I'm not completely certain, but I'll take a stab.  I think this is one of
those examples that shows why a functional or rhetorical understanding of
grammar can be more helpful than a strictly traditional understanding of it.
The best I can do is to mention what you've probably already noticed--that
the prepositional phrase is acting as an adjective (it can be rewritten "I
am his friend" just as "I have a watch of gold" can be written "I have a
gold watch").  In a case like "I am afraid of him", my best guess would be
that it is acting as either as an object or perhaps as an adverbial
(answering the adverbial question "why?").

How far off does that sound?

Maureen Fitzpatrick
Associate Professor, Johnson County Community College

        ----------
        From:  Michael Kischner [SMTP:[log in to unmask]]
        Sent:  Wednesday, July 07, 1999 6:49 PM
        To:  [log in to unmask]
        Subject:  Re: Yet Another Grammatical Question

        To give everybody a rest from Henry James:

        An ESL student in my class wrote, "Now I am a friend of him."  Is
there a
        good reason I can give him for why it should be "of HIS"?

        It gets funny with proper names, too.  If we knew each other well, I
might
        describe myself as a friend of Bill Clinton's.  But, at least for
the
        first four or five days of his term, I would have described myself
as a
        supporter of Bill Clinton.  Go figure.  Please.