“my friend” vs “a friend of mine”

Question

I always found it weird to hear people say things like "My friend asked me to come" (with no prior mention of said friend), as opposed to "A friend of mine asked me to come". To me it seems as though the former would imply that the speaker has just one friend. I think this usage is well widespread though, but is there any concern about its correctness?

I don't see a similar pattern in use for words other than "friend" (perhaps for family members such as "brother" as well?). Correct me if I'm wrong, but I think "You can read about that in my book" would be an unusual thing to say if I'm the author of several books on the same subject matter, unless the particular book I'm referring to is clear in context.

Answer 1

Actually, usage does fit that pattern for many other words:

My teacher told me to study for the upcoming test.

My book sold 1 million copies!

My brother just scored a perfect game in bowling.

Depending on how loose you are willing to take the phrase:

I offered my hand to the stranger.

We can take my car.

It is my hope that we exceed our profits from last year.

Essentially, my means a with a personal implication:

A friend asked me to come

Answer 2

If you want to convey that you have one friend in total, you use the phrase "my only friend". Just saying "my friend" is (possibly intentionally) ambiguous.

In short:

• "A friend of mine": total number of friends is greater than one.
• "My only friend": total number of friends is equal to one.
• "My friend": total number of friends is unknown.

At least, that's how I interpret it. I prefer interpretations that infer the least.

P.S. Thinking about it, "a friend of mine" could imply the total number of friends is at least one. To imply the total number of friends is greater than one, the phrase "one of my friends" (note the plural antecedent) might be better.