Echo is very important to me. I love the repetition of motifs, or the slight alteration of what's been said before. This is part of how one creates a mood, a psychological caul, in fact, around the reader.

The shape the words end up taking are themselves the meaning of the words, they are retrospectively what we meant to say. There's no way of knowing this until you register it in visible form. But the other side of this is that you do have some idea of where you are going.

I couldn't remember what life was like before I started walking.

It's an Obama book, certainly. I was delighted, and astonished, to hear recently that he was reading it. It's a book about a new kind of American reality, one that takes diversity for granted. It doesn't celebrate diversity, actually, it just says: this is how we live now.

Killing a bunch of people in Sudan and Yemen and Pakistan, it's like, "Who cares - we don't know them." But the current discussion is framed as "When can the President kill an American citizen?" Now in my mind, killing a non-American citizen without due process is just as criminal as killing an American citizen without due process - but whatever gets us to the table to discuss this thing, we're going to take it.

It is a work of psychogeography, albeit in a less explicit sense than Iain Sinclair's or Will Self's. It had to be fiction though, because I needed that freedom of including whatever belonged, and cutting out whatever didn't. The main fiction in it was matching Julius' generous and self-concealing character to New York's generous and self-concealing character. I think this also adds to my answer about New York's personality in the book.

Our biggest art forms are film and television, and there hasn't been a great film about 9/11 yet, nor has there been a great television series. Something like The Wire gives us a rich and fully achieved picture of the wasteful, cruel War on Drugs; something like The White Ribbon gives a perspective on World War I that could only have been presented long after the event itself.