Flowers in the attic

Edgar Degas was one of the great figures of Impressionist painting; what's less well known is that he was also the father of modern sculpture. A new show explains why

The last major Degas exhibition was organised by New York's Metropolitan Museum of Art in 1988. It was an enormous retrospective covering the whole length of the artist's career, from his first self-portrait of 1855 through the years of innovation to the last Impressionist Exhibition of 1886. Then it had a section on Degas's late years from 1890 to 1912. This part of the show contained about 100 works in all media. The same ground is covered, with about the same number of exhibits, in the National Gallery's "Degas: Beyond Impressionism". But the intention and effect are different. The Met's interpretation gave a coda to a life whose achievements were somewhat in the past. The National Gallery presents Degas in his final years as an other-worldly obsessive.

The result is magnificent and more than a little strange. The motifs are highly recognisable. Here are all the usual dancers and women combing their hair or stepping out of the bath. These had been Degas's subjects for years and decades. But we now suspect that they were part of the artist's self-examination. We know that he was sociable, widely curious about art, that he was a collector and receptive to new inventions, in particular the camera. And it can be proved that these things affected Degas's art. None the less, the atmosphere of this show is enclosed, as though the old man had no intellectual life beyond the boundaries of his own creations. And, surprisingly, such creations look odder and odder the more one considers them. They turn out not to be familiar at all.

For once, the dark basement galleries of the National's Sainsbury Wing seem appropriate to the work they contain. Richard Kendall, whose exhibition this is and who has written a catalogue that immediately becomes a classic, begins his analysis with a revealing description of the artist's home in the rue Victor Masse, where he lived from 1890 onwards. It was a big building, and Degas had the top three floors. The lowest of them, always locked, was Degas's "museum", in which he stored his previous paintings and his vast collection of work by other artists. The next floor was the living area, containing a dining-room, two long salons hung with paintings, a room for the housekeeper and so on.

At the top of the house was the studio. It was sordid, unlit and never cleaned. There were linen drapes over the big north-facing windows to keep out the light, for in his sixties Degas's weak eyes were more troubled than ever by brightness. In the disorder of this studio were not only the materials needed for painting, print-making and sculpture but also Degas's props: dancers' dresses and shoes, a conductor's podium, a piano, a spiral staircase taken from a theatre, curtains and other drapes, double basses, a divan and a bed, a zinc bathtub and a number of moveable panels. All these could be rearranged to form the backdrops for bathing scenes, ballet rehearsals or whatever. Thus this studio floor was the universe of Degas's art.

And then there were the models. We know little of them, though it is certain that they were well known to Degas both in their naked forms and as individuals. Note that if they were recognisable as people the character of Degas's nudes would be lost. He never posed them frontally for just this reason. So in a way they evade our scrutiny. Degas's attitude to the nude is both intense and anonymous, and this despite the fact that Degas was a great portraitist. It's still not known why he gave up portraiture. Degas abandoned the genre at about the time that this exhibition begins. Here is Helene Rouart in her Father's Study, a moving and also peculiar picture because one cannot tell whether she belongs to her father's environment or to the top floor of Degas's strange house. Anyway, it is his adieu to portraiture. Human features now disappear, while the human figure is all the more examined.

This is the background to Degas's devotion to sculpture. Surely this sculpture is the most important aspect of the art of his old age. The exhibition wants to emphasise that he expressed himself in all media, that the sculptures are studies for work on canvas or paper, and vice versa, the two-dimensional work feeding the sculpture. Despite the obvious truth of this theory the sculpture stands alone. It is more radical and innovative than anything else in Degas's oeuvre.

Furthermore it shows a personal devotion to beauty that is equalled only by the very best of Degas's paintings, and his best paintings do not belong to his last years. For me, the Grand Arabesque, Second Time and Dancer Looking at the Sole of Her Right Foot, with the Woman Taken Unawares and the Dancer With Tambourine, are more poignant than anything else in the exhibition.

I wonder if it is right to call them masterpieces. They are so private and unconcerned with the world at large. The contrast must of course be with Rodin, who exemplifies the sculpture of Impressionism and was very much in the business of producing masterpieces. Degas was the truer artist. He also announces more about the nature of modern art. More than anything else, Rodin wanted a place in the world. Without denigrating that ambition, how much more truthful it was of Degas to produce these little figures and keep them away from the public gaze in his upstairs studio - modestly, despite their awesome theme that they are about existence itself. For these descriptive titles about dancers are for convenience only: really the sculptures represent a metaphysic of female humankind.

Degas took up sculpture late in life and without any professional training, therefore without preconceptions or respect for convention. In this way, chronologically and temperamentally, he may be called the original sculptor of modern art. This isn't quite so of his painting. The sculpture, however exquisite the results, is quite without artifice. Degas's late work on canvas may sometimes be startling but it still comes from the hand of a man who grew up under Ingres. And then there's the artifice of his favourite theatrical subject matter. Intelligent Gauguin, who observed Degas closely, remarked that "On the stage, everything is false, the light, the scenery, the hair of the dancers, their corsets, their smiles. Only the effects produced by these, the arabesques, are right..." There spoke the future primitive, and it's tempting to interpret Degas's sculpture as the part of his work that did not seek to create effects, everything else being relatively sophisticated.

At the National Gallery there are of course many works that proclaim Degas's mastery of theatrical grace. It's interesting to see how he handles pastel in his old age. As we know, pastel can easily be too sweet and when used with any vehemence can just as easily become harsh. Degas always knew how to avoid these dangers. Now he could heat pastel colour dangerously high or give it a sombre, brooding look with his most mature use of charcoal. These pastels, related paintings too, came to have an unorthodox, pessimistic air. If we did not know Degas's earlier work so well they would strike any observer as weird. As it is, we are disturbed even though we recognise their origins. So it often is when we look at anyone's old age, artist or not.

Upstairs in the Sunley Room (admission free), there's an exhibition of works from Degas's collection. At first it looks miscellaneous; then the display quickly makes sense when you think of the second floor of the artist's house and read the informative introduction by Anne Dumas. It must be said that the most dramatic works we already know, for they found their way to the National Gallery's permanent collection many years ago. These are the great Delacroix portraits of Louis-Auguste Schwiter, Manet's Execution of Maximilian and three perfect paintings by Ingres. Of the rarer classical items, there are drawings by Ingres and landscapes by Corot. The Manet still-life is a treasure, and so are his prints. A wonderful little Cezanne nowadays belongs to Jasper Johns, which makes me think that life is unfair. There are two good Gauguins and an ugly, mad Van Gogh which you wouldn't have thought would fit with Degas's taste.

! 'Degas: Beyond Impressionism': National Gallery, WC2 (0171 747 2885), to 26 Aug; pounds 5 (pounds 3 concessions).