Quote Originally Posted by it-ogo View Post
I think it is accusative if it is used in the sense of "I am sorry for you". If it is used in the sense of "I don't want to give you away (grudge)" then it can be either accusative or genitive (мне жаль книгу/книги).
I think that it-ogo’s post sorted things out fairly well. It’s just that it was a bit confusing because he used the phrase to give away, which means to reveal or betray, to mean to give something to somebody, to lend. So, if I feel sorry for the book, for it was a great book but it burned down in a fire and I don’t have it anymore, then:
Мне жаль книгу.
If I grudge giving the book to you, I don’t want to part with it, then:
Мне жаль книги. Although it wouldn’t be much of a mistake or any mistake at all to say in this case Мне жаль книгу too.