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.