This reader wants to know why we write 1980s and not 1980’s.
I understood that making text entities with non-letter characters into a plural form, you separate the s from the term with an apostrophe – 1900’s, Jones’, Smith’s, or Bang!’s. So, why no apostrophe with 1980s?
A lot of writers share this reader’s understanding that non-letter characters are pluralized by adding apostrophe s.
Alas, indeed. That pesky apostrophe raises a lot of blood pressure for writers of English.
If I had my druthers, we’d phase out altogether the use the apostrophe to form the possessive of nouns. What meaning would be lost if we wrote my mothers birthday, the cats tail or the cats tails?
Teachers and editors could save their red ink for dealing with the apostrophe and plurals.
NOTE: I’ve received so many protests regarding these facetious remarks that I hereby withdraw them. We do need the apostrophe to form the possessive. Mea culpa, dear readers.
I can’t really answer the reader’s question. What I can do is lay out what the Chicago Manual of Style says about when to use an apostrophe and when not to. And it has a lot to say. Here are only some of the rules this style guide offers.
Don’t use an apostrophe to pluralize a proper name or other capitalized noun:
Many Pakistanis have immigrated to the U.S. (not Pakistani’s)
I’ll be occupied for the next three Thursdays. (not Thursday’s)
The Jeffersons live here. (not the Jefferson’s)
NOTE: The CMS suggests that if you want to pluralize an awkward name like Waters or Rogers, you may want to reword the sentence to avoid writing the Waterses or Rogerses. (or Maddoxes?)
Don’t use an apostrophe to pluralize a title:
I have three Madame Bovarys and five Animal Farms. (Type the title in italics and the s in Roman face.
When forming the plural of words and hyphenated phrases that aren’t nouns but are used as nouns sometimes you do and sometimes you don’t:
I want no ifs or buts.
Here are the dos and don’ts of blogging.
I’ve written 25 thank-yous.
I’m tired of all his maybe’s.
DO NOT use an apostrophe to form the plural of capital letters used as words, abbreviations that contain no interior periods, and numerals used as nouns:
the three Rs.
NOTE: For the abbreviations p. (page), n. (note), and MS (manuscript), the plurals are pp., nn., and MSS
And for you scientific types, special rules apply for the plural of SI symbols:
No periods are used after any of the SI symbols for units, and the same symbols are used for both the singular and the plural. Most symbols are lowercased; exceptions are those that stand for units derived from proper names (A for ampere, etc.) and those that must be distinguished from similar lowercased forms. All units are lowercased in their spelled-out form except for degree Celsius (°C).
For those of you who, like me, hadn’t heard of SI symbols, you’ll find a list here.
DO use the apostrophe to form the plural of an abbreviation that combines upper and lowercase letters or has interior periods:
The department graduated five M.A.’s and two Ph.D.’s this year.
NOTE: If you leave out the periods, you can write MAs but you’d still have to write PhD’s.
DO use the apostrophe to form the plural of lowercase letters:
Mind your p’s and q’s.
DO NOT use the apostrophe to form the plural of capital letters:
What the CMS actually says is
Capital letters do not normally require an apostrophe in the plural.
One could write a sentence like this without confusing a reader:
You need to improve the formation of your Ts and Zs.
But one might be tempted to reach for the apostrophes with a sentence like this:
You need to improve the formation of your Ss, Is, and Us.
And finally—DRUM ROLL–our reader’s question about using an apostrophe with non-letter characters:
DO NOT use an apostrophe to form the plural of a number:
The 1920s were noted for excess.
I bowled two 300s and two 238s.
Source: Chicago Manual of Style, paragraphs 7.9, 7.12, 7,14, 7.15, 7.16, 7.65, 9.59.