Q. I’m confused about this issue of whether to add a space after the abbreviation “w/” (with). A previous answer said that there should be a space because the abbreviation stands for a full word, which would have a space after it if written out. But CMOS 6.116 shows no spaces around a slash that stands for “per” or that is used in an abbreviation like “c/o” (in care of) or “n/a” (not applicable). So why is “w/” treated differently?
A. In an expression like “km/s” (kilometers per second) or “$450/week” (450 dollars per week), the slash is a stand-alone abbreviation for “per.” If you were to add a space in either of those expressions, you’d need two of them (one before and one after the slash). In an expression like “c/o” or “n/a,” the slash is a kind of shorthand that tells readers to interpret the letters as abbreviations; it belongs equally to both letters.
The abbreviation “w/” is very much like “c/o” and “n/a” but with only one rather than two abbreviated letters. (Each of those could be written instead with periods, but the slash nonetheless became the convention.) But whereas c pairs with o and n with a, that w is, as our original answer suggested, a single entity that doesn’t normally pair with anything, so it’s usually separated from what comes next by a space.
That’s the editorial logic anyway. The abbreviation “w/” is casual. Any rule regarding its use should be taken w/ a grain of NaCl (and with the understanding that no rule is w/out exceptions).
[This answer relies on the 18th edition of CMOS (2024) unless otherwise noted.]
Q. When referring to two doctors in a letter, should they be addressed as “Dr. A and Dr. B”? Or “Drs. A and B”?
A. For extra formality, use Drs., which echoes the old-fashioned Messrs. (the plural of Mr.) and would be especially well suited to the salutation. But if your letter isn’t especially formal, or if you’re simply naming the two doctors (as in the body of the letter), use Dr. before both names.
[This answer relies on the 18th edition of CMOS (2024) unless otherwise noted.]
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.
[This answer relies on the 18th edition of CMOS (2024) unless otherwise noted.]
Q. Could we have some prescriptions for sentence-initial “i.e.,” “e.g.,” “ibid.,” and the like in notes and parentheses? Capitalizing the first letter is widely felt to be awkward (see June Casagrande, “A Word, Please: A Guide to Using Latin Abbreviations, E.g. and I.e.,” December 12, 2015, in the Los Angeles Times), and at least one legal style guide prescribes lowercase “ibid.” at the beginning of a footnote (OSCOLA: Oxford University Standard for the Citation of Legal Authorities, 4th ed., Faculty of Law, 2012). Other style pundits have recommended periphrasis.
A. Chicago would apply an initial cap to each of those abbreviations at the beginning of a sentence, including at the beginning of a numbered footnote or endnote (Chicago styles these like sentences), where “ibid.” would often be the first word (see CMOS 14.34 for examples—and for why we prefer to use a shortened form of the source in favor of “ibid.”):
1. Ibid., 83.
We’d do the same for “i.e.” and “e.g.” (i.e., writing “I.e.” and “E.g.”). But those two abbreviations usually occur in parentheses in Chicago style, and there are no examples of either in the seventeenth edition of CMOS at the start of a sentence or a note. (Attentive readers will have noticed the initial caps for each in the title of the LA Times article in your question, which we decided were being used as nouns when we applied the rules for headline style at CMOS 8.159; “I.E.” and “E.G.” could also work, but we’d reserve that treatment for an all-caps heading. Cf. this Q&A on sp. and spp.)
We do make one exception that’s directly related to your question—for the abbreviation “p.” (page) in a parenthetical page citation at the end of a block quotation (which isn’t Latin but does occur in source citations). Because the “(p. 142)” at the end of the second block quotation in CMOS 13.70 follows a period, one might think that the p should be capitalized: “(P. 142).” But we decided that we prefer consistency for those lowercase p’s relative to other such parenthetical p’s—and that we don’t consider “(p. 142)” to work like a sentence in that context (though the word see may be implied before “p.”).
[This answer relies on the 17th edition of CMOS (2017) unless otherwise noted.]
Q. In dialogue, when a character says “Nam” referring to Vietnam, is an apostrophe necessary? The official name is one word, yet “Viet Nam” is more historical. That would suggest the apostrophe is not needed?
A. The spelling “Viet Nam” reflects how that country’s name is rendered in Vietnamese, which, according to the entry for Vietnam in the CIA’s World Factbook, is “Cong Hoa Xa Hoi Chu Nghia Viet Nam,” which translates to “Socialist Republic of Vietnam.” Vietnamese words are written using the Latin alphabet (usually with diacritical marks, not shown here).
