'I lob stones,' says the speaker in 'Messiaen's Piano', the opening poem in Fiona Sampson's Common Prayer. In a collection intensely preoccupied with the challenges of form, with its fragile yet dogged conditions, the stones suggest stanzas and syllables; the act of lobbing them, poetry itself. And about her form Sampson is, in this opening flourish, assertive and unapologetic. The 'beautiful world hardly responds' to these offerings, these notes, but they will go on. From a writer who migrated to poetry from an early career in classical violin, these notes of determination come as no gentle prelude, but as a manifesto, burnished by realism and edged by a palpable unease; Sampson's epigraphs, from Woolf and Lacan, attest to the difficulties of singing the 'real', of refusing to disguise 'the black God' in sweetness and light. Sampson, from the outset, is not celebrating the possibilities of art and form. She is fighting for them tooth and nail.

This preoccupation, immediately taken up again in the following poem, 'The Looking Glass', with its striking image of the nib in the writer's hand like a 'a crochet-hook/ pulling things across', echoes through almost every poem in the collection. Faced with moments of arch perfection outside the poem, the poet struggles to strike a comparable clarity, an equal stillness. A piece of grain is a 'secret mark of grace'. A sheet of glass 'absorbs shadow/bottomlessly', its colour 'deeper than image'. Ocean wind carries 'language you hear/but can't grasp'. Condensation, nature's own complex poetry, works with an enviably light touch: 'hot and cold/ which can't simply be folded/ into each other/ as if this were that' ('At the Sex Frontier').

The notion that language, with 'every name a displacement', always brings with it the risk of a hasty or inexact 'folding' is one which reaches all the way back to Sampson's first collection, Folding the Real. On the poet's page, there gapes a chasm, one which these new poems seem determined to recognise and to grasp. And although Sampson's engagement with the challenges she thus raises falls short of the fuller metaphysics of form and of art which her work, at first, seems set to offer - never fully interrogating that chasm, never going far beyond a casting and recasting of that challenge - yet there is in that naming of the chasm a striking, visceral brilliance which is something of a metaphysics in itself. A longing for the purity of natural light, for the starkness of whatever pervades these poems, fortifying Sampson's aesthetic with a raw urgency, a sorrow and anger.

It is in Sampson's poems on grief and illness that this battle with the sovereignty of nature is enacted most powerfully. 'The Plunge' and 'Scenes from the Miracle Cabinet' evoke the surreal misery of the watcher by the sick bed. A loved one shouts with pain: 'the giant listening on my tongue/ swells/ with the sound'. 'The sly music/ of the periodic table' enters a patient's mouth, a trace of an earlier poem's 'woody taste of steroids/ in sweat', the invasion and incursion of chemicals. Suffering is constant, rhythmical, almost mundane, and yet extraordinary in its cruelty.

Against these burdened incarnations, nature, with its reincarnations, seems heartless in its indifference. Yet Sampson's poetry does not settle for so defeatist a tune. A 'tree spawn' may be 'so sweet with pheromones' that a nurse will say it brings 'death indoors' but it is we who cut the tree-spawn, we are who arrange it, we who present it for pleasure or for reflection: the drivenness of the artist, the stone-lobbing tenacity of the poet are the reason enough for the notes to go on. For if the beauty of the human is harder still; the beauty of the suffering other, of the broken, already-grieved-for body. "I'm tired... of never-ending countryside,' says Sampson, in a poem which just happens to be pastoral, 'of everything that isn't you.' Which includes language, which includes water and purity of light. Sometimes what the poem wistfully longs for is in fact much more easily graspable than what the poem has already grasped: the pain of being human, of embodiment, of the vulnerable architecture of physical form. Sampson's poems do not merely understand the pain; they become it.