- an acquaintance of his;
- a colleague of hers;
- some projects of theirs;
- a cousin of mine;
- a protégé of Michelangelo’s.
The classic example posits the obvious difference between a photograph of Lord Snowdon and a photograph of Lord Snowdon’s. We know who’s in the first picture, but we can’t be sure about the second. In this example, the meaning turns on whether the possessive or nonpossessive form appears. The writer’s choice is straightforward, depending on the intended meaning.
But which is correct in this construction: a friend of John or a friend of John’s? Although the practice is sometimes erroneously stigmatized, using a possessive with of has long been considered acceptable. You can say either The car belongs to a friend of Brent or The car belongs to a friend of Brent’s. Of course, it’s also possible to avoid the double possessive by rewording the phrase {the car belongs to Brent’s friend}.
Yet the double possessive is impossible to avoid in constructions with personal pronouns. You would never say He’s a friend of me. No — it’s a friend of mine. Likewise, idiom demands an admirer of hers, not an admirer of her.
One usage commentator, the late Wilson Follett, insisted that client of Zuber’s is preferable to client of Zuber: “The neglect of this possessive [‘s in Zuber’s] mars the all too common mode of referring to a book of Conrad, a letter of Lincoln, a canvas of Picasso. . . . All these require changing to the possessive ‘s, . . . or else the replacement of the preposition. One can always say a book by Conrad, a letter from Lincoln, [etc.].”
The construction comes up most naturally when the relationship between the subject and the object is not an exclusive one {Dan is a friend of Pat’s}. When the relationship is exclusive, the double possessive is inappropriate {Dan is the father of Pat}. The article reveals the nature of the relationship (a friend vs. the father).
The double possessive is generally unidiomatic when applied to inanimate things {a friend of the court [not of the court’s]}. And by the way, despite an old superstition, it’s fine to use possessive forms for inanimate things {the hammer’s handle} — just not in conjunction with of {the handle of the hammer [not the handle of the hammer’s]}.
Most educated speakers habitually use double possessives: