Claude Monet, Grand Palais, Paris

Describing any work as the centrepiece of a show of nearly 200 works is always risky, particularly when that work isn’t even in the show; all the more so when it isn’t by the show’s subject. Nonetheless, Edouard Manet’s absent Déjeuner sur l’herbe is at the heart of a new exhibition at the Grand Palais, which is strange, given that the exhibition is called Claude Monet.

In 1863, Manet painted his infamous picnic, posing his brother and brother-in-law as Baudelairean dandies and eliding his favourite model and long-suffering wife into the lady with whom they lunch. That this lady is naked as a jaybird made the picture an immediate succès de scandale, as Manet had known it would. This annoyed his younger rival, Monet, mightily. In 1865, he set about painting his own Déjeuner sur l’herbe, meant to outdo Manet without the dirty tricks. Not only was Monet’s six-metre wide Luncheon on the Grass to be much bigger than Manet’s, it was to be more ambitious – six ladies to Manet’s two, all of them fashionably clothed, with Courbet as a model to boot. With its vast scale, Monet’s picture would bring the traditions of history painting to the painting of everyday life, making it genuinely revolutionary in a way that Manet’s was not. And to cap it all, the work would be done out of doors, en plein air, this immediacy putting it in the vanguard of a new style which, seven years later, would be dubbed “Impressionism”.

It bombed. Faced with the realities of lugging a vast canvas around French woods, Monet got no further with his Déjeuner sur l’herbe than the unfinished, quarter-size study now on loan from the Pushkin Museum. Given this difficulty, one of the surprising things about the work is how finished it is, every detail – leaves, buttons, bits of bark – rendered with a completeness already unfashionable by the 1860s and unusual for Monet. You feel that his starting point is a defiance of Manet's bravura brushwork, the older man's taste for the open mark of Goya. Setting out to paint a picture which defines itself as not being by someone else is seldom a good idea.

The subsequent story of the two works sums up the respective local histories of their makers. While Manet's picnic has pride of place in the Musée d'Orsay, Monet's hangs in a back room in Moscow. And while Manet has been the subject of countless exhibitions in France, this is the first full-scale monograph show Monet has had there for 30 years. As you'd guess, the point is to change the way he is thought of in France – roughly, good enough for Americans but too vapid for the French – while luring 700,000 visitors through the Grand Palais' doors. The d'Orsay sketch-fragments of Déjeuner sur l'herbe are given most of one wall of a long, curved gallery, the Pushkin study its own partition opposite. This, the hang says, is serious stuff, easily the equal of Manet.

The show's five – five! – curators have additionally trawled collections in 14 countries for its 170-odd works, which could be off-putting. Blockbusters kill. With Monet, though, enormity makes sense. Part of the plan is to present us with an all-new artist, the one who painted the Chardin-like Still Life with Melon in the same year – 1872 – as the picture that gave Impressionism its name, Impression, soleil levant. (This is not in the Grand Palais show, a curmudgeonly Musée Marmottan having refused to lend it.)

Many of the works are shockingly un-Monet-like, and, coming from private collections, normally hard to get sight of. But it is the repetition of those familiar Monet images – the façades of Rouen Cathedral, the haystacks and water-lilies – that really hits home in this magisterial show.

For Monet, history – and, ergo, history painting – was made up not of single events set in stone but of an endless succession of fleeting moments, each unique. It is why he came back to haystacks again and again, often from the same angle but at different times of day or year. Seeing five Cathédrale de Rouen or identical views of the Thames is an extraordinary experience, and probably an unrepeatable one: the Grand Palais' curators may not have prised Impression, Sunrise out of the Marmottan, but they have managed to borrow such historic unborrowables as the Metropolitan Museum's Terrace at Sainte-Adresse. Like all exhibitions, this one has its tics and flaws. Why throw in Roy Lichtenstein's homages to Monet as proof of his modernity when the pair of weeping willows the old man painted in the 1920s look so like Jackson Pollocks? But it is a magnificent show for all that. Book now and go.

Grand Palais, Paris (+33 1 44 13 17 17) to 24 Jan 2011

Next Week:

Charles Darwent goes Post-Impressionist with Gauguin: Maker of Myth at Tate Modern