Is this sentence correct?
This is John's car, a friend of mine.
Or do I need to say this?
This is John, my friend's car.
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Sign up to join this communityIs this sentence correct?
This is John's car, a friend of mine.
Or do I need to say this?
This is John, my friend's car.
Neither of those is correct!
This is John's car, a friend of mine.
means this car (that belongs to John) is my friend.
This is John, my friend's car.
means my friend's car is named John.
I think you understand the sentence "This is John's car" and "John is my friend." The basic structure of "This is John's car" tells us how to do it; it is "This is noun-phrase's car." So what is a noun phrase we can use to capture "John is my friend"? My friend John.
So if we put those together, we get
This is my friend John's car.
The first example tells us that the car is your friend. The second says that the car is named John. Both seem unlikely!
It seems you want to tell two pieces of infomation "The name of my friend is John". and "This car belongs to John". If you have two pieces of unrelated information you should usually put them in separate sentences, or separate clauses joined with "and". Or you might realise that part of the information is actually not needed, in which case you say "This is John's car" or "This is my friend's car" (because the person doesn't need to be told that "John is my friend")
But if both items are needed then you could say:
My friend's name is John, and this is his car.
In addition to the existing answers, you could combine the two facts by saying:
This car belongs to John, a friend of mine.
Here the second half of the sentence is a description or elaboration of "John" as you intend, and not the car.
(If you did want to add information about the car in this format, you would need to use "and" to imply that there are two separate facts: "This car belongs to John and [it] is a friend of mine.")
"the car of a friend" is a friend's car.
the car of YOUR friend is YOUR friend's car.
If your friend's name is John, or your friend is John, then that would be your friend, John's car. If your friend was a male, and you've already mentioned to the police that you got the car from your friend, John, then you can say "this is his car" (pronoun).
If you want to add "my friend" to clarify who John is, then that is being used as an appositive phrase, and if you're using it appositively, you need a comma after it: "This is John, my friend's, car". However, that phrasing makes it unclear what the possessive 's applies to; it's supposed to apply to both "my friend" and "John", but that isn't really supported by the phrasing. You could rephrase it as "This is the car that belongs to John, my friend", "This is the car that belongs to my friend John", "This car belongs to my friend John", or "This is my friend John's car".
In speech, you'd probably reword it as per other answers. (Though in this case, I think the indented meaning is clear enough anyway.)
But in writing, this is an option:
This is John (my friend)'s car.
This clearly links both ‘my friend’ and ‘car’ with John, not with each other, and avoids too much restructuring.
You need the parentheses in order to clearly separate the possessive, so it wouldn't work with the other common ways to indicate a parenthetical remark (dashes or commas).