Bruce Nauman is one of the most admired and influential artists in America, so it seems slightly incongruous that for three decades he has lived on a horse ranch in the middle of New Mexico.

He does get around, though. In 1999 he shared (with Louise Bourgeois) the Golden Lion Award for best artist at the Venice Biennale. He'll be a major presence in Venice again this year, thanks to the Philadelphia Museum of Art, which is curating the American pavilion.

The Biennale, after more than a century still one of the most prestigious international art exhibitions, opens June 7 and runs through Nov. 22. Art Museum curators Carlos Basualdo and Michael R. Taylor, the U.S. commissioners, have prepared a thematic investigation of Nauman's career, which began in the mid-1960s.

Besides a more or less conventional display in the American pavilion in the Giardini della Biennale, the main exhibition site, Nauman is creating site-specific installations for two educational institutions in the city - one housed in a palazzo on the Grand Canal and the other in a former convent near the railroad station.

A tripartite presentation, especially taking his art into the city proper, should allow Nauman plenty of latitude to display his mastery of multiple media, from sculpture to video, and including photography, illuminated neon, installation, body art, conceptual art, and performance.

Nauman is the quintessential postmodern artist, interested more in investigating the nature of art and aesthetic experience through experimentation than in producing objects. Perhaps more than any other American, he represents the forceful reaction against, and rejection of, the seriousness and dogmatic ideology of modern art.

The 67-year-old artist has devoted more than 40 years to testing the boundaries of art, as Marcel Duchamp, retrospectively the first postmodernist, so famously did nearly a century ago. But where Duchamp challenged orthodoxy with objects such as his commercial "ready-mades," Nauman creates unusual and uncomfortable situations, environments, and sensations.

Most of all, he poses questions about where ordinary life ends and art begins. He proceeds from the proposition that anything an artist does, especially in his studio, is ipso facto art - a debatable proposition.

A pioneer of video art during the 1960s, he made a series of videos in which he "mapped" the studio space by positioning his body in various ways within it. He doesn't describe experience, as a painter would, he initiates it for viewers, particularly in his recent works.

One of these, an outdoor piece at an international sculpture show in Holland several years ago, particularly impressed Basualdo. It prompted him to think about proposing a Nauman show for Venice to the State Department's Bureau of Educational and Cultural Affairs, which administers the American pavilion.

The piece was a shallow pyramidal depression in the earth, about 80 feet on a side and paved with concrete. At its lowest point, a person of average height was eye-level with the rim of the depression, which functioned as a horizon that cut off the world outside the bowl. Basualdo recalls Square Depression as being a "clear, simple, and powerful" statement.

Mundane actions are intrinsic to Nauman's method. He once photographed himself pretending to be a fountain spouting water. His pieces can be irreverent and lighthearted, but they usually express an idea worth considering, and sometimes difficult to resolve.

Some of what he has done or made seems, in retrospect, to be too trivial to qualify as art. Some of it resonates powerfully when experienced for the first time, but doesn't stand up to repeated exposure. This effect is endemic to conceptual art, which typically succeeds or fails on the complexity or ambiguity of its core conceit.

A prime example by Nauman is a neon piece that the Art Museum recently acquired, The True Artist Helps the World by Revealing Mystic Truths. This phrase is spelled out in a colored neon spiral; it resembles a beer sign one might see in a tavern window.

The phrase can be accepted as profound or dismissed as ironic or, worse, as trite. It's an open-ended piece not only in its spiral form, but also in its intellectual pretension.

Nauman is like Duchamp in that much of what he has produced has come to seem disarmingly obvious and simple, like visual one-liners. Yet the questions he asks about the nature of art remain fascinating because a century after Duchamp, they still haven't been answered satisfactorily.

Whether the Biennale will make Nauman's work more accessible will depend in large part on the installations he creates for the Università Ca Foscari (the Grand Canal palazzo) and Università IUAV di Venezia at Tolentini (the former convent).

His presentation is called "Topological Gardens," from topology, the field of mathematics that examines the continuity of space amid changing conditions. Nauman studied topology at the University of Wisconsin before getting a master of fine arts in California, and his interest in translating topological principles into art dates to his early "mapping" videos.

Topology involves the interchangeability of inside and outside - and, by extension, of public and private - a consistent thread in Nauman's work.

Basualdo, who teaches in Venice for part of each year, describes the city as experiential because of the way people move through it. "Maybe in some way the city could tell something about Nauman's work and vice versa," he said.

Basualdo and Taylor, his curatorial partner, have organized Nauman's art into three thematic groups - Heads and Hands (a reference to the artist's frequent use of body parts in many works), Sound and Space, and Fountains and Neons.

Each of the three sites will display a mix of these themes, although the proportions will differ. The university installations, in which students will participate, promise to be the most topological for visitors.

On reflection, and contrary to my initial reaction to Nauman's selection, he seems like an inspired choice to represent America's national character. His art has been consistently innovative, daring, and provocative. He hasn't been reluctant to try out new ideas, or squeamish about falling flat or coming up shallow.

He has been inspirational for young artists in many countries, and, like Jasper Johns, whom the Art Museum presented in Venice in 1988, he has become an acknowledged master of his generation. Yet his work continues to feel fresh because he doesn't regurgitate old ideas.

As Basualdo observes, "It's very tough work to understand, but if you spend time, it opens itself up, then gives itself up - but not immediately." No sir, definitely not immediately.

Contact contributing art critic Edward J. Sozanski at 215-854-5595 or esozanski@ phillynews.com. Read his recent work at http://go.philly.com/ edwardsozanski.