What is the possessive of a noun ending in ‑s? Are these both right, or is the second one wrong?
the boys' books
the boss' car
Your example sentences confuse two different problems.
For nouns that are plural (such as "boys"), the possessive formed in writing by adding an apostrophe after the plural -s. This is pronounced the same as the plural and the singular possesive:
For singular nouns that end in -s, the possessive is formed by adding -'s, just as with other nouns. This is pronounced as if the spelling were -es:
There is a partial exception for proper names that end in -s. These names sometimes form their possessive by simply adding an apostrophe, and without changing their pronunciation. Thus, we often see:
However, this doesn't apply when the name ends with a letter other than s, even if it's pronounced with an s. These names form their possessive as normal:
In the opposite case of a name which ends in a silent s, the possessive is usually formed by adding an apostrophe in writing, but the apostrophe causes the silent s to be pronounced:
On singular nouns that end with an "s" or "z" sound, Wikipedia has a say. According to the article, there is no hard and fast rule on this one and different "authorities" prefer different styles.
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