[Grammar] I'm a friend of Charlie's

[Chicken Sandwich]

I'm Bill Shraeder. I'm a friend of Charlie's.

Can someone explain to me why it would be incorrect to say: "I'm a friend of Charlie".

I do understand why it's correct to say "I'm staying over at Bill's", because in that sentence, "house" is understood to be included.
Or: I'm having lunch at McDonalds's (= I'm having lunch at McDonalds's restuarant).

 

[5jj]

It's not incorrect, but it has a slightly different shade of meaning.

"I'm a friend of Charlie" places slightly more importance on the friendship relationship.

"I'm a friend of Charlie's" suggests the more neutral , "I am one of Charlie's friends".

 

[BobK]

It's not incorrect, but it has a slightly different shade of meaning.

"I'm a friend of Charlie" places slightly more importance on the friendship relationship.

"I'm a friend of Charlie's" suggests the more neutral , "I am one of Charlie's friends".

:up: Perhaps students would find it useful to have an example of the first usage (widely, but mistakenly, taken to be 'incorrect': 'Of the people at my office, I'm a friend of Charlie, but the rest are just nodding acquaintances.' As the 'incorrect' belief suggests, this usage is far less common.

b