Q. How would you write the first parenthetic instance of an acronym or initialism when the first defined use is plural? For example, if the first use of the term “part number” happens to be plural, would the initial declaration of the initialism be “(PNs)” or “(PN)”?

A. If you can’t rephrase the first mention to use the singular “part number,” then the initialism should be plural: “part numbers (PNs).” The usual assumption is that readers introduced to the singular “PN” will figure out what “PNs” means if that form occurs later on in the same document. It seems fair enough to expect the reverse—that readers will understand the singular from the plural.

Q. Hi, I have a question about painter’s tape. I have an actual roll of blue masking tape that has “Professional Painter’s Masking Tape” on the label. Some say it should be “painters tape,” while others believe it should be “painters’ tape.” ScotchBlue’s website says “painter’s tape,” but a professional editor with many years of experience says the apostrophe should be deleted. Thoughts?

A. Chicago’s preference would be to retain the apostrophe. Tools of the trade and the like tend to form singular possessives, which would mean painter’s tape rather than painters’ tape. The same goes for painter’s gold, plumber’s snake, printer’s devil, and similar terms (not limited to the p’s). Each of those terms refers to something or someone used (or formerly used) by an individual in the context of an occupation.

Exceptions—like confectioners’ sugar, discussed in another Q&A—are rare. As for a plural attributive like painters, that’s more common when a plural possessive might make sense, as in farmers market (traditionally farmers’ market, a market for farmers) or Veterans Day (a day to honor veterans, which might plausibly be spelled with an apostrophe).

In sum, we agree with the usage of 3M’s ScotchBlue: painter’s tape. For more on words that end in ’s or s’—and why the word possessive doesn’t apply in the literal sense to most—see CMOS 5.22 (on the genitive case). See also 7.27.

Q. I would like to ask if there is a rule in CMOS for writing the numbers on a telephone keypad. For example, when writing the following: “To speak with a specialist, press 3. To cancel your contract, press 4.” Should the numbers be spelled out or kept as figures?

A. Use digits, as you’ve done in your question. The relevant advice is in CMOS 7.81, 7.82, and 8.156, which cover how to style the names of apps, devices, keys, menu items, file formats, and the like. The numbers on a phone qualify as keys on a device or an app, even if the phone predates modern computing.

Most phones, now and in the past, have used numerals for the numbers on their dials or keypads (physical or virtual), as on this rotary dial from Western Electric (ca. 1960, National Museum of American History):

Numerals were also the natural choice as part of telephone exchange names, as in BUtterfield 8, the title of a 1960 movie (based on a novel of the same name by John O’Hara) featuring an Academy Award–winning performance by Elizabeth Taylor. Note the all-caps BU and numeral 8, which together add up to 288 (because B = 2 and U = 8 on a telephone dial/keypad), an exchange for Manhattan’s Upper East Side.

For more on telephone numbers, see CMOS 9.59.

Q. Does CMOS prefer the use of “persons” or “people” when describing a collection of human beings, such as you might find at a grocery store?

A. More than one person at a grocery store would normally be referred to as people, not persons. According to Garner’s Modern English Usage, the traditional distinction between persons for smaller numbers (especially of specific people) and people for larger numbers (especially of people considered more generally) has fallen out of style in favor of people in most contexts (5th ed. [Oxford, 2022], under “people. A. And persons”).

So one might have once referred to the people at the grocery store but the two persons ahead of me in line. Today, people is usually considered to be the more natural choice for both and can be used just about anywhere the plural is called for.

Q. A few years ago, Vox published an article making a distinction between titles, subtitles, and “reading lines” for books (“ ‘A Novel’: An Article,” by Eliza Brooke, February 14, 2019). The article claimed that when a work has the form of Title of Book: A Novel, “A Novel” is not a true subtitle but instead “explains its contents to a potential reader and serves as a useful signpost when you’re rooting through an unsorted stack of books.” How should these “reading lines” be treated in citations? If they appear not solely on the book cover but also on the title page, it would seem to me that they should be treated as a subtitle. Is that right? Or should these reading lines be omitted since they are not real subtitles as argued in the Vox article, and if so, what is a good guideline for distinguishing them from subtitles?

A. Assuming authorship and other relevant details have been supplied, most books can be identified from a main title alone. Subtitles are often informative, though, so we would advise including them in the titles of books that have them at least once, as on first mention or in a full note or bibliography entry.

But we agree with the Vox article that a subtitle that merely identifies a book’s genre isn’t a proper subtitle. The phrase “A Novel” does that, so you can leave it out, even if it appears on the title page (see also CMOS 13.91). By contrast, you’d want to include a subtitle like the one for the book All the Ways We Said Goodbye: A Novel of the Ritz Paris, by Beatriz Williams, Lauren Willig, and Karen White (William Morrow, 2020).

Not that there’s anything wrong with including a generic subtitle in a source citation, especially if it appears on the title page. But when that subtitle is shared with countless other books and doesn’t say anything special, it’s usually safe to omit it.

