Several times in the last month or so, I've heard discussion of the use of the Chicago Manual of Style to edit novels. Chicago is a very useful, comprehensive style guide, but its purpose has little to do with fiction. Its purpose is to create uniform methodology and typography for research documents ranging from student papers to textbooks. Though some of its rules can certainly be applied to fiction, its purpose is not generally aimed at fiction.
To really understand this, it might help to know something about the process copy editors use to edit fiction manuscripts. For each individual project, they create style sheets. These style sheets contain everything from story details (correct spellings of character names, physical descriptions, etc.) to narrative details (that particular author's comma usage patterns, for example). The style sheet is a reference guide that the copy editor then uses to check consistency throughout the document. Some copy editors turn in their style sheets when they turn in the finished project so that the author and lead editor can see the style rules applied.
A house can create a style sheet or style guide that is meant to apply to all manuscripts generated by the house. This house guide is meant to simplify the copy editing and production process by taking the guesswork out of common style questions, such as when to include periods in certain acronyms. (Ph.D. or PhD?)
So, in the beginning, the University of Chicago press created a style sheet for its typesetters and compositors to help them figure out things like citation notation, and how to use archaic alphabets, and how to set scientific equations and symbols. It was an academic style system for academic works published by an academic press, and it was good. Many people wanted to use this style system because it simplified the process for all of them. The Chicago Manual has been through many revisions over the years and is now in its 15th or 16th edition.
Here's the thing, though. Academic grammar and style conventions are more formal than the everyday sorts of grammar and style rules that most people commonly use. If you understand the different philosophies of grammar and the ways the rules bend and shift to accommodate those different philosophies, then you will know that many writer quarrels stem from these philosophical differences. Most comma rules, in fact, can change depending on which style approach you take. The more formal and academic the document, the more commas it will contain.
I mention commas specifically because this came up on an author list recently. An author was complaining that her different copy editors each used different comma rules, and each insisted that her rule was "grammatically correct" with that sort of lead-pipe blunt force common to those who know how to apply a rule but can't explain why they're doing it. Now, I've worked with a lot of copy editors over the years, and I know that the best among them tend to get a little shrill over their pet rules. But the best among them also know that there are multiple rules sets, each of which can be applied to create a different but equally valid finished product. They can argue outcomes and the logic behind their style choices like the sharpest trial lawyer. And what I heard on that author on that list made me think these were not good copy editors arguing grammar philosophies, but quite a different sort of creature.
This creature is someone who studied hard in school and made good grades. She probably has been praised for her writing. She has the rule book and she knows how to use it, but she's probably never taken an advanced grammar class. She might not know that opposite rules can be equally correct -- that is, for example, that one style guide can require a comma after a single introductory transition word, and another can ban it, and each can be correct. She might not know how to choose which rule to apply or how to apply it, and yet, she can still legitimately consider herself "good at grammar" in the ordinary sense.
I suspect, but cannot prove, that the recent blossoming of direct publishing is leading a lot of these creatures to try to drum up some side income as copy editors. I suspect, but cannot prove, that some of them are out there promoting themselves by saying they are adept in Chicago style. They know that this is often reckoned the most sophisticated and detailed of the academic style guides, and they think it says something about their skills to claim competence in it. And it does say something. It says they're competent in Chicago style.
But here's the question. Do you want Chicago style for your manuscript? Maybe you do, and maybe you don't. What baffles me is the number of people suddenly requesting it. Whenever a novelist says she wants me to edit her work with any particular academic style -- Chicago, APA, MLA, whatever -- my first question is, why? Sometimes they'll give a well-reasoned response, such as the woman who recently told me she used Chicago herself and wanted to be sure her editors could manage it. She was looking for consistency between her approach and that of her content and copy editors. That made sense. But others don't seem to know why they're requesting it. It's become a buzz word, something people talk about because they're hearing about it.
If you want to use Chicago, use Chicago. It's a legitimate choice, albeit a choice that will create a more formal text. And if you're writing genre or commercial fiction, this might not be the best choice for your book, but maybe you want it to sound more formal or academic. But know what you're getting, because it might not be what you want.