Arakawa, a Japanese-born conceptual artist and designer, who with his wife, Madeline Gins, explored ideas about mortality by creating buildings meant to stop aging and preclude death, died Tuesday in Manhattan. He was 73. 

He had been hospitalized for a week, said Ms. Gins, who declined to give the cause of death.

“This mortality thing is bad news,” Ms. Gins said by phone from her studio on Houston Street. She said she would redouble her efforts to prove that “aging can be outlawed.”

Arakawa, who was known professionally by his surname, and Ms. Gins explored their philosophy, which they called Reversible Destiny, in poems, books, paintings and, when they found clients, buildings.

Their most recent work, a house on Long Island, had a steeply sloped floor that threatened to send visitors hurtling into its kitchen. Called Bioscleave House (Lifespan Extending Villa), it featured more than three dozen paint colors; level changes meant to induce the sensation of being in two places at once; windows that seemed too high or too low; oddly angled light switches and outlets; and an absence of doors that would have permitted occupants even a modicum of privacy.

All of it was meant, the couple explained, to lead its users into a perpetually “tentative” relationship with their surroundings, and thereby keep them young.

“It has to do with the idea that you’re only as old as you think you are,” Steven Holl, the Manhattan architect, said of the couple’s work, which he said was deeply rooted in Japanese philosophy. He added, “It may take years for people to fully understand it.”

Arthur Danto, the art critic and philosopher, who had known Arakawa for nearly 40 years, said, “He really felt they were doing the most important kind of work, to overcome death.” But, Mr. Danto said, “How that was going to happen was never clear, to anyone outside Madeline and him.”

When Mr. Danto met Arakawa and Ms. Gins, they were focused on completing 83 large canvases called “The Mechanism of Meaning.” “It was considered by a lot of people I knew to be very important work,” he said.

In 1997, “The Mechanism of Meaning” was shown at the SoHo branch of the Guggenheim Museum as part of a retrospective of the couple’s work. Calling the paintings “a bridge between Dada and Fluxus and the soon-to-be Conceptual Art,” Roberta Smith, writing in The New York Times, noted that “their philosophical or linguistic puzzles can stretch the mind in briefly pleasant ways.”

In recent years, the Arakawa and Ms. Gins’s work was taken up by philosophers and scientists, and they were the subject of several symposiums.

Shusaku Arakawa was born on July 6, 1936, in Nagoya, Japan, and studied art in Tokyo, where he became known for his neo-Dadaist creations. He moved to New York in 1961. In his pocket, he said, were $14 and the phone number of Marcel Duchamp, who he said became his mentor.

Two years later Arakawa enrolled in art school in Brooklyn (for the visa, he said, not the education). There he met Ms. Gins, a fellow student, who had grown up on Long Island.

Within days they had become a couple. (They married, she said, in 1965.) Over the next several decades, living in a loft building on Houston Street, they produced a body of work that gradually extended from poetry and prose to architecture.

In 1996, Herbert Muschamp, the architecture critic of The Times, reviewed their room-size installation at a museum in Japan. He called it “a comic stroke with cosmic intentions.”

In 1998 they won a competition, sponsored by the city of Tokyo, to build a vast housing project on 75 acres of landfill. The project, to be called City of Reversible Destiny, was never realized, but several apartments were built following their ideas.

Around the same time, they were commissioned to build the house on Long Island. When it was completed in 2008, Arakawa pranced across the sand-dune-like floor. He said he felt like the first man on the moon, adding, “If Neil Armstrong were here, he would say, ‘This is even better!’ ”

In the 1990s, the couple invested money with Bernard Madoff. After Mr. Madoff’s fraud was exposed in 2008, they were forced to lay off staff and close their office. “He pulled the rug out from under us,” Ms. Gins said at the time.

But, she said this week, her husband shrugged off things as trivial as money. There was a bigger morality in play.

“It’s immoral,” Ms. Gins said, “that people have to die.”