In an interview with The Guardian, author Philip Pullman spoke on how he never had a genre in mind while writing it and bemoaned the categorisation of fiction into genres.
“I’m often asked whether the stories about Lyra are children’s books or not, because apparently, they don’t seem like it. Sometimes categories like children’s book seem like the idea of species in the era before Darwin: divisions that are fixed, essential, ordained by God. But labels such as true crime, biography, fiction in translation, children’s books, travel, mind body and spirit and so on are there to help publicists, booksellers, librarians, marketing researchers, literary editors, and (ultimately) accountants. They were not developed to help writers. Our job is to tell the story as well as we can, not to decide how to sell it or work out which shelf to put it on; that’s someone else’s job. Northern Lights and its successors were initially marketed for children, reviewed by children’s literature experts, sold in children’s bookshops, confined to children’s libraries and so on, not because that was what I had wanted or intended or hoped for, but because they were published by a children’s publisher, so they had to be categorised as children’s books, for reasons that had more to do with algorithms than with anything else.”
The point he is making is valid because classifying books into genres can limit the readership of a novel. His Dark Materials is classified as a children’s book, despite having rather heavy themes that most would truly appreciate after a certain age, Pullman is also considered a fantasy writer which he doesn’t seem happy about; for he said in the article. “Surely it should be possible to write fantasy (if that was what this was: I still don’t like that term) so as to embody a theme from the real world?”
The classification of fantasy also seems childish to some and it’s a pity because the book explores the way religion, science and spirituality can be at odds with each other without euphamising how dangerous it could all be. Harry Potter author J.K. Rowling too said she wasn’t thinking of a particular age group while writing her novel and Narnia author C.S. Lewis best summarised in the dedication of the first book,'”…some day you will be old enough to start reading fairy tales again.”