Poetry anthologies are hotbeds of controversy, exciting rows over who's in and who's out. Peter Middleton on the latest addition.

An 80-something American poet once asked me with considerable pathos whether I thought his name would live on, saying that he had begun to doubt this since the editors of a new poetry anthology had written asking for permission to print just half of one of his shortest poems. He felt his once major reputation had sunk to half of a poem.

Poetry anthologies are often treated as a Who's Who of poetry, in addition to their functional role as textbooks and introductions, but if this was all they were, they would not matter as much as they do. Asked what satisfied her about editing The Bloodaxe Book of 20th-Century Poetry , Edna Longley said that it was the giving of pleasure to readers, introducing them to poets and poems they did not know and providing "an intelligible overview of a complicated field".

Anthologies are notoriously hard work to edit. Editors take them on because of their passion to "adequately represent the history", as the American scholar Keith Tuma told me he had aimed to do in his new Oxford University Press Anthology of Twentieth-Century British and Irish Poetry . It is this that also often makes them highly controversial.

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Anthologies such as A. Alvarez's The New Poetry , Michael Horovitz's Children of Albion , Blake Morrison and Andrew Motion's The Penguin Book of Contemporary Poetry , Gillian Allnutt, Fred D'Aiguiar, Ken Edwards and Eric Mottram's The New British Poetry, Michael Hulse, David Kennedy and David Morley's The New Poetry , Iain Sinclair's Conductors of Chaos , Peter Quartermain and Richard Caddell's Other and Longley's anthology, all marked significant moments in the history of recent poetry and poetics. They mapped out groups, themes and formalisms in new ways and, at their best, offered cultural histories of experience otherwise silenced or inarticulate. What they were not able to do was to bring together two opposed tendencies in British poetry, neither of which is easily named, which give different values to syntax, linguistic indeterminacy, performance, voice and the discourses of modern knowledge.

It is this representational deficit that Keith Tuma aims to make good. Not since Edward Lucie-Smith's useful 1970 survey in British Poetry Since 1945 has an anthology attempted this. Tuma's volume includes first and second-wave modernists (notably recovering figures like the Welsh poet Lynnette Roberts and the Jewish writer John Rodker), alongside Georgians, 1930s poets, Movement poets and Next Gen writers. Like Longley's anthology, it acknowledges the cultural federalism of the UK and Ireland by its inclusion of Irish, Welsh and Scottish writing.

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Because of its ambition to display a "variety of modernisms" and "give them a hearing among other poetries", this is sure to be a contentious anthology, as well as a historically important one. Set out chronologically in order of birth date, it places Bob Cobbing next to Philip Larkin, Roy Fisher with Ted Hughes, Lee Harwood with Seamus Heaney and John Wilkinson with Jo Shapcott.

Already it has provoked reader rage from the poet Sean O'Brien, who denies that modernism has gone unrepresented in previous anthologies and condemns much of the anthology's modernist offerings as "dull, pretentious, tin-eared, parasitic, fraudulent poems". This blunt dismissal quickly elicited a spirited defence from Michael Schmidt, who replies that such judgements are unfounded, although he concedes that the anthology is "provocative" as well as "intelligent".

What is this provocation? British poetries have long been divided by their attitude to modernist and avant-garde poetics, and as sometimes happens after long conflict, there is no overarching history of why and how this happened, no agreement about the conceptual names for poetic differences, and attempts at rapprochement easily result in the mediator pleasing no one. Those largely opposed to avant-garde poetics have had much more ready access to the larger publishing houses and better access to funding for magazines and prizes, but the avant-garde has often responded with its own sweeping dismissals of poetry created within that world and disengaged from dialogue.

David Kennedy recently wrote that "the reality of the past 50 years has often seemed like a kind of apartheid - two poetics in one country - in which nearly everyone is complicit". This is not a division between revolutionaries and conservatives. It is much more a dispute about how to contribute to the public spheres of contemporary Britain.

