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What is the correct possessive for nouns ending in s?
When did it become correct to add an 's' to a singular possessive already ending in 's'?
I've always heard that when talking about stuff belonging to either a Jones or many Jones, you'd write Jones' (pronounced "Joneses"). But recently I've stumbled upon a book which consistently uses Jones's when talking of a single Jones.
What's the correct way of using possesives?
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Both are used. This is an area of controversy where no 'correct' way has been established. Some sources would say that Oliver Twist is Dickens' character while other sources (like Strunk & White) would say that he is Dickens's character. See this page for a brief exploration of some of the rules different sources use in different situations.
It's probably safest to stick with the 's ending unless it would make the pronunciation awkward or violate historical usage. For instance, you would want to write Achilles' heel, not Achilles's heel.
The rule I was taught when I was young was that one would use the s' when there is more than one syllable in the name, and s's when there is only one. The s following the apostrophe is pronounced whenever it occurs in writing.
