is necessarily false - but they both point up an oddity about the way that we so often encounter individual works of visual art as an element in a larger narrative. It simply doesn't happen to the same degree with other art forms. The British Film Institute might well run a Scorsese season, but only dedicated cineastes will watch the films in order. And when you get the new Martin Amis, it doesn't come in a banded pack with his juvenilia obliging you to draw up a trajectory of artistic progression. Quite a lot of us will do it anyway, of course - but we work from memory and prejudice. And for a lot of people, the author's 10th novel or director's seventh film will be their first. The works can introduce themselves without surtitles such as "Return to Form", "The Search for Purity Goes On" or "Startling Departure in Style".

The paradox is that it should be contemporary art that has adopted this way of presenting artists' work. It is a field in which formalism has been a devotion for nearly 80 years and which has - to put it mildly - an ambiguous relationship with the old grand narratives. "Just look at the work," we are repeatedly told, "and forget all that irrelevant stuff about biography and intention and cause and effect. Stop asking what it's 'about'." And yet there, in the very structure of the retrospective, the old human stories lurk. Like Guston, we know it's not quite the done thing to care about them, but like Guston, we can't quite stop ourselves.