Possessives shouldn’t be difficult. In many languages, they’re not.
In French, for example, to talk about the car belonging to Robert, you just say “the car of Robert”: la voiture de Robert.
Spanish works the same way, with “de,” meaning “of”: el auto de Robert.
English isn’t as fond of simple formulas. We rarely use “of” to show possession. Far more often we use an apostrophe plus an S. It sounds simple, but in practice it’s anything but.
For example, when you’re talking about two phones on the table, one belonging to Beth and one belonging to Sam, are they Beth and Sam’s phones, or Beth’s and Sam’s phones?
Why do expressions like “three years’ experience” take an apostrophe?
If two attorneys general are on the same case, whose case is it?
Why is “whose” possessive while “who’s” is not?
And how do you show it when two passersby share ownership of something?
In the past, this column has looked at the basics of forming possessives, with a special emphasis on words whose singular forms end in S (because they seem to cause the most confusion).
But there are a number of oddball possessives that are just as confounding. Here’s how to navigate a few of them.
Shared possessives. When you’re talking about Jane’s house and Jack’s house, would you write “Jane and Jack’s houses” or “Jane’s and Jack’s houses”? What if they own the house together? Is it “Jane’s and Jack’s house” or “Jane and Jack’s house”?
The answer depends on whether the parties share possession of the items or whether they own them separately. If Jane and Jack have one house between them, it’s Jane and Jack’s house. The same is true if they co-own multiple houses: Jane and Jack’s houses.
These are called a shared possessives, meaning that just as they share the house, they must share a single apostrophe and S. If they own houses separately, you would say Jane’s and Jack’s houses.
Quasi possessives. When you get two weeks’ pay, the money belongs to you, not to the weeks. Yet we treat that as possessive, anyway. It’s best not to question why. We just do. Note that these are called quasi possessives and move on.
Possessives of abbreviations ending in capital S. How would you make a possessive out of the abbreviation IRS if you wanted to talk about, say, the agency’s headquarters?
Too often, I see “the IRS’ headquarters.” That seems to be a misunderstanding of the rule that says words ending with S can take just the apostrophe without an extra S.
But IRS isn’t a word. By my reading of the rules, it’s imperative you add an S: the IRS’s headquarters.
Possessive of passersby. Here’s one you could figure out on your own, but it’s weird enough to warrant mention. The singular passerby, also written passer-by, forms its plural in a very unusual way with the S in the middle.
With most words, you put the possessive marker in the same place where you put the plural marker: at the end. So it would make sense that you might want to try that here: “passers’-by”; “passers’by”? Clearly there’s only one place to put the possessive marker: at the end. So, “the passersby’s view.”
Possessives of in-laws. Mother-in-law, mothers-in-law, father-in-law and so on work the same way as passersby. You put the possessive marker at the end even though the plural marker goes in the middle. “So many mothers-in-law’s good intentions are overlooked.”
Possessive pronouns. In school, we heard over and over that a possessive takes an apostrophe. But the lesson about possessive pronouns doesn’t seem to get as much play.
“Whose,” “his,” “her,” “your,” “their,” “my,” “our” and, especially “its,” are pronoun forms that show possession but do so without an apostrophe.