Q. Here’s a funny question. How do you treat a source where the author name or pseudonym is the same as the name of the website or blog? Is there a way to eliminate repetition from the entries below?

Mercer, Ilana. 2017. “Article Title.” IlanaMercer.com. August 1.

Bionic Mosquito. 2015a. “Blog Post Title.” Bionic Mosquito, August 5.

Thank you!

A. Your first author-date reference list entry, for the Mercer article, is fine as is. It’s clear that a URL featuring the author’s name must be the author’s website. It also happens to reflect the website’s copyright line: “© 2008-2025 ILANAMERCER.com”; applying caps to only the I and M (domain names aren’t case sensitive) increases legibility.

Your second entry is also fine as is. Most readers would figure out that the italics for the second instance of Bionic Mosquito mean that it’s a title rather than an author or publisher. But you can help readers out a little with one or two clarifications:

Bionic Mosquito [pseud.]. 2015a. “Blog Post Title.” Bionic Mosquito (blog), August 5.

We’d recommend adding that first one—which clarifies that “Bionic Mosquito” is a pseudonym (the square brackets show that it’s an editor’s interpolation). The parenthetical description “(blog)” is less important to include but could be helpful for an audience that may not know the source material. In both cases, include a full URL at the end of the citation—or, in published form, provide a link from the title or elsewhere. See also CMOS 13.6, 13.82, and 14.105.

Q. When a printed work misspells an author’s name, how should that name be represented in notes and bibliography entries for that work? Should the misspelled name be used, silently corrected, or somehow pointed out? If the author on the title page is “Ezra Fisk” but the correct spelling is “Ezra Fiske,” might we use “Fisk[e], Ezra” as the bibliography entry? I suppose that similar questions could also be asked of typos in other bibliographic information.

A. Your solution is a good one. But not all readers can be expected to understand the nuances of bracketed insertions, so you could instead do something more explicit than a bracketed e:

Fiske, Ezra [spelled “Ezra Fisk” on the title page]. Title of Work. Publisher, date.

Readers will then be more likely to know what to expect when tracking down the cited source. (If the variant spelling occurs on more than the title page, adjust the bracketed comment accordingly.) For additional considerations, start with CMOS 13.82; see also 12.70.

Q. I copyedit a technical journal, and I have a question about how CMOS would handle the term “Fortune 500.” Is “Fortune” (as the name of a publication) set in italics while “500” is not, or is “Fortune 500” treated as a standalone brand or fixed term akin to a trademark, where “Fortune” would be set roman? Thanks.

A. That term could go either way, but we’d refer to it as the Fortune 500, without italics for “Fortune,” following CMOS 8.174: “When the title of a newspaper or periodical is part of the name of a building, organization, prize, or the like, it is not italicized.”

The Fortune 500 (an annual ranking of the top 500 companies in the United States published by Fortune magazine) is analogous to a prize, and the fact that the word “Fortune” is part of the name of the list is what determines our choice.

The Billboard Hot 100 presents a similar case. Some editors would style that as the Billboard Hot 100. But we’d use italics only if referring to that list in terms of the magazine that publishes it, as in Billboard magazine’s Hot 100, or Billboard’s Hot 100 for short.

Q. Which is correct: “one should do one’s duty” or “one should do his or her duty”—or, using singular they, “one should do their duty”?

A. In your example, one is closer to the personal pronoun you than to the indefinite pronoun everyone. Everyone would normally pair with his, her, or singular their, as in everyone should do their duty (see also CMOS 5.51). One, by contrast, can simply switch to the possessive case like other such pronouns:

I should do my duty; you should do your duty; he should do his duty; she should do her duty; they should do their duty; we should do our duty; one should do one’s duty

According to Bryan Garner, however, writers have tended to pair one with he (and, by extension, one with his), despite objections from “strict grammarians” and others (see Garner’s Modern English Usage, 5th ed. [Oxford, 2022], under “One . . . he”).

We can only hope, then, that we’re doing our duty as arbiters of style by recommending a pairing of one with one’s.

Q. Hello, Chicago. Thanks for your time. I’d like you to confirm the optional comma after a one-word adverb of time (tonight, yesterday, today) starting a sentence. One of my fiction authors is upset because Word is showing blue lines under those words. I told her a comma is optional and Word doesn’t get the nuances. Would you please confirm this so I can calm my jittery author? Thanks again.

A. It can be hard to ignore Microsoft Word’s blue underlines, especially when they’re worded in a way that suggests you’d be wrong to keep the text as is: “After an introductory word or phrase, a comma is best.”

But you can tell your author that we agree with you. In the words of CMOS 6.34, “Although an introductory adverbial phrase can usually be followed by a comma, it need not be unless misreading is likely. Shorter adverbial phrases are less likely to merit a comma than longer ones.”

