300 collections. A milestone worth marking, and also a small number: a tiny fraction of the library of real bookshelves we hope to build, and far too few to say anything about readers in general. We ran the analysis anyway, to see what would show through. Five things did.
The 300 shelves belong to people with nothing in common except that each took a shelfie of their books. Pick any 2 and more often than not they share no title at all. With millions of books in print, that is expected. What follows is what recurs anyway.
1. Books come in 9 familiar groups
Authors that keep landing on the same shelves form 9 groups, and every one is a group you already know. We counted, for every pair of authors, how many shelves hold both, against the number expected by chance. 3 times as many pairs travel together as chance allows. Chained together, they give these 9. The number is how many of the 279 shelves analysed hold at least 3 authors from the group.
- Postwar American fiction (159): Steinbeck, Vonnegut, McCarthy, Hemingway, Morrison, Didion.
- The European canon (141): Dostoevsky, Austen, Dickens, Orwell, Tolstoy, Homer, and, oddly but consistently, Murakami.
- Epic fantasy and science fiction (135): Tolkien, Herbert, Martin, Sanderson, King.
- Book-club fiction of the last decade (84): Tartt, Towles, Hannah, Backman, Owens.
- History and biography (74): Beard, McCullough, Chernow, Isaacson, Dawkins.
- Romantasy and young adult (61): Maas, Madeline Miller, Bardugo, Jenkins Reid.
- Philosophy (61): Plato, Marcus Aurelius, Nietzsche, Camus, Marx.
- Business and self-improvement (56): Clear, Gladwell, Harari, Taleb, Covey.
- Contemporary literary fiction (45): Rooney, Plath, Yanagihara, Moshfegh, Han Kang.
Nothing here is surprising, and that is the point. Shelves that share no titles still sort, one level up, into categories everyone knows. The categories are real. They are just not categories of people.
2. Almost no one has a single-track mind
The typical shelf draws on 3 of the 9 groups, and only 1 shelf in 12 belongs mostly to one. You can read a person from their books, but what you read is a composition of a few interests, usually 3, not a single type.
Among shelves of 50 to 100 identified books, the median shelf holds at least 3 authors from each of 3 groups. Only 8% of shelves have one group covering most of their recognisable authors. And half the authors on any shelf belong to no group at all: the private books nobody else in the set owns.
In practice: Tuchman and Keegan beside Sanderson and Tolkien beside Aristotle and Schopenhauer, on one 74-book shelf. Chomsky, Taleb and Hayek within the same 70 books.
3. Some groups keep company; one pair never does
The 9 groups form 2 camps, fiction of the present and books of ideas. The classics are the only group at home in both, and romantasy and philosophy rarely meet.
Book-club fiction and contemporary literary fiction share a shelf at 2.5× the chance rate; book-club and romantasy at 2×. History and business at 1.9×; history and philosophy at 1.7×. Those are the camps. The European canon is drawn to American fiction, fantasy and book-club fiction, and equally to history and philosophy. No other group crosses the line. Romantasy and philosophy share 6 shelves where 13 would be expected. Everything else tolerates everything else.
4. The one real wall is fiction versus fact
People keep fiction and non-fiction apart. The evenly divided shelf is the rarest object in the set. 41% of shelves are at least 80% fiction. 15% are at most 20% fiction. Shelves between 40% and 50% fiction: 5 of 249. Where a shelf holds both, a third sorts them onto separate rows more sharply than chance would. The rest of the sorting, one suspects, happens between bookcases, where a photograph cannot see.
5. Books stand in the order they were read
Series stand in reading order, authors lean towards publication order, and a series is either complete or barely begun.
Where a series occupies part of a row, its volumes run left to right in reading order 76% of the time and in reverse 4%. For 5 volumes, chance would manage that under 2% of the time. An author’s books stand in strict publication order 25% of the time, against 8% for a shuffle.
Across 32 series, 45% of holdings are the complete run and 29% are the first volume alone, with little in between. Which side a series lands on is a property of the book. The Lord of the Rings is complete on 95% of its shelves, because it is sold as a set. Dune is on more shelves than any other novel here, and 59% of its owners have only Dune. The first volume is a classic. The rest are for the people who stayed.
So what does a shelf tell you?
Not a single type. A shelf is 3 or 4 groups mixed, fiction kept apart from non-fiction, books standing in the order they were bought. The groups themselves are the least personal part: they are how books reach people, through school, the airport, the front table, last year’s recommendations. What is personal is the mix, the order, and the half of the shelf that belongs to no group at all.
300 shelves are enough to see that much. We are now more curious about what 3,000 will show.