Ajax Jquery + HTML Partial View and Error Message Handling

Perhaps someone has already asked this.  I am new to ajax and would need assistance in handling and linking ajax jquery with MVC ModelState.AddModelError.  I would like the message in ModelState.AddModelError to be displayed as an alert in the error or success function of ajax jquery.  As a background, the general method is that once the controller is called, it will return a PartialView to the ajax jquery to display in a particular <div>.  If there is an error, the message should be displayed as an alert and there should be no change to whatever is currently displayed.

Below is a sample simple controller (HttpPost) and the ajax jquery routine. 

Controller:

        [Authorize]
        [HttpPost]
        public PartialViewResult Add()
        {
            int currentUser = (int)WebSecurity.CurrentUserId;
            Book myBook = new Book();

            myBook.GetChapter(currentUser, "Draft");

            if (myBook.Chapters.Count() > 3)
            {
                ModelState.AddModelError("", "Too many chapters.");
            }

            return PartialView(myBook);           
        }

The ajax call to post:

   function submitaddbook() {$.ajax({
            url: '@Url.Action("Add", "Book")',
            type: "Post",
            data: $('#addchapter').serialize(),
            success: function (data) {$("#notes").html(data); 
            },
            error: function (data) {
                alert(data.errormessage);
            }
        });
    }