The sainted Claes His 'Clothespin' holds up the case for public art.

Ever give much thought to a clothespin? A button? A three-way plug? They make our lives easier. They're useful, durable goods we take for granted.

But objets d'art?

Only in the eyes of Claes Oldenburg and Coosje van Bruggen. These sculptors make the ordinary extraordinary by reversing visual polarity and tampering with physics. Tiny becomes huge; hard becomes pliable. What we know becomes something else.

By converting everyday objects into outdoor sculpture, this team shattered the convention of monument as a bronze man on a horse.

And that subversive redefinition began in Philadelphia with Clothespin, installed in 1976 at 15th and Market.

"Clothespin forever transformed that corner," says Penny Balkin Bach, director of the Fairmount Park Art Association. "Nowhere else on earth looks like that."

In a city teeming with public art, Clothespin stands as the bridge between old and new. Just look at its neighbors: The Civil War statues of McClellan and Reynolds in front of City Hall; Jacques Lipchitz's bizarre Government of the People in Thomas Paine Plaza; Robert Indiana's LOVE logo in Love Park; and the abstract Triune by Robert M. Engman across 15th Street.

In Philadelphia, there's room for them all. Tonight, on Clothespin's 25th anniversary, the Fairmount Park Art Association is appropriately commending Mr. Oldenburg and Ms. van Bruggen for their pivotal role in bringing variety to public art.

Clothespin, created just before Mr. Oldenburg began collaborating with Ms. van Bruggen, came about through the Redevelopment Authority's wise "Percent for Art" program. It requires private developers who get the authority's assistance to incorporate public art into their projects - an idea that has been been widely copied.

Developer Jack Wolgrin had seen a print of Mr. Oldenburg's clothespin concept issued by the Philadelphia Museum of Art. He commissioned it for Centre Square - not without naysayers, even today.

"Most people are not indifferent to Clothespin. They have a response," Ms. Bach says. "It makes people look. It makes people think."

That's because Oldenburg-van Bruggen works challenge the convention that the content of art is by definition profound and its maker earnest. The works are unexpected, brash and funny.

Oldenburg pieces have wonderfully literal names: Soft Toilet (1966); Giant Three-Way Plug (1970); Split Button (1981); Spoonbridge & Cherry (1985-86); and Torn Notebook (1996).

They're democratic and accessible, yet they evoke very different interpretations from different people. To some, they're multilayered metaphor. To others, just whimsical fancy. That, in the art world, is success worth honoring.