A reader asks,
What are your thoughts on double possessives? For example:
Friends of Sue’s
Friends of my aunt’s
Friends of his
Friends of her’s
Friends of theirs
Friends of mine
You will find the double possessive question and animated discussions of it on hundreds of language sites all over the web. It remains popular because it has no simple answer.
First let me say that the reader’s fourth example, “friends of her’s,” would never be an option for anyone: the pronoun must be spelled either her or hers.
The “double possessive” is so called because the preposition of, the possessive pronouns hers and theirs, and the ’s all signal possession. The construction is also called “double genitive” and “post genitive.”
The objection to “friends of Sue’s” and “friends of mine” is that the of ought to be sufficient.
Granted, “friends of Sue” is a reasonable option, but no native speaker is likely to say “friends of me.”
The intractability of the question lies in the fact that in some contexts the double possessive is idiomatic. As far as a rule can be stated, it is this:
Generally, what follows the of in a double possessive will be definite and human.
For example, we might say “friends of Sue’s,” but not “friends of the university’s.”
Another guideline is that what precedes the of will usually be indefinite. For example, “a friend of Sue’s.” When the preceding word indicates something definite, the second possessive is dropped: “the best friend of Sue,” “that friend of Sue.” On the other hand, one might say, with some emotion, “That dog of Sue’s is a nuisance.”
Sometimes the double possessive is needed to avoid ambiguity. Compare:
The mansion contains portraits of the owner.
The mansion contains portraits of the owner’s.
In the first sentence, the portraits are of the owner (i.e., they present a likeness of the owner). In the second, the portraits may be of anyone, but they belong to the owner.
The most practical rule for writers is to avoid having two possessives in formal writing. If they occur, rewrite the sentence.
As for informal use, the double possessive is idiomatic in English and has been for a very long time.