Claude Monet, Grand Palais, Paris

    Monet. A powerful name. For the organisers of exhibitions, it spells money and huge crowds of enthusiastic visitors. Everybody loves Monet and will queue around the block to encounter him. For President Sarkozy, I see, it offers a chance to bask in spurious reflected glory. In real life, had Sarkozy turned up at Giverny, Monet the radical would have sent him packing with a swift boot to the pants and a gruff bellow of “Vive les gitans!”. In the false world of political spin, though, the newest Napoleon in Paris is oleaginously keen to reclaim him for the state and to blather on in catalogues about Monet being “an unmistakable emblem of the international influence of French culture”. Oui, monsieur le Président. Léchez mon cul.

    For the serious art-lover, for those of you who still believe that art is a barometer of civilisation, not a publicity tool, and that the best art tattoos itself indelibly in the imagination, Monet’s contribution remains strangely indistinct. Show me an art-lover who is certain of Monet and I will show you a crazy optimist. Yes, he was a pioneering impressionist who loved water and lilies, cathedrals and haystacks. Yes, other painters invariably acknowledge him to have been the possessor of the supreme painter’s eye. But what he actually set out to see with that great eye is endlessly debatable, and has, indeed, been endlessly debated. Monet’s final worth is as hard to discern as dappled light on a lily pond.

    All of which is a roundabout way of saying that the time is right for a full Monet retrospective. How marvellous that the Grand Palais, in Paris, has given us one. It’s a superior whopper of a show, too, the largest collection of significant Monets gathered under one roof, the first comprehensive Monet exhibition in France for 30 years, the most eagerly awaited art event in Europe this autumn. You’d be silly to miss it.

    The show sets out to understand Monet’s achievements in a new way.

    Perversely, his problem has always been his close association with impressionism — it’s too close. Ever since he took part in the first impressionist exhibition of 1874, and his much mocked view of Le Havre at dawn, Impression, Sunrise, accidentally gave its name to the most revolutionary ism of them all, it has been Monet’s fate to be understood as the quintessential impressionist. Which is fine when he is one, but not when he isn’t. Which turns out to be most of the time.

    If you actually count the “typical” impressionist views on show here, you will find ridiculously few.

    Of the 200 or so pictures in the Grand Palais’s Monet extravaganza, only a few dozen would look perfectly at home on a chocolate box. The rest roam hither and thither in mood and angle, location and viewpoint, indoors and out, from still lifes to portraits, from dark, belching studies of trains puffing out of Paris in the winter to ecstatic colour fests recording the sizzle of summer in Algeria. As Gainsborough once complained of Reynolds: “Damn him, how various he is.”

    The trouble with being seen as the ultimate impressionist is that observers of your work invariably assume that your ambitions extend only to looking. It makes some sense when Monet is painting, say, shimmering, sun-drenched views of boaters on the Seine, or parasoled ladies in floaty dresses flitting through poppy fields like cabbage whites. These are paintings that weigh little more than an Aero and delight in lightness.

    How, though, does a harrowing close-up of his wife, Camille, distorted with expressionist terror on her deathbed, fit in? Or the Ibsenesque interiors that loom up halfway round the journey, in which gloomy family members gather around twilit dinner tables and listen to the tick-tock-tick of the clock? When did Monet turn into Munch?

    At birth, it would seem. His innocent eye was never actually innocent. By sticking to a rough chronology, the show allows us to recognise strange developments in one of the longest and most momentous careers in art. Monet’s six decades of relentless invention begin with some quiet trees painted in the forest of Fontainebleau when he was in his twenties and end with a suite of shimmering water lilies that obsessed him in his eighties. His journey spans the changeover from the 19th century to the 20th. It has about it a natural heft. In big-picture terms, it took us from the past to the modern age.

    Sadly, Impression, Sunrise is not involved in the rethink. The Musée Marmottan was reluctant to lend it. Even if it had been here, though, it would not have affected the transparent desire of this superior retrospective to place Monet the impressionist in a pen of his own, then surround him with a much bigger Monet: a poet, not a realist; a dreamer, not a witness; a heart, not an eye.

    Cleverly, the show keeps darting sideways into lively thematic detours. Just as the Seine seems to do an awful lot of winding as it flows from Paris, where Monet was born in 1840, to Le Havre, where he grew up, so the Grand Palais’s life of Monet keeps finding excellent reasons to dawdle and digress.

    One particularly foggy cluster sees him staggering about the Gare St Lazare in 1877, trying to paint the smoke belching out of a train shed full of steam engines. Monet, I read, bribed the station master to hold back all the trains from their onward journeys and to cram them instead into a single shed, where their puffing could grow jointly apocalyptic.

    Clearly, he was influenced here by Turner, whom he encountered in England in 1870, having fled to London to escape the invading Prussians. In fact, England played an unexpectedly key role in his progress. Another thematic detour takes us to a suite of foggy views of the Houses of Parliament, painted when the vapours were at their thickest from the window of his favourite hotel, the Savoy. Once you have seen these Turneresque fogs and glows of London arranged in spooky rows, the mystic ambition of Monet’s nearby haystacks, glowing in the evening sun, becomes unmissable.

    In a big coup, the show also brings together all the far-flung picnic scenes he painted in the 1860s, in which he set himself the fiendishly difficult task of painting direct sunlight as it falls on girls in white dresses and the big brown trees they sit under. It was an experiment in looking, and the resulting pictures don’t quite work, because the contrasts between sun and shadow that he provoked are so huge. But what superb ambition he shows, here and everywhere, digging a trench in the garden so that he could lower the life-sized Women in the Garden into it and paint the top of his picture, on location, without a ladder.

    As expected, water is a constant presence, as subject and challenge, but also as an intoxicant. In his most impressionist early moments, it is the shimmer of the Seine as the boaters glide over it on happy Sunday afternoons that enraptures him. A bigger chunk of the show, however, is spent by the sea, notably in a superb series of views of Etretat, in Normandy, where the ocean throws itself against the rocks with the recklessness of a suicide bomber.

    There is no tougher challenge in painting than the convincing capture of thrashing water, but Monet nails it by inventing a whole new set of squiggles and dashes to represent the swirls and bangs.

    For those who have seen too much impressionism on too many chocolate boxes to thrill at the thought of a Monet show, I recommend the following cure: get close. It is on the paint surface itself, in the marks he makes, the painterly risks he takes, that he is at his most revolutionary. Lean closer to the turbulent views of the sea at Etretat and you will find the invention of Van Gogh’s brushstrokes taking place a decade before Van Gogh. In the flooded rivers he painted in Vétheuil in the 1880s, his brush strokes for the summer are completely different from his brush strokes for winter, and his marks for water are different from his marks for land. An entire Oxford dictionary of new painterly expressions is being invented from scratch, with no let-up for peace or success.

    Because he is so ambitious, he remains, throughout his career, eminently capable of failure. There are plenty of Monet duds scattered about the museums of the world, and a fair few on show here, madcap over-reachings that seem too gaudy, too ripe, too kitsch. Has any painter ever produced this many glorious failures?

    Yet the chief ambition here — to out Monet as a poet who, even when he was at his most impressionist, was trying to capture what he felt as well as record what he saw — is achieved with conviction to spare. Every impression is shared here between the eyes and the heart. Once noticed, this desire to combine sight with thought explains everything and successfully unites the many strands of Monet. It’s as true of the quiet forest glades at the beginning of his journey as it is of the shimmering water-lily surfaces at its end.

    Will there ever be a better Monet show, or one that successfully rethinks this successful rethink? Not in my lifetime.