Many years ago I gave a lecture at Queen’s University Belfast on a theme I have long since forgotten. After the lecture Prof Singh of the Italian department came up to say hello and to invite me, if I were so inclined, to listen to a tape recording of a recent lecture given at Queen’s by the literary critic FR Leavis. The subject was William Butler Yeats.

I was indeed so inclined, especially as Dr Leavis had turned down my request that he write an essay for An Honoured Guest, a collection of new essays on Yeats that JR Mulryne and I were compiling. Leavis’s assessment of Yeats was hard to find – he did not write on him as often as on TS Eliot – so his lecture would be a pointed occasion. The following morning, before catching the train to Dublin, I listened to it in silence with Prof Singh.

Leavis began by asserting that although Yeats was obviously a major figure, it was difficult to point to a single poem in which his genius was manifest. Without more ado, Leavis chose to comment on three poems: Sailing to Byzantium, Byzantium and Among School Children, in that order.

The poems of Byzantium did not in the end survive his most concentrated attention. Leavis dismissed them, although with blessings on their heads: they were too dependent on Yeats’s private scheme of reference. When he turned to Among School Children, I felt that nothing less than western civilisation was in question. If the poem survived Leavis’s scrutiny, than civilisation would have a chance: if not, not.

Leavis’s commentary was far-reaching, a quest of significances for which the local detail of Yeats’s language in the poem was resorted to for evidence. I still recall the tension and the excitement I felt as Leavis’s phrases leaned one way or another in the commentary: they seemed to hold themselves in reserve, endlessly postponing the verdict.

To my nearly exhausted relief, Among School Children passed with honours; it survived Leavis’s concerned analysis; it was a fully achieved thing. Not only did the poem withstand any degree of critical pressure as a poem, but it also testified to cultural possibilities that might be invoked in its name.

I was immensely gratified and took the train to Dublin with Among School Children and Leavis’s commentary almost equally in my head. In the meantime, and perhaps because of Leavis’s praise, Among School Children is accepted, so far as my reading goes, as Yeats’s finest poem. The two Byzantine poems are argued over, sometimes given a splendid pass, sometimes not.

I hope that my recollection of Leavis’s recorded lecture is accurate, but it may not be. Many years later I find that, in his Lectures in America (1969), he declares both of the poems of Byzantium to be “triumphs of a wholly original art of creative expression that is contemporary with Eliot’s”. Speaking of The Tower, Leavis said that “the volume containing Sailing to Byzantium and Among School Children impressed one – and impresses – as coming from a major poet”.

This points to another instance of unanimity. It is universally agreed that Yeats became a great poet, not merely a post-Victorian lyricist, with the publication of Michael Robartes and the Dancer (1921), The Tower (1928), and The Winding Stair and Other Poems (1933).

In these books he achieved a poetry of which even Leavis, a critic not disposed to admire it, wrote: “There is no element of a man’s experience in the twentieth century that, of its nature, it excludes.”

Anyone is free to admire some earlier and some later poems, as TS Eliot admired Who Goes with Fergus?, The Folly of Being Comforted, Adam’s Curse and Pardon, Old Fathers. Conor Cruise O’Brien spoke well of the very late Cuchulain Comforted, and nearly everyone likes The Circus Animals’ Desertion.

Still, the crucial poems are still thought to be those of the three central books. I would cast a vote for The Wild Swans at Coole (1919), if only because it contains In Memory of Major Robert Gregory, A Deep-Sworn Vow and Upon a Dying Lady. But to make a case for that book is another day’s work.

Michael Robartes and the Dancer, The Tower and The Winding Stair and Other Poems are the books in which Yeats solved, or came closer than any other modern poet in English to solving, the problem that defeated so many of his contemporaries: how to reconcile the claims of common speech, morally responsible, with the insisted-on autonomy of the poem, a reconciliation of image and discourse, meaning and form, a claim to unity inherent in the symbolism that modern English poetry inherited from French.