The adverbs yesterday, tonight, and today aren’t phrases, but each of them derives from one (yesterday comes from Old English giestran dæg), and it’s clear that each is grammatically equivalent to a phrase like next week or in 1965. Plus, any one of these words would qualify as short in the context of introductory adverbial phrases.

To be fair to Word, tonight is the only one among the words and phrases mentioned above (from yesterday through in 1965) that Word’s grammar checker flagged in our tests when it wasn’t followed by a comma (as of July 1, 2025). Conversely, Word didn’t stop on any of them when they were followed by a comma. So it’s not that far out of line with CMOS.

Tip: To avoid falling under the influence of Word’s blue underlines, some writers prefer to toggle them off as they draft. A convenient way of doing this is to add a button to the ribbon. In Word for Windows (the desktop version), go to File > Options > Customize Ribbon. Then select All Commands under “Choose commands from” and scroll down until you find Hide Grammar Errors. You can then add that command to a new group under the Home tab (or wherever you want it to appear). Steps for Word for Mac will be similar.

If you use the option under Customize Ribbon to assign a keyboard shortcut to the equivalent command (look for ToolsGrammarHide under the All Commands category in the separate dialog box for keyboard shortcuts), keep the button, which has the important advantage of showing whether it’s on or off (via shading/outline).

Q. Does a term following the word “called” need to be in italics or quotation marks—or neither? For example, “a series of bends called meanders.”

A. CMOS takes a relatively hands-off approach to terms introduced by called, known as, referred to as, and the like. The idea is that these are simply extensions of the linking verb to be:

Those are potatoes.

or, more specifically,

Those are called potatoes.

But if you want to draw attention to such a term for any reason, you can use italics (or quotation marks). CMOS does this, for example, in certain passages in chapter 5 where we wanted to emphasize grammar-related vocabulary—as in the following sentence from CMOS 5.180:

A phrasal preposition, sometimes called a complex preposition, is two or more separate words used as a prepositional unit.

For the related issue of what to do following so-called (where quotation marks are considered unnecessary in Chicago style), see CMOS 7.62.

Q. “. . . go to high school in Washington[, D.C.].” Is the final period necessary? Delete it? (Yes, it’s the last of a longer quotation.)

A. In your version, where you’re using brackets to supply not just the abbreviation but the comma that would normally go with it, you don’t need that final period; we can assume that your bracketed interpolation includes all sentence punctuation, including any final period. And that’s what we might expect if you were supplying the end of a sentence that’s missing or illegible in the source. In other words, your brackets restore the end of a sentence that would normally be punctuated like this:

“. . . go to high school in Washington, D.C.”

But if you’re simply clarifying for readers that the text is referring to the district rather than the state, don’t add that comma. Instead, put “D.C.” in brackets and add the sentence-ending period:

“. . . go to high school in Washington [D.C.].”

That extra period is needed for the same reason you’d add a period to the end of a sentence like this one (from CMOS 6.13):

His chilly demeanor gave him an affinity for the noble gases (helium, neon, etc.).

But there would be no periods in an initialism like DC in current Chicago style, so you’d normally write this:

“. . . go to high school in Washington [DC].”

See also CMOS 6.110 (which has a similar set of examples but without periods) and 12.70–74 (on editorial interpolations and clarifications).

Q. For author-date parenthetical text references, CMOS 13.123 says to list “as many [authors] as needed to distinguish the references.” My reference list includes two articles where the first seven authors are the same. In that case, can I use the letters instead of listing more authors? The articles are both from 2006 in the journal Latin American Antiquity: “Smokescreens in the Provenance Investigation of Early Formative Mesoamerican Ceramics” and “Methodological Issues in the Provenance Investigation of Early Formative Mesoamerican Ceramics.”

A. Yes, you can use letters to differentiate the two articles in your text. Per CMOS 13.107, a source by more than six authors would be listed in your references by the first three, followed by et al. Because the first three authors are identical for those two articles (each of which lists thirteen authors), adding a and b after the year of publication would distinguish them in the text. Here are the reference list entries (in alphabetical order by title; see 13.114) and text citations:

Neff, Hector, Jeffrey Blomster, Michael D. Glascock, et al. 2006a. “Methodological Issues in the Provenance Investigation of Early Formative Mesoamerican Ceramics.” Latin American Antiquity 17 (1): 54–76. https://doi.org/10.2307/25063036.

Neff, Hector, Jeffrey Blomster, Michael D. Glascock, et al. 2006b. “Smokescreens in the Provenance Investigation of Early Formative Mesoamerican Ceramics.” Latin American Antiquity 17 (1): 104–18. https://doi.org/10.2307/25063039.

(Neff et al. 2006a)

(Neff et al. 2006b)

Alternatively, you could cite by title in the text (and omit the letters in the reference list entries and text citations):

(Neff et al., “Methodological Issues,” 2006)

(Neff et al., “Smokescreens,” 2006)

But the letters are more concise.