You may not have known what it was called, so you couldn’t even Google the answer, but I’m here to tell you, friend, it is compound possession, also known as joint possession! That’s right; it’s that tricky little scenario that makes your fingers falter across the keyboard when you’re writing about two subjects in possession of something. Does each subject have an apostrophe and an S or does only the last subject in the group have the apostrophe and the S?
For instance: George and Mary’s cats are always escaping.
From this sentence, we can assume that George and Mary live together and are in possession of a herd of fugitive felines. The rest of the story would probably bear this out. But what if George and Mary are actually neighbors in possession of separate mobs of moggies who escape for midnight sessions of group yowling on the fence between their properties?
Then the sentence would look like this: George’s and Mary’s cats are always escaping.
Your decision will be based on whether or not the two subjects are in possession of shared items or separately owned items. You may be saying, “Yes, but George and Mary both owned cats, and since cats are the same thing, shouldn’t it always be like the first example?”
Consider this: George’s and Mary’s coats are in the front closet.
Clearly, George and Mary aren’t going to wear the same garment. They own separate coats. The same applies to their cats. Now if George and Mary could just contain their wayward beasts, the rest of the neighborhood could sleep in peace.