For example, one Unidentified Flying Object is UFO, but many is UFOs, so should I write:

… the Middle Persian Pahlavi literature of the 9th and 10th c.s ᴀ.ᴅ. …


… the Middle Persian Pahlavi literature of the 9th and 10th c. ᴀ.ᴅ. …


… the Middle Persian Pahlavi literature of the 9th and 10th centuries ᴀ.ᴅ. …

2 Answers 2



I searched Google Books for the phrases "1st cs AD", "2nd cs AD", "3rd cs AD" etc. (Google handles "cs.", "c.s" and "cs" the same) and "1st centuries AD", "2nd centuries AD" etc. Among the results, only a handful of books use a plural abbreviation for centuries in this context while thousands don't abbreviate centuries AD. Google Ngram Viewer shows that c AD and cs AD are much more rare than century AD and centuries AD:

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The abbreviation seems so uncommon, that I, personally, wouldn't use it. Section 10.42 "Scholarly abbreviations" of the Chicago Manual of Style, where the abbreviation "c. century; chapter (in law citations)" is listed, recommends: "In formal prose, Chicago prefers to confine such abbreviations to parentheses or notes."

To me, in the body of your text, it seems stylistically better to write:

... Persian literature of the 9th and 10th centuries AD ...


Section 7.15 "Plurals for letters, abbreviations, and numerals" of the CMOS specifies that "abbreviations usually form the plu­ral by adding s". Examples similar to c. are "vols." and "eds." Exceptions, such as pp. for "pages" or MSS for "manuscripts" are explicitly listed. No exception for "centuries" is given. Therefore, if you want to use the abbreviation, the correct form seems to be:

... Persian literature of the 9th and 10th cs. AD ...

Note that ranges expressed with to and alternatives expressed with or and nor take the singular! (CMOS 7.8 "Plurals for centuries")

  • the eighteenth and early nineteenth centuries
  • in the fifth through eighth centuries


  • from the twentieth to the twenty-first century
  • the fifth or sixth century
  • eighteenth- and nineteenth-century technologies
  • Thanks for the detailed answer, I’ll not use c. cs. outside of parenthesis Commented Mar 23 at 14:02
  • @VincentDesrosiers After reading the answer by Jay, I found that some books use the abbreviation cs. for centuries while others use cc. The latter seems slightly more frequent, but still rare overall. I couldn't find any style guide that explains what their correct abbreviation is for the plural of centuries. I would either ask your publisher what abbreviation to use or try and contact the editorial team of your style guide — or just use what you find is more frequent in your field. (Did you see cs. or cc. in any of your sources? If not, maybe better avoid the abbreviation.)
    – Ben
    Commented Mar 24 at 19:53
  • I am a student so I would ask my teacher, though I do agree with Jay that I should keep abbreviations to parentheses and, as of now, I dont use centuries in any parethesis. cc. does make sense, though, since the plural of p. is pp. Commented Mar 24 at 21:27

I don't think it's common to abbreviate century to "c", so the question of the plural would rarely come up. I presume if you wrote "2nd c. BC" that readers would guess that "c." stood for century, but, etc.

In general, to make a one letter abbreviation plural, we double the letter. Like the abbreviation for line is "l", so the abbreviation for lines is "ll". Page is "p" so pages is "pp". Etc. By that rule, if you abbreviate "century" to "c" then you should abbreviate "centuries" to "cc". But would most readers know what you meant? Probably not. Many people are confused by this double letter rule as it is. Like, people sometimes abbreviate copy to "c" and thus copies to "cc". But I've heard many people read "cc" as "carbon copies", because they're not familiar with the convention and are struggling to make sense of the abbreviation.

Personally, I'd just write "centuries".

  • Could you give a source for the rule that all single letter abbreviations are doubled to form the plural? The Chicago Manual of Style has a rule to form the plural of an abbreviation by appending an -s and explicitly mentions those abbreviations that deviate from this rule. And while they list pp. (pages), vv. (verses), nn (notes) and other double letter plural abbreviations, the abbreviation for "century" is listed without a deviant plural, so I assume it must be cs., following the general rule.
    – Ben
    Commented Mar 24 at 20:12
  • @ben A source that says ALL, 100%? I'm sure I could not. English is full of special cases and exceptions. In any case, I checked the Chicago Manual of Style on line and couldn't find any listing of "c" as an abbreviation for "century". I would have expected it on this page: chicagomanualofstyle.org/16/ch10/ch10_sec071.html Are you saying you found such an entry somewhere? If not, to say that they didn't include an abbreviation under a list of exceptions to a general pluralization rule, when they didn't include the singular form, would not seem to prove much. Even if they do ...
    – Jay
    Commented Mar 26 at 16:25
  • ... list it somewhere, it might have been overlooked in a list of exceptions to a general rule. I'd be very reluctant to assume that any list of exceptions includes 100% all exceptions to the general rule.
    – Jay
    Commented Mar 26 at 16:27
  • c. century is in section 10.42 "Scholarly abbreviations" of the Chicago Manual of Style. I referred to it in my answer. That list also lists all the exceptions, some of which I quoted in my previous comment. It therefore seems to me that c. must follow the s-plural rule. —— And if you write, as you do in your answer, that "[i]n general, to make a one letter abbreviation plural, we double the letter", that is quite an all-encompassing rule and should be stated somewhere, if it existed.
    – Ben
    Commented Mar 26 at 18:56
  • @ben Wow, you seem very emotionally invested in this! As I said, when someone states a rule and then lists exceptions, I'd be VERY reluctant to assume that that list is 100% all of the exceptions that have ever existed or ever will. As to the general rule about doubling the letter, in a brief search I couldn't find a page on the Internet that states this as a rule. But one can easily find numerous citations of "pp" for "pages" and "ll" for "lines. Do you want links? So there's clearly some such rule. I do not claim it is a 100% ironclad rule. Few rules in English are 100%.
    – Jay
    Commented Mar 27 at 4:08

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