A colleague has asked about whether it’s better to use, for example,
a close friend of Jack’s and Diane’s
or
a close friend of Jack and Diane
She notes that the first one looks a bit funny, but that you’d use possessive (genitive) with the pronoun:
a close friend of theirs
In fact, both are actually correct. With pronouns, we use the genitive (but see below); this is a holdover from when English had a more thoroughgoing use of case (and indeed in German, which kept the inflections, you would use just the genitive and no preposition: ein enger Freund Jacks und Dianas). We used to match case variably to prepositions; this is why we can see from whence in old texts as normal. But we have moved away from heavily inflecting nouns in general, and we no longer generally vary case according to preposition, which is why those who “stop and think about it” sometimes declare that from whence is redundant — we think of case as a paraphrase of preposition plus noun, or vice versa, which it isn’t really. To return to the issue at hand, in Modern English, as a standard rule (to which the genitive pronoun structure shown above is an exception), the complement of a preposition is structurally in the accusative case (though non-pronouns don’t manifest a difference morphologically between nominative and accusative), and so the non-’s version works.
There is a distinction that can be made in some contexts: compare
that criticism of his
with
that criticism of him
We use the possessive (genitive) in cases where there is a sense of belonging or attachment; we use the accusative where the of is functioning not as a genitive but as another kind of relation. In theory we can make the same distinction with regular nouns, and it works in some cases:
that criticism of John’s
that criticism of John
But in the case of a word such as friend there is no important distinction to be made. And in fact we can get away with the accusative even on the pronoun:
a close friend of them
It’s not quite as nice as
a close friend of theirs
but it is acceptable. When you go over to the actual nouns, however, it tends to be more natural the other way. Adding the ’s on the names might give a greater sense of belonging or attachment (and without it of a greater unidirectionality), or it might not; your results will vary.
Sesquiotica 