"It's a difficult book to talk about," says John Banville of his latest novel, Eclipse. An hour later, we're still talking about it - which doesn't necessarily disprove the point. It is, though, a difficult book to pin down, a book of shifting surfaces, translucent presences, not-quite-silences.

Its narrator, Alexander Cleave, is an actor who, having "corpsed" on stage, has returned to his childhood home and is living - hiding? - there, to the consternation of his abandoned wife, Lydia. Cleave insists that, stripped of his performing masks for the first time in his adult life, he simply needs to be alone to confront his past; but the house isn't as empty as it seems, and he is himself confronted by a series of apparitions, some ghostly, some all too human.

Looking back on his acting career, Cleave muses; "I played best the sombre, inward types, the ones who seem not part of the cast but to have been brought in from the street to lend plausibility to the plot . . ." Could this, in a wider sense, be said of many of John Banville's narrator/characters?

"I suppose it could be said of all of them, really," he says. "They're all playing at being themselves. Since my so-called scientific books, my characters have all been people who are trying to discover some kind of authenticity. They're all the same voice; Freddie, Alexander, Victor. Although this guy seems more troubled and more lost - ironically, since he hasn't murdered anybody and he's not a major spy.

"Eclipse, more than any of my books, has the atmosphere of a dream. Cleave seems to have lost an essential connection both with himself and with the world. He seems to live entirely within his own skull. And that's an interesting progression for me, because The Untouchable was such a big public mural, covering lots of time, lots of characters and so on. This is just one man."

And a strange one, at that - but once the reader is drawn into his skewed, surreal world, Cleave is absolutely compelling. Was he a difficult character for his creator to identify with? "I made him more of a swine than I am - I hope," says Banville. "He really is so self-obsessed he can't see anything beyond his own concerns. He behaves dreadfully to his wife, for instance. But I didn't find it hard to identify with him, because he's what we all are when we don't turn the mask on. I hope people can identify with him, not willingly perhaps, but wincingly. One of the things about the people who narrate my books is a kind of hideous honesty. They're certainly not sentimental: frequently that means that they also lack sentiment. But I hope they convey passion on the page."

In Eclipse, Banville appears to be concerned with the spaces between things as much as with the things themselves - with "a flaw in the atmosphere, a lingering ripple where someone had passed through". At times, it strikes the reader that he is experimenting - dangerously, surely? - with the sound of silence. "Any writer who's honest with himself wants to go silent," he says. "The only utterance that can be perfect is silence; it can be perfect, but it can't be eloquent, at least not for very long. But yes, there's certainly a move toward emptying of the content. It has become a kind of mantra with me that the problem with writing at the end of the 20th century, or the beginning of the 21st, is that we have these two enormous figures behind us, Joyce and Beckett. Joyce put everything in; Beckett took everything out; my solution is put everything in and then deny it all.

"But what I've always been trying to do is make prose have the weight of, and be as demanding as, poetry. Of course people's hearts sink when they hear this, but I'm not talking about moons and Junes and dance and lance; I'm trying to get more purity, I'm trying to get more intensity, and I'm trying to get simpler. And these are very difficult things to do, because a novel doesn't offer simplicity; it offers complexity and prolixity, the ebb and flow of life itself. "I think people imagine that novelists, especially, try to get closer and closer to life - in fact I think it's the opposite. They try to get as far away from life as they possibly can. They try to make their work as unlike their own lives and the lives around them as they possibly can - certainly European writers do - in order to make some essential statement."

Rigorous observation of the world, however, has always been a vital component of Banville's fiction. "Surroundings are very, very important. I think of myself as a posthumanist writer - for me, human beings are not the centre of the universe. This is why the books are constantly sliding away from people to talk about what surrounds them; the light, the colours, the atmosphere. Under the guise of being nature poets, the English Romantic poets actually wrote about their own sensibilities as reflected in nature. What I'm trying to do is the opposite; to have nature, the world itself, reflected in the characters, so that you can almost see through them. They almost become transparent. This is why reviewers are constantly complaining about my lack of human interest, my lack of interest in characters and so on. I'm trying to do something new, and when you're trying to do something new, you only know what it is when you've done it. I'm encouraged, somehow, by Eclipse: I think that it's as near as I've got to writing a book that has no real centre."

Banville's attention to light, colour and atmosphere inevitably produces lyrical and evocative, though never effusive, images. But while he has always insisted that he is a European writer and not an Irish writer, hasn't a heightened awareness of nature, and of our relationship with nature, been one of the distinguishing themes of Irish fiction? "In the past Irish fiction was essentially pastoral," he says. "Not just that it was set in the country, but pastoral in the classical sense of allegorical stories with a generally benign view of nature. I grew up outside a small town and spent most of my childhood wandering around the fields with my dog and so on; and nature, as I observed it, was, not necessarily threatening, not necessarily malign, but indifferent. And this always fascinated me. That there were trees and fields and skies and cows; and then there was us. Completely different to anything else that was around. And I conceived very early on that we were nature's greatest mistake, as well as nature's greatest glory, these creatures walking around with these strange ideas in our heads.

"The only piece of prose fiction that I've ever written that is my voice is a paragraph in The Book of Evidence where Freddie says he thinks our presence here is a cosmic blunder, that we were really meant to be on some other planet. And then he wonders about the earthlings who were meant to be here - how are they getting on out there? And he concludes that they couldn't have survived in a world that was meant to contain us."

It is, he admits, a pretty bleak artistic vision. But then art, John Banville believes, is a pretty bleak business. "Writing is a total obsession. When people ask me how much time do I give to writing, I say `24 hours a day'. I may not be at my desk, but I'm a machine that writes. That's what it does. The rest is amusement and diversion, and it's a terrible way to live your life. It's not really living, or it's not living well enough. One is, perhaps, privileged to have this obsession; but it is an obsession, and the cost is very, very high."

"In our post-religious age people are inclined to take novelists and poets as priests, almost; as people who will tell you how to fix your life and save your soul. And maybe the work of art does do that; but the artist doesn't. He's just trying to get this bloody thing out of the way and get on to the next."

For Banville, the next is a novel called Shroud. My God - bleak and bleaker? He laughs. "It's called Shroud because it's set in Turin. Eclipse is freestanding, and none of the characters from Eclipse will be in this book, but it is a continuation. There's a seam that I haven't fully worked."

Eclipse is published tomorrow by Picador