In moments of uncertainty, it sometimes helps to step back. To try to make sense of the myriad changes that have taken place in museums in recent years—changes of scale, character, and outlook—I’d like to take the long view and propose that we are now in the “Third Phase” of the great age of American art museums that began in the last quarter of the nineteenth century with the founding of institutions such as the Metropolitan Museum of Art, the Boston Museum of Fine Arts, the Art Institute of Chicago, and what would come to be known as the Philadelphia Museum of Art. What makes this period so different from those that preceded it is the questioning, even overturning, of many of the premises and principles that had guided museums in the past.

The museum regarded itself as a proactive force: an educator and arbiter of taste.

That first phase, let’s call it the Foundational Phase, saw the raising of great buildings to house their collections; the emergence of private benefactors such as J. P. Morgan to support them; and the professionalization of the institution—the insistence, for example, on displaying only original works of art and not copies, and on installing those objects by period or school and in other ways breaking with the “cabinet of curiosities” model epitomized by Charles Willson Peale’s museum. The mission was clear: to convey a sense of the unfolding history of art; to instill a discriminating taste; and to understand the language of art. The museum regarded itself as a proactive force: an educator and arbiter of taste, with the work of art the focus and center of the visitor experience. This process continued in the early twentieth century with the creation of the Museum of Modern Art, the National Gallery of Art, and the house museums established by the private collectors Isabella Stewart Gardner, Albert C. Barnes, and Duncan Phillips, though of course Barnes’s wasn’t a museum as such but an educational foundation.

We can mark the close of the Foundational Phase precisely: November 3, 1961. That was the day the National Gallery opened “Tutankhamun Treasures.” The first-ever exhibition of artifacts from the tomb of the New Kingdom pharaoh, it traveled over a period of nearly six years to eighteen cities in the United States, six in Canada, and three in Japan before concluding the tour in Paris. Thus began the second phase: a new, more ambitious and energetic one that would come to be known as the Blockbuster Era.

King Tut, in fact, became the emblem of the era, the gift that kept on giving. For the National Gallery’s show was the first in what would turn out to be four globe-trotting Tut shows over as many decades, making the Boy King the only Pharaoh to spend his afterlife not in the company of the gods Ra and Osiris but as a passenger aboard the Flying Dutchman.

One other event helped define this period: the appointment of Thomas P. F. Hoving as director of the Met, on March 17, 1967. Where, in the Foundational Phase, museums had gone about their business quietly, being to some extent rather sleepy affairs with a small, elite public, now, with Hoving setting the pace, museums began to adopt a healthy populism, working as never before to make their collections and art in all its aspects as exciting and accessible as possible. There were spectacular acquisitions and extraordinary exhibitions. Museums initiated lectures, concerts, and all manner of educational and public engagement programs. Amenities like dining and retail were ramped up. Architecture acquired a new importance, with signature buildings like Marcel Breuer’s Whitney and Louis Kahn’s Kimbell. Attendance soared. Yet for all these changes, museums’ central mission remained the same: educating the public in the history and language of art, with the art object at the very center of that effort.

There is a similarly clear-cut beginning to the Third Phase, the era of the Postmodern Museum, as there was with the Blockbuster Era. The pivotal moment came with the turn of the millennium: the opening in October 1999 of the first of moma’s “ModernStarts” exhibitions, and the opening in May 2000 of Tate Modern, the London Tate Gallery’s newly consecrated space for modern and contemporary art in a repurposed power station in the city’s Bankside district. Both events seemed commonplace enough at the time, yet in retrospect they appear to be auguries of the future.

The best way to understand the changes that have taken place during this period is to think in terms of a series of altered relationships. I identify three:

First, an altered relationship to the past. This is the most sweeping change, as it takes many forms. There is, first of all, the priority given to contemporary art, which is so overwhelming as to make it an absolute value. Acquisitions, exhibitions, curatorial appointments, board seats, and expansion plans all now revolve around contemporary art to an extent not seen previously. There is nothing wrong in principle with museums showing the art of our time. Indeed it can be useful, as a kind of “first draft of art history.” But contemporary art is best understood in relation to the past, and this becomes hard to do when, as is increasingly the case, it is promoted as an end in itself.

