BLOCKBUSTER shows are phantoms, impossible objects. The bigger they are, the more notional the experience they offer. Henri Matisse: A Retrospective is the Museum of Modern Art's most expensive exhibition yet, and the largest Matisse show ever. Paintings - it concentrates on his paintings - have been gathered from America, Europe and the important Russian collections. Most things you've ever seen in a picture book or on a poster are included, along with many that have hardly ever been shown. If it's Matisse you want, it's here in unprecedented, probably unrepeatable abundance. MOMA expects 750,000 visitors over the next three months.
They have more than 400 exhibits before them. And it's been rightly noted that if a viewer spent just one minute on each, and added a little time for walking, resting and reflection, that would mean a visit of more than seven hours - not very likely. The promise of Total Matisse becomes only an ideal experience, which you might have had, if you were you gifted with extraordinary powers of attention.
And then there are the crowds. Through them you can gauge how unwisely people pace themselves. They dwell long in the first rooms, and pack them out. It's certainly curious to see the earliest pictures - quiet, neat, subfusc studies - and how rapidly, at the turn of the century, the gear changes, in a sudden liberation of brushwork and colour. In Fauvism, the throngs are still quite heavy. And then, around 1908, when Matisse was painting primitive mythological images for the Russian collector Sergei Shchukin, the crowds start to thin out.
There's still a long way to go - through the encounters with Cubism in the 'teens; through the subsequent decades of home-life scenes and lazy odalisques in Nice; and finally into the last 10 years of Matisse's life, when, with the most graceful sign-off, he turned to paper cut-outs. Here animal and vegetable, human and geometric forms swim freely and happily together in their two-dimensional world. It's enough to pick up the most flagging of attentions. But if, as Matisse hoped, his art offers 'a soothing, calming influence on the mind, something like a good armchair which provides relaxation after physical fatigue', then this is relaxation under considerable pressure.
Matisse in New York: it might be anywhere, but Matisse has a special relationship with New York. The last big Matisse show at MOMA was in 1951, when the great Matisse scholar Alfred H Barr was the museum's director, and New York's most influential critic, Clement Greenberg, was pronouncing the artist to be the exemplary modern master. It was also the time of Abstract Expressionism - the art movement with which the US wrested the leadership of Modernism from Europe, and which was vigorously supported by MOMA. And the art of Matisse had a part in this act of succession. He was the old king, the essential forerunner of the new 'Triumph of American Painting'. It was of course a Matisse with abstract tendencies that was emphasised.
But why a great Matisse retrospective now? The present exhibition has no comparable circumstances. It's not easy to imagine Matisse making much of an input to the current New York art scene. One looks for an anniversary - but no, Henri Matisse, 1869-1954, doesn't provide one. Still, the show has its timeliness. Like all big retrospectives, it seeks to alter our view of the artist, by making him a figure of more contemporary interest. The emphasis now is not on pure painting, but on questions of content, meaning, language. What's wanted is not the proto-abstractionist, but an artist who never actually abandoned representation in some shape or form - a Matisse we can talk about. It may not prove easy. And in his catalogue, the show's curator John Elderfield has a long and thoughtful study of the artist, entitled simply 'Describing Matisse' - as if that modest-sounding task were still the real issue.
But surely Matisse is the last artist who should be involved in 'issues' - or in time-and-motion studies. He is the painter of pure pleasure, of immediate sensation. That's what has made him the best-loved of all modern painters, and that's what will feed the 750,000. You need only look to feel this. There's an almost physical uplift. It comes before any question of what his work is about; indeed it's the reason why anyone would stop to ask that question. Matisse has a magical knack of making one colour chime with another, of orchestrating a whole ensemble of colours so that each voice sounds clearly. Sometimes they fall in stormbursts, sometimes in delicate patchworks, sometimes - as in the Red Studio of 1911 - in a gorgeous flood. One of the results of Matisse's liberation of colour from realistic depiction was to make every element of the picture - whether figure or background - play an almost equal part. No dark brown corners to be overlooked. The world looks both lucid and incredibly full. You can call this decoration, or a kind of paradise. But the force of this painted world is to make you not think of anything else - not even of the artist himself.
