The story of Dr. Paul-Ferdinand Gachet (1828-1909) is a great art-world tale. Friend to Pissarro, van Gogh and Cézanne, he could swap his homeopathic remedies for examples of their work. (More doctors should be art collectors!) In his youth, Gachet hung out in Paris cafes with Courbet, Manet and Baudelaire. In 1872 he moved to the village of Auvers-sur-Oise, where his neighbor Pissarro introduced him to Cézanne and Armand Guillamin. He met Monet, Renoir and scores of others less known today.

Gachet was there when Cézanne sneered at Manet's masterful Olympia and dashed off his own version, A Modern Olympia (Sketch), saying it was "mere child's play." Gachet snatched it up and later lent it to the 1874 Impressionist exhibition, entering history as one of the first fans of the great proto-modernist.

Gachet tended Van Gogh in his last days, and even made several death-bed drawings of the artist. In the 1980s art boom, it was van Gogh's Portrait of Dr. Gachet that sold at auction for a record $82.5 million. Who says history doesn't have a sense of poetry?

But the tale doesn't end with Gachet's death in 1909. For the next 40 years, the Gachet collection was kept hidden away by his daughter Marguerite (1869-1949) and son Paul (1873-1962), a reclusive scholar who spent most of his adult life writing a history of van Gogh's 70 super-productive days at Auvers. After Marguerite passed away, the collection eventually ended up in the Musée d'Orsay.

But there were further complications. Both Gachet père et fils were ardent amateur painters and copyists. For a time, the elder Gachet (who showed his paintings as Paul van Ryssel) worked side by side with Pissarro, Guillaumin and Cézanne in the attic of his Auvers house. In 1956, Gachet fils boasted of his close study of works in the family collection, "copying them so well that I dare write here, and for the first time, that without classes or lessons, I am at heart and soul, Paul Cézanne's student."

What's more, the good doctor had early on conceived a plan to publish a book on van Gogh, and enlisted several people to make copies of his work -- notably Blanche Derousse, the seamstress-daughter of a neighbor. She is responsible, for instance, for a copy of van Gogh's 1889 Self-Portrait -- in watercolor.

As a result, no one is quite sure who made some of the Gachet pictures. Especially since van Gogh seems to have made a few copies of his work himself. Even more interesting is the degree of difficulty, in our postmodernist age, of establishing esthetic superiority for some of these originals.

The exhibition, which premiered at the Grand Palais in Paris and will travel to the Van Gogh Museum in Amsterdam, contains some 130 items in all. It has to be the most free-wheeling show the Met has ever mounted. In addition to a handful of historical novelties like van Gogh's palette, a still-life pot that Cézanne painted and even the famous white sailor hat Gachet wore in that multimillion-dollar portrait, it features works in questionable condition, of uncertain quality and dubious authenticity. It looks like this stuff was stashed away for 50 years.

And everywhere, original is posted next to contemporaneous copy. Sometimes the copy is wretched. Sometimes it's scary close.

That's what makes the show so fascinating. There's way too many versions of a Cézanne green apple. There's a wall of 14 watercolor copies of van Gogh works by Derousse that have to be seen to be believed. There's a Renoir portrait of a girl with a patch of skin on her nose that looks like it was painted by Lucien Freud. There's Pissarros and Guillamins that look crappy -- but that's the way their stuff is half the time. And there's a great 1879 Cézanne still life, called The Accessories of Cezanne, from the period when the artist still favored gummy paint texture and lots of black. It was done on cardboard and probably would have fallen apart if Gachet hadn't been such a fan.

There's lots more. Go see for yourself. You'll be a postmodernist yet.