What constitutes art? What is its essence? Where does art begin and end? Answers, and questions, are suggested by a house, a collection, a book - the collaboration of many, the ensemble creation of one.

Light and the natural environment are catalysts in an alchemy that occurs on a hilly parcel in the posh reaches of New Jersey, where suburbia recedes and a long, low vista of hills and horizon wraps from one periphery to the other.

Up an incline and at the end of a route obscured by dark woods and meandering curves lies a house. More accurately, it is a monumental sculpture for living, a collection of massed rectangles interrupted by the occasional trapezoid. There are Constructivist echoes in its palette of graphite, persimmon, and buff.

Rising from its footing of fractured bedrock, the structure designed by four architects - Michael Rotondi and Clark Stevens of California, and Michael Brandes and Don Maselli of New Jersey - is of the earth, not at odds with it. Its challenging geometries initiate a dialogue with sky and soil that extends inside. There, light plays on a medley of well-honed materials and dances on a collection of folk sculpture, perhaps the best in private hands.

Time, they say, waits for no man. The owner of this house has at least found a way to harness time, to graph the trajectory of sun and moon the way the ancients did, against immobile stone and wood. Time travels across well-weathered ship's figureheads, weathervanes, decoys, and other carvings. Color and contour by day, the figures are stark silhouettes by night.

Day/night, light/dark, ancient/modern, formal/folk, masculine/feminine, vertical/horizontal. Polarity is the governing scheme. It establishes structure, defines limits. It is crayoned lines to be colored in. Contrasts set off reverberations within the house, whose essence architecture critic Paul Goldberger has described as a "combination of exactitude and ease..".

The collection is a meritocracy of talent, a congress of creativity from Diebenkorn to the anonymous creator of a tin figure of Uncle Sam. The collector's influences, from Bernini to Donald Judd, are many. His guiding principles are universal, classical, reductive.

In folk art's inner circles, the collection has been known longer than the collector. It is studded with icons: Captain Jinx, the transcendent carving of a Civil War soldier that stopped traffic at the Philadelphia Antiques Show; the long-billed curlew that Gary Guyette and Frank Schmidt auctioned in 1987, then again in 1997; the perfect nest of Nantucket baskets that sat in the sun on a folding table at a Portsmouth, N.H. tent sale in 1996.

It is important to know that the collector is a lover of film and opera, both directorial media. He is justifiably proud of the expertise he has marshalled in his professional life as a corporate consultant. Art and business have always been part of his life. Indeed, he views the three as one.

In selecting folk sculpture, he drew on the resources of many of the fields most illustrious dealers and collectors. In the final pages of Spiritually Moving, the catalogue to the collection, credit is given to Marna Anderson, Mickey Baten, Morry Cohen, David Davies, Frank Gaglio, Fred and Kathryn Giampietro, James Grievo, Tim and Pamela Hill, Bill and Jackie Holland, Allan Katz, Joel and Kate Kopp, Frank Maresca, Steve Miller, Judith and James Milne, Roger Ricco, Charles Santore, David Schorsch, Peter Tillou, and Don Walters and Mary Benisek.

The man who identified and assembled this talent was Harvey Kahn. An artist's agent from New Jersey, Kahn and his wife, Isobel, collected folk art even before they bought their Eighteenth Century home, Hessian House, in 1953. The Kahns are founding members of the Folk Art Society and unwavering supporters of the Museum of American Folk Art. Eight years ago, they were introduced to the collector.

Disarmingly casual and understated, Harvey Kahn possesses considerable aplomb. He is good at the well-placed remark, the humorous aside. Petite and elegant, Isobel Kahn has been wholeheartedly involved in their collecting pursuits.

Working with the collector has been a highlight of Harvey Kahn's long career. "It has combined all my abilities and knowledge," he says. "I brought 40 years of experience to this project. I got into collections that my client was proud to be looking at. Sometimes we walked out with one piece, or nothing. But we had entree."

Occasionally, the process required that the client live with a piece before he bought it. "He looks for something that grabs him, an inner feeling that he has that was developed from many years of collecting modern paintings. It has to work on his psyche."

Kahn explains, "I'd never before built a collection of this magnitude. I don't know if it could be done again. His doubts are echoed by Don Walters, who contributed an essay to Spiritually Moving. The Massachusetts dealer and former Colonial Williamsburg curator explains, "He began at a time when several important collections were turning over -Howard Feldman's, Bill Holland's. I'm not sure it could be done again. There's the irony of things not coming on the market until they reach a certain dollar value or level of public acceptance. In that sense, the collection is a statement of hope."

Like the collector, Kahn takes a connoisseur's approach to folk art. "I'm interested in its formal qualities. I couldn't care less what the people who made it were trying to say. I look at an object. It moves me or it doesn't. I can't get too involved in academics. It's the art I'm interested in."

Spiritually Moving takes its title from a list of qualities the client insists all objects he owns must have. Emotionality falls under the general heading of "passion." "It has to have a powerful presence, to be joyful or whimsical," elaborates Kahn. "Second, it has to be art. That is, it has to be beautiful, classic, be best of form, and, when possible, unique. A third criterion is that it have integrity. It has to be authentic and have great surface."

