Organizing Books On Shelves

I have been watching as one of my colleagues has been organizing his books in his new office. First he put them in stacks by topic, then he made category tags which he put on the shelves, then after putting the books on to the shelves by category he has been rearranging them. I have not yet been able to figure out what process he is using to organize them within the categories; it is not alphabetical by author or title, and it does not appear to be by date or size. Eventually, I will break down and ask him. Everyone I know seems to organize the books in their personal library a little differently. I was in a relatives home recently who organized the books by size and color. I found this humorous until I realized that I do the same thing with my Easton Press leatherbounds. In Casanova Was A Book Lover , John Maxwell Hamilton writes about how some people have chosen to organize their books; After restoring long-packed-away books to shelves, German author Walter Benjamin ref...