Most poets would see themselves as democrats, but the second-wave modernists would probably not agree with Simon Armitage and Robert Crawford, whose introduction to The Penguin Book of Poetry from Britain and Ireland Since 1945 claims that poetry should aspire to a "democratic voice". The modernists would surely argue that their non-discursive techniques are as good or better a means of generating greater democracy and that the linguistic complexities many of them employ do not produce an esoteric or elite art.

These poets agree on much more than they sometimes realise. When Kathleen Jamie says in a new (but disappointingly partisan) collection of essays on poetics, W. N. Herbert and Matthew Hollis's Strong Words: Modern Poets on Modern Poetry , that "poetry is a moral and democratic place where language concerns itself with truth", she might be describing the aims of second-wave modernist poets too.

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This could apply to Maggie O'Sullivan's performance-based treatment of words as objects of mystery that fracture dangerously under contemporary social pressures, or Peter Riley's thoughts in Excavations on death, history and Englishness - thoughts as much in the manner of John Donne as of deconstruction. And when Allen Fisher says in The Topological Shovel that the best recent poetry "sees that culture can only be challenged, and consciousness raised, by experimenting with new forms of art, which involves participation in a more active manner than most forms of poetry reviewed", this could fit Medbh McGuckian's layering of metaphors from private and public worlds that enables her to write of fruit as "an accomplished terrorist", or Paul Muldoon's use in Incantata of a flexible line whose opening word endlessly repeats while its length varies with the intensity of elegiac emotion.

Raising consciousness and challenging culture is just what Sarah Maguire, also writing in Strong Words , means when she says that "it's precisely because the poem can render the most intimate and elusive of subjective experiences in language that it's able to bear witness to what's excluded from dominant discourses".

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A few anthologists work around the problem by breaking away from the standard model of the anthology. Nicholas Johnson's Foil: Defining Poetry 1985-2000 is a stimulating collection of new work by younger poets that is not so much a "best of" as a set of examples of activist improvisation with different traditions and media. When an editor breaks away altogether from author-based organisation, as Wendy Mulford does in The Virago Book of Love Poetry , or Jo Shapcott and Matthew Sweeney do in the more recent Emergency Kit , and present poems arguing and confiding in one another through intensities of thought, emotion and ethical vision, irrespective of authorial identity, the result can be transformative.

Tuma's revisionary history of modern British poetry suggests that what is needed if we are to do justice to the remarkable range of British and Irish poetry over the past century, is a greater understanding of the interactions of social and literary history.

For most of us, lived experience in the past 50 years has been a matter of hard, puzzling, crucial and often finely graded social divisions based on many different types of education, regional loyalties, hierarchies of employment, other language cultures and religious roots. These divisions bring great pressure to bear on poetry because the wider culture has done far too little work towards creating a many-voiced democratic voice. Both poetic modernism and the democratic voice can be too easily negatively misrecognised as cultural capital, generating oppressive difference.

After the second world war, literary rhetoric became widely suspect as having been complicit with the extremes of ideology. This combined with a long tradition of reticence about public debate in aesthetics (no manifestoes please, we're British) to make it hard to articulate sincerely held differences of method in poetry without resorting to mudslinging.

Of course, there are some excellent essays on poetics, mostly little-known and isolated by poetry politics - I often wish someone would edit a truly ecumenical collection of them. Academic literary criticism has made the situation worse by turning away from close reading to literary theory, cultural studies and historicism and hanging on to outmoded ideas of the lyric. Much of what we see in poetry on all sides goes on unstudied: in shifting modalities of emotion, voicing, and subjectivity; in the use of changed prosodies and non-metrical techniques which create their own aesthetically satisfying forms; in the appeal to new reading competencies shaped by television, or specialisms such as philosophy and natural science; in the unstable orality of performance; and the widespread use of poetry as a valuable form of cultural memory.

As a perceptive outsider, Keith Tuma has been able to compile a scholarly yet enjoyable anthology that will give pleasure to readers while prompting new research into literary form, language and history. Maybe it will even encourage new conversations between poets who suddenly find themselves between the same sheets.

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Peter Middleton is senior lecturer in English at the University of Southampton and co-author of Literatures of Memory , Manchester University Press, ?20.39.