Why do you say "friend of mine" instead of "friend of me"?

Solution 1:

In the construction

friend of mine

the "mine" means "my friends", so literally

? he is [one] friend of [all my friends]

or more idiomatically,

he is one of my friends

If I only have one friend and he is my only friend, we cannot then say "he is a friend of mine", because the "mine" doesn't mean a group of people. If I introduce my daughter I would never say

* this is a daughter of mine,

always

this is my daughter.

Solution 2:

Mine is used to refer a thing belonging to (or a person associated with) the speaker.

Since it is about a friend (who is associated) mine must be used instead of me.

Adapted from NOAD

Another usage:

• The picture is mine = It is my picture. (possessive pronoun)
• The picture is me = I am in the picture. (object pronoun)

Solution 3:

Is there a specific situation when you use one or the other?

"Friend of mine" would generally be used when you're saying something like "Kim is a friend of mine," in other words, at the end of a phrase or sentence. "My friend" is often used when saying "Kim is my friend", or in the construction, "My friend, you have a rip in the back of your shirt."

Solution 4:

Ok, sorry, long two-part idea.

1. "of someone" in this case is not really about possession. My impression is that English speakers do not like to use "of" simply to show possession; we have other grammatical constructions for that. Instead, "of" is used to refer to patterns of association or constituency in some larger whole, as in "out of" "consisting of".

2. "a friend of mine" is really a shortened form of "a friend of mine (friends)" as argued by other comments. This means, literally, "one friend out of my several friends". The OED etymology sections have a long but clear explanation of the history of "mine" and "my" that more or less clears this up. Historically, "my" originates from a singular version (min) and "mine" from a plural version (mine) which were otherwise grammatically the same. Therefore, "mine" probably does have something to do with the plurality of friends in this case. Just like "mine eyes" probably made sense in the the past, but not "mine nose". One thing that either clinches or messes up this interpretation is that people say "of hers". OED calls this a "double possessive" which developed by extrapolation from 's. But some dialectical variants use "of hern" instead, which was definitely plural in the past. Therefore. "hern friends" was used in the past. Was "hers friends" ever grammatical? I'm inclined to think this is (historically) about plurality and not about double possession. Maybe phrases like "of John's" were originally in the plural possessive sense "of Johns" where John has many of something, not where there are many Johns, but were reanalyzed as a new special kind of possessive when this kind of plural possessive was lost. Therefore, the idea of double possession is a later way of explaining why people speak like this.