Where does it belong on your bookshelves?

I wrote most of this post in April of 2012 and I guess forgot about it.  As it is still an issue I struggle with, I thought it would be interesting to post and see what you all have to say.

In one of my graduate seminars, we would always end our book discussions with the question “Where does this book belong on your bookshelves?”  This question was designed to make us think about what sub-field(s) of history we thought the book belonged to.  Thinking about this meant we had to articulate and define sub-fields, in addition to pretending to be those librarians who actually categorize and decide where libraries shelve these books.

I was terrible at answering this question, as I am the sort of person who has a terrible time categorizing or labeling things.  I have such a hard time categorizing things because I feel like nothing really fits into a particular box just perfectly.  But this is a question that keeps coming back to me as I blog and track and talk about what I read.  How do I categorize what I read so that it is useful piece of knowledge for both my readers and myself?  Should I even bother trying?  How do I decide where these various books fit on my imaginary internet bookshelves?

Normally, I either make my best guess based on the opinions of other people or don’t even both trying to pick a genre (general fiction, it is!).  I mull over the genre tags on Goodreads to see what other people have said.  In the end, I don’t usually tag my blog posts with a genre, but will make note of it on my book-tracking spreadsheet.  And then go back and change it.  But usually I feel mired in ambiguity when it comes to the question of genre.

Seeing as how I am terrible at this game, I thought I’d ask for your feedback.  How do you decide where a book belongs on your bookshelves?