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Possessives and Attributives
Q. When using a pronoun to replace the first noun when two nouns show possession of one item, which case should the pronoun be? For example, in the sentence “I’m going to my uncle and aunt’s house,” “uncle” is not in the possessive case. So which case should the pronoun be? “I’m going to him and my aunt’s house”? “I’m going to he and my aunt’s house”? Or, “I’m going to his and my aunt’s house”? And, if the answer is “his,” how do you reconcile that the pronoun is not agreeing with the noun it replaces in gender, number, and case? And what is correct if the pronoun replaces the second noun? “Megan’s and his room”? Or “Megan and his room”?
A. The trick of showing joint possession with a single apostrophe s is possible only with two items that can take an apostrophe s. Hence a car owned by John and Jim can be expressed as “John and Jim’s car.” This is clearly a convenient shorthand—helped out by the fact that, normally, you can assume readers will not think that you’re writing about John, on one hand, and Jim’s car, on the other. Most pronouns do not form the possessive with an apostrophe s. “One” becomes “one’s,” but “he” becomes “his” and “I” becomes “my.” Therefore you generally cannot use shortcuts in cases of joint possession involving a pronoun. You must make both owners possessive:
his and my aunt’s house
Megan’s and his room
You can reconcile the first as equivalent to “my uncle and aunt’s house” by remembering that the apostrophe s after “aunt” also applies to “uncle”; “his” is technically replacing “uncle’s” not “uncle.”