However, we are living in a period of poetry in which interest in narrative techniques, in anecdotal writing, in direct political comment, are peculiarly developed. Even though the modernists in general, and TS Eliot in particular, are under fire at the moment, we have to acknowledge that this change has a lot to do with them. The changes that they wrought in English poetry are permanent and unassailable. "The Waste Land" was not just a poem that turned conventional ideas of pastoral on their head, it made room for material that had traditionally been the prerogative of fiction. Shelf space was made for everything, from soda water to suspenders.
More recent poets - Auden, MacNeice, Larkin - continued to expand our sense of what can be included in a poem: the detritus of recognisably contemporary life. The notion that poetry might exist primarily to help us endure our existence has been diversified. Poetry rinses out and makes us see the familiar world more clearly. Inevitably, this has meant that poets have had to devise a language that is flexible enough to accommodate clutter, language that is both urgent and personal but not specifically reserved for poetry. To that extent, the walls between poetry and prose - and between poetry and song lyrics - have crumbled.
In the past few years, poetry's profile in our culture has become significantly higher. Poetry appears on the Tube, it pops up in newspapers. Poets are regular visitors to schools and academies. And yet, and yet... However much time poets spend in the classroom, however often poems turn up on television or the Underground, we need to remember that poetry is, in a sense, written in stolen time. It is against the grain. It is inherently subversive. It often arrives at truths by telling them slant, as Emily Dickinson might say. It does not often argue that a thing is true but allows us to realise the truth by making us, in Keats's great phrase, "feel it on our pulses". Whenever we talk about the need to promote poetry, or to celebrate a carnival such as National Poetry Day, we must insist on this sense that it comes at orthodoxies from an oblique angle.
Sometimes very oblique: poetry communicates a vital part of its meaning by other than rational means. The great American poet Robert Frost had a wonderful idea about "the sound of sense". To illustrate this, he told a story of walking down a lane in Gloucestershire with Edward Thomas, and shouting at a man cutting corn in the middle of a field. The man was too far away to hear exactly what Frost was saying. The farmworker shouted something back that Frost could not quite hear either. "You see," he turned to Thomas, "we know what he means, even though we can't understand what he's said."
We do not often go to a poem to collect information, or to discover something that we didn't know beforehand. We go to a poem to be jilted out of our complacency, to rediscover things we had forgotten we knew. This is the sense in which it is uniquely private. It is also the means by which it defines and discovers its public.
Andrew Motion was talking to Adrian Turpin
Andrew Motion is Professor of Creative Writing at the University of East Anglia and vice-chairman of the Literature Panel of the Arts Council of England. A poet and biographer, he is currently researching the life and work of John Keats