Modernist, like romantic or liberal, is one of those words that has been used for so long, to mean so many different things, that it is now paralyzed by connotations. Even in its narrow art-historical sense, the word raises more questions than it answers. Do the novels of Virginia Woolf really share some common inspiration with the architecture of Walter Gropius, the music of Arnold Schoenberg, and the films of Sergei Eisenstein? If so, is that spirit liberating or exclusive, democratic or authoritarian, beautiful or terrible? Can a single period — roughly 1890 to 1930 — engross the name of modern, so that everything that comes after it is somehow less modern, even though it is newer? Are we doomed, in an age that still names itself postmodern, to try to endlessly recreate the modernist shock of the new — and can that shock even exist, now that the old canons of art have been so thoroughly abolished?

These are the questions that one might expect a book titled “Modernism” (W.W. Norton, 610 pp., $35), by a historian as eminent as Peter Gay, to try to answer. In this big book, however, Mr. Gay — whose work on Freud and Weimar Germany has previously shed so much light on the wellsprings of modernism — opts for breadth over depth, information over insight. What he offers is a sort of gazetteer to the art and literature of the early 20th century, rehearsing the most famous features of the most famous works, and peering into a few lesser-known corners.

Yet this intellectual tour ends up leading nowhere, because Mr. Gay offers no compelling analysis of what modernism was or what it meant. Instead, he leaves the reader with the impression that modernism was just the result of a bunch of geniuses getting born at around the same time, so that, if more geniuses were to arrive, the modernist era could be prolonged indefinitely: “Music or painting still await their Stravinskys or their Picassos,” he concludes. “That is all we now know.”

The best way to approach “Modernism,” then, is as a highbrow crib — a way of getting up to speed on the names and works that every educated person is supposed to know. Mr. Gay devotes a chapter each to painting and sculpture, literature, music and dance, architecture, and theater and film. In each genre, he focuses on a few important artists, giving capsule biographies and touching on their major works. He rounds out the picture with a summary of minor figures, and of the movements and grouplets in which modernism was so rich.

The section on painting, for instance, devotes several pages each to Kandinsky and Picasso, but also makes room for painters of lesser achievement whose lives or ideas have an emblematic significance — Ensor, Duchamp, Magritte. Mr. Gay sketches the evolution of painting from Impressionism through Fauvism to Cubism, then picks up the story decades later to show the collapse of the modernist impulse in the gamesmanship of Pop Art. His survey course touches on all the expected bold-face names: Here are “The Scream” and Der blaue Reiter, Suprematism and ready-mades, Dali’s melting watches and Mondrian’s grids.

The chapter on painting is probably the best in “Modernism,” thanks in part to the copious illustrations. Yet even here, the problems with Mr. Gay’s method are apparent. For one thing, his summaries of the lives of major artists lean heavily toward trivia. It is not crucial to the history of modernism to know that when Mondrian came to the United States, Robert Motherwell sometimes took him out to dinner, or that Ensor’s father owned a souvenir shop. These sorts of details seem haphazard, the result of boiling down a full-length biography into a few pages. When characterizing an artist’s achievement, on the other hand, Mr. Gay is usually too vague. Does a reader unfamiliar with modern painting gain much sense of Picasso’s achievement by being told that “painting was indeed stronger than he was,” or that Kandinsky “worked vigorously, often in troubling uncertainty, on each of his pictures, and all that his audiences could do was to experience them”? Such summaries have a perfunctory air, as though Mr. Gay was more concerned with putting the subject to rest than with getting to the bottom of it.

These problems are still more troubling in the other chapters of “Modernism,” where the artworks cannot be reproduced in an illustration. The section on literature, for example, deals at length with Kafka, Woolf, and Joyce, yet quotes extraordinarily little from any of them. Instead of undertaking actual literary criticism, Mr. Gay restricts himself to unilluminating generalities. For example: “Joyce’s Ulysses is at once the freest and the most disciplined of novels.” Any sense of the particularity — what Stephen Dedalus might call the quidditas — of Joyce’s work is missing.

