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.