Poems and Prose, By Elizabeth Bishop

That Elizabeth Bishop is a key figure in 20th-century American poetry is not in doubt. Her influence has even helped refurbish today's British verse, allowing it to escape the traditional face-off between Modernism and the lyric tradition. However, since 1994, when her selected letters were published as One Art, she has also come to be seen as a significant prose writer. In fellow American poet Robert Lowell's claim, "When Elizabeth Bishop's letters are published... she will be recognised as not only one of the best, but one of the most prolific writers of our century". Words in Air, the engaging duet that is his own correspondence with Bishop, appeared in 2008. Now these centenary editions of Prose and Poems have the responsibility of sustaining her reputation in coming decades.

Although published together, these volumes are not editorially symmetrical. While Poems is broadly inclusive, taking account of further unfinished work discovered since Alice Quinn's 2006 edition of uncollected material, the Prose is lightly selected. It omits for self-evidently practical reasons most of Bishop's translation of the book-length Diary of "Helena Morley". The only correspondence it includes are hitherto unpublished letters, rich in biographical detail and thoughts on the art of poetry, sent to Anne Stevenson while she was researching a monograph on the poet.

This scarcely matters for the reader new to Bishop's work; except that the writer who emerges can seem carefully accomplished in prose, yet risk-taking, even inconsistent, as a poet. It's a paradox that is probably intrinsic to the project. Bishop's method of composition – and indeed publication – was famously revisionary, and any reasonably comprehensive edition will necessarily unpick some of that revision.

Included here are, whisper who dare, poems whose heavy-handed use of rhyme sets up an unappealing, oddly-naive clangour. "Pink Dog", from the last year of the poet's life (1911-1979), may conceivably be imitating the folk art of the Brazilian Carnival, where it's set; but other uncollected poems sound frankly occasional.

Yet rhyme is what structures many of Bishop's canonical poems – such as "One Art", the experience of loss clicked shut in a villanelle, or "The Moose", five pages of "dreamy divagation" set on an long-distance bus – with her characteristically light yet steely touch. These major pieces manage a subtly patterned disobedience - "One Art" doesn't repeat its key couplet quite faithfully, the full rhymes of "The Moose" are irregularly distributed – which feels organic, or "slant". Rhyme, like all strict form, must pull against some aspect of a poem to create its pleasurable tensions.

However, Bishop's verse is oddly inhospitable to such complexity. Her poems are characteristically univocal, "spoken" by a kind of wandering or wondering, apprehension, often limpidly conversational:

Oh, but it is dirty!
–this little filling station,
oil-soaked, oil-permeated
to a disturbing, over-all
black translucency.
Be careful with that match!

"Filling Station" offers us a companionable narrator whose wry, fuss-budgety tone exemplifies the secret of Bishop's enduringly contemporary feel. When Christopher Isherwood wrote "I am a camera", he was helping usher in a post-war era in which objectivity would be personal, and authority relative. These poems, many written around the same time, do something similar. In place of omniscience they create a persona, a literal-minded character who leaves no room for narrative ambiguity or resonance. In the absence of those qualities, the language itself must take on poetic "second life" as patterned sound.

Bishop knows "that we are living in a material world". Indeed, it's in her exceptionally vivid observation that her processes of writerly distillation come into their own. From the hyper-real rock roses of "Vague Poem (Vaguely love poem)" – long circulated as lesbian samizdat – to joyously comprehensive poems of place, particularly those collected in A Cold Spring (1955), she pays patient attention to the obvious as well as the unobvious: "Bluish, associated with their shadows, /a million Christmas trees stand /waiting for Christmas" ("At the Fishhouses").

Sometimes the narrator herself appears, engaged in observation ("I have seen it over and over, the same sea, the same,/ slightly, indifferently swinging above the stones"), conversation, or even shampooing a lover's hair. Yet however much we follow her in thought and action, she remains a strangely affectless figure. Even "In the Waiting Room", a famous portrait of alienation, reads more as a thought experiment than as confessional verse.

In that poem Aunt Consuelo gives a "cry of pain that could have/ got loud and worse but hadn't." Bishop observed the constraints on prose slightly differently. "The Village", a remarkable memoir of a childhood marked by her mother's mental illness, famously opens, "A scream, the echo of a scream, hangs over that Nova Scotian village." In this and other, shorter, "Memoirs and Stories", there is so much telling to be done that it seems we can afford a little emotion. Although editor Lloyd Schwartz's categorisation seems both unnecessary and awkward, "A Trip to Vigia" is witty and exact about both place and human nature, while "The U.S.A. School of Writing" will strike a chord with anyone who has ever taught creative writing: the "primitive writer seems in a hurry to get it over with". Though Bishop's critical writing seems at times too withheld to achieve real engagement, what she has to say about poets like Marianne Moore, in whom she had personal investment, sheds vivid light on both writers' work.

If these prose pieces don't establish their own importance in quite the way that Bishop's finest poems do, maybe this doesn't matter. Better perhaps to read them as part of a broad version of the poet's work. Concerned, like her verse, with "Geographies" and with translation, they are further evidence of a brilliant, disciplined sensibility. Bishop is a poets' role model, and a reader's delight: her verse consummately its own justification. To have that work revisited by this centenary celebration can only be good.

Fiona Sampson's 'Rough Music' was shortlisted for the Forward and TS Eliot Prizes 2010