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?

Here's how.