In this difficult-to-classify book, Ian Sansom – best known for his mystery novels, which I’ve read and enjoyed – rambles through (or beside) one of the great modern poems: ‘September 1, 1939’ by W H Auden. It’s a poem I’ve read many times over the past forty years or so. Like Sansom, I’ve loved it dearly, been baffled by it, been inspired and annoyed, wished it were different, envied its perfections, sniffed at its imperfections and been generally grateful for the brilliance of the man who created it.

This book is not literary criticism, so don’t enter these gates with your head bowed. In fact, there has been very little real literary criticism since Erich Auerbach published Mimesis in 1946, which Sansom rightly calls ‘one of the last great, readable works of literary criticism’. The university presses continue to publish monographs that purport to tell us something about literature, but it’s generally a depressing spectacle. On poetry, it’s usually the poets who have something to say: Pound or Eliot, Winters or Jarrell, Brodsky or Heaney.

Auden has, more than most poets, attracted the best and the brightest among academic critics, and Sansom nods to all of them, especially John Fuller and Edward Mendelson. ‘Writing about Auden after Fuller and Mendelson is like playing tennis after Federer and Nadal,’ he says, somewhat cringingly. Sansom is a good cringer. If anything, he cringes too much. I got a little tired, at times, of his hand-wringing moments of self-doubt, though occasionally these approach high comedy, as in one aside where he recalls a reading he gave at a library where he was introduced as C J Sansom, the popular bestselling author of historical crime fiction. ‘When I explained that I was not, alas, C J Sansom, two women in the audience got up and left,’ he tells us. ‘The other half of the audience remained.’

It can’t be easy to write a critical book on Auden, who was among the most insightful critics of the last century. (Indeed, many of his best poems are criticism, such as his elegies for Yeats, Freud and James, or his incomparable reflection on Bruegel’s Icarus.) Sansom quotes (twice) Auden’s memorable lecture on poetry at Oxford in which he mused on his approach to criticism:

Speaking for myself, the questions which interest me most when reading a poem are two. The first is technical: ‘Here is a verbal contraption. How does it work?’ The second is, in the broadest sense, moral: ‘What kind of a guy inhabits this poem? What is his notion of the good life or the good place? His notion of the Evil One? What does he conceal from the reader? What does he conceal even from himself?’

It’s probably unwise to stray too far from these key questions, and Sansom knows this. When he turns periodically to the poem at hand, he’s remarkably good at describing the verse in technical (but not too technical) terms, and he gives us a broad sense of the kind of man behind the poem, dipping into biography again and again, but never systematically.

There is nothing systematic about his book, which consists of bits and pieces, quotes from other authors, reflections on Sansom’s own life in relation to Auden’s, as well as fiercely intelligent readings of individual lines and stanzas. For me, the book’s best moments are when Sansom is most critical of Auden: ‘Auden had a tendency throughout his career to reflect upon and attempt to solve and explain problems using the simplifying logic of the child.’ That is bold but accurate, though it also points to a strength in Auden that has always struck me: his ability to speak in abstract terms in a way that seems memorable in part because it has a childlike simplicity, one that can seem naive but nevertheless strikes at truth, as in: ‘Hunger allows no choice/To the citizen or the police:/We must love one another or die.’

The astonishing text at the heart of this book, after 9/11, acquired a prophetic as well as a diagnostic quality. Perhaps great poetry is always both of these things, showing us our future by revealing our present, if not our past. To illustrate this, Sansom quotes Auden’s unforgettable graduation speech at Smith College from 1940. It’s a poignant afterword to his poem, which he wrote only a year earlier:

On this quiet June morning the war is the dreadful background of the thoughts of us all, and it is difficult indeed to think of anything except the agony and death going on a few thousand miles to the east and west of this hall. While those whom we love are dying or in terrible danger, the overwhelming desire to do something this minute to stop it makes it hard to sit still and think. Nevertheless that is our particular duty in this place at this hour.

Few political poems strike emotional pay dirt with such consistency and effect as ‘September 1, 1939’. In the sprung rhythm of his three-beat line, with each of his eleven-line stanzas containing one sentence, the language leaps at our hearts and minds. Auden’s infamous cleverness and his wide allusiveness continue after many readings to startle in satisfying ways, even when we don’t recall exactly ‘what occurred at Linz’ or really know ‘What huge imago made/A psychopathic god’. What follows, of course, from these puzzling lines is the poem’s most clarifying moment: ‘I and the public know/What all schoolchildren learn,/Those to whom evil is done/Do evil in return.’

I had the good fortune to meet Auden at Oxford in 1972, a year before his death, when he had effectively come home to Christ Church to die. He was, at this time, a kindly and yet deeply witty and acerbic man who seemed to be in search of his dotage and failing badly to discover it. I asked him, as only a callow young man might do, which of his works he preferred, and he scolded me: ‘Never ask a poet to choose among his dogs, his children, or his poems.’ Yet I don’t doubt that he knew what he had achieved in this poem, with its bracing challenge to a world at war, its shocking intimacies and its vast historical echoes. Sansom has given us a book in which all serious readers of Auden will find something to value. He has chosen exactly the right poem for our times to anchor his thoughts on this man who came to define a generation.