Possessive

[dilodi83]

- Who's that?
- He's a friend of Jack's.

Now, my question is: why that 's after the name? Would it be wrong to write "a friend of Jake"? or, does the 's stand for "Jack's ones"?

[5jj]

We use this 'double' indication of possession with other words, not just names.

We cannot in English say *a Jack's friend, *a my father's friend, * a my friend. Instead we say: a friend of Jack's, a friend of my father's, a friend of mine.

There is a slight difference betweeen these two:

a friend of my father's - one of my father's friends
a friend of my father - her relationshiop with my father is that of being a friend.

[Bennevis]

Going a bit off-topic, I'll quickly point out that there are regular possessive pronouns, like my, your, our, and absolute possessive pronouns, like mine, yours, ours.
We say This is my book.
But we say This book is mine.
We cannot say This book is my.

So we say This is a book of mine, not a book of I or a book of me.

Think of it that way, and you'll understand why He is a friend of mine helps you say He is a friend of Jack's.

[Bennevis]

Although I must admit that fivejedjon's explanation crosses all the t's.

[5jj]

Although I must admit that fivejedjon's explanation crosses all the t's.

.

As usual, when I manage to get things right, it's because I read it in Swan at some time. I've just checked in Practical English Usage, and my words clearly owe more than a little to the Master.