It may be impossible to define outsider art adequately, but I'll try. It is eccentric, engaging, and often apocalyptic. It stands outside the standard schools and movements, and is produced by artists who are usually self-taught and often judged insane. It includes some of the most compelling, disturbing, and/or simply strange painting, sculpture, and even literature and music being produced today. Like pornography, I know it when I see it; and like pornography, its boundaries are hard to locate.

Joe Coleman has just hit one of those boundaries. Whatever outsider art might be, Coleman is one of its biggest stars, with vivid paintings of riots, demons, serial killers, and sideshow geeks, all rendered in an instantly recognizable style. His 1996 painting Faith does not merely include a scantily clad woman with a crucifix around her neck saying Come here, you bad boy above the caption Mommy says: Come visit me in Heaven. It puts her in a tableaux that also includes internal organs, Hindu deities, Richard Speck, and—surrounded by all that and much else—Coleman himself, his skull exposed, an armless clock in the center of his face.

Yet New York's annual Outsider Art Fair, which flirted with barring Coleman's paintings last year, has decided not to include him when it reopens its doors next month. The chief problem, says co-director Caroline Kerrigan, is that Coleman has been to art school, thus removing him from the ranks of the self-taught. "This is a fair for outsider artists," she says. "We feel his art would be more appropriate in a contemporary fair." Coleman claims that money is the real issue: When the organizers excluded him, he asserts, they described him as "too aware of the whole business process of selling" his work. "They seem to want to promote an art in which they're dealing with people who are either emotionally or physically incapable of protecting themselves," he complains. "Or dead."

It does seem strange that the Outsider Art Fair, which has shown Coleman's work since 1997, would choose to exclude him now. It's not as though it only just learned that the painter attended the New York School of the Visual Arts, and it's not as though he's the only artist at the fair with such a background. One, Alex Grey, actually teaches art. That's a far cry from Coleman, who was tossed out of school and happy to be on his way. "I didn't learn anything in art school," he says. "You don't learn to do the kind of work that I do in art school. When I was there they were very much into minimalism, and they felt that figurative work was illustration, not art. They were painting over my paintings."

Suspicious motives don't negate the fair's right to deal with whichever people it pleases. Coleman will survive whether or not his work appears at this particular venue, and the venue will survive whether or not its patrons have to go elsewhere to find one past participant's paintings. The conflict is important for a different reason: because it exposes certain assumptions about "primitive" art. One reason outsider art is increasingly popular is because it seems so unmediated, as though it tumbled directly from the creator's mind onto the canvas. The discovery that the creator actually guided its fall with some skills—skills, worse yet, that he deliberately honed—can feel like a betrayal, at least for those who've romanticized the artist as an untutored primitive without any self-awareness.

During the postwar folk-music revival, rural musicians faced a similar mixture of adulation and condescension: For many middle-class whites, they were mediums tuned to the soul of the American people, not creative individuals drawing on but adding to the traditions of the past. At times, such disrespect opened the door to behavior not unlike the exploitation that Coleman accuses the art fair of perpetuating today. Song collectors like the late Alan Lomax would copyright their "discoveries" in their own name, collecting royalties for songs he neither composed nor played.

Even as the myth of the collective folk machine receded and individual creators received their due, another misconception remained. Musical forms like bluegrass—a pop form created in a completely commercial context, just a few years before the folk revival began—were regarded as older, purer, and somehow unsullied by commerce. As bluegrass performers migrated from the country market to the folk one–a distinction that didn't really exist until the McCarthy era–its practitioners adapted to the new audience's expectations. John W. Rumble illustrated the point nicely in an essay on the mandolinist Bill Monroe: "most folkies knew little of his tent show years or his ties to minstrelsy, medicine shows, and vaudeville. Awed by his natural country dignity, they didn't stop to think that his first two radio sponsors were laxative companies."

Unlike Coleman, I'm painting with a broad brush. There were plenty of listeners who understood that folk musicians were hard-working creators as well as emissaries from the underclass, and plenty who understood they were commercial entertainers as well as artists. And there are many critics and curators today who believe the former to be true, and the latter potentially true, of outsider artists. Joe Coleman may be schooled, but he has never let any school define, contain, or even seriously influence his work. He may take an interest in his paintings' sales, but he has never been known to moderate his vision for the sake of its salability. For most people, that's enough, which is why Coleman is a star of the outsider-art world.

Others, obviously, have a narrower definition. As is often the case with artistic categories, it reveals more about the categorizer than about the art.