They are both correct, although I much prefer the latter.
Student or Learner
Which one is right, he is a friend of Tom's OR he is a friend of Tom.
Thanks in advance
I prefer 'a friend of Tom's', because I'd say 'a friend of mine' rather than 'a friend of me'.
***** NOT A TEACHER *****
In my opinion:
1. In formal writing (a university report, a business letter, etc.), I would definitely feel more comfortable writing, "As a friend of Tom, I can tell you that he is an ethical person who deserves this position."
2. In ordinary conversation, I have heard the so-called "double possessive" so often in my 70+ years that I would say, "As a friend of Tom's, I resent your nasty words about him."
A few years ago, I also found another opinion:
3. "I am a friend of Eliot's." = Eliot regards me as a friend (of his).
4. "I am a friend of Eliot." = I regard Eliot as a friend (of mine).
[IF -- if! -- you buy that opinion, then I think that people who personally know Her Majesty would say, "I am a friend of Queen Elizabeth's." I, of course, would merely say, "I am a friend [supporter/ fan] of Queen Elizabeth." That is to say, I admire her or approve of her views, but -- of course -- she has never heard of me!]
The source for #3 and #4: Re: Friend of yours www phrases.org uk.
Last edited by TheParser; 10-Dec-2015 at 13:30.