When T. S. Eliot published his seminal manifesto, he could boast only a thin volume of poems and a handful of essays, but he had confidence to spare. Photograph by Bachrach / Getty

Sometime during the early days of September, 1919, T. S. Eliot—just thirty years old and working as a clerk in the foreign-exchange division of Lloyds Bank in London—sat down and wrote his manifesto as a poet and critic, “Tradition and the Individual Talent.” Its effects were hardly immediate. The essay appeared in the September and December, 1919, issues of The Egoist, the London-based little magazine for which Eliot had been serving as an assistant editor since June, 1917. These would turn out to be the last issues that the magazine would publish. A “Notice to Readers” in the December issue announced a hiatus for 1920; the editor Harriet Shaw Weaver wanted to focus her energies on publishing books. That pause would prove to be a full stop. Not many could have been disappointed at the announcement: The Egoist, by its end, boasted a print run of just four hundred, and a mere forty-five subscribers. In “Paradise Lost,” Milton argued for the sufficiency of a “fit audience . . . though few”—but there are limits.

Though “Tradition” was initially seen only by a coterie audience, it is Eliot’s most important essay—and arguably, the most influential English-language literary essay of the twentieth century. From that modest début, its reach has grown exponentially. Within a year, the piece was included in Eliot’s first critical collection, “The Sacred Wood,” published in November, 1920. It subsequently appeared in the three other volumes assembled by Eliot, including “Selected Essays,” which itself went through three different editions. In that collection, “Tradition” has the pole position.

And it wasn’t the first choice of Eliot alone. “The Norton Anthology of English Literature,” that canon-creating textbook par excellence, has included the essay in every one of its ten editions, dating back to 1962; in that first edition, Eliot is the only twentieth-century poet whose criticism is represented. “Tradition” is further reproduced in all nine editions of Norton’s American-literature anthology (as an American expatriate, Eliot is hard on taxonomies, and both the British and the Americans tend to claim him) and many other literature textbooks. The essay has been an important part of the literature survey curriculum for more than half a century. “Tradition” is the criticism that critics read when they’re figuring out that they want to be critics. In the literature and literary criticism of the twentieth century, it’s simply unavoidable.

In 1919, Eliot could boast only a thin volume of poems and a handful of essays and reviews, but he had confidence to spare. In a letter sent to his mother, back in St. Louis, in March of that year—six months, that is, before he published the first essay he would deem worthy of reprinting—he wrote, “I really think that I have far more influence on English letters than any other American has ever had, unless it be Henry James.” It’s an outlandish claim, even if one allows for the kind of hyperbole to be found in a letter meant to impress one’s parents. (To be fair, he does go on to admit, “All this sounds very conceited. . . . ”) “Tradition” is stamped with the voice of a young man intoxicated with a belief in his own authority; as he wrote in that same letter, “I can have more than enough power to satisfy me.” In “Tradition,” we first see him flex those muscles.

The essay is a challenge to the conventions of early twentieth-century literary criticism. Eliot’s most concise statement of his thesis comes at the start of the December installment: “Honest criticism and sensitive appreciation is directed not upon the poet but upon the poetry.” That literary criticism should focus on texts might seem axiomatic; that it ought not pay attention to the author is perhaps less obvious. Eliot is reacting to a wave of criticism in which study of the poet had too often been substituted for study of the poetry—an orientation sometimes known as biographical criticism and which, in the generation following Eliot’s essay, would be dubbed the “biographical fallacy.” In Chapter 2 of “Ulysses,” Stephen Dedalus’s employer, Mr. Deasy, lectures him about frugality: “But what does Shakespeare say? Put but money in thy purse.” Stephen mutters a single word under his breath in response: “Iago.” Stephen is, after his fashion, pushing back against the biographical fallacy. “Shakespeare” didn’t “say” that; rather, it was voiced by perhaps the most monstrous of all his characters. Iago’s statement reflects nothing, necessarily, about Shakespeare’s own values and judgments. As Eliot writes of the poet in general, “emotions which he has never experienced will serve his turn as well as those familiar to him.” And this applies not just to named literary characters—the “I” that speaks in lyric poetry is also a character, not entirely coincident with the writer who formed that character on the page. “The more perfect the artist,” Eliot insists, “the more completely separate in him will be the man who suffers and the mind which creates; the more perfectly will the mind digest and transmute the passions which are its material.” This is the creative license that makes imaginative literature possible. And, in 1919, Eliot thought it to be in jeopardy.

“Tradition” is filled with mannerisms that become familiar across the body of Eliot’s critical writing. For instance, he betrays a particular fondness for the vast generalization and the unsupported assertion—unsupported, that is to say, but for the magisterial tone and sonorous sweep of his prose. Take, for instance, the opening gambit of “Tradition”: “In English writing we seldom speak of tradition, though we occasionally apply its name in deploring its absence.” Before the era of big data and text mining, what would evidence for such a claim even look like? By means of that “we” (not the royal “we” so much as the faux-communal “we”), Eliot as much as suggests that this is conventional wisdom—what kind of a pedant would insult our intelligence by proving it? Likewise, two years later, in “The Metaphysical Poets,” he will insist, making a virtue of necessity, “We can only say that it appears likely that poets in our civilization, as it exists at present, must be difficult.” One of the most daring critical pronouncements of Eliot’s career—the assertion that difficulty isn’t an unfortunate artifact but actually the litmus test of advanced writing—is just dropped on the page as if it were too painfully obvious to warrant discussion. The scholar Leonard Diepeveen aptly describes this feature of Eliot’s critical prose: “Though he regularly asserts the need for evidence, Eliot doesn’t often provide it.”

What makes “Tradition” such a durable touchstone? In it, Eliot essentially declares Romanticism dead to rights, insinuating that modernism (without employing that label) is the new king. (His friend, the poet-critic T. E. Hulme, had already performed the autopsy roughly seven years earlier, in his essay “Romanticism and Classicism”—but Hulme was killed in the First World War, and the piece wasn’t published until 1924.) William Wordsworth, in the key text of Romantic poetics, the preface to “Lyrical Ballads,” from 1800, had urged that “all good poetry is the spontaneous overflow of powerful feelings . . . recollected in tranquility.” (Which is nothing if not categorical—unproven and unprovable. Eliot wasn’t the only poet partial to such pronouncements.) In “Tradition,” Eliot explicitly rejects that formula, calling it “inexact”: “it is neither emotion, nor recollection, nor, without distortion of meaning, tranquility.” Rather, Eliot insists, “Poetry is not a turning loose of emotion, but an escape from emotion; it is not the expression of personality, but an escape from personality.” And then the rim-shot, at which Eliot excelled: “But, of course, only those who have personality and emotions know what it means to want to escape from these things.”