A 2012 study found that 55 percent of YA novels are bought by adults. In large part, that boom was caused by Harry Potter, which became a surprise crossover hit adored by different generations, and which made it acceptable for adults to read books that are ostensibly for children.

But for some critics, that’s a worrisome development, suggesting that adults are too stupid and/or lazy to appreciate challenging literature. Harold Bloom, a former professor at Yale and author of ‘How to Read and Why‘, for example, though the first Harry Potter book was not well written.

“It is much better to see the movie, ‘The Wizard of Oz,’ than to read the book upon which it was based, but even the book possessed an authentic imaginative vision. ‘Harry Potter and the Sorcerer’s Stone’ does not, so that one needs to look elsewhere for the book’s (and its sequels’) remarkable success,” Bloom wrote.