Contemporary art is best understood in relation to the past.

As a corollary to this, there is the changed relationship to the past represented by the objects in a museum’s permanent collection. The 1980s are famous for the epidemic of deaccessioning. Yet it didn’t go away—if anything it has become more acute, enough so that the Association of Art Museum Directors, the professional body responsible for standards and practices, felt compelled to revise its policy on deaccessioning not once but twice, first in 2007 and again three years later.

Exhibit A in this regard is the Albright-Knox Gallery in Buffalo, which in 2006 consigned some two-hundred objects from its permanent collection to auction. Among the objects disposed of were an ancient Chinese bronze wine vessel that The Buffalo News reported to be one of only a handful in existence and a tenth-century, life-size statue of the god Shiva. Regarding this object, a Sotheby’s specialist told the Associated Press at the time that it was “without question the most important Indian sculpture ever to appear on the market.” African, Pre-Columbian, and Egyptian objects as well as Old Masters were sold. The purpose of these sales? To raise money for modern and contemporary art acquisitions.

Various euphemisms and other linguistic fig leaves are routinely employed to explain and justify such actions—“refining the collection,” “focusing on our core mission,” etc. But the fact remains that however much museums regard the art of the past as part of a rich tradition informing the present, or as so many irreplaceable objects, historically valuable in their own right, to be held in trust for future generations, they also see it, as never before, as a negotiable financial instrument to be liquidated in the marketplace as the need arises.

Then there is the changed relationship to the past we know as the history of art. moma’s ModernStarts exhibitions were significant, first, because the museum abandoned, for the first time, the chronological installation of its permanent collection, its longstanding view of the history of modern art as a steady evolution driven by a succession of innovators, in favor of one that mixed artists, periods, styles, and media in order to, as it said at the time, “explore relationships and shared themes”; and second, because in so doing the actual and implied value judgments that are integral to such a reading of history were abandoned. Instead, we got a level playing field where all artists were accomplished, and notable for their “affinities.” Thus Paul Cézanne’s Bather (ca. 1885) was juxtaposed with a 1993 photograph of a boy in a bathing suit by the contemporary Dutch photographer Rineke Dijkstra, thereby transforming the man famously described by Picasso as “the father of us all” into just one more paint-slinger taking the human figure as his subject.

What made those shows a watershed event is that this approach—the museum stepping back from its historic role of explaining, through its displays, the story of art—soon became the norm, the model for displaying modern and contemporary art. moma institutionalized it when it reopened in 1995 after expanding, as have Tate Modern, the new Whitney, and others. Thus Glenn Lowry, in announcing moma’s latest expansion plan two years ago said, “Our goal is to provide visitors with the pleasure of finding their own meaning within a singularly inclusive constellation of twentieth- and twenty-first-century artistic practices.” More recently, Martino Stierli, the museum’s chief curator of architecture and design, told The Wall Street Journal that the overall goal of “From the Collection: 1960–1969,” its reinstallation of work from the Sixties, was “to come away from prescribing art history to the audience.” Rather than assigning each gallery a specific subject, the article continued, “we did it the other way around, and let the objects start a conversation between themselves.”

This new approach is different from the non-chronological hanging in a place like the Barnes Foundation. There it serves to demonstrate the essential unity of all art—ancient, Old Master, and modern—and to invite the viewer to discern that commonality by engaging in close, comparative scrutiny of a diverse array of objects. This one is value-free and as such a perfect reflection of our relativistic, postmodern zeitgeist—hence the name I have given to this phase of museum history. To get an idea of just what it implies, imagine walking into a museum’s Renaissance galleries and instead of starting with Giotto the first work you saw was by a Mannerist, then Mantegna, then Gentile da Fabriano, then Raphael, then Sassetta, and so on. You wouldn’t know any more about Renaissance art when you left than when you walked in. Or as the art critic for The Daily Telegraph put it when he previewed the new Switchhouse galleries at Tate Modern this spring, “By removing chronology as a way of understanding art, the rehang risks losing all sense of meaning.”

Pure aesthetic experience vies with the delivery of “information.”

