Snow Water
by Michael Longley
84pp, Jonathan Cape, £8

In "An October Sun", his elegy for Michael Hartnett, Michael Longley comes face to face with the kind of otherness that fails to put his poetry at its ease: "Something inconsolable in you," he writes, "looks me in the eye." The inconsolable is not, as Longley's readers will know, this poet's favoured subject; indeed, a great deal of his success over the past 13 years (with Gorse Fires in 1991, and its prize-laden successors The Ghost Orchid and The Weather in Japan in 1995 and 2000) has been owing to his gifts as a consolatory elegist, whose work has brought a unique gravity - and stylishness - to contemporary lyric poetry. It is a strength of "An October Sun", as well as its problem, that such accomplishments are seen to count for nothing: in Hartnett's imagined gaze, to which Longley gives the image of "An October sun flashing off the rainy camber", there is "something ironical too, as though we could / Warm our hands at turf-stacks along the road."

This irony from the dead, with its promise of only the coldest of home comforts, is at odds with much that Longley's poetry cherishes and celebrates. The poem has enough courage to expose itself to the irony, though it ends by translating this into its own terms:

   "Good poems are as comfortlessly constructed,
   Each sod handled how many times. Michael, your
   Poems endure the downpour like the skylark's
   Chilly hallelujah, the robin's autumn song".

"Comfortlessly" is important: its opposite may be the comforted (like the ideal audience for an elegy), or it may be the merely comfortable (like the writer at home in his environment and medium). Somehow, the idea of the comfortless sits awkwardly beside a compliment, even one paid with this degree of memorable elegance.

Snow Water marks a decisive moment in Longley's poetic development - as decisive, perhaps, as that signalled by Gorse Fires. But it is a mixed book, where the genuinely original has not quite broken free from the overly mannered. For poets, all stylistic and formal breakthroughs can become repeatable tricks, and much of Longley's best writing has created a repertoire of subject and style that can seem, at times, a slightly predictable routine: the townland of Carrigskeewaun in County Mayo, observed and celebrated repeatedly by its holidaying poet; wildlife and botany, recorded with spare and beautiful precision; family and friends, merging with flora and fauna; and the use of classical poetry - Homer especially - in the light of both Irish pastoral and modern horrors. In terms of form, the Longley poem has been characterised by long, immaculately cadenced lines, supple (sometimes miraculously stretched) syntax, and an increasing tendency towards overall brevity, with poems weighing in at four, two, or even single lines.

What is best in Snow Water begins to move in another direction, away from what has become both comfortable and (maybe too readily) comforted, towards the "Something inconsolable" that dazzles - however briefly - "An October Sun".

Some of the strongest of Longley's new poems revisit old preoccupations, but cast them into disarmingly strange shapes. Ever since youthful masterpieces such as "In Memoriam" (in his first book, No Continuing City, 1969), Longley has brought a startling clarity of imagination to the first world war, and has found in this a focus for both family and artistic concerns - his father, who served in both wars, is repeatedly elegised in this context, as are poetic heroes like Edward Thomas. Longley's war poetry can stand comparison with the best of its century; and Snow Water adds to the distinguished total, while also doing something radically new. "The Front" reads, in its entirety:

   "I dreamed I was marching up the Front to die.
   There were thousands of us who were going to die.
   From the opposite direction, out of step, breathless,
   The dead and wounded came, all younger than my son,
   Among them my father who might have been my son.
   "What's it like?" I shouted after the family face.
   "It's cushy, mate! Cushy!" my father-son replied".

Intimacy and catastrophe are as closely intertwined as ever here; but the intimacy has become confused and confusing, and the catastrophe a surreal combination of terror and comfort. "Cushy" (a word with its first currency in the Great War) seems here an unstable mix of irony and archaism - but it gains new, and arresting, life in the process: whatever else it does, "Cushy!" does not console, but disconcerts. The poem's deterministic repetitions reinforce the sense that Longley is here compressing his habitual material to the point where it starts to lose its recognisable features.

"The Front" is not alone in Longley's new collection in its radical refashioning of an already perfected manner. "Sleep & Death", one of two powerful new poems taken from Homer, chisels out a lyric from a piece of narrative in The Iliad; Longley has done this magnificently in the past, but now the poem shapes itself entirely around two passages of near-repetition, as Zeus gives detailed instructions for the removal of Sarpedon's corpse from the battlefield, then Apollo performs - to the last detail - the specified list of tasks. The close repetition is there in Homer, but in Longley's poem it is all there is, and the effect is one of eerie doubling, as Apollo hands Sarpedon over to "Sleep and his twin brother Death, who brought him / In no time at all to Lycia's abundant farmland". Care takes over where carnage has left off - but twice, and with a ritualistic attention to particulars mirrored in the act of verbal repetition. As a lyric, Longley's poem is almost a gesture of defiance against the momentum of telling a story.

In opening his poetry to increased levels of strangeness and unpredictability, Longley remains as immaculate a craftsman as ever; and Snow Water contains some wonderfully constructed lyrics of real delicacy and strength. But the book has its weaker moments: several poems relate to other artists, and there is a note of forced camaraderie to these, along with more than a hint of sentimentality, which sometimes pushes Longley too close to the downright twee ("I love it," he tells the poet John Montague, "when you link your arm with mine").

More interesting are the poems addressed to the Scottish sculptor Helen Denerley, whose reworkings of scrap metal into naturalistic representations of animals clearly speak to the poet's deepest, and most genuine, creative instincts. "I subsist," Longley says in one poem, "on fragments and improvisations": this is true of some of the new book - and of all that is best in it - but it also glosses Denerley's techniques, and seems to acknowledge her patient acquisition of bits and pieces, waiting for the time when they will unexpectedly come together. Longley's fine sonnet "Helen's Monkey" calls this "a long evolutionary autumn / Until you came across the unimaginable"; and again, this describes his own new work at its best - the imagination cutting adrift from its habitual comforts, and risking exposure to the comfortless. To ask, as the last poem in Snow Water does, "Is this my final phase?" appears self-regardingly beside the point when compared to such an insight. The unimaginable, like the inconsolable, is still able to surprise, challenge, and provoke Longley to his best.

· Peter McDonald is Christopher Tower student and tutor in poetry at Christ Church, Oxford