In chapter 7 of Alice’s Adventures in Wonderland, Alice sits down for tea at the Mad Hatter’s tea party, flanked by the March Hare and the snoozing dormouse:

The table was a large one, but the three were all crowded together at one corner of it. “No room! No room!” they cried out when they saw Alice coming. “There’s plenty of room!” said Alice indignantly, and she sat down in a large arm-chair at one end of the table.

“Your hair wants cutting,” said the Hatter. He had been looking at Alice for quite some time with great curiosity, and this was his first speech.

“You should learn not to make personal remarks,” Alice said with some severity: “It’s very rude.”

The Hatter opened his eyes very wide on hearing this; but all he said was “Why is a raven like a writing-desk?”

Thanks to its fast-paced exchange of jokes and nonsense—and thanks to the long-lasting popularity of both the book and the numerous adaptations of it—the Mad Hatter’s tea party is one of the most famous scenes in all of children’s literature. Meanwhile the Mad Hatter’s riddle remains one of Lewis Carroll’s most enduring, and most notoriously unsolvable, puzzles.

A lecturer in mathematics at Oxford University’s Christ Church College, Lewis Carroll (the pen name of author, academic, and Anglican minister Charles Lutwidge Dodgson) composed dozens of riddles and logic puzzles throughout his lifetime, including several acrostic poems and a later set of seven verse brainteasers, “Puzzles from Wonderland,” published in 1870. But for some reason the Mad Hatter’s riddle remains a firm favorite—so why exactly is a raven like a writing-desk?

In the original story, after much deliberation, Alice gives up and asks the Hatter for the answer. “I haven’t the slightest idea,” he replies. But the fact that the Mad Hatter himself left his riddle unsolved has led to fans of the book (and fans of word games and logic puzzles) proposing countless potential solutions over the years since Alice in Wonderland was published in 1865.

One suggestion is that both ravens and writing-desks have “bills” and “tails” (or “tales,” in the case of a writer’s desk). Another points out that they both “flap” up and down (an allusion to the wooden rolling tops fitted to some old-style desks and bureaus). And both of them were famously used by Edgar Allan Poe, whose poem "The Raven" had been published 20 years earlier. Explanations like these (and the countless more like them) are all perfectly workable, but none satisfied Carroll himself—who finally admitted in the preface to an 1896 Christmas edition of Alice’s Adventures in Wonderland:

Enquiries have been so often addressed to me, as to whether any answer to the Hatter’s riddle can be imagined, that I may as well put on record here what seems to be a fairly appropriate answer, viz: ‘Because it can produce few notes, tho they are very flat; and it is never put with the wrong end in front!’ This, however, is merely an afterthought; the riddle, as originally invented, had no answer at all.

While some researchers have claimed that Carroll originally spelled never "nevar," (raven backwards) before the joke was “fixed” by a helpful editor, it appears Carroll’s riddle was not intended to have an answer at all—but that’s not to say that it’s entirely without explanation.

Despite holding a lectureship at Oxford for more than 25 years, Carroll had numerous ties to the north of England. At the age of 11, his father Charles was made rector of the local Anglican church in Croft-on-Tees in North Yorkshire, and the church house remained the family home for the next 25 years. Two of Carroll’s sisters, Mary and Elizabeth, lived in Sunderland on the northeast coast of England (along with several of his cousins, nieces, and nephews) where Mary’s husband Charles Collingwood was reverend of a local Anglican church. And one of Carroll’s closest friends at Oxford University, the Dean of Christ Church College, Henry George Liddell, was a member of an established family and cousin of the Baron of Ravensworth, who had family and property across the northeast of England.

As a result, Carroll reportedly liked to spend as much time as possible in the north of England during university semesters visiting friends and family in the region, and, as it happened, inventing stories to entertain Henry Liddell’s young daughter, Alice.

It’s well known that a young Alice Liddell was the inspiration for the title character in Carroll’s Alice in Wonderland stories; Carroll is often claimed to have made the story up during a boating trip down the river at Oxford not long after Alice and her sisters moved to the city with their father in 1856. But it’s possible that at least part of Alice in Wonderland—namely, the Mad Hatter’s fiendish riddle—was either written in the north of England, or written with Carroll’s ties to the northeast in mind. When visiting the Liddell family estate, Carroll would stay at an inn (now named the Ravensworth Arms) in Lamesley, close to the Liddells’ ancestral home at Ravensworth Castle in Gateshead. It’s believed that, at around this time, Carroll was working on the first draft of what would become Alice in Wonderland. If that’s the case, it may be that the “raven” in Carroll’s notoriously unsolvable Mad Hatter’s riddle is actually an allusion to the Liddells’ Ravensworth Estate, which essentially served as Carroll’s “writing-desk” while he worked on the book.

Carroll is known to have incorporated a number of people and places from his time in the north of England into his work: The beach at Whitburn, close to where his sisters Mary and Elizabeth lived in Sunderland, for instance, has long been presumed to have provided the inspiration for The Walrus and the Carpenter, while Carroll’s monstrous Jabberwock is believed to have been based on local legends like the Lambton Worm, a fierce dragon-like creature said to have once inhabited the hills and rivers around Durham. Could it be that the Ravensworth connection is just another example of Carroll taking inspiration from his time in the north, and that’s why a raven is like a writing-desk? It might not solve his most famous riddle, but it does at least provide a tantalizing explanation.