Keith Sonnier, who infused functional materials like sailcloth, foam rubber, steel rebar and neon with a sense of poetry and play that tweaked the solemnity of Post-Minimal art in the late 1960s and made him one of the movement’s more unconventional standard bearers, died on July 18 in Southampton, N.Y. He was 78.
His death, at Southampton Hospital, was announced by his studio and by Pace gallery, which has represented him for many years. The cause was colon cancer. He lived nearby in Bridgehampton.
In both the manifold building blocks of his works and their titles — “Ba-O-Ba,” “Ju-Ju,” “Palm Saw Tooth Blatt,” “Bison Bop”— Mr. Sonnier came off at times as an irreverent sensualist alongside peers like Bruce Nauman, Eva Hesse, Jackie Winsor and Robert Smithson, who employed some of the same materials. Among his first works, made in 1965 and 1966 under the influence of his teacher, the artist Robert Morris, were deadpan soft sculptures that mechanically inflated, often appearing to breathe.
“I knew I could make these very eccentric, abstract boxes, and I wanted to connect them transparently, like Wonder Woman’s airplane,” Mr. Sonnier told Artforum magazine in a 2018 interview.
Almost immediately upon completing his first mature pieces, he was enlisted in a disparate group known as eccentric abstractionists, a term coined by the curator Lucy Lippard, whose landmark 1966 exhibition “Eccentric Abstraction,” at the Fischbach Gallery on West 57th Street in Manhattan, helped set the terms of Post-Minimalism.
Breaking with the seriality and restraint of Minimalism, many of these younger artists embraced the cacophony and material surfeit of the world around them, much like a generation of counterparts in Italy, who were grouped under the label Arte Povera (“poor art”) for their unorthodox, sometimes humble, materials.
“Incongruity, on which all humor is founded and on which Surrealism depends so heavily, is a prime factor in eccentric abstraction,” Ms. Lippard wrote about the group she had gathered, which included Ms. Hesse, Mr. Nauman, Louise Bourgeois, Alice Adams, Gary Kuehn, Don Potts and Frank Lincoln Viner. “But the contrasts that it thrives upon are handled impassively, emphasizing neither one element nor the other.”
Before his first decade in the art world was out, Mr. Sonnier had been included in a dizzying number of exhibitions now considered watersheds: “9 at Castelli,” at the dealer Leo Castelli’s Upper Manhattan warehouse in 1968; “When Attitudes Become Form,” at the Bern Kunsthalle in Switzerland in 1969; “Anti-Illusion: Procedures/Materials,” at the Whitney Museum of American Art in New York that same year; and Documenta 5 in Kassel, Germany, in 1972.
He began using neon tubes, a material that would become his calling card, in 1968, often deploying them in unabashed candied colors: baby blue, hot pink, lime green, tropical yellows and oranges. But Mr. Sonnier was formally restless, and, particularly in the early years, his work could appear to come from completely different hands, involving collaborative performance, ephemeral sculpture, cutting-edge technology and communications theory.
“As his art developed,” Roberta Smith of The New York Times wrote in a review of two shows in 1989, “it came to have the feeling of a just-finished performance that, by the way, just happened to produce this marvelous if temporary thing to look at.”
James Keith Sonnier was born on July 31, 1941, in Mamou, La., a small town in the heart of the state’s Cajun country, where one of his grandmothers spoke primarily in Cajun dialect. (He absorbed it well enough himself to be able to use into adulthood.)
His father, Joseph Sonnier, a voracious reader who owned a hardware and electrical supply store, and his mother, Mae Ledoux, a florist and local singer, were Roman Catholics whom Mr. Sonnier described as “very devout and also very eccentric.”
He was among the first in his family to attend college, graduating in 1963 from the University of Southwestern Louisiana (now the University of Louisiana at Lafayette). After a stint in Paris studying painting and life drawing, he earned a master’s degree in 1966 at Rutgers University, which had become a hotbed of art experimentation under teachers like Mr. Morris, Allan Kaprow and Robert Watts.
Barely out of college, Mr. Sonnier attracted the attention of the influential dealer Richard Bellamy, who quickly sold an untitled 1967 sculpture that Mr. Sonnier had made with pink satin stretched over foam rubber and wood (it evokes a long, segmented pink caterpillar) to the architect Philip Johnson. Mr. Johnson donated it to the Museum of Modern Art, where it remains today.
Mr. Sonnier married Ms. Winsor, in 1966 (they met at Rutgers), and the two settled in Manhattan, plunging into the downtown New York art world, particularly the overlapping scenes that coalesced around the art magazine Avalanche and 112 Greene Street, a raw loft space in SoHo where groundbreaking performance, dance and installation work emerged.
Mr. Sonnier’s work with light intensified in 1969, when he began a series that he would continue until his death: abstract constructions of lines, circles and squares typically made from neon and clear glass. He called the series “Ba-O-Ba,” based on a Haitian Creole phrase that can mean “bathing in moonlight.”
Though his work resides in many prominent public American collections, Mr. Sonnier had a stronger following in Europe. His first major survey in the United States was in 2018, when the Parrish Museum, in Water Mill, on the East End of Long Island, organized “Keith Sonnier: Until Today,” a well-received show that traveled to the New Orleans Museum of Art. In spring 2022, Dia:Beacon, in the Hudson Valley, plans to open a long-term installation of several newly acquired foundational works made in the late 1960s and early ’70s.
His marriage to Ms. Winsor ended in divorce in 1980. A second marriage, to Nessia Pope, also ended in divorce, in 1998. He is survived by a daughter, Olympia Sonnier, from his second marriage; and a brother, Barry.
During his last three decades Mr. Sonnier devoted himself to large public works commissioned for airports, government buildings and cultural spaces in Europe and the United States.
Even when creating at that architectural scale, and having to satisfy the needs of municipalities and corporations, he strove for what he called a gossamer sense of “astral movement.”
“When you’re in a productive state, the work begins to lose that element, that special quality — astral, soul, whatever we call it,” he told the historian Richard Shiff in 2016. “I want the work, when you look at it, to be recognizably mine, but to have this element in the work that allows your perception to move you on to this other dimension of vision.”