First recall what's been said:
(A) Greg Nowell wrote:
(1) > I went to visit a friend of Brian's.
> Je suis alle rendre visite a un ami de Brian.
> Note that the French has a simple genitive. Why can't
> we just say
(2) > I went to see a friend of Brian?
(B) C. G. Estabrook wrote:
> The double possessive in English distinguishes between subjective and
> objective genitives. E.g.,
>  I disagree with that opinion of Doug's
> doesn't mean the same as
>  I disagree with that opinion of Doug.
(C) Eric Beck:
(1) > We talked about Jason's being a fool.
> Why not:
(2) > We talked about Jason being a fool.
What's evident from these 3 examples is that (B) produces a difference in meaning, while (A) and (C) do not. Meaning is the key here. Content determines form.
When the content moves us to want to discard a more complex form that carries no added information, this is evidence of the process that cognitive linguists study.
As this process proceeds over time, language becomes very quirky, since formal uniformity is the victim. The language get richer precisely because, over time, people break the rules in a lawful manner. (B)(1) and (2) are preserved as distinct forms, while (A)(1) and (C)(1) get discarded as archaic complications, despite the fact that they are formally identical with (B)(1).
By legitimizing what people tend to naturally do, as reflective of how the mind works, cognitive grammar sides against old-fashioned King's gramarians without a whole lot of unnecessary obscurantism.
-- Paul Rosenberg Reason and Democracy rad at gte.net
"Let's put the information BACK into the information age!"