Most manuals of style say that "Sanders's" is most correct, but will allow for "Sanders'". I strongly prefer the former. It's logical if you think of it: s' is always for plural nouns that end in S, 's is always for singular. "The cats' milk" vs "James's hand." This way also matches pronunciation.
It gets tricky to keep straight when you have plural nouns that don't end in S. I know "Men's clothes" is correct. But I'm not sure what to do with fish. "The fish's pond"? "The fishes' pond"?
(In any case, just because a word ends in S does not mean it needs an apostrophe. Many, many English writers need this lessen pounded into their head. I lose brain cells every time I see someone write "want's".)
As a natively speaker let me just confirm: English is a very inconsistent language, where rules just as often result in doing the wrong thing as they do the right. Many native speakers get the 's/'/s/ies thing wrong, as well as two/too/to, and so on.
As a German native speaker who generally has a lot of difficulty learning languages, I can assure you that English was a lot more feasible for me compared to anything else I tried.
(Of course you'll find an error in this comment - that is bound to happen in any comment talking about language mistakes)
I've heard a nice explanation of the difference between learning English and learning German:
The rules of English are relatively simple but there are a ton of exceptions that take a long time to get right and will give it away you're not a native speaker.
German doesn't have as many exceptions so you can easily reach near-native levels of fluency once you know all the rules, but there are far more rules you need to be aware of (and even then you'll need to keep track of grammatical gender).
In other words, you can learn German by simply following all the rules and memorizing the vocabulary, but it's far easier to do for English (where you'll miss a ton of exceptions if you only do that).
Let's just say I'm happy I'm a native German speaker already -- I probably couldn't be bothered to become as fluent in it as I'm in English as a second language.
In my experience, German was a piece of cake. Sure, it's a bit difficult at first, but pronunciation is easy once you figure it out and the grammar is not that hard.
Dutch, on the other hand... :)
I've been trying for five or six months now to pronounce 'Groningen' right, but I never succeeded. If there's one 'g' in a word, I can pronounce it. If there are two letters 'g' in one word, it's practically impossible for me.
The only quirk to me is using "much" to modify an adjective ("feasible"), which in my experience (admittedly southern American English) a native speaker would not choose to do.
Maybe it's the trauma from compiler design, but in times of multiple stylistic options in English I try to trend towards standardization / the more broadly applicable version.
Drop in the bucket, but my small part towards decreasing the number of exceptions.
Edit: and just personally, I try to mentally associate homophones (two/too/to) with another word that helps clarify them (e.g. too:also).
As a rule of thumb, if you attach "'s" to something ending with an "s", only attach the apostrophe. But there's no problem if you do it wrong, it's just a stylistic convention to reflect the phonetics.
And for plural "s": if the word normally ends in a "s" or "sh" or "z" sound (or possibly even "zh", i.e. the "j" in French "je") add an "es" instead of "s". Some words are irregular but irregular words by definition don't follow the rules.
The real confusion comes with possessive pronouns. It is "the boy's pet" but it is "his pet" (not #"he's pet"). They're not nouns (they're pro-nouns, i.e. something that is used instead of a noun) so the apostrophe-s rule doesn't apply to them, they just take on special forms.
The confusion really just stems from English regularly allowing contractions like "-'s"/"-'" for "is" and "-n't"/"-'t" for "not" or "-'d" for "would". Pronouns can have contractions as suffixes (e.g. "he's" for "he is" or "he'd" for "he would") but nouns normally can't (#"the boy'd" isn't normally permissible, at least not in writing).
It gets even worse if you consider that whether words can only be contracted additionally depends on their pronunciation (and role) within the sentence. You can't answer the question "Is he dead?" with #"He's.", for example.
Oh, and I haven't even touched upon similar-sounding but entirely different things like "their" vs "they're" -- and I even caught myself accidentally mixing them up while writing this comment.
As coldpie mentioned above, your rule of thumb is definitely up for debate. I understand that one can't be overly prescriptive in grammar, but it's still very common to append "'s" to a word ending in "s" already to make it possessive, depending on context, and this is recommended in many modern style manuals.
Well, yes. Sander's is right out. But that comes from a lack of understanding of how to make words-that-end-in-S into their possessive form, which is what I was addressing.
It's hard because the plural form of "fish" is usually "fish." I think we allow "fishes" when "fish" is ambiguous, like my example. Maybe we should just change to "fishes" all the time :)
Deep in the weeds here, but the plural of a single species of fish is 'fish', while multiple species of fish are 'fishes'.
'Swimming with the fishes' means you must have wound up on the wrong side of a boat in a diverse body of water. It would be a shame to have to 'swim with the fish'. So ambiguous.
The plural "fish" is more than one fish of the same species. The plural "fishes" is multiple species. At least biologists make that distinction. edit: what Alex Young said.
Mmh, not really. "Its" is consistent with other possessive pronouns like "his" and "hers". "It's" is consistent with other contractions, where letters are removed ("it is" or "it has").
No, because that's not his name. His name is Bernard Sanders and he goes by "Bernie." So Bernie Sanders, or expanded out to Sanders's or Sanders' are correct.
The way I always understood it is that originally the s's (Sanders's dog) style was considered correct, and that the s' (Sanders' dog) style was a shorthand version for informal writing (so in formal writing it would be "sanders's dog" and in letters to a friend it might be "sanders' dog").
But as with all things, informal writing was more popular than formal writing, and eventually the s' style grew in such popularity that it became valid and understood in its own right.
So now effectively we have two "correct" ways of representing the same thing, a "long form" version and a "short form" version. The way I was always taught it (in a stuffy English secondary school) was that consistency within a single text is the most important thing, if you write s's once, you have to use it everywhere else also (ex. quotes).
I think it's much more likely that s' is and has always been incorrect, but the error is so frequently committed that it has become "correct". Language does evolve, after all.
Snark: Given the current rate of apostrophe-abuse, I look forward to the apostrophe merging with the S at the end of words to form a new final-S character, which eventually usurps S entirely re'sulting word's that were 'spelled wrong becoming correct, and creating very weird form's of po's'se's'sive noun's: Jame's''s.
It gets tricky to keep straight when you have plural nouns that don't end in S. I know "Men's clothes" is correct. But I'm not sure what to do with fish. "The fish's pond"? "The fishes' pond"?
(In any case, just because a word ends in S does not mean it needs an apostrophe. Many, many English writers need this lessen pounded into their head. I lose brain cells every time I see someone write "want's".)