The poem, whatever its materials, must be one, complete, independent, as articulate as a piece of music, a painting or a dance by Balanchine, which it resembles in everything but the fatedness of speech.

Yeats made this achievement difficult for himself by writing poems in response to occasions. Something happens that makes something else happen in its turn. Robert Gregory was killed. Then we get In Memory of Major Robert Gregory, one of the classic poems. Most of Yeats’s poems are occasional. Something arouses him to anger, rage, disgust, love, pity: he writes a poem, and perhaps with Jonathan Swift for master he puts aside for the moment the supreme need of his art to ensure that the aesthetic function will prevail.

Eliot never worked in this way. He was a man of the world, he paid attention to nearly everything that was going on, but when he was impelled to intervene he consigned his words to an essay, a lecture, an editorial in the Criterion, a letter to some editor. He kept his poems at a distance from such provocations. Yeats was also a man of the world, but he took its observances differently.

Leavis thought Eliot’s way the better one. “Where Eliot is in question, it is the economy, concentration, perfected art and assured creative purpose of the body of achieved poetry that tells.” The jury on that question is out.

In A General Introduction for My Work (1937) Yeats made an attempt, laborious indeed, to distinguish between the poet and “the bundle of accident and incoherence that sits down to breakfast”. The poet “has been reborn as an idea, something intended, complete”. “Idea” doesn’t convince, if he means the poet concentrating on his craft and the tradition he honours. Yeats tries again: “he is more type than man, more passion than type.” That is no help.

There is always a phantasmagoria, Yeats says, and I presume he means that the poet’s imagination is all the time working, as if independently, projecting a bizarrerie of images, scorning what goes on at the breakfast table.

Then Yeats gives us a sentence we can use. We adore the poet, he says, “because nature has grown intelligible, and by so doing a part of our creative power”. Presumably he means that it is the poet’s business to show this growth happening, or to make it happen.

So Yeats has been intuiting the life common to all forms of it and bringing particular forms to the state of being intelligible. This is easy with landscape, because landscape has nothing to say for itself: if it seems to be eloquent, it is our eloquence. In The Wild Swans at Coole the streams are “companionable” not because they just are but because Yeats sees them as such, bringing them to that version of intelligibility.

It follows that the intelligible must be conveyed in common speech, and that much of the work is done by adjectives, which indicate modes of existence. As in The Second Coming:

. . . somewhere in sands of the desert

A shape with lion body and the head of a man,

A gaze blank and pitiless as the sun,

Is moving its slow thighs, while all about it

Reel shadows of the indignant desert birds.

“Indignant” does the work of intelligibility; it is what we would feel if we were a desert bird. In Leda and the Swan:

Did she put on his knowledge with his power

Before the indifferent beak could let her drop?

“Indifferent” is one of our feelings, not an attribute of beaks. If a reader were to point to the tyranny of adjectives in these and other poems, I don’t see how I could defend the words: they convert the natural modes of being to human modes, inexorably. But that is our way of being alive. Everything ends up in the humanity of speech. Nouns are more resistant, such as “stone” in Easter 1916: they are what they are. I see no way out of these quandaries.

No matter how often I read Among School Children I still find it thrilling – and would be quite willing to see the fate of western civilisation hang in its balance. The first stanza – “I walk through the long schoolroom questioning” – is just as stirring as the great last lines, gnomic as they are:

O chestnut-tree, great-rooted blossomer,

Are you the leaf, the blossom or the bole?

I would say: all of the above, like St Patrick’s shamrock, three things in their unity one:

O body swayed to music, O brightening glance,

How can we know the dancer from the dance?

A harder question. I would say: we can’t know the dancer from the dance, if by knowing you mean the same knowledge that distinguishes leaf, blossom and bole. But I can’t imagine under what conditions, and with what motive, we would need or want to practice such knowledge. Dancer and dance are two names for the one figure, an act of culture, not of nature, which comes to intelligibility in the form of appreciation. That, too, is part of our creative power.

Denis Donoghue is university emeritus and Henry James professor of English and American letters at New York University