Nam without an apostrophe would be correct then as a shortened form of the Vietnamese spelling of the country’s name. On the other hand, ’Nam would also be correct—as a contraction of “Vietnam.”
So you could choose one form and be consistent—or you could defer to the OED. Although two of its five quoted examples in support of its entry for the word “Nam” (which it labels colloquial) include an initial apostrophe, the headword in the OED is spelled without one.
[This answer relies on the 17th edition of CMOS (2017) unless otherwise noted.]
Q. When an abbreviation is first mentioned in a footnote, should the abbreviation be spelled out in both the footnote and at the first mention of it in the body of the text, or is spelling it out in the footnote alone sufficient?
A. It can be perfectly acceptable to introduce an abbreviation in a footnote, but if you’re worried about readers who might skip the note, rework your text to define the abbreviation there rather than in the note. You’ll want to do this especially if the meaning of the abbreviation would be difficult to figure out without an explanation—or if you’re using endnotes rather than footnotes.
For an example of how you might use a note to introduce an abbreviation for the title of a frequently cited work (preferably in a footnote rather than in an endnote), see CMOS 14.59.
[This answer relies on the 17th edition of CMOS (2017) unless otherwise noted.]
Q. I am seeing everywhere now that people are putting acronyms in parentheses instead of words, as in “Food and Drug Administration (FDA)” versus “FDA (Food and Drug Administration).” Can you explain to me why this is becoming more common? Parentheses have always been intended for additional information or words of further explanation, which is the opposite of an acronym. It just seems so backwards to me, and if you’re searching for what the acronym stands for, it’s hard to find because the acronym is in the parentheses and used from then on. Please help me understand the logic people are following with this style.
A. It makes sense to put the abbreviation first when the abbreviation is the better-known term—as is arguably the case for the FDA. But there’s no rule against putting the abbreviation in parentheses. In fact, when you introduce an abbreviation primarily as a space-saving device, the convention is to put the abbreviation in parentheses the first time it appears. For example,
According to the Abbreviation Appreciation Society (AAS) . . .
which is shorthand for
According to the Abbreviation Appreciation Society (which we’ll hereinafter refer to as AAS for the sake of convenience) . . .
And though it’s true that you lose a bit of clarity through abbreviation, there are a couple of strategies that can help readers. First, consider reintroducing the spelled-out term alongside the abbreviation in each new chapter or other major division in which it appears. And if your text features many otherwise unfamiliar abbreviations, consider adding a list as described in CMOS 1.44.
[This answer relies on the 17th edition of CMOS (2017) unless otherwise noted.]
Q. What is the stance of CMOS on single-letter abbreviations for days of the week? In US higher education, the single-letter abbreviations (M, T, W, R, F, S, U) are ubiquitous, though I find no mention of these abbreviations being codified (ISO uses numbers). In prose, I often find myself using these abbreviations in lists of upcoming deadlines.
A. CMOS doesn’t cover those single-letter abbreviations, but we’d consider them to be a convenient shorthand. In the same way, “1/5” can be a handy way of writing January 5.
But because the meaning of “U” and “R” especially may not be clear, and because “1/5” means May 1 for many readers, we don’t recommend either of those forms in formal writing. Where brevity is the main consideration, our preference would be for Su, M, Tu, W, Th, F, and Sa. For those options and two others, see CMOS 10.40. For all-numeral dates, see CMOS 9.35.
[This answer relies on the 17th edition of CMOS (2017) unless otherwise noted.]
Q. When should you capitalize AM and PM?
A. Capitalize “AM” and “PM” not only in the morning and afternoon but at any time of day or night—unless you’re following Chicago style, in which case use lowercase and periods (10:30 a.m., 5:30 p.m.). See CMOS 10.41.
[This answer relies on the 17th edition of CMOS (2017) unless otherwise noted.]
Q. How do I abbreviate the word “number”?
A. Avoid num., which is normally reserved for “numeral,” and n., which in Chicago style usually means “note.” For casual prose, the number sign # is common. But even though “number sign” is its Unicode name, that symbol has a number (sorry) of other uses, including as a hashtag and in URLs that point to a specific part of a page.
In most contexts, the best choice is no.—a common form that abbreviates the Latin word numero. That’s what we prefer in source citations for journal articles, as in Critical Inquiry 49, no. 3, which refers to volume 49 (we omit the abbreviation “vol.” in this context), issue number 3, of that journal.
[This answer relies on the 17th edition of CMOS (2017) unless otherwise noted.]