If I understand you correctly, you're saying that a defining characteristic of Modernist art was its appeal to an elite audience. This was accompanied by a corresponding contempt for the vulgar masses and for middle-class philistines who are not "really, truly in love with art." Pop Art brought about the end of Modernism by erasing these distinctions—that is, by making high art that appealed to a popular audience. Unlike the "difficult" paintings of Picasso and Braque, or Pollock and DeKooning, works of Pop Art were, as you write, "all too easy to understand."
The problem with this argument, as I see it, is that Pop Art really doesn't appeal to vulgarians and philistines. While Andy Warhol did achieve a certain degree of fame and notoriety during his lifetime, he never came close to the genuine popularity of artists like Edward Hopper, Andrew Wyeth, or LeRoy Neiman—or, to take a more recent example, our current, unrivaled master of kitsch, Thomas Kinkade. In fact, most art-world outsiders still seem to regard Warhol as a charlatan and a fraud, or as Robert Hughes once put it, "a cashiered Latin teacher in a pale fiber wig." And it wasn't only Warhol's swish, deadpan persona that alienated the public at large; it was also the brashness and stubborn ambiguity of the art itself.
Pop Art drew its imagery from lowbrow sources like comic books and tabloid news photographs. But this doesn't mean that the art itself was easy for a popular audience to understand or interpret. Let's take as an example Warhol's iconic Brillo Box (1964), which, as you astutely point out, rivals John Cage's silent composition 4'33" in its sheer decisiveness. The questions raised by Warhol's Brillo Box—What is a work of art? How do you distinguish an art object from any other artifact or thing in the world?—are not easy ones to answer, for philosophers or philistines. The fact that Pop Art deliberately undermined many of the qualities that people had come to expect from art—like uniqueness, originality, and individual expressiveness—only made this work more difficult for "ordinary" people to appreciate.
Though I don't think Pop Art brought about the end of Modernism by democratizing art, I do agree that Modernism suffered a kind of slow death in the early 1960s. The primary cause of death—and I'm certainly not the first to suggest this—was the steady assimilation of Modernist avant-gardes by mainstream institutions like museums and universities, and by the market. By the 1960s, Modernism had metastasized into the official culture of art. The shock of the new had grown old, and Modernism's taboo-shattering transgressions gradually evolved into the highbrow equivalent of classic rock.
Which brings us to my next question: What comes next? In your final chapters, you entertain the possibility of a Modernist revival, pointing to the novels of Gabriel García Márquez and the architecture of Frank Gehry as works that carry the torch of Modernism into the 21st century. You end the book on a personal note, describing your experience of a recent visit to Gehry's titanium-sheathed Guggenheim Museum in Bilbao. You convey your enthusiasm for the "wealth and elegance of the forms" through loving descriptions of the building's "assortment of curves, of weight-bearing, slightly twisted pillars, of curved internal bridges, of enticing balconies, all of them enlivened by museum-goers wandering about the spaces." Your verdict: The museum is a "Modernist masterpiece."
Now, Gehry's Guggenheim is surely innovative and thrilling to behold, but is it Modernist? Like many independent-minded artists, Gehry doesn't like to be connected with any particular style or movement. Nonetheless, his work has been widely discussed in terms of architectural Postmodernism, and even more specifically, in terms of Deconstructivism, a style that arose in the late 1980s and is often associated with the work of Peter Eisenman, Rem Koolhaas, Daniel Libeskind, and Zaha Hadid, among others. Like these architects, Gehry rejects the Modernist principles of "form follows function" and "truth to materials." His designs represent a radical departure from the straight lines and ordered rationality of International Style architecture. So, I wonder if you could say a little more about why you consider Gehry's Guggenheim to be a Modernist, as opposed to a Postmodernist, work? And more broadly, I'd be interested to know what you think of Postmodernism as a term to describe the cultural and stylistic tendencies (like irony, fragmentation, hybridity, and self-reflexiveness, to name just a few) that have surfaced since Modernism's demise in the 1960s.
I've enjoyed our brief exchange, Peter, and I'm sure that your excellent study will find a place on the bookshelves of cultural cognoscenti for many years to come.