Is It a Mirror or a ‘Mirror’? Ask Joseph Kosuth.

It was 1965, and Joseph Kosuth was a 20-year-old undergraduate at the School of Visual Arts when he made the pieces that made his career. Their premise was simple enough: He’d take an object, like a crate, a wooden door, or a shovel, and either hang it on or lean it against a wall. To one side he’d place a life-size photo of that same object, as installed in that place, and to the other, a dictionary definition, enlarged and printed on poster board.

The most famous iteration is “One and Three Chairs,” consisting of a chair, a photo of a chair and the definition of “chair,” which the Museum of Modern Art acquired shortly after it was made. But “One and Three Mirrors” (1965), the version that appears in his current show, “Future Memory” at Sean Kelly Gallery, is even better. It is as fresh now as the day it was made, and well worth revisiting, both because of its broad influence on contemporary art practice and because it offers such a clear example of the Conceptual approach.

Like the chairs, Kosuth’s mirrors raise fundamental questions about art — is it an object, an image or an idea? It’s easy enough to pose such questions, but realizing them in an artwork, with actual objects, gives them a special urgency, because they become practical instead of hypothetical. If you’re standing in front of “One and Three Chairs,” you have to decide what you’re looking at: Is it a chair, or a “chair”? Making the same piece with a mirror, which reflects you, your gaze and the gallery you’re standing in, only adds to the categories being so thrillingly destabilized.

Along with a recent show at Sprüth Magers in London and an upcoming exhibition at Lia Rumma in Naples, Italy, “Future Memory” amounts to a kind of deconstructed retrospective for Kosuth, who just turned 80. It’s the first gallery show he hasn’t designed himself as an overall installation, and it includes a work from nearly every decade of his career, from the 1960s to the present.

Seeing the whole arc laid out this way, it’s easy to recognize both the infinite promise and the inevitable pitfalls and dead-ends of his austere approach. The fusion of the concrete and the abstract in “One and Three Mirrors” feels as exciting now as it must have been in the 1960s; if human museums still exist in a thousand years, I expect it will feel the same. His subsequent work, however, because it attempts to build on basic questions that don’t really have answers, gets very narrow; he’s essentially trying to wrestle art into a specialized branch of philosophy. (This is more or less what he cops to in his 1969 paper “Art After Philosophy.”)

In a 1991 piece, he silk-screens a quotation about whether any two things can really be “identical” onto two contiguous pieces of aluminum. The piece works the same way as “One and Three Chairs” — it presents a concrete example of a philosophical question related to art making for the viewer to contemplate. The question itself just doesn’t strike me as equally interesting. And some pieces, as when he silk-screens quotations from Piet Mondrian’s writings onto reproductions of his paintings, or the Gertrude Stein line, “If you can do it, why do it,” onto a giant clock, would frankly be better as written descriptions. The only thing you get by actually building them is something to sell.

Still, there’s something heroic about Kosuth’s lifelong devotion to the relationship between idea and object, and there’s an argument to be made that his entire trajectory is a performance piece in itself, one about time, mortality and the ultimate futility of intellectual arguments. As Kosuth himself puts it, in white neon letters that quote Ludwig Wittgenstein, “In mathematics process and result are equivalent.”

Joseph Kosuth

Through April 18. Sean Kelly, 475 10th Avenue, Manhattan; (212) 239-1181, skny.com.