My book just spontaneously became 20% less done than it had been.
I'm currently writing the methodological and theoretical sections of the introduction and began to rethink things when I wrote the sentence: "Although this study takes for granted the notion of text and history as a continuum it is, with the exception of chapter five, decidedly not a work of New Historicism." I go on to make a case for the historiographic work that the book does despite having taken the "linguistic turn." But the caveat about chapter five started to bother me and I began to question the wisdom of having a solitary foray into a related but distinct methodology at the end of the book.
My hair-brained solution, which obtained for all of about four hours, was to cut chapter five and publish it as a stand-alone article and then not write the as-yet-unwritten chapter four, leaving a very tightly-focused three-chapter book. However, it was impressed upon me that I'd never get a book contract like that, and so I went to plan B.
Now, the first three chapters will be part I of the book because they are very tightly coherent and related to each other. What are now chapters four and five will form the backbone of a part II that focuses broadly on reception history. What is now chapter five, the New-Historicist, anecdotal look back at the reception of the material, will become chapter six, following a new and, definitionally unwritten chapter five, which will constitute a more standard reception history. Part I will focus on the creation of Arabic as a prestige language among Andalusi exiles, and Part II will focus on various aspects of the later reception of that prestige language in creating a history of al-Andalus and its exiles. In a certain respect I regret it because it definitely means that I will be prioritizing quantity over quality. It still will be a good book, but it won't be quite as tightly wrought as I might like and I won't be able to spend as much time carefully crafting and revising each chapter because I just have to get the flipping book finished.
Perhaps tellingly, when I went to modify the table of contents, I mistyped the new addition as "chapter sux." No need to page Dr. Freud, even.