The problem, it seems, has to do with Mr. Gay’s uncertain sense of his readership — which is to say, of the purpose of his book. Usually, he assumes that his reader is so familiar with modern masterpieces that he can simply allude to them, rather than explain or introduce them. Such a reader is, perhaps, a subscriber to the New York Review of Books, familiar with the latest biographers’ gossip about Bloomsbury (“Virginia Woolf has become such a celebrity … that her life requires little elucidation,” Mr. Gay write at one point), or the controversy over T.S. Eliot’s anti-Semitism. Yet if he is rehearsing information the reader already knows, Mr. Gay is not teaching him anything. On the other hand, if the reader of “Modernism” is not already initiated into the knowledge Mr. Gay takes for granted, the book will leave him out in the cold, overhearing a conversation in which he cannot take part.

The greater confusion of “Modernism,” however, lies in Mr. Gay’s attempt to distinguish the qualities that allow us to instantly recognize certain works as modernist. After a ritual invocation of Potter Stewart on pornography — “he knew it when he saw it,” he writes, and “noteworthy modernist works … leave precisely that impression” — Mr. Gay proposes two definitions of the modernist ambition: to be transgressive and to be radically subjective.

The first of these impulses is easy to recognize. The common theme of avant-garde rhetoric, from Baudelaire down to the present day, is hatred of the bourgeoisie, that fabled repository of cowardice, convention, and greed. In the middle of the 19th century, Flaubert called himself a “bourgeoisophobe,” while more than 100 years later, Claes Oldenburg was still calling for an “elevation of spirit above bourgeois values.” Much of the initial power of the great modernist artworks, from “Nude Descending a Staircase” to “The Waste Land,” came from their sheer violation of convention. Like the powder in a bullet, the charge of outrage in such works helped to propel them through the hard hide of public indifference, to lodge them in the heart of the 20th century.

Yet it is hard to see, from Mr. Gay’s account, what the modernists’ transgressions had to do with their other supreme principle, “the commitment to a principled self-scrutiny, which entails an exploration of the self.” For this “subjectivity,” as Mr. Gay also calls it, is precisely what is missing from the most genuinely modern artwork. Where is the self in “The Waste Land,” a poem that notoriously has no “I,” and whose speakers seem to follow one another like voices overheard in a crowd? What could be more “objective” than the geometric grids of a Mondrian painting, which could almost be generated by an algorithm? Yet Mr. Gay writes that for Mondrian, “subjectivity was all,” because “he trusted his intuition alone.”

Here Mr. Gay seems to be using “subjective” as a kind of synonym for “autonomous.” But an interest in subjectivity, one might more truly say, was characteristic of the era that preceded the modern, of Romanticism; what emancipated the moderns from Romanticism was precisely their rejection of the subjective. The modernist insistence that the artwork be autonomous — beholden to no traditions, no conventions, no audience — was only a facet of their ambition for an art that is completely objective. Modernists aspired to create self-sufficient artifacts, whose value did not lie in representation of feeling or experience, but simply in their own poised presence.

Another way of putting it is that modernism was the idolatry of art — the belief that art could be a sufficient source of value for human life. Such a frail hope could only have arisen in the doomed culture of pre-World War I Europe, where a nihilistic undermining of all received values had left the intelligentsia with nothing to believe in except art. This worship of art explains the demanding sublimity of the best modernist works; but it also accounts for what Mr. Gay has a very difficult time explaining, the affinity of modernism for authoritarianism and illiberal politics.

For Mr. Gay, committed to the premise that modernism was liberation, the phenomenon of what he calls the “anti-modern modernist” — the modern artist who was a foe of liberty — is a conundrum. He can only write off each new example as “a tribute to the sheer complexity of human nature” — to quote his verdict on T.S. Eliot. Yet as these cases multiply — Mr. Gay names Marinetti and Hamsun, but could also have instanced Celine, Pound, and others — it becomes clear that the alliance of modernism and authoritarianism was not accidental. It was inevitable: Once aesthetic values take the place of spiritual and human values, there is nothing stopping the artist from seeing human beings as raw material, to be manipulated and disposed of in the name of some higher good.

Indeed, while Mr. Gay is right to say that Lenin’s Russia and Hitler’s Germany persecuted their avant-gardes, there is a sense in which these regimes were themselves modernist through and through — in totalizing vision, aestheticization of society, and contempt for “bourgeois” amenities like liberty and legality. Mr. Gay’s parting verdict on modernism — “It has had a good long run” — seems altogether inadequate to the power and ambiguity of the phenomenon his book discusses, but does not manage to explain.

akirsch@nysun.com