When specifying possession, my understanding is that one adds an apostrophe if modifying a plural ending with an 's', or adds apostrophe followed by an s if not. How does one specify possession of one of a group?

For example, when discussing a ball belonging to a friend of mine, should I assume 'friends' is plural and use:

That's one of my friends' ball.

or should I assume 'one of my friends' is singular and use:

That's one of my friends's ball.

...Obviously, I could just use "That's my friend's ball", but assume in this case that I don't want to reword as such (maybe I want to point out in the same sentence that I have multiple friends).

  • Here, usage is such that 'grammar' takes a back seat to pronunciation guidelines. Do you read << friends' / friends's >> as having one syllable or two? Jul 23 '19 at 18:55
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    The possessive clitic attaches to one of my friends, which is a singular noun phrase (to test, just add a verb: “one of my friends is” or “one of my friends are”?). However, you can always write the possessive of any element that ends in s, z or x with just an apostrophe, regardless of whether it’s singular or plural, so it’s up to you which one you want to use here. Jul 23 '19 at 19:36
  • @JanusBahsJacquet I thought it had to be "'s" for singular? That is, "My boss' car" should be corrected to "my boss's car"?
    – Sarov
    Jul 23 '19 at 19:37
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    Possible duplicate of What is the correct possessive for nouns ending in "‑s"? Jul 24 '19 at 11:56
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    @EdwinAshworth: The questions are different. The question here is about whether a noun phrase like [one of my friends] (headed by the singular (pro)noun one, not by the plural noun friends) can take the -'s genitive, and if so, how to realize the -'s genitive in this situation.
    – herisson
    Jul 25 '19 at 3:08

English has several ways to indicate possession. Adding -'s or -' to the end of a word is just one of these ways. In the rest of this answer, I will call this construction the "-'s genitive". It is not only used to indicate literal possession.

I said in the preceding paragraph that -'s or -' is added to "the end of a word". This accurately describes the way it is pronounced and written, but it doesn't describe the syntactic rules about how, why, and where it gets added.

The syntax of the -'s genitive is fairly complicated to analyze. Semantically, the construction applies to a noun phrase. But the -'s or -' isn't always suffixed to the word that functions as the head of the noun phrase. In noun phrases that don't end in the head noun, the -'s genitive attaches either to the last word of the noun phrase, or to the noun phrase as a whole (linguists have debated between these two formulations of the rule).

There are situations where it sounds unnatural to use this construction rather than an alternative way of indicating possession. There are also situations where different speakers have different realizations of this construction.

The multiple forms of the -'s genitive: a brief summary

You may already know about the variability between the forms -'s and -' (sometimes but not always related to variation in pronunciation). When to use -'s vs. -' after a noun is the subject of the prior question What is the correct possessive for nouns ending in "‑s"? Basically, the form -' is always used at the end of a head noun ending in the plural-noun suffix -(e)s. The form 's is always used at the end of a head noun, singular or plural, that doesn't end in a sibilant sound. There is some variability between the forms -'s and -' at the end of certain singular head nouns (or names) ending in the sound /z/ or /s/.

However, your question is not about a noun, but about a noun phrase "one of my friends". As you say, this noun phrase is singular because the head, one, is singular. But it ends in a plural word friends.

There are noun phrases that don't sound natural with the 's genitive

I would say that it is just not usual to use the -'s genitive with a singular noun phrase ending in a plural noun that is not the head of the noun phrase. And if it is used, native speakers may disagree about how to realize the genitive suffix in this context. I discuss this a bit more in my answer here: What's wrong with “One of my children's name IS John”? So I would recommend using an alternative structure, instead of trying to form "[one of my friends] + -'s-genitive suffix + ball".

Alternative ways to say what you want to say

In writing, you could indicate that you are talking about one of your many friends by using the form "one of my friends' balls". This is not built on the noun phrase "[one of my friends]": instead, the syntactic structure is "one of [[my friends'] balls]". Here, the -'s genitive is applied directly after the plural suffix at the end of the head noun friends, so it is clear that the genitive must take the form -'. This form implies that more than one of your friends has a ball, or at least that your friends collectively have more than one ball.

In speech, "one of my friends' balls" sounds identical to "one of [[my friend's] balls]", which is also valid but has a distinct meaning. This form wouldn't indicate that you have multiple friends, but that you have (at least) one friend with multiple balls.

If you want something that is unambiguous in speech, or if you don't want to imply that you have multiple friends with balls, you should use a longer rewording like "That ball belongs to one of my friends".

  • Some forms are more infelicitous than others. If pressed you might be able to get away with referring to the mother of a friend of yours as a friend of mine''s mother but when it's instead the mother of a friend of hers it seems awful, and tantamount to impossible when it's the mother of a friend of his.
    – tchrist
    Jul 26 '19 at 15:06

You are going to be in terrible trouble no matter what you do, if you insist on not rephrasing the sentence in some way.

Even if you consider one (or both) of the sentences to be grammatically and stylistically correct, and leaving aside where you should put the apostrophe, it sounds wrong because of the phrase one of my friends followed by the singular ball.

Even if you pronounce the phrase as one of my friendses, it has the same issue with the singular ball following it. (Not to mention that friendses sounds like something Gollum from The Lord of the Rings would say.)

Both of these sound completely natural:

one of my friends balls
one of my friendses balls

Neither of these do:

one of my friends ball
one of my friendses ball

(And it's not the specific noun that's causing the problem. Replace ball with any singular noun and the same problem will result.)

Different style guides will give different advice on whether it should be one of my friends' or one of my friends's. And different people will pronounce the result differently.

Note, however, that one of my friends is singular. Adding the apostrophe to the end of anything that ends in s is one way of indicating its possession. I don't think it's the most common style, but it's certainly used by enough people to still be discussed. It just adds a bit more confusion in this situation, however, because a plural possessive would be styled identically.

But no matter how it's styled, or how it's pronounced, the result will still sound at least somewhat odd (if not more than that to some) with the singular ball following it—even if it's completely correct in terms of syntax.

As mentioned in the question, this sounds and looks completely normal:

That's my friend's ball.

However, it doesn't impart the same idea of having multiple friends, and the friend with their ball being just one of them.

The only real way to preserve the sense of plurality, while still having the possessive with a singular ball not produce something strange either in style or speech, is to rephrase it in a way similar to this:

That's a ball of one of my friends.
That's a ball belonging to one of my friends.
That's a ball owned by one of my friends.

In short, ball needs to come before one of my friends, which also involves dropping the use of the apostrophe to indicate possession.

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    What style guide would recommend writing "one of my friends's balls"? I think that the usual form is "one of my friends' balls", which is undeniably punctuated according to the standard when the syntax is parsed as "one of [[my friends'] balls]".
    – herisson
    Jul 25 '19 at 3:29
  • No, one of my friends is not a singular noun, as it is a noun phrase, not a noun. And it does not involve some mythical non-rule about grammatical number and punctuation. Do not say that friends is singular because it is not. The rule is a sound law that even the unlettered unconsciously obey.
    – tchrist
    Jul 25 '19 at 3:56

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