possessive apostrophe (')
Definition - The apostrophe (') that is used to show possession.

1. According to the OED, the possessive apostrophe "originally marked merely the omission of e in writing, as in fox's, James's, and was equally common in the nominative plural […]; it was gradually disused in the latter, and extended to all possessives, even where e had not been previously written, as in man's, children's, conscience' sake. This was not yet established in 1725."

Example -
Bob's aunt


1. For plural possession, pluralize the noun first, then add the apostrophe.

two boys' dogs
the Joneses' dog

2. With singular compound nouns, put the 's at the end of the word.

my father-in-law's dog

3. With plural compound nouns, pluralize it first, then add the apostrophe.

my two fathers-in-law's dogs

4. If two people possess the same thing, use 's after the second name.

Bob and Steve's contract will not be renewed.

5. If they don't possess the same thing, use 's after both names.

Bob's and Steve's contracts will not be renewed.

6. Because they already show possession, don't use apostrophes with possessive pronouns (e.g. his, its, and whose).

The cat hurt its tail.
Yours truly

7. However, use a possessive apostrophe with the word one when it is acting as a possessive pronoun.

a room of one's own

8. Use possessive apostrophes before gerunds.

Bob's partying was getting out of hand.

9. If a pronoun precedes the gerund, use the pronoun's possessive form with no apostrophe.

I hated your inviting me to lunch.

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