Mother of all aesthetes: Andrew Graham-Dixon finds James McNeill Whistler, archetypal dandy and art-for-art's sake aesthete, too tasteful for his own good

Ruskin's rather too famous attack on Whistler for, as he put it, 'flinging a pot of paint in the public's face', is an insult which can easily be turned into a compliment. How bravely and aggressively modern it makes Whistler sound - and that, rather than its presumed philistinism, is what is really wrong with the remark. It is an indictment that credits Whistler with a recklessness and an abandon which he never actually possessed (and which would have made him a more considerable painter). Whistler did not fling.

Whistler arranged.

The most famous of his 'arrangements' may also be the most revealing of his pictures because it is the only one in which he confronted his own most pronounced emotional characteristics as an artist: a profound and slightly debilitating fear of things, a wary distrust of the world, of life and light and colour, which both made him who he was and held him back all his life.

He called it Arrangement in Grey and Black, but the world now knows it as 'Whistler's Mother' and it is currently to be found at the centre of the Tate Gallery's beautiful, exemplary but in the end somewhat dispiriting retrospective of this intriguing artist's work.

The most common misreading of Whistler's best-known picture assumes it to reveal a gap between the painter - the sophisticate and aesthete, the art-for- art's-sake dandy - and his plain old homespun Ma. In fact it demonstrates a secret alliance between mother and son, and there may also be a sad and accurate prophecy locked up in the demonstration. Whistler would never quite release himself from the attitudes of the woman who gave birth to him. This tired (but alert) and deeply Protestant old lady is not only the mother of Whistler but of almost all that he did. She is not a merely quaint misfit affectionately included in his elegant world, she is its only begetter.

Whistler's eternal preference for low tones, his love of monochrome effects, are seen to have been foreordained in her stern and puritanical dress sense; his nervous, guilty asceticism to have been predicted in her similarly black-and- white resolve not to enjoy anything too much. Even his reserve and his silence, so much the hallmarks of his mature painting, are shown to have had their origins in her. Whistler was interestingly irritated by those who persisted in seeing Arrangement in Grey and Black as the depiction of a person rather than as a pleasing disposition of forms. 'What can or ought the public to care about the identity of the portrait?' he exclaimed, protesting a little too much. Perhaps he found his own picture a little too painfully confessional for comfort.

Whistler remains an enigmatic artist partly because it is so difficult to get to the heart of him - to separate his experiments, with any great degree of confidence, from the works in which he seems most completely himself. The impression given by the Tate's retrospective is, time and again, of an undeniably gifted draughtsman, painter and etcher reluctant to settle to anything for long enough to make it his own. This almost certainly reflects the great difficulty Whistler had in establishing his identity as an artist, which may have been partly the product of his unusually peripatetic early life. He was born in a manufacturing town in Massachusetts, a fact of which he was always rather genteelly ashamed. He first studied art in St Petersburg, where his father worked for a time as a railway engineer; he later moved to Paris where he was a pupil of the minor academic painter Charles Gleyre; and at 25 he went to London where he spent most of the rest of his life. Whistler is an artist who still seems forever caught between things: not really a French painter, not altogether English, somewhat but by no means entirely American. This could have been a strength but it became a weakness.

A contemporary and acquaintance of both Manet and Degas, the young Whistler is conventionally credited with having introduced the British to the new and powerful realism of early modern art in France. What is most striking about the earlier pictures at the Tate is their curious impassivity in the face of what they record. Whistler, an astute observer of the painting of his time, clearly understood as Degas did the tremendous originality and power of Manet's cropped and often almost accidental-seeming habits of composition.

His early etchings of Paris and London have precisely that glancing, snapshot quality which would produce so much of the most extraordinary art of the early modern period - that sense of the city as a disconcerting patchwork of lives being lived, in every corner, too intensely to be ignored and too variously to be comprehended. But somehow Whistler's etchings of unsafe tenement buildings and their occupants, of grim meals eaten in grubby cafes, of backstreet or dockland low-life seem more historically significant than morally or emotionally engaging.

