Is it art? For performance artist Tino Sehgal, it's immaterial.

Got a yen to collaborate on an art project? Here's your chance. Until March 10, the Solomon R. Guggenheim Museum is showcasing "Tino Sehgal," a "performative installation" that's interactive to the max. This art requires visitor participation. No passive onlookers allowed. As the 34-year-old artist said when a similar work appeared at London's Institute of Contemporary Arts in 2007, "When you enter my work, you are also constructing it."

Call it a conversation piece. Sehgal, who was born in London but lives and works in Berlin, aims to elicit two-way conversations through what are called "constructed situations." For the past decade, casts of trained interpreters have sparked viewer input in London's Tate Modern, at art fairs, and the 2005 Venice Biennale, where Sehgal represented Germany.

At Sehgal's show in New York's Marion Goodman Gallery in 2007, six interpreters chanted in unison, "Welcome to this situation" as visitors approached. They initiated conversation by quoting thinkers like Jean-Jacques Rousseau or Karl Marx, then asking, "What do you think?" An impromptu discussion of economic and philosophical issues ensued. Although improvisatory, the encounter was conceived and structured by Sehgal over the course of two years.

Even though no material relic of Sehgal's work remains after its presentation, in 2008 the Museum of Modern Art acquired his work "Kiss" for $70,000. In accordance with the artist's purist principles, the purchase (completed with an oral agreement and handshake) entails only the right to reproduce the work. No tangible document changed hands.

For those who need a bit of background on why the artist eschews conventional art objects: A student of economics and former dancer and choreographer, Sehgal maintains that the developed world has too much stuff. His favored means of creating art does not diminish Earth's dwindling resources or contribute to the excess of consumer goods. His art exists only transiently and leaves no physical trace. Like Brigadoon blossoming one day each century, Sehgal's art lives during the experience and afterward persists in memory and legend.

Instead of transforming material like canvas or a chunk of marble into an art object, Sehgal's medium is the human body, mind, and energy. His goal is to transform participants' thoughts and values. It's the Socratic method made visible, as much linguistic and dramatic as it is visual art.

Tino Sehgal takes to an extreme the art-world trend toward "dematerialization of the art object," which debuted when Conceptual Art got off the ground 40 years ago. In 1969, artist Douglas Huebler said, "The world is full of objects.... I do not wish to add any more." Artists such as Joseph Beuys, Bruce Nauman, and Vito Acconci, as well as members of the Fluxus group, Allan Kaprow (father of the quasi-theatrical "Happenings"), and Gilbert and George in their 1970 "Singing Sculpture" pioneered performance art. These artists used their bodies as raw material; they recorded their actions and sold the documentation as art. Sehgal goes further: He permits no photographic, video, or audio record and no catalog or wall labels.

The mise-en-scène at the Guggenheim has two parts: one is a visual tableau and the other requires direct participation. The former ("Kiss," an early Sehgal work from 2002) shows a young man and woman sprawled on the floor of the soaring rotunda, enacting in slow motion scenes from works of art that involve a kissing couple. Like animatronic wrestlers they assume poses reminiscent of, for example, Rodin's and Brancusi's sculptures, both entitled "The Kiss."

The participatory part, called "This Progress," winds up the ramps of the Guggenheim's famous spiral. "It's the perfect place" for this work, Sehgal said in an interview. "Every museum promotes the Western idea of progress, and this one epitomizes it" in its spiral form ascending to an oculus of pure light. It also suggests that progress, Sehgal says, is "nonlinear."

He hopes to catalyze fresh thinking about the concept. "In the last 200 or 300 years, the Western idea of progress," he says, "is to transform the earth through human labor into material things, which we consume and derive income from and which make us happy." He denies that "having the next gadget" increases happiness and proposes an alternative of "higher level" satisfaction found in interpersonal relationships.

"This Progress" consists of serial conversations between each visitor and four interpreters ranging in age from 8-year-old schoolchildren to senior citizens. On entering the bottom ramp, a child says, "This is a work by Tino Sehgal. May I ask you a question? What is progress?" You stroll up the ramps discoursing on progress, which the child attempts to repeat, generally mangling the concept but retaining a few key words. The child then passes you off, like a baton in a relay race, to the next interpreter, a teen who continues the conversation, asking more questions and offering different viewpoints.

You stroll and chat some more, like sages gabbling under the stoa in ancient Athens, always ascending the ramp. Your next interlocutor is an adult who offers observations – personal and philosophical – which may be vaguely or explicitly relevant to the topic. Two ramps from the top, you meet a white-haired man or woman who further delves into the subject. As you reach the top of the building, the conversation ends abruptly.

Talk about no closure! Just when the conversation gets really deep, you're abandoned. "That's part of it," Sehgal says. "You keep thinking as you go down. Afterwards you can be in a contemplative mode," continuing the dialogue as an internal monologue.

A further "twist," he says, is that you "go backwards in time, with the people getting older as you go up." The children, whom he calls "the future," are at the bottom – the embryonic foundation of progress, as it were.

This visitor's elderly guide, a retired classics professor named Walter, confided that although "we had some rehearsals, nobody told me what to say." Empowering both his interpreters and visitors to ruminate freely is a key ingredient for Sehgal. "It's psychologically important to go beyond myself" in his art, he says, to avoid becoming "static" and to incorporate multiple viewpoints and experience. "It's a trade-off," he says. "You lose control and precision, but you gain complexity."

At a recent visit, overheard snippets of conversation ranged from the trite to the profound. A middle-aged woman said there's been no faith in progress since the atomic bomb. Some called into question every technological advance, like antibiotics and assembly-line production. Others allowed there has been human progress, like the abolition of slavery and protection of civil rights.

One elderly gentleman took a narrow view, saying, "This new restaurant at the Guggenheim is great! That's progress. And the cellphone – that's progress!" The conversations ranged from jabbering and pontificating to thoughtful analysis and engagement.

Whatever the content, and no matter how artificial the impetus, discussing significant issues related to quality of life – that's progress.