That's a question I've been asking myself for years. And the best answer I've come up with is that the English language has a debilitating S addiction. Think about it. We use S to form plurals: One cat, two cats. We use it with an apostrophe to show possession: The cat's tail. We use it with an apostrophe to stand in for "is" or "has": The cat's sleeping. The cat's had a rough day. Plus, we use S to form some verb conjugations: I walk. He walks. They think, she thinks.
Alone, that wouldn't be so tough to deal with, but combine that with some other rules, and it's just too easy to get confused. For example, there's a different rule for forming plurals of words that end in S. You don't just add S, as you would to cat. You add es: Bosses, masses, losses. Then there's the rule that says that for any plural ending in S — be it cats or bosses — you form the possessive not with apostrophe S as you would for the singular, but with a lone apostrophe. They own cats. They are the cats' owners. These are the bosses' orders.
Then come all the plurals that aren't formed with S: Men, women, children, buffalo, media, data, fish.
Then, as if all that weren't enough, style guides disagree on how to deal with proper names ending in S. The "Chicago Manual of Style" says that you form the possessive of proper names ending in S the same way you handle plain-old nouns: Add apostrophe and S. The boss's house. Ross's house. "The Associated Press Stylebook," which governs most of the print news sources you read, says to form the possessive of a proper name ending in S by adding only an apostrophe — Ross' house — even though that's different from generic nouns — boss's house.
It's all just too much.
The secret to getting it right? Take it slow and keep track of which rules apply to your sentence.
But if you want to make it plural and possessive, then you have to take it in two steps. First, form your plural: You're visiting the Rosses. Then make it possessive: You're going to the Rosses' house. Remember, because this is plural, there's no dispute on how to make it possessive. Use just an apostrophe. No extra S.
But, there is no situation in English in which an apostrophe alone can form a plural. A possessive, yes: Jess' hat. But a plural never.
Take it slowly, and you'll never have to worry that you'll be the inspiration for a grammar column.
JUNE CASAGRANDE is author of "It Was the Best of Sentences, It Was the Worst of Sentences." She can be reached at JuneTCN@aol.com.