when to use plural or singular form of genitive/possessive noun phrases for item of individuals in group

Question

Phrases like "our passport[s]" that refer to an item owned by members of a group (where each individual has one and the group collectively has multiple) are sometimes expressed in plural or singular form. I'm trying to understand when the singular or plural form is appropriate.

For example:

• A: We have our passports. (not "our passport")
• B: Each of us has [their/our?] passport. (not "our passports")

Here "our passport[s]" is the direct object of a verb phrase, and whether we use plural is determined by the subject. So does the subject determine which is correct? Not necessarily, because we can create examples where the subject does not matter:

• C: He gives us our passports. / He gives our passports to us.
• D: He gives each of us [their/our?] passport.

in C&D the subject is unrelated, and the plurality is determined by the indirect object. So it seems the indirect object can also influence whether singular or plural is used.

• E: He gives our passports to someone else.
• F: We give each of us [their/our?] passport.

In E neither the group is not mentioned as a whole or as individuals (no "we" or "each of us") and it seems the plural is preferred. In F both "we" and "each of us" are mentioned, and the singular form of passport seems appropriate. So should we default towards "our passports" unless the group is referred to as individuals then we use the singular? Maybe.

But in G below "each of us" in mentioned and the plural is used. And in H "each of us" is not used and the singular seems more appropriate.

• G. He would give a speech on each of our birthdays.
• H. He would give a speech on our birthday[s?].

I'm not really sure how to clearly ask the question, to be honest. But does anyone see where this is going? When referring to an item owned by members of a group, how do we decide to refer to it as plural or singular?

Someone suggested Singular noun objects of plural subjects as being an equivalent question, but it spends more time dealing with whether the possessed object is of the group or of each member of the group (in this case I'm only asking about the later) and I don't think it addresses G or H. Likewise for Do you pluralize the singular possessions of individual members of a plural group? in that it does not seem address G or H.

Answer 1

You're asking about singular/plural agreement, but you've chosen distracting pronouns. I will use "she" as the singular specific person, "they" for plural, and the old fashioned "he" (instead of "they") for gender neutral, singular, nonspecific.

Let's stick with the case that each person has only one of the named item.

Their passports are on the table.

She gives them their passports.

She gives each of them their passports.

She gives each of them his (own) passport.

She would give a speech on their birthdays.

She would give a speech on each of their birthdays.

She would give a speech on each birthday.

The number agrees in each subject and object. In a noun phrase such as "[each of [their birthdays]]", the inner noun phrase "their birthdays" is plural but the outer noun phrase "each of their birthdays" as a whole is singular: "Their birthdays are equally special. Each of their birthdays is equally special." The noun phrase "each birthday" is also singular. "Each of" is often short for "each one of", therefore singular.

There are languages where a plural referent would have a singular item, such as French, which would express it as "She gives them their passport." This does happen to a lesser extent in English, but generally the number of the referent and the item agrees.

Changing third person plural to first person plural makes things a bit more confusing:

She gives each of us our (own) passport(s).

Prescriptively it should be "our passports", but descriptively there are enough uses of "our passport" to make it idiomatic, including:

Reflections Of A Country Girl: Stories Poems Memories

Somewhere, it must have been in Amsterdam, our passport was stolen. Going south, we had to cross into other countries, showing our passport at each border.

Later, the author writes "our birth certificates" (plural) and "our passport" (singular) in the same sentence.

Orientation: a Journey: Trip Through Europe Asia and Africa

Maria, who had resumed her duties as our primary tour guide in Iberia, alerted us to take out our passport. I began to search for my passport as we drove to the Spanish customs, where a Spanish customs agent entered the bus to inspect our passport. When he came to me, I had some difficulty finding my passport, buried in my hand luggage.