Für AE: Ausser bei bestimmten Personen aus der Klassik (z.B. Aristoteles) bekommen auch Namen, die auf 's' enden ein Genitiv-s angehängt, z.B. Ross's. Ich habe hier momentan kein "Chicago Manual of Style" zur Hand, vielleicht kann jemad anderes "chapter and verse" zitieren.

At least in AE, the choice between a simple apostrophe ['s] and an apostrophe-s ['s] after names that end in s is a stylistic choice. It is neither slang nor colloquial usage. Personally, I prefer to always use apostrophe-s. The consistent use of one option or the other is more important than which one you use.

I know "...s's" is used on occasion, but it's a bit outdated and definitely not in use for most of modern journalism. The Associated Press Stylebook and Libel Manual (my copy is from 1990), for example, has it differently. Under "apostrophe" in its "Guide To Punctuation" chapter, it says, "Possessives: Singular Proper Names Ending in S: Use only an apostrophe: Achilles' heel, Agnes' book, Dickens' novel, etc."

I know there are authorities who prescribe the use of possessive 's after words and names ending in s or z, but that's not how I had been taught and I think it looks rather inelegant.

That said, I have to admit that although I would write, for example, "the Jones' car" I often hear, and also find myself employing in speech, an additional [&z] sound in certain cases where the word is a monosylable with final [s] or [z].
Oddly, I would not add this sound in the phrase "Mr. Jones' car" almost as if Mr. Jones formed a polysyllabic unit.
The Bliss' car: I would say [blis&z] in all contexts.
The Gross' car: I would either say [gros&z] in all contexts or follow the pattern for "Jones" above.
Moreover, it would seem that the occurance of a longer consonant cluster at the end of the monosyllable discourages me from using the additional syllable.
The Parks' car: I would not add [&z] in speech.
The Forbes' car: I would not add [&z] in speech.

While the discussion of current usage is interesting, it is not entirely germane to the question. dermitdemziel is reading "Huckleberry Finn", published 1884. At that time, the 's on the end of words ending in -s was standard, irrespective of what is done today.

Also, für das Jahr 1884 ist Phelps's sawmill korrekter Genitiv und kein Slang.

And, in fact, for today. I think calling it a completely free stylistic choice is a bit misleading to learners.

Granted, there's a lot of variation in usage among the general public. I would put that down to the fact that a lot of people just aren't aware of the traditional rule. However, editors still usually do know the rule, so it surprises me that the AP stylebook drops the 's.

To my knowledge, other more general style guides still definitely insist on the traditional rule. I think I've quoted before here in the forum from Fowler and/or Garner and/or Chicago and/or BE style guides such as the Times and Guardian online, with examples such as Dickens's and Charles's. But I don't feel like looking through the archive or my files at this hour.

My hunch is that the AP decision is motivated primarily by the desire to save space, which is a consideration for journalists and headline writers, but hardly relevant for most other writers.

I also don't really believe that many people say Jones' -- if you think about it, surely you realize you actually say Jones's.

So for me, Phelps's is not only not wrong, but absolutely right. And in fact, I would still strongly recommend that people learning English learn to form the possessive by adding 's even when a word ends in S (with only the very few exceptions Norbert mentioned above).

Guardian:

The possessive in words and names ending in S normally takes an apostrophe followed by a second S (Jones's, James's), but be guided by pronunciation and use the plural apostrophe where it helps: Mephistopheles', Waters', Hedges' rather than Mephistopheles's, Waters's, Hedges's.

http://www.guardian.co.uk/styleguide/page/0,,... (go to "apostrophes")

Times:

apostrophes with proper names/nouns ending in s that are singular, follow the rule of writing what is voiced, eg, Keats's poetry, Sobers's batting, The Times's style (or Times style); and with names where the final “s” is soft, use the “s” apostrophe, eg, Rabelais' writings, Delors' presidency; plurals follow normal form, as Lehman Brothers' loss etc. Note that with Greek names of more than one syllable that end in "s", do not use the apostrophe "s", eg, Aristophanes' plays, Achilles' heel, Socrates' life, Archimedes' principle.

Beware of organisations that have variations as their house style, eg, St Thomas' Hospital, where we must respect their whim. Also, take care with apostrophes with plural nouns, eg, women's, not womens'; children's, not childrens'; people's, not peoples'. Use the apostrophe in expressions such as two years' time, several hours' delay etc.

Sorry, forgot the link for the Times's style guide:

http://www.timesonline.co.uk/tol/tools_and_se...

(Also go to "apostrophes")

vielleicht ist auch in einer der früheren Diskussionen(sicher nicht vollst.) zum Thema Erhellendes zu finden:
Diskussion wurde gelöscht
Siehe auch: possessive apostrophes
Diskussion wurde gelöscht
Siehe auch: Genitive of words ending with s
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Siehe auch: Regel bzgl. Apostroph
Diskussion wurde gelöscht

Robert raises an interesting and important point. As others have pointed out, major newspapers tend to have their own house styles. Since I mentioned the Chicago Manual of Style above, here is a quick excerpt of the major rules listed there:

Chicago Manual of Style, 15th ed.:
THE GENERAL RULE
7.17 Most nouns. The possessive of most singular nouns is formed by adding an apostrophe and an s, and the possessive of plural nouns (except for a few irregular plurals that do not end in s) by adding an apostrophe only. [...]
a bass's stripes
[...]
7.18 Proper nouns, letters, and numbers. The general rule covers most proper nouns, including names ending in s, x, or z, in both singluar and plural forms, as well as letters and numbers. [...]
Kansas's legislature, Burns's poems, Marx's theories, Dickens's novels, Josquin de Prez's motets
[...]
EXCEPTIONS TO THE GENERAL RULE AND SOME OPTIONS
7.19 Nouns plural in form, singular in meaning [...] politics' true meaning, economics' forerunners [...]
The same rule applies when the name of a place or an organization [...] is a plural form ending in s, such as the United States [...] Calloway Gardens' former curator
7.20 [...] The possessive is formed without an additional s for a name of two or more syllables that ends in an eez sound. [...] the Ganges' source, Xerxes' armies
[ Even more arcane exceptions follow in additional sections ]

Many thanks!