Cliches are strange beasts. They can dominate thinking about a subject, but they almost never get probed as deeply as a novel idea. One hoary cliche of art history explains the origins of impressionism. That artistic movement, the legend goes, had British landscapist J.M.W. Turner as its Methuselah in the early 19th century. He begat American artist James McNeill Whistler in the 1860s, who begat French painter Claude Monet, whose "impressions" of nature finally gave the Parisian movement its name in the 1870s.

This cliche is finally being put under the microscope in an international loan exhibition called "Turner, Whistler, Monet." The show, which has been drawing huge crowds, was initiated by the Art Gallery of Ontario in Toronto and then co-organized in London by the Tate and in Paris by the Musee d'Orsay and the consortium of national museums of France. The exhibition wraps up in Toronto on Sept. 12, heads to Paris in October and moves to London in February. It includes 100 pictures, borrowed from 34 public and private collections on both sides of the Atlantic.

"Turner, Whistler, Monet" doesn't exactly confirm impressionism's hallowed Genesis myth, since it turns out that hard evidence of influence -- who saw what, where and when -- is hard to come by. But it doesn't quite explode the myth, either: Though museums around the world contain plenty of pictures by Whistler and Monet that have nothing Turnerian about them, this show suggests moments of shared sensibility among the three artists. (Some cases of particularly close parallels, however, involve pictures by Turner that Whistler or Monet could never have seen.) But to my eye, the most important thing the exhibition proves is that the cliche has got things backward: It was Monet and Whistler who "influenced" Turner -- though they were still kids when the British painter died in 1851.

Our Turner, the painter of vaporous, impressionist-y skies and water whom we know and love, was born only after Whistler and the French impressionists had finally hit it big. Turner's most misty paintings, sometimes so blurred that the pink and yellow skyscapes in them read as pure abstraction, started to claim museum space in London in 1906, three years after Whistler's death and toward the end of Monet's career. (The Frenchman died 20 years later, at age 86, but made his last visit to England in 1904.) In Turner's own day, and for several decades afterward, those pictures had been largely dismissed as unfinished studies not worth serious contemplation. The handful that came on public view at all were billed as useful teaching aids that showed the steps Turner took on the way to his highly finished works.

Late in his career, Turner exhibited works that included areas -- but only areas -- of wild blurring and proto-impressionist effects. And he was reviled for that "insane" sloppiness by critics on both sides of the English Channel. The powerful art critic John Ruskin, Turner's committed champion, either ignored the radicalism of Turner's wildest late moments, or found a way to bill it as a preternaturally accurate way of capturing extreme effects of light and weather, and the emotional response they cause in us.

That ultraconservative critic managed, that is, to present Turner's willful novelty as a natural next step in the history of traditional realistic picture-making. It's no wonder that both Whistler and Monet denied strong links to Turner, and sometimes spoke out against his work -- or that Ruskin himself should have lashed out against the new artists. Both Turner and Ruskin represented a past from which the younger men imagined they had made a clean break.

The Turners that Whistler and Monet would have had easy access to during their stays in England -- Monet first visited in 1870, after his impressionistic style was already underway and before he'd seen any Turners at all -- mostly fit the conservative interpretation that Ruskin always had of his hero.

"Mortlake Terrace," a picture from the National Gallery in Washington that was first exhibited in 1827, is a relatively standard, highly finished canvas in the Dutch and French Old Master traditions, except for an innovative patch of setting sun dead center in the frame. "I too have seen beside the Thames these remarkable effects of the conflict of sun and fog and dust," wrote one prominent French critic, after seeing it in an 1857 show that Whistler also visited.

Most of the other Turners that were well known and well loved in the 1850s and '60s would have sat comfortably with this kind of naturalistic interpretation. The current exhibition tends to fudge this fact, however, by choosing to show Turners that are more extreme than would have been the norm in the early days of Whistler and Monet. In place of the finished watercolors that were in wide circulation, the show privileges the raw, "impressionistic" studies for them that only a few art students had any access to.

There's also a wildly eccentric, awkward oil painting of Napoleon in exile on St. Helena that, as the novelist William Makepeace Thackeray quipped, might have much the same effect hung upside-down. And the show includes several explicitly unfinished canvases taken from Turner's studio after his death; they didn't get a public showing until the 1880s or even later, after Turner had already been roped in as impressionism's illustrious forerunner.

To a modern audience reared on Monet and Rothko, these flashy, brushy Turners are patently exquisite pictures, abstracting nature down to her most impressive moments of color and light. But they aren't necessarily what would have counted as Turner to two young artists looking for something new to say in the 1860s.

