On Saturday, Apr. 7, 2007, Sol LeWitt died at the age of 78 from complications from cancer. He was an artistic giant whose contributions were so far-reaching that he straddled the categories of Minimalism, Conceptualism and Postminimalism. In the late 1960s, LeWitt created an enormous opening for other artists. So much so that in 1973 John Baldessari sang all of LeWitt’s paradigmatic "Sentences on Conceptual Art." The same year Carl Andre claimed LeWitt’s wall drawings were "an entirely new art form." Since the l980s many of Le Witt’s drawings evolved into what could look like airport abstraction. Yet, the transporting strengths of LeWitt’s conceptual art are how opulently visual and intellectually scintillating it is.

In the late ’60s, LeWitt was a principal player in one of the more excellent palace coups in avant-garde history. Back then, artists weren’t trying to build a new academy, they were trying to pare down and even destroy the old one. Reducing art to various essences, taking it to esthetic ground zeros, LeWitt drew on walls. Meanwhile, Barry LeVa ran into them, Mel Bochner measured space, Joseph Kosuth exhibited definitions, Dorothea Rockburne folded paper and On Kawara counted.

Declaring Minimalism "a dead end," LeWitt laid down the terms of this insurrection in his tremendous "Sentences" and "Paragraphs on Conceptual Art." These two texts should be required reading for every art student. LeWitt wrote that "the idea or concept is the most important aspect of the work," adding that art should be "emotionally dry" and "free from skill," "caprice," "taste," "whimsies" and "subjectivity." But the genius of LeWitt is that he found a way to make art that was as visually juicy as it was smart. Basically, LeWitt is to Conceptualism what Émile Zola was to naturalism: a founding father clever enough not to follow his own dictums too rigidly. Playing a classic Trojan-horse gambit, LeWitt partnered up with institutions, and opened the gates for everyone to follow.

Unfortunately, nearly everyone did. To his credit and detriment, LeWitt was the number one jewel in the Conceptual-Minimalist crown -- the best of a good thing that started a long time ago, just kept going and now has gone stale. Call it Installationism, our equivalent of the French Academy; in this ism institutions fill exhibition halls, atriums, corridors and stairwells with permanent or provisional arrangements that everyone agrees are works of art but pretends are radical and revolutionary, all the same. Like the old academy, the new academy has kept mediocre artists busy, boardmembers happy and audiences from getting bored. LeWitt was often called on to fill space in this manner, but at his best he was always better than the rest.

The key component to Le Witt’s art are the "Wall Drawings." His "structures," as he called his skeletal white sculptures, are lucid illustrations of sequence but can feel somewhat "period" on their own. The nuts and bolts of LeWitt’s wall drawings are well known. Following a set of instructions -- e.g., "vertical lines, not straight, not touching" -- a team of assistants renders a drawing directly on the wall. Since 1968, LeWitt executed nearly 1,000 of these works. Initially, only straight lines were used; subsequently arcs, circles, squares and triangles were added, then isometric geometric figures. Materials went from pencil to chalk, crayon, India ink and colored-ink washes.

Using this hands-off, guided-by-voices formula, LeWitt created an extraordinarily supple system whereby language generated form in ways that were simultaneously radical and classic, visual and stringent, unexpectedly rich and transparently complicated. So adaptable and intriguing is this method, it makes you wonder what would have happened had Rothko titled one of his paintings, Two Fuzzy Rectangles, One Red, One Chestnut, One over the Other, with Orange Borders.

The best part of LeWitt’s art, however, isn’t how it’s made, it’s what it does. The finest wall drawings -- and these, by and large, were designed before 1993 -- render one of art’s most invisible qualities, content, visible. They make you understand architecture as material; why the wall is a subject; how image, abstraction and text connect; and what logic, authorship and even capitalism look like when they’re thrown into question. This is no mean feat; it’s almost miraculous.

The next to last of LeWitt’s "Sentences on Conceptual Art" is a sort of word of warning to the contemporary art world from the past: "When an artist learns his craft too well he makes slick art."  

JERRY SALTZ is senior art critic for New York magazine.