Auden's affirming flame burns on

T. S. Eliot in "The Dry Salvages" wrote: "The sea has many voices, many gods and many voices." W. H. Auden, early and late, had many gods and many voices. But like the river with which Eliot in the same poem contrasts the sea - "the river is within us, the sea is all about us" - Auden's development as poet was shaped by the changing landscape of his inner life and his untiring attempt to find "a valid way of presenting the modern consciousness" in poetry and prose.

His gods, as this admirable and deeply attentive book by Edward Mendelson shows, were often shaped by his reading. Without having read Rudolph Kassner's Zahl und Gesicht , Auden could not have written "The Shield of Achilles", although by the time he wrote it, as Mendelson points out, "he had absorbed Kassner's meanings and made them his own". These gods, which Auden often pressed upon his friends as works that they too must seize upon, were left behind as he sought to discover new voices in his poems. Like the medieval craftsman, he never ceased to search for new masters from whom he could learn, and who enabled him to make full use of his "gift". As a poet he never ceased to acknowledge those from whom he had learnt most, for example Thomas Hardy, Goethe and Rilke, but the time came when in order to learn how not to be himself he had to move on.

Mendelson has followed Auden in his restless journeying, aware that at times the obscurities in his poetry are scarcely worth disentangling. An almost boyish enthusiasm for some new discovery leaves what is being said in the poem unfocused. As happens in The Age of Anxiety , some details "make sense only in terms of the little-known book in which Auden found them". But Mendelson never loses sight of where these currents are bearing the river, or their intricate relationship to Auden's personal life. The move to Ischia for the summers of ten years from 1948, like the subsequent move to Kirchstetten in Austria, were indispensable for the discovery of new poetic terrain, as his pained relationship with Chester Kallman was a constant in it. Ritual, whether through an ideal of married love, or the liturgy of the Anglican church, provided the meeting point between his two visions, neither wholly separated, nor wholly unified, of Eros and Agape. And neither could be detached from "the situation of our time" that "surrounds us like a baffling crime". Auden once wrote of Yeats that because he continued to be moved by what happened to him, "his work will always have that authentic ring which we recognise as poetry". Something comparable is at work in this book. Mendelson's commitment to Auden's art ensures that his immense knowledge amplifies the poems, and never magnifies the critic.

When, for example, he quotes Wittgenstein: the world "is everything that is the case", he illuminates the point of Auden's "nothing is lovely,/not even in poetry, which is not the case." Four hundred pages of this book are taken up with the years from 1939-58; and only a hundred with the last 15 years of Auden's life. In a letter written in 1966, Auden claimed that as a poet he had "got better". The title of this book suggests that unlike some artists - Yeats or Eliot - Auden did not have a final period in which a life's work culminates; but to claim as Philip Larkin did that Auden ceased to appeal to the imagination is plain wrong. As a comment on the darkness that has descended on us all, the penultimate stanza of "The Shield of Achilles" in its terseness and laconic understatement could not appeal more directly: "A ragged urchin, aimless and alone,/Loitered about that vacancy, a bird/Flew up to safety from his well-aimed stone:/That girls are raped, that two boys knife a third,/Were axioms to him, who'd never heard/Of any world where promises were kept/Or one could weep because another wept."

Whether writing figuratively, or aphoristically, or in a style that combines both kinds of language, Auden is at his best when he is not being difficult. Should not every student of history and war be asked to memorise these lines: "To save your world you asked this man to die:/Would this man, could he see you now, ask why?" And all those who live in these islands recall: "Winds make weather; weather/Is what nasty people are/Nasty about and the nice/Show a common joy in observing."

When the language is lyric, it is again the directness which tells: "My Dear One is mine as mirrors are lonely,/As the poor and sad are real to the good king,/And the high green hill sits always by the sea."

The feeling, as in much great poetry, cannot always be translated into other words but remains fixed in memory by its music and its suggestiveness: "Altogether elsewhere, vast/ Herds of reindeer move across/Miles and miles of golden moss,/Silently and very fast."

The power to objectify a personal feeling and turn it into a statement of general validity recurs again and again in these poems, and gives them their hold on imagination, though the hold is not always consistent, or sustained throughout a poem at the same level. Even "In Praise of Limestone" contains passages in a much lower key than its unsurpassed ending: "when I try to imagine a faultless love/Or the life to come, what I hear is the murmur/Of underground streams, what I see is a limestone landscape."

What runs through the later Auden, in the poetry's confrontation with all the fault lines of the 20th century, is an "affirming flame", recorded on the commemorative tablet in Christ Church cathedral: "Bless what there is for being". It comes partly (how partly one can never be sure) from the lines in "Nones" on Good Friday: "wherever,/The sun shines, brooks run, books are written,/There will also be this death."

It comes certainly from the knowledge of having been happy, as in "Goodbye to the Mezzogiorno", from the power of love to "astonish", as in "Since", from the friendships that survive even death, as in his poem for Louis MacNiece, "The Cave of Making", and from the magician's love of his art:

"for you the Ischian/wave shall weep,/When we who now miss you are American dust,/and steep/Epomeo in peace and war augustly a grave-watch keep."

How Horatian in style, how Miltonic in its love of the music of names, and how English in its spirit and humour! These were lines, as Mendelson reminds us, written for a cat, Lucina, buried at sea off Ischia. But, in his art too, he was aware of the wound in the poet's role, expressed in his prose poem Dichtung und Wahrheit , "words cannot verify themselves". Later Auden reveals the wound but also how far the strongly stretched bow could shoot.

Peter Mudford is reader in modern English literature, Birkbeck College, University of London.