Second, an altered relationship to the object. As we have seen, up until now the art object was considered central to the museum experience. But increasingly it is being relegated to a supporting role. It is by now a commonplace for our experience of the object to be mediated by technology—an app, a handheld device of some kind or, in the case of the Cleveland Museum of Art’s “Collection Wall,” a vast touch screen with almost an infinity of images from the collection which the visitor is invited to move and explore as he or she pleases. In all these cases, pure aesthetic experience vies with the delivery of “information.”

Then there is the Selfie Culture. Museums that permit selfies in their galleries—and almost all do—are downgrading the works in their collections to the status of stage props, things you stand next to and photograph instead of standing in front of and contemplating.

We see the art object diminished too in the new attitude toward museum architecture. However much a “statement” in its own right, the best museum architecture of the recent past did more than house artworks. It also served as a kind of handmaiden of the art experience itself. Here I think particularly of Louis Kahn’s Yale Center for British Art, so splendidly renovated and reopened this spring. Though it is powerful and deeply moving as an architectural experience in its own right, everything about its design, proportions, and spaces is geared to setting off the works of art to best advantage and creating conditions conducive to looking at them.

Beginning with Tate Modern, a very different set of imperatives has driven the design of museums. In part because of the increased scale of contemporary art and the extraordinary popularity of museums today, the premium is now on vast, barely articulated spaces that do not invite—and in some cases don’t even permit—stopping and looking at something. Instead art and the object have been subordinated to the accommodation and fluid motion of crowds.

This is a problem the Whitney sought to address in its recent expansion by having low-ceilinged, modestly sized permanent collection galleries on one floor for its pre–World War II easel-scaled paintings and larger ones on other floors for the work made since then. But they have been only partially successful. I wonder how many visitors to the recent Stuart Davis exhibition were struck, as I was, by the way much of the sizzling pictorial energy of Davis’s work was leached out by the cavernous spaces in which they were displayed.

Most alarmingly of all, in the upper councils of arts policymaking the art object is now considered virtually an anachronism. Last spring Karen Mittelman, director of the Division of Public Programs at the National Endowment for the Humanities, wrote in the latest issue of that agency’s magazine, Humanities, that

[i]f you walked into a large museum in the 1980s or 1990s, you would have seen galleries full of objects from the museum’s collection, carefully chosen and arranged by a curator with a label . . . explaining what you were looking at. Today this kind of static display seems almost antiquated.

And what sort of display does Ms. Mittelman think should replace it?

The art object is now considered virtually an anachronism.

This brings us to our final change, the altered relationship of the museum to its traditional mission. Today, museums are increasingly being called on to put aesthetics aside and serve as venues for politically and socially engagé programming. Thus, after dismissing the “almost antiquated” “static” displays of yesteryear, Ms. Mittelman lays out her vision of the brave new world of museums.

Museumgoers now have the expectation, when they walk into a museum, that they will be interacting with the content on display—curating their own virtual exhibits, sharing information about museum artifacts via social media, or participating in some kind of public dialog around issues important to them.

And what might those issues be? Why, “inequality, immigration, health and aging,” she informs us—not accidentally perhaps, all issues dear to the hearts of our progressive politicians.

But there’s more. “[U]ntil quite recently,” she continues, “neh’s grant guidelines did not speak directly to this vital role for museums, libraries and historical societies.” Not to worry, though, because, “In the neh Division of Public Programs, we have been reenvisioning our grant programs to respond to these changes.”

The message is clear: henceforth institutions hoping for neh funding are going to be expected to fall into line and “serve as ‘town halls,’ spaces where citizens can come together to talk and debate issues of significance to their communities.” And because Endowment grants are looked to as the Good Housekeeping Seal of Approval by private-sector funders, museums hoping to secure additional corporate and foundation support will have no way of avoiding compliance with what amount to government diktats.

At the outset of this essay, I wrote that we were in the third phase of the great age of museums, thereby implying the latest stage in a continuum. But are we? Or have we entered a new, altogether different era of museums?

The changes I have described are profound, transformative even, and give every indication of being far-reaching, if not permanent. The focus of these changes is the museum’s very essence, its raison d’être: the primacy of the art object and the visitor’s experience of it. One thing is certain: a new kind of art museum is taking shape before our eyes. What its final form will be, and whether it will bear any relation to the institution as we have come to know it, only time will tell.