The paintings Whistler made in London in the early 1860s -- when the suggestible young American ought to have had his most important contacts with Turner's art -- present a relatively standard, highly finished surface, but with a novel social realism Whistler had picked up from the avant-garde while studying in France. An ambitious picture called "Wapping," again on loan from our own National Gallery, shows the seedy side of life along one of the roughest stretches of London's Wapping docks, complete with hooker, john and pimp. But rather than a casual, snapshot glimpse of found reality, Whistler's picture, painted and repainted between 1860 and 1864, is a carefully calculated and constructed fiction. His friends posed as the riffraff in the picture; the river scene behind is built up from many different observations of the shipping on the Thames, brought together according to a complex and rigorous compositional geometry.

This hard-nosed Whistler is, in fact, the revelation of this exhibition. All the critics and artists and art lovers whom I've spoken to about the show came away finding the American more interesting than they had ever imagined.

Whistler has always had a reputation as a dandified aesthete, more caught up with superficial grace and charm than with the toughest issues of art making. But the pictures on display in "Turner, Whistler, Monet" showed how the strong bones of early realist paintings like "Wapping," or of the etchings of the Thames that came at the same time, sit under the pretty skin of his later works. The gray washes of Whistler's moonlit "nocturnes" now seem more like spare minimalism, built around the scaffold of a modernist grid, than like the pretty wallpaper many used to see in them. They feel less like the delicate Chopin nocturnes that gave them their name than like the full-blown sonatas of Johannes Brahms, whose pleasing melodies are always backed up by substantial structure.

It's Monet who sometimes comes off as the decorative one in this exhibition.

Turner had used veils and flashes of attractive paint to render moments of sublime light and atmosphere in nature; even in the unfinished Turners where nature can barely be made out, the natural sublimity remains. Monet, on the other hand, often uses broken splotches of paint -- very different from Turner's -- all across the surface of his pictures, almost regardless of subject matter.

There is real daring in Monet's willingness to make this modern move: His pictures are as much about interesting illegibility as convincing illustration; they're about unlearning the great traditions of illusionistic oil painting, rather than perfecting them. This sets him off from the Old Master-ish tradition that Turner was still working in, and which underlies Whistler even at his most pared-down. But it also risks turning his art into a series of bravura displays of brushwork and color.

Turner's "impressions" of nature come off as more convincing than Monet's official impressionism.

Turner is about light and atmosphere, evoked through a complex, varied, sometimes radical technique. With Monet, there's a sense that sunsets and foul weather are used as an excuse for effects of surface and palette that, in his own day, would have seemed shockingly unnatural and avant-garde. I'd argue that the impenetrable London smogs that Monet liked to paint aren't really the subject of his pictures, which look more fractured and prismatic than foggy and veiled. Instead, those smogs act as a metaphor for the modernist obscurity his paintings asked his first viewers to wade through.

One of Turner's most flamboyant later pictures, the 1834 "Burning of the Houses of Lords and Commons" now owned by the Philadelphia Museum of Art, uses frantic passages of red and yellow paint to conjure up a building in flames, and contrasts those moments to calmer brushwork elsewhere in the scene. The Toronto exhibition pairs and compares that picture -- which Monet almost certainly never saw, and which Whistler at best might have glimpsed at his dealer's in 1873 -- with several of Monet's 1904 pictures of the newly rebuilt Houses of Parliament. The pairing makes Monet's landscapes come off as decorative arabesques, only incidentally linked to the subject they represent.

Turner's picture captures the look and feel of a conflagration, with flames leaping from the ground into the air. This time, it's Monet's view that would mean almost as much turned on its head. It doesn't present an "impression" of the real-world scene, so much as a distant derivation from it.

It's not clear that Whistler or Monet needed Turner's example to get where they were going. As they insisted, and this show demonstrates, their goals were different from the Englishman's -- sometimes even opposed to his -- and you can see them heading there before they would have known his work, and in pictures that have nothing in common with what he made. Turner, however, could not be the painter that we now see him to be without Whistler and Monet.

"Turner, Whistler, Monet" is at the Art Gallery of Ontario in Toronto through Sept. 12. It then runs at the Grand Palais in Paris Oct. 12 through Jan. 17, and at the Tate Britain in London Feb. 10 through May 15.

J.M.W. Turner's "The Dogano, San Giorgio, Citella from the Steps of the Europa": Abstracting nature down to her most impressive moments of color and light.J.M.W. Turner's "The Burning of the Houses of Lords and Commons": Frantic passages of red and yellow paint conjure up a building in flames. The show includes Monet's "San Giorgio Maggiore at Dusk," above, and Whistler's "Nocturne in Blue and Silver: The Lagoon, Venice."