When Paul Cézanne advised his young disciple Emile Bernard to "treat nature by means of the cylinder, the sphere, the cone", he did not mean the advice literally. Many years later the American artist Sol LeWitt was to apply it that way. LeWitt, who has died in New York of cancer aged 78, was one of the most eminent of the conceptualist artists who came to the fore in the 1960s, along with Donald Judd (obituary, February 22 1994), Dan Flavin (obituary, December 5 1996), and Carl Andre.
Their work looked at the time like the driest of ultimate follies, and Andre of course took the flak in Britain for his ground-hugging sculpture Equivalent VIII (1966), better known as the Tate bricks. LeWitt, too, worked with single anonymous basic modules, an open cube, say, multiplied into a series, or nested, or constructed into a framework ziggurat, painted white or black. His work was not sculpture but structures, he said, though it hardly needed saying.
Today it all looks different, and as LeWitt moved into drawing and painting as well as structures, his art took on the diverse appeal first of primary reds, yellows and blues and irregular elements, and then increasingly of sensuous colour surfaces, in a restrained Quakerish kind of way similar to the minimalist work of Agnes Martin (obituary, January 10 2005). The logical constructions he had made now began to incorporate intuitive elements.
He left in his wake a gaggle of the world's most ponderous art critics disputing over whether he was a conceptualist or a minimalist or both, while he himself bent his own rules with wiggly lines, irregular geometrical shapes, and even splotches of paint. One group of aquatints featuring wriggling lines was called Horizontal Bands (More or Less). In 1968, he heralded this move away from minimalism with a work which he buried in a garden and gave the Pooh-like title of Buried Cube Containing an Object of Importance but Little Value.
LeWitt was born in Hartford, Connecticut, the son of Russian immigrants; his father was a doctor, his mother a nurse. He studied art at Syracuse University, New York, and was drafted into the forces in 1951 to serve in Korea in the Special Services, an organisation that covered peaceable operations such as entertaining the troops and, in LeWitt's case, designing posters.
Following Korea, he worked as a graphic designer for Seventeen magazine in New York and then in the office of the architect IM Pei. He found his vocation while he was working in the bookshop of the Museum of Modern Art, where other employees included a number of aspiring artists, including Flavin.
LeWitt himself was attracted to the work of the Russian constructivists, men and women like Vladimir Tatlin and Lyubov Popova who believed in a utilitarian art for an industrialised age and were making their own revolution before the red revolution shut them up.
He treated simple forms as his ideal lexicon, and sometimes the simplicity seemed nothing much more than that: an octagon surmounting a cube, say, might look like nothing more inspired than a Lego version of part of a Wren steeple. He used words as simple building blocks as well: recalling this early period from the distance of the 1990s he said: "I decided I would make colour or form recede and proceed in a three-dimensional way."
He was a modest man, genuinely uninterested in the personality cult of postwar American art, though as he became successful and employed assistants to execute his wall-size "drawings" (which were quite likely to be mural paintings), he did point out that architects produced designs that builders executed and were still regarded as artists. At the same time, he would often allow his collaborators to have fun with their own variations to the template, something no architect would allow.
Late in life this prolific artist made a long-term loan of his big collection of the art of his contemporaries to the Wadsworth Atheneum in Hartford, where his mother had taken him as a child to his first drawing classes. He liberally dispensed his own work to younger artists and, to give them a leg up, would exhibit with them.
He lived during the 1980s in Italy and then returned to the US to spend the rest of his life in Chester, Connecticut. The San Francisco Museum of Modern Art organised a LeWitt retrospective in 1990, which travelled on to the Museum of Contemporary Art in Chicago and the Whitney Museum of American Art in New York. It contained some of his wall drawings in spectacular shapes and colours and was an unexpected crowd pulling success for this most modest of men.
His wife Carol and two daughters, Sofia and Eva, survive him.
· Solomon LeWitt, artist, born September 9 1928; died April 8 2007