Okay, so this is something I feel I've seen both ways and either one feels right, but I'm sure there has to be one that is actually right. Maybe it's one of those cases where it depends. Take the name Dennis. Which sentence is correct? Dennis's car smelled brand new. Dennis' car smelled brand new.
What I learned is that they're both correct. A quick google says ... well, mixed results. I prefer "Dennis's" because that's more how I say it -- it reads better imo.
I think Dennis' is a lot more common than Dennis's, but I do believe both forms are used and accepted as being correct.
Whenever I'm writing a name that ends in 's' and I need to show possession, I always add another 's' after the apostrophe. Not only is it correct, but it reflects how you're likely to say it. If it's something belonging to Thomas, you're not going to say 'Thomas toothbrush.' You'll say 'Thomas-ez toothbrush.' So writing it that way - Thomas's toothbrush - seems to work better. Same if it's a plural OF a plural name. The man's name is Thomas Adams. His house, where he lives with his family, is "the Adams's house."
To a pedant like me, ending with an apostrophe is more correct than preferred to the other way, when written.
Well, let's say the family's name is Smith instead of Adams. There are five Smiths living in the house. Which of these would you actually say? Just keep going till you get to the Smith-zez house? Just keep going till you get to the Smiths house? You'd write it and punctuate it the way you'd say it: Just keep going till you get to the Smiths' house.
Now I'm even more confused. Are you saying that whether it's apostrophe-S or S-apostrophe when written, depends on how you'd say it verbally? That does make sense, but I gathered from your other post you were saying that it should always be apostrophe-S.
No, what I was saying is that if the name ends in 'S' like Thomas (first name) or Adams (surname), I would put an apostrophe and an EXTRA s after the apostrophe, when denoting possession. It is grammatically correct to do this. (It's also grammatically correct to just use the apostrophe and leave off the extra s. This is one of the rules of punctuation where you actually have a choice!) I prefer the extra s, because that's the way you'd say it. If you were reading the sentence out loud, for example, you would never mispronounce "Is this Thomas's shoe?" However, you might stumble over the sentence if it was written "Is this Thomas' shoe?" Both are correct, but one of them makes more sense to me. In my opinion, an apostrophe-s ('s) indicates possession. It shouldn't matter what the last letter of the person's name is.
I'd always been a staunch believer in ending on an apostrophe when a name ends in S, but in truth I think it was only because I thought it was 'correct'. As it happens, I think your logic makes far more sense.
I think we could simplify it further. No matter whether the name ends in 's' or not, if it's singular, it needs an " 's". But if it ends in 's' and it's also plural (but one of those plurals which are the same same spelling as the singular) then it would be " s' ". But not adding in another 's', obviously. Make sense?
I hate to differ with the noble and esteemed @jannert. But in the case of the plural possessive of a surname ending with S, it would be "the Adamses' house." As in , "the Adamses live there." Otherwise, with the singular, absolutely correct. The only exceptions are major ones. You never hear of "Moses's staff," it's always "Moses' staff." And never "Jesus's disciples," always "Jesus' disciples." I believe it's to cut down on the sibilants. If you're talking about people named after these figures, that might not apply. But even in those cases, all those Ss in a row would be too much. Most likely.
But you're not cutting down on sibilants when you say these possessives though, are you? You don't say "Moses staff." You don't say "Jesus disciples." (Moses and staff are difficult, because the word Moses ends in s, and the word staff begins with s. Not to mention the internal s in his name as well as Jesus's name. But I challenge you to say the sentence out loud: "Who knows where Moses' staff is?" You will give a slight extra sibilance, I reckon. It's an awkward thing to say. But still.... When writing it, I prefer the clarity of: "Who knows where Moses's staff is?" But again, it's a matter of preference. One of the few times we can agree to disagree and we'll both be right! I don't know about the Adamses, though. I'll look into it. It would make a certain kind of sense, I suppose, to do it that way. However, Adams's sounds more or less the same when spoken aloud, doesn't it? Without actually changing their name to Adamses? And making the possessive read: Adamses' ? Hmmm.... Aren't you just substituting an e for an apostrophe, and then adding an apostrophe on the end as well? Seems a bit like overkill to me. But I suspect it's also a form that is considered correct.
Well, no, it wouldn't be changing their name to "Adamses," when referring to more than one Mr. or Ms. Adams . . . any more than it would be changing the name of Mr. or Mrs. Smith, when referring to the whole family as "the Smiths." It's simply following the normal rule for forming plurals in English where the final letter of a singular noun is s or z or sh or ch, etc. But anyway, actually, I do say "Jesus' disciples." All the time. And "Who knows where Moses' staff is?" is quite easy to say out loud. For me, anyway. But then, maybe I'm weird. And yeah, for clarity in writing, adding the 's to a word or name ending in s definitely does achieve that. But it hits me that in your response you weren't referring to plural Adamses, were you? It could have been something on the order of "Samuel Adams's horse," correct? I was following on from the previous reference to the Smiths, and assumed the plural . . . mea culpa.
Actually, I've just had time to check my Webster's Compact Writers Guide, and you are correct about the -es ending to words that end in s, x, z, ch, or sh. If you are making them a plural, then -es is right. I stand corrected on that. I'm terribly bad at quoting 'rules,' and now I'm wondering if I would automatically have done that or not. I'm trying to think of examples. Would I have written 'keeping up with the Joneses?' If not, what WOULD I have written? Dunno... Never to old to learn, I guess. Thanks for the boot up the backside.
