Art and design have been on a collision course since the early 20th century: The Museum of Modern Art inaugurated its design department in 1930, and just a few years before that the artist Josef Albers created a set of four stacking tables with colors that mirrored his highly geometric paintings. Yet the two fields for the most part have existed in separate commercial galleries, auctions, and fairs.

Now, however, art and design are coming together more closely than ever in how they are sold and marketed. On Wednesday night, Phillips de Pury & Company will hold its first separate Design Art sale, which is expected to bring in between $1.7 million and $2.3 million. The new sale has works that are distinctly different from those in its twice yearly Design sale, which is estimated to make between $3 million and $4.1 million.

“It is a move to differentiate works that have a more sociocultural basis and are blurring the line between furniture and art,” the Phillips design department head, Alexander Payne, said. The French designers Ronan and Erwan Bouroullec’s limited-edition treehouse bed “Lit Clos” (2000), estimated between $80,000 and $100,000, would fit in seamlessly with artist Andrea Zittel’s installation of living pod units currently at the Whitney at Altria, for example.

Phillips also is inaugurating its new space in London this October with its first sale that mixes Contemporary Art and Design Art, the latter a category of post-1980 conceptual design for which the market is “in its infancy but continuing to rise,” Mr. Payne said.

From June 13 to 16, the most important contemporary art fair, Art Basel, will be joined by the Design Miami Basel fair, the follow-up to Design. 05 Miami. It is the first time that a separate design fair has attached itself to the annual Basel Art Fair, held this year from June 14 to 18. For the inaugural Design Miami last December, design galleries brought their Jean Prouvé tables and Donald Judd desks to sell in open booths, as is similar to the Art Miami Beach Fair down the road.

Zesty Meyers, co-owner of R 20th Century in Lower Manhattan, is headed to Basel. He’s planning to bring plastic furniture by Wendell Castle and a “sculptural tabletop piece” by New Yorker Jeff Zimmerman, among other objects. “We gave Miami three years to take off,” Mr. Meyers said. But he was so ecstatic about the reception there, he said, he now figures that “by this December, it is going to explode.”

Phillips moved its sale up a week this year to allow collectors to buy furniture, then art. “It’s specifically aimed at our clients who will be in Basel,” Mr. Payne said. Those clients are, in part, contemporary art collectors who find top contemporary design relatively cheap. Consider the market for Judd’s work. At Sotheby’s 20th-century design sale, on June 14, a limited edition 1986 Douglas fir Donald Judd desk is expected to make between $80,000 and $100,000. At Christie’s contemporary art auction last month, a plywood 1989 Judd box sold for $352,000, three times as much.

The highlight of Sotheby’s sale, which is expected to total between $7.2 million and $10.6 million, is Marc Newson’s riveted aluminum Lockheed Lounge, which is estimated to bring in more than $800,000. Made in 1986 in an edition of 10, the streamlined, handmade chair was featured in Madonna’s “Rain” video. Another edition sold at Christie’s contemporary art auction in 2000 for $105,000. “This chair really is a sculpture,” Sotheby’s director of 20th century design, James Zemaitis, said. “It’s that morphing of contemporary art and design.” He added that five or six seriously interested collectors were all buyers of contemporary art as well.

Christie’s 20th century design sale on June 13 is emphasizing earlier Art Deco and midcentury modernism. It is expected to make $7 million or more. The sale is anchored by a 1927 Art Deco iron table by Pierre Chareau, with 11 accompanying chairs, estimated to sell for $800,000 to $1.2 million.

Within the past year, design also has been shown increasingly within art galleries, and the galleries are bringing art-sale sensibility to the field of design, emphasizing limited production and original works. Lehmann Maupin earlier this spring showed sculptural metal works by the French designer Maria Pergay. The gallery commissioned the 76-year-old Ms. Pergay to make a new body of work for the show, which emphasized work on the outer edge of functionality.

