A friend of Susan's

[branflake81]

Is this grammatically correct? Surely it should be "a friend of Susan" and the possessive is superfluous?

I would have thought a friend of Susan. Or Susan's friend.
Otherwise, the meaning is friend of Susan's x (sister, aunt brother??).

It doesn't sound right without the ess sound

A friend of Susan - no
A friend of Alice - yes
A friend of her - no
A friend of his - yes

A friend of mine, not mine's.

friend of Susan
or Susan's friend

A friend of your??

Yes but it's a friend of her's, a friend of your's etc etc so it follows it should be a friend of Susan's but somehow it seems wrong.

I never use the possessive here. But I've heard that it is in fact correct (not obligatory but correct). I'm not sure that I remember the rationale, but it might have been this: 'A friend of Susan's' is an eliptical way of saying 'A friend (who is) part of Susan's circle of friends'.

you wouldn't use the apostrophe when you say a friend of hers or yours surely?

No, probably not

This is called a double possessive and is correct. You use it for relationships to people (a friend of hers), but not for objects or organisations (a fan of the band, an employee of the company).