This is a friend of my father's
This is my father's friend. (Este es el amigo de mi padre). It is clear that this sentence is correct.
But what happens with these other sentences?
This is a friend of my father. (Este es un amigo de mi padre).
This is a friend of my father's. (Este es un amigo de mi padre).
Are both of them correct?. Or, is it only possible the latter?. I would like to know how the double genitive woks. Thank you.
9 Answers
Hi Nila
What about?
That man is a friend of my father's.
This example is what is sometimes referred to as "the post genitive construction," and it is quite common and correct to use. In fact, it is probably even more common to use this type of construction than to use your original option of "that man is a friend of my father."
Have a look at this thread which has this to say about the use of the "post-genitive." possessives
Do we say "a friend of my uncle" or "a friend of my uncle's"? In spite of the fact that "a friend of my uncle's" seems to overwork the notion of possessiveness, that is usually what we say and write. The double possessive construction is sometimes called the "post-genitive" or "of followed by a possessive case or an absolute possessive pronoun" (from the Oxford English Dictionary, which likes to show off). The double possessive has been around since the fifteenth century, and is widely accepted. It's extremely helpful, for instance, in distinguishing between "a picture of my father" (in which we see the old man) and "a picture of my father's" (which he owns). Native speakers will note how much more natural it is to say "He's a fan of hers" than "he's a fan of her."
What the article doesn't elaborate and which is probably important to note is that the post-genitive is only correct to use when the noun phrase that follows the preposition is definite and human.
So
That man is a friend of my father's would work, but
That man is a captain of the ship's (to say that he is the ship's captain) would not work because the noun "ship" does not meet the criteria of being both definite and human. In the same way you might say
The roof of the house but not The roof of the house's
Here is another link that is heavily loaded with terminology related to grammar but that has some very good examples of proper usage of the post-genitive. The relevant information appears on page 385 or can be found by doing a word search within the title for the word "post-genitive"
Mastering English: an advanced grammar for non-native and native speakers
Nila, while the double genitive may be acceptable as an idiom, it is not proper grammar. Here is an article that discusses it: http://grammar.about.com/od/grammarfaq/f/FAQdoublegenitive.htm
The citation does not support the notion that the construction is improper. On the contrary, it attests to its well established pedigree (and cites several authors of repute who have used it). Although the article mentions some who have objected to the construction, it categorizes them as people who tend to object to any construction in English that does not have a close analogue in Latin (falling only slightly short of characterizing them as saying "We really should be speaking Latin rather than English [since the former is, so obviously, the "superior" language]).
After reading your comments I have come to the conclusion that "this is a friend of my father's" and "this is a friend of my father" has the same meaning.
Thank you.
I would like to know how the double genitive works
Nila, while the double genitive may be acceptable as an idiom, it is not proper grammar. Here is an article that discusses it: http://grammar.about.com/od/grammarfaq/f/FAQdoublegenitive.htm Of course there are varying degrees of improper English speech forms that are spoken/heard by us all. The double genitive is very common.
This is a friend of my father.
Proper, and a translation of: Este es un amigo de mi padre.
This is a friend of my father's.
Informal, and something like: Este es un amigo suyo de mi padre.
However, like any commonly used non-grammatical speech form, it is nearly impossible to explain in which instances it is or is not appropriate to use. The best learning method then would be to imitate English speakers with whom you communicate regularly. They may not be grammar professors, but if they say it a certain way, then they will understand you when you say it! 
I believe both of them are correct
What about?
That man is a friend of my father's.
i believe he is right, accept for the second one, lol
Wrong point of view.
The second is probably not grammatically correct, but it is common usage - like so much in the English language.
