How does an essay differ from pornography or a country song?

Justice Potter Stewart said he couldn't define pornography but knew it when he saw it; Kris Kristofferson couldn't define a country song but knew one when he heard it. But nobody, it seems, knows what essays are supposed to look, sound or feel like - and many readers don't recognize one when they read it.Literature professors around the country are hailing the "return of the serious essay," but not many are going into print with a workable definition. Do Dave Barry's newspaper columns qualify as essays? Robert Fulghum's warm meditations on kindergarten? How about Connie Chung's pithy TV editorials?

"If it's short and it's non-fiction, we usually shelve it under essays," explains Betsy Burton of the King's English bookstore. "Whatever essays are, they do sell well. We sell as much E.B. White as anything else in the store. Nature essays are really popular. And people seem very interested in political and humorous essays these days."

Indeed, the market for essays is much greater than the market for poems and fiction. Most magazines, quarterlies and newspapers will accept an essay for publication but they don't always take poetry. And essays pay better. Reader's Digest will pay as much as $3,000 for nifty little ruminations.

Besides, many writers feel that essays can cover more territory in more ways than any other form of writing.

"When I write essays I try to corral the whole world," says Elouise Bell, a professor at Brigham Young University. Bell's collection of newspaper columns, "Only When I Laugh," recently won the "best essays" award from the Association of Mormon Letters.

"I do consider many of my columns essays," she says, "though some are a little looser and don't have the substance of an essay. I think of those as `thumbnail recommendations.' "

Bell names E.B. White and Ellen Goodman as two of her favorite essayists. She also acknowledges there's a problem in knowing what is an essay and what isn't.

"I had a friend who got a letter back from a magazine," she says. "The editor loved what she'd written but asked `Is this a short story or an essay? Our magazine only publishes short stories.' So my friend wrote back and said `Of course it's a short story,' even though the piece had won a local essay competition."

One of the most successful essayists of our time, naturalist Wendell Berry, seems to enjoy blurring the distinctions. Often his novels have more to teach and a more political point of view than his expository writing. As the late John Gardner said of Saul Bellow's novels, "His success lies in writing long essays and calling them novels."

At times our "genre blindness" -as William Gass calls it - keeps us from seeing the poetry in short stories and the essay inside a poem.

Still, the pure, non-fiction essay offers writers a chance to be a witness to their lives and times that can't always be had in fiction.

Ken Brewer, a poet and professorat Utah State University, has been turning away from poetry and more to the essay for such reasons.

"I still write poems, but there's something liberating about the essay that I used to feel about poetry but don't anymore," he says. "I see the essay as a warm, human expression between the writer and the audience. I think that's part of the appeal, why so many of us are turning to it. I feel I speak to my audience more effectively in essays. The essay doesn't have that external structure that a poem has.

"In my opinion the essay is the hottest genre in the country. Some of our best writers are writing them: William Kittredge, Edward Hoagland, Joan Didion, Carol Bly. There are quite a number of essayists today."

For readers interested in "getting their feet wet" as essay readers, a good place to start are the classic examples of the form found in Samuel Pepys and Michel Montaigne.

More contemporary versions can be had in Norman Mailer's "Existential Errands," the immortal E.B. White, Nancy Mairs, Pauline Kael and collections of newspaper columns by George F. Will, Mike Royko, Russell Baker and Erma Bombeck.

On the regional level you might want to try Ed Lueders' "Clam Lake Papers," "Goodbye to Poplar Haven" by Ed Geary and the religious insights found in "Mormon Women Speak," "Dialogues with Myself" by Eugene England, and the various collections of essays by Lowell Bennion, Neal A. Maxwell and Emma Lou Thayne.

And then, of course, there's the man that many consider the "dean of essays," V.S. Pritchett. Pritchett has brought out eight collections of essays over the years - most of them on literary topics. Now, at age 90, he has published "Lasting Impressions," his ninth.

"He's a very unpretentious writer," says Nye Thuesen, a Pritchett admirer who works at Zion Book. "There's nothing flamboyant in his work, but every opinion he presents in his essays seems to come right from heart. I think he's one of the major writers of our time."

And as appreciation and interest in the essay go up, Pritchett's stock will only rise.