Q. Would “secretary of homeland security” be lowercase in a sentence without that person’s name?
A. Just as you’d refer in Chicago style to a president of the United States or other country with a lowercase p (as in this sentence), you’d use a lowercase s when referring to a secretary of homeland security.
But note that the generic phrase “homeland security” (like “transportation,” “state,” and other such terms) becomes a proper noun when it refers to the administrative body—as in the Department of Homeland Security, or Homeland Security for short.
So you’d refer to the secretary of the US Department of Homeland Security. But this can get tricky: Does “homeland security” in “secretary of homeland security” refer to the department or only to the role? If in doubt, capitalize (“secretary of Homeland Security”). See also CMOS 8.22 and 8.63.
And before a name, secretary would be capitalized, as in US Homeland Security Secretary Alejandro Mayorkas, or Secretary Mayorkas.
Q. Hello! I’m wondering if you can give me some guidance on flight numbers. Chicago doesn’t seem to mention them, but flights appear to be capitalized when they follow the airline’s name from what I can see online—for example, Pan Am Flight 103 (the one in the Lockerbie bombing). So I’m thinking a flight should be, say, “flight 900” when used alone (as in “I took flight 900 to Geneva”), or Big Airline Flight 900 when it appears after an airline’s name. Does that sound about right to you? Many thanks!
A. In strict Chicago style, flight numbers would be lowercased—like room numbers, page numbers, and other such identifiers. Accordingly, we’d write “Pan Am flight 103” and, for subsequent mentions, “flight 103.” That’s the style Britannica follows in its article on the tragedy. According to this usage, “Pan Am” is a proper noun, whereas “flight 103” is not.
But you’re right that many sources capitalize flight numbers. If you’re going to go that route, however, you should still treat the airline name and flight number as separate terms, which would require a capital F even when the flight number is used alone: Pan Am Flight 103; Flight 103 (but the flight).
Q. Would CMOS lowercase the noun preceding the number in each below? Yes or no?
He was called to aisle 8.
The meeting was at building 50.
The accident happened on interstate 90.
Tom got off at exit 12.
Holyfield fell in round 4.
The cashier stole cash from register 7.
The incident happened at terminal 1.
Thank you.
A. Words like “interstate” and “highway” are generally considered part of the name and capitalized: Interstate 90, Highway 66. But all the other terms in your list—from “aisle 8” to “terminal 1”—would be treated as generic and lowercased.
Q. Do you lowercase occupational forms of address like “waiter,” “driver,” “bartender,” and “cook”? It seems that I got different opinions on various websites. Thanks for your input.
A. None of the terms you mention would normally be capitalized in direct address, even when standing in for a name:
Where are you taking me, driver?
Hey, bartender, where’s my drink?
But if the occupation can also be used as a title, capitalization is the norm:
How bad is it, Doctor?
What’s the rush, Captain?
Either convention can be broken, however.
For example, capitalization would make sense for a fictional character known by occupation alone, even if the occupation isn’t also a title—as in the case of the character known as “Driver” in the novels Drive and Driven, by James Sallis (Poisoned Pen Press, 2005 and 2012). And titles that aren’t being used literally are less likely to merit capitalization: What’s up, doc?
For some additional considerations, see CMOS 8.34–37.
Q. When indirectly referring to Catholic nuns, should the term “sisters” be capitalized?
A. According to Merriam-Webster, “sister” is “often capitalized” when referring to a member of a religious order, Catholic or otherwise. CMOS takes that “often” as permission to use lowercase: “The sisters left the convent at noon.”
Q. Does CMOS allow random capitalization in poems?
A. We would, provided the randomness worked on some level. If a publisher has accepted the poem, then it probably does. A copyeditor might query any choice that doesn’t seem to be intentionally random—on the off chance that it might be a mistake—but otherwise, it’s usually up to The PoET.
Q. Hello! I work in marketing, and I’m wondering if lowercasing the words “off” and “under” in these headlines is correct: “50% off Body Wash” and “Gift Sets under $40.”
A. If you’re in marketing, capitalize both of those words. Why be quiet about savings?
Q. Debating with an editor over capitalization of the word bicentennial. When it’s an adjective (“bicentennial year”), I agree that no cap is needed, but I contend that when it’s a noun (“the Bicentennial”), a cap is needed. Agree—or not?
A. The noun bicentennial, like anniversary or birthday or even golden jubilee, is normally lowercased. But if you’re referring to a specific bicentennial, like the one the United States celebrated in 1976—“the Bicentennial”—a capital B might be warranted. Or so it seems in hindsight.
According to a Google Ngram comparison of the lowercase b and capital B forms of the word, there have been three notable jumps for “Bicentennial” in books published in English since 1900:

The two biggest bumps align with major bicentennials in the US (1976) and France (1989). The third peak—ca. 1932—corresponds to the bicentennial of George Washington’s birthday. (The ngram doesn’t tell you any of this—and there are other possibilities—but it’s fun to guess.)
In a publication that discusses one of the national bicentennials, a capital B would make sense. But note that both nouns and adjectives would qualify: the US Bicentennial, the Bicentennial celebrations in the US.
Q. Current guidelines on French capitalization in CMOS are mostly directed at an all-French context. In the case of an English text with a heavy dose of French proper names, it feels a bit awkward to leave the first word in a name such as “théâtre de la Porte Saint-Martin” with a lowercase t. What does the University of Chicago Press do in these cases?
A. The advice in Chicago is supposed to highlight conventions that can be retained when importing bits of French into an English-language context, and capitalization is one of these conventions. But an initial article like le or la is most often changed to an English the, so to use your example, we’d refer to the Théâtre de la Porte Saint-Martin (starting the name with a capital T) even if, in a French context, it might be referred to as le théâtre de la Porte Saint-Martin (the theater’s website, however, capitalizes that first t).
To take another example, you might refer in English to the Bibliothèque nationale de France or, for short, the Bibliothèque nationale, both of which reflect French capitalization (which is evident in the abbreviation BnF, with a lowercase n). That would normally be Chicago style—that is, we’d retain the lowercase n in English. But it would arguably be clearer to refer to the Bibliothèque Nationale, with a capital N, so that readers unfamiliar with French capitalization would understand where the name begins and ends. Some editors depart from Chicago style for such terms (and apply English-style caps, a.k.a. headline style or title case) for this very reason.
Note, however, that for the title of a book or article or other work, which would normally be set off from the surrounding text by quotation marks or italics, French capitalization would always be retained (see CMOS 11.27). But for the name of a theater or a library or the like, you could make some exceptions for the sake of your readers.
Q. In CMOS 9.48, on numbered places of worship, shouldn’t the example “Twenty-First Church of Christ” read as “Twenty-first Church of Christ”? Why is the second number uppercase?
A. The word “first” in “twenty-first” is an adjective, so it gets a capital F as the second part of a hyphenated compound in the name of an organization or the title of a work—or in a street name or whatever else would normally be capitalized. See CMOS 8.161, which also says specifically to capitalize the second element in a hyphenated spelled-out number. This advice was new to the 16th ed. (2010); until then, CMOS would have advised “Twenty-first,” but our editors agreed that the convention for lowercase wasn’t strong enough to continue to allow for an exception to the rule about adjectives. “Twenty-first” isn’t wrong, then, but it’s no longer Chicago style.