In the contemporary design market, as in the art market, rarity makes a difference. Earlier 20th-century design objects were often produced in unknown quantities. Living designers can cater to the fine art-buying public by making limited-edition pieces whose elusiveness helps push prices into the six figures. In November, Perry Rubenstein Gallery, on 24th Street, will show redwood works by Mira Nakashima, in collaboration with the design dealer Cristina Grajales. As with the Pergay show at Lehman Maupin, the dealers have commissioned the works for the exhibition.

Gallerist David Maupin said buyers for Ms. Pergay’s works, which range from $20,000 to $130,000, were mostly contemporary art collectors. “She crosses the bridge between sculpture and design furniture,” Mr. Maupin, who is also a contemporary design collector, said.”I think that my generation — people in their late 30s, early 40s — just doesn’t believe in these rigid boundaries and can find beauty in utilitarian objects.”

The usefulness of an object has long served as the dividing line between art and design. (Can you actually drink from Meret Oppenheim’s furcovered teacup and put it down on Josef Albers’s colorful nesting tables? No and yes.) Marcel Duchamp’s 1917 “Fountain,” the urinal far removed from plumbing pipes, helped art critics classify art as something nonfunctional, a definition artists have toyed with ever since. Ms. Zittel, for example, makes her own clothes and lives in her pods and calls that art.

Still, those boundaries persist, even as designers, collectors, and dealers struggle to stretch them.An exhibition last year of design objects by minimalist and post-minimalist artists at the Cooper-Hewitt, National Design Museum was titled “Design Is Not Art: Functional Objects From Donald Judd to Rachel Whiteread.” One way to define boundaries today, Mr. Maupin suggested, is “by the intention of the maker.”

“Function is very difficult to define,” the New York-based designer Rama Chorpash, whose Sono tables will debut at Grajales’ booth in Design Miami Basel, said. “There are many functions, such as spiritual. In some ways, a piece of art might be more functional than a cooking pan.”

That said, Mr. Chorpash walked the thin but real line between art and design when he collaborated with Eli Sudbrack,
the artist who goes by the name Assume Astrid Vivid Focus on a Public Art Fundsupported dance floor and DJ booth at the Central Park roller skating area.”We didn’t sell anything, and as a designer I always have a client. It was a real labor of love,” he said.

On the other hand, for a designer who, like Mr. Chorpash, is interested in the ideas of community and accessibility, a mass-produced $18 knife, which he designed for Culinform, can reach more people than a table of which just 10 copies exist. In addition, art often depends on the maker’s reputation and consistency, Mr. Chorpash said.”What’s so poetic about design is that there is no author.”

The Brooklyn-based designer Jason Miller, who will be in the Cooper-Hewitt’s upcoming design triennial, said he believes that recognizing the distinction between the fields helps make for better objects. “When you create an object that is something other than just being comfortable or functional, it still needs to speak to the user,” Mr. Miller said.

Comfort, for instance, is still a legitimate design criterion. His Duct Tape lounge chair is full of conceptual references, but is also a cozy place to sit. “I’m trying to create objects that can exist up on a podium and exist functionally as well,” Mr. Miller said.

In the end, something as crass as price may serve as a convenient arbiter of whether something is considered art, design, or something in between. Mr. Miller’s Duct Tape chair, for example, retails for about $5,000. The person who pays approximately $1 million for Mr. Newson’s chair may feel less comfortable letting friends come over for a test ride. “If someone’s going to pay a quarter million for a piece of furniture, are they going to sit on it?” Mr. Meyers said. “Some clients do; some put it on a pedestal like it’s in a museum.”

“Design” at Phillips de Pury & Company, 10 a.m., June 7, 450 W. 15th Street, between Ninth and Tenth Avenues, 212-940-1200.

“Design Art” at Phillips de Pury & Company, 7 p.m., June 7.

“Important 20th Century Decorative Art and Design” at Christie’s, 10 a.m., June 13, 20, Rockefeller Center, between Fifth and Sixth Avenues, 212-636-2000.

“Important 20th Century Design” at Sotheby’s, 10:15 a.m., June 14, 1334 York Avenue at 71st Street, 212-606-7000.