We’ve all seen it and cringed: The sign advertising “Antique’s for Sale,” the one in the supermarket boasting about it’s “fresh cucumber’s,” or the sign on the neighbor’s house saying “Welcome to the Smith’s.” Few among us (or so we hope) don’t know that those are wrong.

Yet its showing up everywhere, even in “edited” copy. Can anyone explain it? Perhaps there’s a bad grammar textbook somewhere, or one teacher incorrectly taught thirty students, who taught thirty more …

The phenomenon is sometimes called “the grocer’s apostrophe,” because it seems most prevalent at the grocery store, though it’s spreading faster than the swine flu. The disease seems to particularly affect words ending in vowels. Nonetheless, lets try to stamp this out. Tell a friend, and ask that friend to tell a friend: Apostrophe’s are not used to form plurals.

Except, of course, when they are.

Yes, there are a few rare cases when an apostrophe is used to form plurals. For example, an apostrophe is needed in the plural of a single letter or number, as in “mind your p’s and q’s” or “digital binary code uses only 0’s and 1’s.” Without the apostrophe, it would be almost impossible to read “ps and qs“ or “0s and 1s.” The plurals of acronyms and initialisms sometimes take apostrophes (as in CD’s), but that use varies by style. And, again depending on style, apostrophes may be used to form plurals of numbers (her salary was in the low 100’s), or so-called “words as word’s” expressions (there can be no if’s, and’s, or but’s about it).

Apostrophes are primarily used to indicate possession (Sharon’s book) or to indicate omission, as in a contraction, where the apostrophe replaces letters (I can’t ever remember the difference between its and it’s). Apostrophes may also be used, depending on style, to indicate the contraction of a number: “2009” becomes “’09.” In fact, since the possessive apostrophe is really replacing the word “of” (the book of Sharon), you’ll rarely go wrong if you remember that an apostrophe almost always indicates that something has been dropped.

If you remember that last sentence, you’ll also never have the “it’s/its” problem, which is also endemic. If you can’t replace “it’s” with “it is,” your “it’s” is a possessive personal pronoun and should be “its.” And that’s probably the crux of much apostrophe confusion, since possessive personal pronouns—mine, yours, his, hers, theirs—are just about the only possessives that don’t take apostrophes.

One more little apostrophic quirk: Because the possessive apostrophe effectively replaces “of,” you need one in such phrases as “I could use two weeks’ rest” (two weeks of rest) or “he was sentenced to twenty years’ imprisonment” (twenty years of imprisonment). But you’d never say “she’s six months of pregnant,” so you don’t want an apostrophe in the phrase “she’s six months pregnant.”

Now that you know it all, how many apostrophe errors did you spot in this column?*








* There are five intentional apostrophe errors, not counting the examples of erroneous use. (Write languagecorner@cjr.org if you need a key.) If you counted “grocer’s apostrophe,” make it six, because you’re assuming “grocers” is an adjective, not a noun, the way “teachers union” doesn’t need an apostrophe—but that’s another column.

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Merrill Perlman managed copy desks across the newsroom at The New York Times, where she worked for 25 years. Follow her on Twitter at @meperl.