10 Updates in CMOS 18 That Affect Self-Publishing Authors

The editing world was rocked in September 2024 by . . . no, not a scandal (we editors are too boring for that): the release of a new edition of The Chicago Manual of Style (the 18th), or CMOS for short. What is CMOS? It’s the bible of the publishing world, a set of style recommendations and guidelines for writing used in book publishing. (Learn more about CMOS and why you should care about it here.) This new release has made some significant changes in everything from grammar to usage to styling of words, and these changes might be creeping into your editor’s suggestions soon.

Here are 10 updates in CMOS 18 that affect self-publishing authors you might want to keep on your radar as everyone makes the switch to the 18th edition.

This is in no way an exhaustive list; if you like to nerd out over such things, you can find all of the additions and updates to the 18th edition here: https://www.chicagomanualofstyle.org/help-tools/what-s-new.html

Clarification of Editing Levels

It’s sometimes difficult for newbie self-publishing authors to distinguish between the levels of editing and when each should happen in the process. While CMOS has in past editions referred to mechanical and substantive editing levels generally (17:2.48), the 18th defines and clarifies each level in detail (2.53). In particular, CMOS now clearly distinguishes line editing and copyediting as two separate levels with particular functions in the process.

Since the United States does not have an “official” governing body for editing that sets standard terms, rates, or best practices for the industry, the names and definitions of editing levels can be wildly different depending on who you ask (even among individual editors). Now that CMOS has weighed in, the editing (and writing) world can rejoice over this attempt to formalize and standardize the terms and what happens when in the process.

New Guidance on AI and Copyright

CMOS has waded into the AI debate, which I’m thrilled to see (4.5). The manual now takes a copyright-consideration approach (which really, should be the only deciding factor in using AI for writing, IMO), discussing how AI affects an author’s copyright, or lack thereof. Bare bones: CMOS has determined that AI-generated writing is not original.

From the guide: “When a work includes some material that is not original, only the original material is protected . . . The requirement that a human author has created the expression has become significant as the use of generative AI (artificial intelligence) has become significant. If an AI creates expression in response to human prompts, that is not enough to support a copyright. The human in charge must contribute something that by itself will support a copyright, and the copyright will be limited by what that human author contributes.”

Section 4.76 also guides publishers to request that authors disclose AI-created work and warrant that “AI has not been used to create any elements of the work.”

Since last year, my standard letter of agreement has required any author I work with to disclose AI-generated content and confirm that the work is human produced only. It’s validating to see CMOS also take this approach, and it will be interesting to see how publishers interpret and apply the guidance.

Acronyms Related to Gender Identity or Sexual Orientation

Previous versions of CMOS lacked direction on styling acronyms used for gender identity or sexual orientation. The 18th edition added a whole section for such (10.26): “Acronyms and initialisms related to gender identity and sexual orientation are usually capitalized (LGBTQ, AFAB). Their spelled-out forms are lowercased except for any terms that would otherwise be capitalized (ace, aro).” However, the section goes on to say abbreviation choice and styling is up to individual authors. 

Singular They

CMOS has recognized and condoned the use of they and their in the singular sense (replacing he or she) for at least the last thirty years but never formally included it in the actual manual. Now, it has embraced the singular they in a specific section (5.266), particularly as “a substitute for feminine or masculine forms”; when someone’s gender is “unknown or irrelevant or must remain confidential”; or when a person has chosen they and them as pronouns. This reflects the way singular they has become normalized (even preferred) in modern language, and I’m here for it. So take that to any online grammar trolls who say otherwise.

Apostrophe Forms the Plural After a Capital Letter

This one has always tripped up a majority of my clients, and from what I can tell, every author who is not my client, judging by the books I read for pleasure. Previous editions of CMOS recommended pluralizing capital letters without an apostrophe before the ending s: As, Bs, Fs. Looks bizarre, right?

Apparently, the CMOS wizards got the memo, because now (7.68): “Letters used to denote grades are usually capitalized and set in roman type. Plural forms take an apostrophe (a departure from advice in previous editions) . . .”

She finished with three A’s, one B, and two C’s.

Hallelujah!

Capping the First Word After a Colon

Rejoice, colon lovers! Err, the punctuation, not the . . . well, body part.

In the past, CMOS wanted anything after a colon (:) that wasn’t either a question or a series of complete sentences to start with a lowercase letter.

Janie went to the store and bought: eggs, flour, milk.

Janie went to the store and contemplated her options: the choices were eggs, flour, and milk.

And in both of those examples, according to CMOS, what comes after the colon should start with a lowercase letter, even if the sentence is complete, like the second example.

