By way of review, writers simply add ’s to the end of any singular noun to form the possessive. Some writers prefer to add simply an apostrophe when the singular noun is a proper noun ending in s. Though not necessarily grammatically incorrect, I recommended against that and offered my reasoning. Today I’ll share another reason for making that recommendation.
I’ll also attempt to clear the confusion surrounding the use of apostrophes to form possessives of plural nouns.
The basic rules for forming the possessive forms of plural nouns are simple. If the plural noun ends in s, add just an apostrophe (’). Otherwise, add ’s.
Where some writers get confused is with thinking that the singular form of a noun ending in s (very often a proper noun) is actually the plural form. So they then add an apostrophe and nothing more. And they don’t realize their mistake because what they write sounds less awkward than any alternatives.
The best approach when forming the plural possessive form is to form the plural form first and then make the plural form possessive per the basic rules above.
Take the final sentence in the graphic above. When referencing the car which belongs to the Jones family, the plural possessive form is used since more than one Jones possesses the object. The plural form of Jones is Joneses. An apostrophe is then used to indicate the possessive form.
But does the writer place an additional s after the apostrophe or leave the apostrophe without the ending s?
No additional s is needed in this case. For plural nouns which end in s, only an apostrophe is needed to create the possessive form. Thus, the example sentence should be rewritten as follows:
The confusion encountered by some writers comes with forming the plural of Jones, not the possessive. But if you create the plural first (the Jones family possesses the vehicle and so the vehicle belongs to the Joneses) and then make that plural form possessive (the Joneses’s vehicle), you should be okay.
So, to recap, when forming the possessive form of singular nouns, always add ’s. When forming the possessive form of plural nouns, first obtain the plural form and then add just ’ if the plural form ends in s and ’s in all other cases.