Such sweeping standards could, of course, be as easily applied to ancient glass or contemporary studio furniture. The collector says candidly that architectural limitations directed him to sculpture. He hadn't the wall space for paintings. Beyond that, he liked folk art's playfulness, and its relative affordability.

What do we really know about collectors and collecting? In its fullest expression, collecting is an obsessive pursuit; dedicated at the very least to excellence, if not perfection. At its finest, collecting is an artistic enterprise requiring discipline, creativity, discrimination, taste, and judgment. The best collections, like the best art, are original, opinionated, enlightening, influential.

"Every collection is an opportunity to reassess one's philosophy at that particular moment," observes Walters. "There is nothing frivolous about this collection. It avoids all the cliches of folk art that are perpetuated by the home decorating magazines. From my perspective, the collector has gone at it for all the right reasons."

Put another way, collecting is an act of strident self-assertion. As the recently appointed dean of the Yale School of Architecture, Robert A.M. Stern, observed, "To build anything, you have to think differently. It is fundamentally an arrogant act."

The house, the collection, and, finally, the book are the symphonic effort of one who sees life as a work of art in progress. No detail escapes his attention, every nuance is observed. Though the house was designed before the collection was begun, a lively dialogue has been struck between art and architecture, and among the objects themselves.

As with a painting or text of considerable depth, it takes time to fully appreciate an artistic enterprise layered with meaning. The house alone is riddled with rhymes and similes. In the living room, three strikingly different fish weathervane swim in a school alongside Diebenkorn's "Ocean Parkway". In the master bedroom, love and its pursuits are mimed by two weathervanes, a centaur and Diana, locked in an eternal chase of uncertain outcome.

Given the collection's consistent excellence, even its owner has difficulty choosing a favorite piece. Some covet the 60-inch Jewell horse that sails over his bed like the constellation Pegasus. Others admire the lithe energy of a Howard hunting dog. The Gus Wilson tiger that closes Spiritually Moving and appears on its back cover is a stand in for the collector himself. For Walters, a wooden seagull-and-arrow weathervane illustrates better than all else the strength and self-assurance of primitive art. For Kahn, the Gabriel angel on the cover and the long-billed curlew "say everything."

Spiritually Moving is both record and summation. The collector conceived of the handsome, oversized folio both as an art book, and as a book about art. Largely unencumbered by words, it serves up the sensual forms and tactile surfaces of American primitive sculpture in a way that is meant to stimulate the visual appetites of the broader, art-consuming public.

Characteristically, the collector assembled a team to work on the book. Chief responsibility was given to Harvey Kahn and Tom Geismar, a founding partner in Chermayeff & Geismar and a designer the collector has worked with for three decades. Bracketing what amounts to a gallery on paper is Walters' introduction and a 78-entry catalog prepared by Ralph Sessions, an independent art historian whose expertise is in folk sculpture. The stunning illustrations were produced by Dave Hoffman, a still life photographer who clearly excels in lighting.

Distributed by Harry N. Abrams, the $125 hardcover volume printed in Italy will be in bookstores by November 1. "Normally, the publisher is the catalyst. We produced the book and brought it to Abrams as a finished piece of work," allows Kahn. Only 2,500 copies were printed. Some who have already seen the book are suggesting that the number is too few.

Extravagantly beautiful endpapers are the first and last images encountered. The scumbled surface - is it glorious algae bloom or lunar landscape? - is unrecognizable for what it is, the much magnified side of a gilded and verdigreed copper weathervane. At once macroscopic and microscopic, the abstraction hints at delights and challenges to come.

Some will recognize in these pages the carved wooden eagle that Woodbury, Conn., dealer Kenneth Hammitt refused to part with; others will remember the weathered horse that for years belonged to Pat Guthman. But past histories are checked at the door in Spiritually Moving.

Their provenance left behind, the objects are once and forever the property of the collector. Lacking much text, the book is a visual essay on aesthetics. It shows, not tells, and nothing could be more telling than a two-page spread on horse tails. Wrinkled, smooth, contoured, flat, plumey and staccato, the isolated anatomy proclaims the unexpected inventiveness and variety of simple folk art forms.

"Spiritually Moving is not anti-intellectual," says Walters, defending the book's formalist stance. "It's the flip side of the story. Nina Fletcher Little took some of the same objects that might have ended up in this collection and put them in period rooms. This collector wants to extract them from that context as quickly as possible. I think there is room for people to be bold, to say `this is why people collect folk art.'"

What will happen to this collection? Assembled with passion, imagination, discipline, and commitment, it would certainly be the envy of any institution, the pride of all auctioneers. "If he ever parts with it, it will most likely go to a museum," says Kahn, discounting the possibility of a sale. In recent weeks, Kahn has been busy pursuing new leads for his still-active client.

Whatever the final disposition of the collection, Spiritually Moving remains a persuasive argument for American folk sculpture, and an intriguing essay on the art of collecting. As articulated by one man, that art requires "a certain openmindedness and an understanding of abstraction, stylization and surface subtleties, combined with a sophisticated eye for minimalism and the accidental beauty of patina," to borrow from Walters.

John Walsh, director of the Getty Museum, writes in the opening of Spiritually Moving, "Silhouettes belong to the legendary origins of art...These figures of two millennia later, made to trace images against the sky of things loved or feared, still possess ancient magic." In the end, it is the silhouette of the collector, David Teiger, that stands out most sharply against the fading light of the western sky.