The Zombie Stack Exchanges That Just Won't Die
How can I arrange a book (or other physical object) collection, where books can belong to more than one category?
With online information, I can give an article more than one "tag", and use these as facets to find it. The article can belong in more than one taxonomy at once.
With books or other objects, I am limited to choosing only one place. For example, with a book about history of science, I need to place it with the science books or with the history books, but I can't do both unless I have two copies of the book. In reality, I could easily classify a book under three or more categories.
Without indexing the entire collection, how can I arrange my book collection so that the books can be found by browsing readers with different interests?
johntait.org
Generally you choose the subject that the book is MOST about. In your example, the book is more about science than about history, so you would probably put it in science. Most books when published have a cataloging page in them (on the reverse of the title page) that is usually prepared by the Library of Congress prior to publication. It will list the subjects of the book in order of prominence. There is usually an assigned Dewey classification as well which will indicate where a professional cataloger thought the book should go (science being in the 500s and history in the 900s). If there is no cataloging page, you can find cataloging information through the World Catalog (WorldCat) or the Library of Congress for most books.
In your own collection, you are of course not bound to the decisions of the catalogers who have pre-classified the book. In a library, the cataloger on staff may choose to move books to a location that makes more sense to the public being served. For example, books about space are in the 500s (science), books about rockets are in the 600s (engineering) and books about travel to extraterrestrial places are in the 900s (travel). A browser might expect all these books to be together, so a public library will often put them all in science so they are together on the shelf.
It is an imperfect system to be sure, especially since the Dewey Decimal system predates a lot of current technology and has built-in biases based on the time it was created.
Although Mary Jo is correct, there's one major situation when you would not categorize items by what they're most about --
When that's the reason for collection in the first place.
The important thing is that if you're shelving for yourself, you just have to put them where you are likely to think about when you're trying to find them again. You might decide that Dewey works for you, or BISAC, or some specialized taxonomy, or come up with one yourself.
Personally, I have a lot of cookbooks ... so I focus on how I think of the cookbooks. I have beginner cookbooks (because I specifically collect those), community cookbooks, more encyclopedic cookbooks (to include the time-life series that my mom has decided to attempt to fill in for me), specific regions or cultures (some of which are the community cookbooks), those that focus on a tool (eg, crockpot) or a specific result (eg, pancakes, paella, casseroles, cookies) or ingredient (hot peppers, garlic, chocolate), etc. And I have the bookcase just outside my kithen that I use more frequently. Which leads to the gardening books, then the landscaping books, which follows the architecture books.