Manet and Degas were never sentimental, but they painted the fragmented urban world of their times like men who were genuinely affected by the mysterious lives of those among whom they moved. Whistler seems indifferent, and perhaps that is what the oddest of all his paintings in the urban realist vein, Wapping, betrays. He paints the face of the prostitute, lost in her thoughts while her two male companions talk on, as a blur of boredom and depression. But he does not seem truly concerned by her predicament; there is, if anything, something fatally vague about his rendering of her.

Most of the painting is no more than an excuse to linger, with a naturalism that is just as effete as it is attentive, on criss-crossed rigging and creamy sailcloth and all the rest of the dockside's picturesque paraphernalia.

Perhaps to say this is to say no more than what everyone already knows about Whistler, namely that he was an aesthete. He insisted on the fact himself, and the Tate's exhibition demonstrates how quickly he moved away from the painting of the real lives of real people - as if to confirm that he knew he was temperamentally unsuited to their depiction. Whistler, who never could bear too much reality, was much more comfortable painting people as disembodied ghosts, and his most characteristic portraits are The White Girl and The Little White Girl, those spectres in wedding dresses dreamily regretting lost love and lost virginity. The former once looked radical enough for it to be hung next to Manet's Dejeuner sur l'Herbe (at the 1863 Salon des Refuses). But now we can see that Whistler's white girl is really just a Greuze girl in Aesthetic disguise, her vanished maidenhood symbolised by fallen flowers instead of a broken pitcher. The fact that Whistler probably meant the reference as a joke (the white girl of the picture was his mistress, Joanna Hiffernan) makes the picture, if anything, even worse.

Perhaps the uneasy mixture of aestheticism and genre painting in The White Girl begins to get to the bottom of what was wrong with Whistler - not that he became an aesthete, exactly, but that he did not become an extreme enough one. His greatest failing as an artist was that he did not pursue far enough any of the various directions he took during his life. He was forever complicating and diluting things and he never (or only very, very rarely) cut loose and dared to invent a kind of painting that was entirely his own.

In fact, he did it only once, during the relatively short period which saw the creation of his most nearly abstract Nocturnes.

These are hung, asymmetrically, with loving spareness at the Tate - this is the most daringly and effectively displayed exhibition I have ever seen at the museum, for which much of the credit must go to its co-curator, Richard Dorment - and they are certainly Whistler's monument. Gradually, he purifies these pictures of symbolical distractions (ships of life and the like) and irritatingly hamfisted japonismes, to achieve a form of painting which is genuinely original and which begins to feel compelled, shaped for the first time by some kind of pressing internal necessity. Dark, imposing shapes loom up out of blue or emerald depths, lights twinkle in the fog and the world, purged of people, turns nearly abstract. The pictures also begin to achieve, at last, an unembarrassed sensual character, a melting, trembling, dark-toned liquidity.

Then, inexplicably, Whistler stops painting these pictures and reverts to being a less than convincing jack-of-all- trades. He paints tasteful parodies of a lot of other painters' work and indeed of his own. He creates some magnificent, completely decisive decorative designs - although his best work in this vein, for Aubrey House, and for the Peacock Room, coincides with the Nocturnes - but as a painter he is really finished. The last room in the exhibition, in which his attempts to revive English grand manner portraiture produce a series of terminally dull and laboured pictures, seems almost desperate: a sad and painful fade to black.

Why Whistler should have stopped painting his most interesting pictures just when they had become most interesting is a mystery that can never be solved.

Perhaps the answer lies partly in their very subject matter. Fog could become Whistler's preoccupation because he was always too nervous to look at the world straight on. He could paint screens of mist and vapour with the rapture that can be sensed in the handful of his best Nocturnes precisely because they were screens between Whistler and things. But once his preoccupation became an obsession, it seems he felt compelled to abandon it.

We cannot know what made him live his life in such strong and almost continual fear. I think his mother probably knew. But of course it is only a theory.

(Photograph omitted)