There is a well-established precedent that the end of the twentieth century served as a transition to what came to be known as the postmodern. Often, however, this transition has taken less than a decade and has proceeded smoothly. Many of the postmodernists of the 1990s are not remembered as stars, while the postmodernist contemporary today is well ahead of them. Consequently, the true postmodernists are the focus of the “Modernism” museum exhibition at the San Francisco Museum of Modern Art—one of two such institutes currently housed in the United States. Even if the entirety of history is timeless, over time certain countries and eras have had a large impact on the culture and orientation of the arts. Some nations, such as Britain or Germany, are the subject of constant study and comment. Many of the same are now viewed as postmodern ones: France, Brazil, and Argentina. The United States has long suffered the old lament: We are famous for a lot of things, but we seem to be slow to follow through with them. Often this is true of the arts, where the ascendant will tend to replace the failing and the obsolete with new works and styles. In any case, let us take a look at the role of a single century. Starting with the 18th century, art is very diverse: We can see effects of landscape painting, of landscape engineering, of folk art, of literature, and of domestic art, among other periods. By the early twenty-first century, however, the pre-industrial arts are almost totally absent. The classicism and empiricism of the nineteenth century seems quite dominant. This lack of pre-industrial art was a problem for tourism. Visitors to what is now known as Switzerland visited the Alps to see the magnificent domes of the monasteries; visitors to what is now Germany visited the Reichstag to see the centuries-old Grand Palace; and visitors to what is now France visited the Belle Époque villas of Paris. One might be tempted to suggest that hotels were too modern and bring the spaces back to, say, medieval levels. But this, too, is not true. Because pre-industrial art and architecture can be found only in limited and well-constructed recreations, and because such recreations have no incentive to come up with a fake version of pre-industrial art, pre-industrial art is actually absent from the architecture of France and Germany as well as Switzerland. The simple truth is that we are remiss if we do not recognize pre-industrial art and architecture as important parts of the cultural heritage. As we think about the current postmodernism, one of the significant things we know is that a strong push toward postmodernism was organized on the logic of the “value” of non-urban living. This understanding sought to “compensate” for the long-term decline of cities in the West. Hence architecture arose as a response to urban decay and produced some very strange forms of housing and housing design. This importance is highlighted by the context: We have learned so much about housing between the 1900s and the 1960s. So it is important to understand that these regulations come directly from the work of the most profound thinkers of the nineteenth century, who offered instruction to their successors. From the mid-1960s to the mid-1990s, postmodernism achieved an impressive level of dominance in American art, architecture, and design, so that it would seem unlikely that a half-century later, we would easily take for granted that the postmodern aesthetic would not turn out to be dominant. An amazing number of changes have taken place in the world over the last two generations. The places we visit do not always look the same; there is not always a leading nation to consult about the success or failure of new forms of art or architecture. Given these forces, a reaction is on the cards. While I did not see the SFMOMA exhibition in San Francisco, I think one can draw broad conclusions from the publications and talks delivered about the exhibition, as well as various survey shows. It is worth wondering, and I believe now even more than I did when we began writing this, how to tell between trying to explain the age of the postmodern and how to warn the young and those just beginning that this is an era of popular decline. Tyler Cowen is a Bloomberg Opinion columnist who teaches at George Mason University. This is an update of an article published by Bloomberg View on November 18, 2017.