Artdaily_ At the very start of “The Double: Identity and Difference in Art Since 1900,” a brilliant new show at the National Gallery, stands an 8-foot-tall plywood column, painted plain gray without ornament. Standing by itself, it would come across as simply architectonic. But it isn’t alone: An identical column lies on the ground alongside, and the pairing — now inevitably understood as one standing figure and another, recumbent — comes to represent the basic sociability of all humans. The twinned figures in this 1961 piece by Robert Morris, “Two Columns,” can stand for all of humanity.

The 101 modern and contemporary artists in “The Double” prove the vital social impact of twoness.

Or how about another way into this show?

At the very end of “The Double: Identity and Difference in Art Since 1900,” a brilliant new show at the National Gallery, lies a pane of cracked glass without ornament. Lying by itself, it would speak to the fragility that’s basic to the world we live in. But it isn’t alone: Another pane lies beside it, miraculously cracked along the same lines as the first. One was broken with a hammer; the other’s cracks were cut in perfect imitation of the first. The pairing in this 1998 piece, “Parallel Lives,” by Jorge Macchi, explores our basic need to impose meaning and order on the world by copying parts of it.

The 101 modern and contemporary artists in “The Double” prove the vital mental impact of twoness.

Come at this exhibition in Washington, D.C., from either end, and at its more than 120 works from any number of angles, and you’ll be convinced that doubling — sameness, but also the difference it’s in tension with — is a basic feature of the art of our times, and also one of its most compelling subjects. James Meyer, the National Gallery’s curator of modern art, shows how two similar things shown side-by-side mean something different from a single grand statement. They often mean more.

Meyer’s curating mirrors the twinning in the works on view: Instead of finding one powerful, enlightening take on its theme, “The Double” shows how duplication, as a single concept, plays out across more than one dimension.

Twoness, which seems so stable and basic, can speak to instability. In this show’s 1912 collage of a face by Picasso, a reduplicated nose and ear seem to cast doubt on the entire project of orderly representation. Can we really say that any single image can get at what our chaotic world is about? Doesn’t an image that stutters do a better job?

And yet, in that same era, Picasso’s jitters are nowhere to be found in an icon of abstraction that is also two-based. It’s hard to think of any better image of order than Kazimir Malevich’s 1923 drawing of a pair of squares: Rather than calling art into question, it seems to stand for the most stable essence of what art can be. After all, two points define the line that’s at the root of drawing, and two parts are what create the most minimal composition in paint.

The absolute order signaled by duplication can also come across as half-mad compulsion: When certain artists in this show see double, you want to breathalyze them.

About a decade ago, the artist Vija Celmins took an old blackboard, scratched and worn and chalk-smeared, and then had a perfect copy made down to its every crack and smudge. There’s no telling which blackboard came first when you see them in “The Double,” but who can resist the temptation to try? Although our brains are built around the detection of difference — that’s what makes a signal stand out from noise — it turns out that perfect duplication can also be hugely salient, if only because it’s so rarely found.

The preciousness, even fragility, of absolute sameness came clear to me in a piece by Roni Horn. Her “Things That Happen Again,” from 1986, presents two identical cones, each about the size of a basset hound, immaculately machined out of solid copper. The industrial perfection of their duplication is part of their appeal, as I realized when some visitor left a big, greasy handprint on the gleaming copper of one, destroying the match between the twinned pair. National Gallery staff members were distraught, but the damage, soon polished out, only reinforced how much perfect identity mattered to the work’s effect.

The issue of sameness — or is it the problem of difference? — lies at the heart of the most fascinating double work that I know of: The two canvases of Robert Rauschenberg’s “Factum I” and “Factum II,” both of which are in “The Double.” At some point in 1957, at just about the height of America’s craze for the one-off outpourings of Abstract Expressionism, Rauschenberg set out to make a single outpouring appear to us — twice. Each “personal” mark he brushed onto one canvas he then repeated as identically as he could on the other. If he transferred two identical press images of President Dwight Eisenhower onto the surface of one work, he put them in the other as well, doubling the doubling that our age of mass reproduction had allowed.

Rauschenberg had recently begun life as a gay man when he made his two “Factums.” (Jasper Johns, his partner at the time, has a pair of his signature flags in the show.) It’s hard not to feel that Rauschenberg’s sexuality informed his great study of duplication and disparity.

Other powerful works in “The Double” are by gay artists who take on sameness more directly.

Photographs and a video by the duo known as Gilbert & George — Gilbert Prousch and George Passmore, who have lived and made art together in London since 1967 — show them in the matching bank-teller suits that to this day are their trademark. Over the years, they’ve turned the match in gender that troubles homophobes into a prideful mark of their identity: They inhabit the “homo” in “homosexual,” even though it’s usually thrown at gay men as a slur. Yet even as Gilbert & George use art to confirm their coupledom, their gray-flannel camouflage hints that this comes with a loss of individual presence. (An excellent catalog essay by Julia Bryan-Wilson attacks the idea that queerness has much to do with being “the same,” except in the minds of worried straights.)

“The Double” offers artists of color who face an equally vexed relationship to the “identity and difference” that’s mentioned in the exhibition’s subtitle. A 2012 piece by Glenn Ligon presents the word “America” written in neon, once rightside-up, in glowing white letters, and then below that upside-down in black letters that glow only from behind. Ligon captures how blackness in this country is always seen as a dark flip side of white, but he introduces a wrinkle: In black, the nation’s name reads normally; in his white text, the letters turn backward halfway through the word. Whiteness comes across as the source of our confusion, whereas American blackness seems to know where it stands.

If twoness plays out across so many artistic dimensions — racial, sexual, aesthetic, cognitive — that may be because it’s more basic to art than even this show lets on: It turns out that even most single pictures are twins. An older piece at the National Gallery might have made clear the high stakes in James Meyer’s theme. Joseph Wright’s “The Corinthian Maid,” painted in the 1780s, illustrates an antique tale that explained the very origins of art in terms of doubling: Once upon a time, when a young woman’s lover was about to leave town, she traced the outline of his shadow on a wall so as to still have him beside her once he’d gone; all pictures followed from that moment, says the story, as they worked to “make absent things present.”

That tall tale gets something right: Doubling the stuff that matters to us has been central to art since we put bison on cave walls.

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The Double: Identity and Difference in Art Since 1900

Through Oct. 31 at the National Gallery of Art, Washington, D.C.; nga.gov.

This article originally appeared in The New York Times.