Matisse is an artist without a legend. He seems an anomaly among the pioneers of modern art in having no handle. You can run off the labels. Gauguin - drop-out; Van Gogh - madman; Seurat - theoretician; Picasso - satyr. But Matisse? Just painter. There are no myths from which to rescue him, and no telling pieces of biography to assist interpretation. Perhaps the striking thing is the way the life doesn't collude with the art. You have the image of the artist in the early 1900s, living a poor but entirely respectable, bourgeois, wife-and- two-kids existence - and then retiring to his studio to commit outrageous acts of Fauvism. He spent most of his adult life hard at work.
It was an art without words. Matisse wrote well and precisely, but when he spoke of words, it was with violence. To be a painter, he said, 'First of all you must cut off your tongue, because your decision takes away from you your right to express yourself with anything but your brush.' A fan of Giotto, Matisse wrote of that great storyteller: 'When I see the frescos at Padua I do not trouble myself to recognise which scene of the life of Christ I have before me, but I immediately understand the sentiment which emerges from it, for it is in the lines, the composition, the colour. The title will only serve to confirm my impression.' If painting does indeed have a language entirely of its own, what more is there to say?
In 1908, the year he wrote that, Matisse began a painting which he wouldn't finish until 1912. Conversation shows a man in striped pyjamas (the artist) standing opposite a seated woman in a dressing-gown (his wife). The deep blue which saturates the interior around them harks back to the ultramarine backgrounds of the Padua frescos. It's an unusual Matisse in that it shows two people in an eye-to-eye relationship, and in its suggestion that the subject may be confessional. It's perhaps the nearest he comes to representing a psychological drama. The intense blue puts the figures under high pressure. And yet on the point of articulacy the picture goes on hold. The figures are kept mute. It is a conversation to which no caption or imaginary dialogue can be added. This static tension is part of the picture's power. Here, as in other pictures from the second decade of this century, Matisse gets a significant charge from his rather rigid views on the nature of art.
Matisse saw the work of art as a condition of stasis, a self-contained and integrated whole. It might take a lot of pain to achieve the balance and harmony of all the parts, and his pictures often show evidence of correction and adjustment. But that was the ideal. In a way this is an old view of art. But with Matisse, it is taken a step further. He imposes a view of life too, and severe limitations on the subject-matter, for this too aspires to stasis. This excludes anything that might threaten to trespass beyond the carefully composed internal relations of the picture. Any signs of drama, action, suffering, desire are withheld. And while Matisse never abandoned representation, he focused increasingly on a theme that mirrored his idea of art: the dream.
The image that recurs in the Twenties, Thirties and Forties is a woman in a room - eyes closed or gazing into the middle distance, in a sleeping or waking reverie. That is the representational anchor, the clue. But what is pictured is not simply a woman dreaming, but rather a dispersed consciousness spreading out over the whole pattern of the picture. The room, with its rich decor, fruit and flowers, is the woman's dream, or equally, she is the room's dream. There is no central subject. It is all thought-bubble soaked in colour, the self lost in its own interior: ideal contents for the self-contained, wholly integrated work of art.
Matisse's development tells a two-way story. There is a great liberation. There is a great retreat. What he gives with one hand, he takes away with the other. You have sensations of unparalleled beauty, and a formal economy which makes most other pictures look arbitrary and full of redundant gestures. Sometimes you feel his pictures are all that art needs to be. But with that, you have a withdrawal into a cocoon of dreams, from which all the resistant matter of life is expelled. And so Matisse's art provokes this question: is the divide inevitable? Could this transfiguration work with a wider compass? Or did Matisse bite off precisely the amount that he could chew? If we take Matisse as an exemplary artist of this century, he makes a gloomy intimation - that in our time it is only the inner life, prudently insulated against the world, that has a chance of being fully composed. What, gloomy? Our favourite armchair? No, no, he wears the smile of a Buddha. And you can believe it too, with it all before you, while the long moment lasts.
MOMA, 11 West 53rd St, New York (010-1-212 708 9750), daily to 12 Jan, 10.30am-6pm except Wed (noon-6pm) and Thurs (10.30am-9pm). Tickets can be booked at Ticketmaster (010-1- 212-307 4545; admission dollars 12.50, booking fees dollars 3 per adult plus dollars 1.50 per order). A smaller version of the show goes to Paris in the spring.