Last week, JK Rowling officially announced that she was writing a new book. Details are scarce. No one knows what the book is about or when it's coming out. Only one fact has been revealed: it's for adults. The book world freaked out – the world's most successful author is releasing a new novel.

Harry Potter achieved a very special act of actual magic: it made it completely acceptable for an adult to carry around, read and enjoy a children's book. As a New York subway rider, I would look around and count the number of Harry Potters in my carriage as a way of passing the time. I'd see different Potters – some people would be reading the previous books, some the newest. When the sixth and seventh books came out, everything pretty much stopped. My agent and I each bought a copy, retreated to a bench in Central Park and read side by side for hours. And we were not alone.

Something went ping in the collective unconscious. These books were enjoyable, and on many levels. After that came the rise of "young adult" literature, the area in which I write. Slowly but surely, it's become acceptable for adults to read books that are supposed to be for teenagers.

We're still fighting a lot of stereotypes. There's still the idea that young adult books are all about vampires, or are all dystopian visions, or are all very dark, or very frothy. Forbes, the US business magazine and website, described Rowling's forthcoming book as a "proper adult novel". (The author of the article also claims that the term "young adult" is a euphemism. The implication is that there is something inherently unpleasant about writing for adolescents, and that this inherently unpleasant task can be covered up by some – not very – clever wordplay.) This prejudice is something I confront continually in my professional life. "Oh," people will say, "you write for kids. That's nice. Are you going to write a real book?" And they'll mean it nicely (I think).

It seems to be the received wisdom that books angled at the younger set are simply not quite the same thing as books aimed at adults: not quite as challenging to write, not quite as challenging to read. And it is my boring yet constant duty to explain that books for younger readers are some of the most challenging and well-written material out there. Children and young adults (or adolescents, whichever you like) are among the most athletic of readers. Unlike adults, they do not normally restrict themselves to one genre. They read broadly, experimentally, and with considerable passion.

So, JK Rowling is writing an adult book. Among the readers I know – mostly kids – the reaction is euphoria. Among adults in the media, there seems a bit of puzzlement. Will she make it work? Potter sales are only in approximate numbers, but the consensus seems to be that the books have sold about 450m copies. Will this adult book be as successful as Potter? Frankly, it doesn't matter. The success of Harry Potter might be impossible to replicate, and it shouldn't be held as any kind of a standard for anyone. If she fails to sell 450m (or, say, 65m books, as 450m represents the seven-book series), that's hardly a failure. And yet, I feel as if that's how many people are poised to paint it: a children's writer is coming to compete in the adult book world. Can she hack it?

Of course she can. Let the book stand on its own. The bridge can be crossed in either direction. Many adult authors are now streaming over to the younger side, seeing the rich potential audience there. Rowling, who helped to build the bridge, is walking in the opposite direction. And why shouldn't she? She's following her ideas where they take her. Cross-pollination in reading and writing is a good thing: writers moving into new storytelling areas, kids reading "adult" books, adults reading "kid" books. They're all stories.

Harry Potter was one of the most richly populated and complex stories going. If JK Rowling writes an "adult" book even half as good, then readers are in for a wonderful experience. And, frankly, I hope the adults are up for the challenge.

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