Human Chain, By Seamus Heaney

I *Human Chain, the first collection from Seamus Heaney since he suffered a stroke in 2006, the completeness of the poet's recovery is affirmed by the book's quiet intensity, while a sense of human frailty has led him to draw his subjects closely about him in a freshly considered intimacy where elegy and affirmation appear inseparable.

Heaney's parents have long figured in his work, and the new book opens with five poems which revisit them on an evening walk in the fields, or at a wedding meal. The more musically exuberant manifestations of Heaney's skill are set aside here in favour of a bare simplicity of utterance which nonetheless performs a complex series of tasks. As an "ineluctable" ghost from his parents' future, he re-enters the past, witnessing scenes at which he was not present, showing with tactful sorrow how love's unbroken link, part of the title's "human chain", must itself be a form of separation.

The next, artfully situated poem, "The Conway Stewart", revisits Heaney's best-known early poem, "Digging", amending (though not betraying) its optimism in the light of experience. It describes his parents' gift of a pen the day before the poet left home for his secondary education at St Columb's College in Derry. The shopkeeper demonstrates how to fill it, "Treating it to its first deep snorkel/ In a newly-opened ink-bottle" – and immediately we are in the liquid, mysterious, many-layered, freely metaphorical world of Heaney's imagination. Such a transformation entails a cost: the pen's first official task in Heaney's hands is to write a letter home, so that in effect he signs the warrant for his own exile.

The urge is to return to that masterpiece of Heaney's middle period, "The Alphabet", and then page forward to the sumptuous medieval Irish poem here, "My hand is cramped from penwork", in which a scribe describes his quill: "Its bird-mouth issues a blue-dark/ Beetle-sparkle of ink." What can reconcile the poet's sense of loss with the joy of composition? The work itself must try to do so, conducted in the ethical spirit that Heaney's poems disclose.

In the subsequent diptych, "Uncoupled", we infer that it is separation that has enabled Heaney to do such tender honour to his parents. His mother, walking with a pan of ash from the fire, and his father among cattle and the noise of market, are transfigured, like inhabitants of a Virgilian underworld. Like his friend and contemporary Michael Longley, Heaney is the fortunate recipient of a Classical education. Their allusions to the characters of poetry and legend, and their adaptation of its landscapes and modes are not in the derogatory sense academic, but a claiming of an imaginative birthright the rest of us risk losing.

There may be those who would complain that Heaney's largely rural imagination makes him outmoded, but in respect of Human Chain they would have to answer the question of whether, in the light of his work, his parents are people of any less worth and dignity for living where and as they did. The answer, one hopes, is self-evident. Heaney's world of fields and ditchbacks and clustered placenames has never seemed like an escape, and nor has his treatment of the past ever seemed merely nostalgic.

As Human Chain repeatedly indicates, the past is quite as demanding as the here and now, offering both a challenge and a sustaining presence. "The Riverbank Field", written after passages from the Aeneid Book VI (in which Aeneas visits the underworld), addresses that challenge. As at school, the poem conspicuously "shows the working" of itself. Lethe becomes Heaney's native Moyola, complete with native insects, moths and midges for Virgil's bees, and after that there is a congruence of places in "the willow leaves/ Elysian-silvered". Eventually the poet continues "in my own words", evoking "presences" who "Are summoned here to drink the river water// So that memories of this underworld are shed/ And soul is longing to dwell in flesh and blood/ Under the dome of the sky."

When writing of his own illness in "Chanson d'Aventure", Heaney turns naturally to literature as a mode of knowledge. He remembers lying partly immobilised in the back of a car, accompanied by his wife on the way to hospital, and thinking of John Donne's "The Extasie", that intricate, beautifully argued love poem on the relationship of body to soul and of the spiritual union of those whom love "interinanimates": "we might, O my love," Heaney says, "have quoted Donne/ On love on hold, body and soul apart." Like an object lesson in the workings of the auditory imagination, the iambic form and desolate overtones of "apart" lead to another poem, Keats's "Ode a Nightingale", resurfacing in "Forlorn! The very word is like a bell/ To toll me back from thee to my sole self." The clasp of his wife's hand, which the stricken poet cannot feel, leads into Keats's lines to Fanny Brawne which imagine the living wishing to change places with the beloved dead – a thought to set alongside Heaney's description of the drip feeding him through a cannula.

In this very rich and substantial collection, Heaney makes frequent use of the tercet stanza, which posterity may indicate he has done much to render a contemporary forma franca. In his hands it has remarkable flexibility – see the dozen 12-line sections of "Route 110". The stanza moves as though between the epigrammatic hinge of a couplet and the more expansive quatrain, generating drama and extension (as though into the future of the imaginative act) through enjambed line-and stanza-endings.

The triple line, with its echo of terza rima, reels in and out, re-gathering to achieve the tension of resolution - a movement clearly suited to the alert, considering melodies that Heaney so often plays. How fortunate we are to have a poet of such formal mastery, who also speaks to us like an adult addressing other adults, who must like him remember innocence and encompass loss.

Sean O'Brien's new collection, 'November', is due from Picador in February