[Inferno]

One very good reason for the three (Y N and blank) is when someone like me has not yet gone to each book in their library to mark them. I have thousands of books in my library I have not yet marked as Y or N. It is because I have not looked at the specific book to determine if I have read it yet.

If it had only Y or N then when first creating the column it would be necessary to completely go thorough your library to set each book and for some of us that is not practical.

Also, what would new books be marked as? Y or N? If N then adding an old favorite to your library would show it as unread. Much better having a blank to indicate it needs to be looked at.