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.

Q. In a recent Q&A, you insist that “et al.” can be used only for two or more individuals. But cannot “et al.” equally be an abbreviated form of the singular “et alius”? And, as such, can it not be used for a single individual?

A. You’re right, there’s no reason et al. couldn’t stand for et alius (“and another”) rather than et alii/aliae/alia (“and others”). For our answer we (mostly) relied on Merriam-Webster and the OED, both of which define et al. only as “and others” and both of which cite et alii (masculine), et aliae (feminine), and et alia (neuter) as the only spelled-out forms. Maybe the dictionaries are right. Or maybe they’re missing the occasional singular use hidden behind the abbreviation. And it’s not like the world would end if one were to use et al. to stand in for a single person. We’ll keep tabs on this issue and consider reconsidering our advice someday.

Q. When writing units of measurement for fractions between 0 and 1, is the unit singular or plural? For example, “We walked 1/4 mile yesterday and 7/8 mile today,” or “Gently fold in 2/3 cup of blueberries.”

A. Amounts of less than one can usually be treated as singular when expressed as simple fractions—as in your three examples—but plural when expressed as decimal fractions. The difference is related to how such expressions would be spelled out or read aloud:

1/4 mile = one-fourth of a mile or a quarter of a mile or a quarter mile (among other variations)

7/8 mile = seven-eighths of a mile

2/3 cup = two-thirds of a cup

A decimal fraction, by contrast, would normally be read as a plural:

0.25 miles = (zero) point two five miles (rather than twenty-five hundredths of a mile)

But note that an abbreviated unit of measure is usually the same for both singular and plural quantities. So you’d write “0.25 mi.” even though “mi.” would be read as “miles.” See also CMOS 9.21 and 10.73.

Q. Hi, How would Chicago style the name of the AI hardware company that goes by “io,” founded by Jony Ive and recently acquired by OpenAI? Is it a proper name that should be styled “Io,” following the example of Adidas in CMOS 8.70? Or is it an initialism (abbreviating “input-output,” I guess?), and in that case would it be “IO,” like AT&T? Thanks.

A. That’s precisely the problem: Is “io” a word like “Adidas” (rendered as “adidas” by that company in both logotype and text) or an initialism like “AT&T” (“at&t” in a previous incarnation of that company’s logo)?

An article in Wired announcing the merger gave the name an initial cap, which would suggest that it’s a word: “In the fourth quarter of last year, Io and OpenAI entered into an official agreement for OpenAI to receive a 23 percent stake in Io” (see Lauren Goode, “OpenAI’s Big Bet That Jony Ive Can Make AI Hardware Work,” May 21, 2025).*

Meanwhile, a New York Times article from that same day applied all caps, suggesting an initialism: “On Wednesday, Sam Altman, OpenAI’s chief executive, said the company was paying $6.5 billion to buy IO” (see Mike Isaac and Cade Metz, “OpenAI Unites with Jony Ive in $6.5 Billion Deal to Create A.I. Devices”).

We’ve watched the OpenAI video “Sam & Jony introduce io” (which is also from May 21; we’ve preserved the sentence case in the source’s title and lowercase “io”), but we’re still not sure what “io” is supposed to be—though it’s almost certainly just a name inspired by an abbreviation.

We’re leaning, then, toward “IO” (all caps) as the most reader-friendly choice. “Io” could be one of Jupiter’s moons (among other possibilities). And though you could just go with “io” (if you can’t beat ’em . . .), you’d need to decide whether to retain that form at the start of a sentence or heading (or risk the appearance of inconsistency by applying caps). If you’re worried about being called out as wrong by those in the know, consider adding a clarification at first mention: The merger with IO (styled “io” by the company itself) . . .

__________

* The spelling “Io” (initial cap) could mean it’s an acronym in British style, which would call for “Nasa” instead of “NASA” (an acronym) but BBC (an initialism). But Wired (or WIRED as that publication styles itself) clearly follows US style for acronyms, so “Io” in the article mentioned above suggests that it’s a word (specifically, a proper noun). See also CMOS 10.6.

Q. Is it Chicago style to not capitalize clauses in the US Constitution (the commerce clause, the due process clause, etc.)? If so, what is the reasoning?

A. Such terms are not normally capitalized in Chicago style; see CMOS 8.81, which includes the example “the due process clause.” The reason for lowercase is that the Constitution doesn’t have a Commerce Clause or a Due Process Clause—not with those titles anyway.

Instead, “commerce clause” and “due process clause” refer to certain passages in the Constitution that treat commerce and due process. We realize, however, that those terms (and others naming specific clauses) have acquired the status of proper nouns for many writers and are often styled with initial caps in published prose. And Merriam-Webster, though it uses lowercase in its headwords for such terms (see, e.g., the entry for “due process clause”), adds the label “often capitalized.”

If Chicago’s default style is too conservative for you, capitalization-wise, there’s nothing wrong with applying initial caps to such terms as long as you stick to clauses (e.g., the Due Process Clause, but the legal concept of due process).

Q. Hello! I am providing guidance to art history students on creating bibliography and note entries and have a few questions that I’m not sure of the answer to: (1) How would one style the name Hans Holbein the Younger in a bibliography entry? (2) When a work of art doesn’t have a title and is simply a description, I assume it would be in sentence case and not italicized, but is this correct? For instance, this glass ribbed bowl at the Met. (3) I assume for guesstimate dates “ca.” would be preferred, but would “18th century” or “Edo period” be acceptable?

A. (1) For an item in a bibliography attributed to Hans Holbein the Younger, invert the name as “Holbein, Hans, the Younger.” (2) Yes, sentence case would be appropriate for a description in lieu of a title:

Glass ribbed bowl. 1st century BCE. Cast, tooled, and cut. Height 2 9⁄16 in. (6.5 cm), diameter 5 7⁄16 in. (13.8 cm). Metropolitan Museum of Art, New York. Object no. 17.194.197.

(3) Yes, a specific century or named era, if known, can be used instead of “ca.” (about), which usually applies to a more specific date such as a year. In some cases, it will be appropriate to combine a named period with an estimated date (e.g., Edo period, ca. 1800).

Q. I’m wondering how you would treat an online report from an NGO or watchdog organization? What type of source is it parallel to? I’m asking to instruct my students for the author-date format. There is no specific author, just the organization. There is a specific date of publication, not just a year. This is the specific source, but there are others that are similar: https://humena.org/political-satire-in-egypt-a-peaceful-protest-against-repression/. Thank you.

A. Reports are covered briefly under CMOS 14.117, but you’ll also want to refer to 13.86 and 13.127, which show how to handle organizations as authors, including the use of abbreviations in author-date format.

Most freestanding reports can be cited similarly to books. The report at the URL you point to could be cited in a reference list as follows:

HuMENA and RedWord. 2024. Political Satire in Egypt: A Peaceful Protest Against Repression. HuMENA for Human Rights and Civic Engagement in collaboration with RedWord for Human Rights and Freedom of Expression, November 22. https://humena.org/political-satire-in-egypt-a-peaceful-protest-against-repression/.

As with many such documents, the author and publisher are the same. By abbreviating the author, you allow for concise citations in the text. The example above would be cited as “(HuMENA and RedWord 2024).”

Note that the report itself (published as a PDF file) doesn’t seem to list a date of publication, but the page that offers the PDF and announces its publication does have a date, which you can cite as shown above.

For working papers and the like, see CMOS 14.116.