The tune has changed⁠⁠⁠⁠—probably because so many of us looked at that second example and went, “Nah.” The new guidance is (6.65):

“When . . . a colon introduces one or more complete sentences . . . the first word that follows the colon should be capitalized.” 

Janie went to the store and contemplated her options: The choices were eggs, flour, and milk.

Guidance for questions following a colon (capped) and a series of sentences following a colon (also capped) hasn’t changed.

Half Compound Adjectives After a Noun

This one, for me, will take some getting used to⁠⁠⁠⁠—it’s a significant departure from previous style.

Before, compound (more than one word) adjectives using the word “half” were hyphenated both before and after a noun: half-read newspaper, the newspaper was half-read.

Just to keep us all on our toes, CMOS now advises those “half” compound adjectives should be open after a noun (7.96; “half, Adjective forms hyphenated before but not after the noun; noun, adverb, and verb forms usually open”): the newspaper was half read.

Don’t worry about getting this one right (no one does); that’s why you hire editors!

More Dialogue Guidelines

A sanity-saving book came out earlier this year titled The Chicago Guide to Editing Fiction by Amy J. Schneider. The Chicago Manual of Style has always favored academic writing and styling, even though traditional fiction publishing houses have used CMOS for decades, and fiction editors mostly just had to make do or attempt to interpret its guidelines as best we could when applying them to fiction. But Schneider’s book served as a CMOS-endorsed supplement, codifying and clarifying best practices on how to apply Chicago guidelines to novels.

CMOS has incorporated much of Schneider’s book into its Quotations and Dialogue section (12.xx) in edition 18. New topics include speaker tags, interrupted speech, formatting text messages, formatting stuttering, using italics for thoughts, and many others.

So now I can quote chapter and verse from the Big Book when I rearrange those em dashes in your character’s monologue. ????????

Styling Hashtags

Social media posts are styled multiple ways in novels for appearance and readability. CMOS has yet to really weigh in on how social media posts should be presented on the page, but the new edition does now offer guidance on styling hashtags used in such posts and elsewhere (7.86)⁠⁠⁠⁠—and for good reason since screen readers continue to grow in popularity are notoriously bad at rendering in-text hashtags. Here’s what the new guideline says:

“To ensure hashtags are not only sufficiently legible but also accessible to screen readers, it is best to start each word with a capital letter. Single-word hashtags may be capitalized for the sake of consistency with multiword hashtags but need not be. Words like iPhone may be left as is. Note that this advice does not extend to hashtags in direct quotations, which should reflect the capitalization in the source.”

#AmEditing (not #amediting)
#ChicagoStyle
#ThrowbackThursday
#MeToo

Italicizing Foreign (or Made-Up) Words

Obviously, I work with a lot of fantasy novels, which sometimes contain made-up languages, spells, world-specific words, etc., that are decidedly not English. A big part of my job is determining when an author should italicize every mention of every made-up word, only the first mention, or not at all. The current convention is to italicize the first mention of a non-English word, and then leave it as normal text for each successive mention. This has, rightly so, been called out in recent years as “othering” languages that are not English.

CMOS to the rescue. Its latest style recommendation should put this to rest (11.4):

“Non-English words and phrases that would be familiar to a particular author, narrator, or speaker do not necessarily require italics even if they might be unfamiliar to readers . . . Especially in fiction and related genres, using regular text for words from other languages can help establish a narrator’s or character’s authenticity. Whether (and when) to use italics in such contexts is ultimately up to the author . . . By drawing attention to the switch from English to [a foreign language] and back, italics would risk making the dialogue seem less realistic.”

This fits nicely with what I’ve always recommended for made-up languages in a fantasy or sci-fi novel: italicizing the non-English words might take a reader out of their immersion in your world. Treating the words like an everyday part of your worldbuilding could aid authenticity. It’s always and will forever be your choice, but now CMOS is bringing the receipts.

Will I Be Switching to CMOS 18?

Short answer, yes. Long answer: Eventually, all editors, myself included, will adopt the new and updated CMOS recommendations. They’re already incorporated into the online version that I reference in my work every day. However, my traditional publisher clients have not yet indicated they’re moving to the new guidelines, so until then, you’ll still see styles and usage in traditionally published books that appear different from what I’ve outlined here.

During this transition period, I’ll probably start asking authors their preference, and for those that don’t know or don’t care, I’ll use CMOS 18 as my base style guide. I estimate it might take up to a year to get all of my self-publishing clients either transitioned over to 18 or confirmed 17 users for life (authors with series in progress might stick with 17 longer to ensure continuity).

My best advice for you about adopting the 18th edition: Ask your editor for a recommendation about which to use, and take some time to get to know the differences so you can make an informed decision.