Singular or Plural OBJECT

[ckcgordon]

My question is about the object in the following sentence:

All staff must wear their staff identity card/cards?



I don't know if I should use a singular or plural object.
Someone told me that since "their" is used here, we must must the plual object "cards".
I'm not sure about this explanation. Each staff member only has one staff card. I think it's okay to use "card" in the above sentence.

A related issue is the choice of the possessive pronoun. Is "their" the only option in the above sentence?

[Khosro]

My question is about the object in the following sentence:

All staff must wear their staff identity card/cards?



I don't know if I should use a singular or plural object.
Someone told me that since "their" is used here, we must must the plual object "cards".
I'm not sure about this explanation. Each staff member only has one staff card. I think it's okay to use "card" in the above sentence.

A related issue is the choice of the possessive pronoun. Is "their" the only option in the above sentence?

Not because of "their". It's quite possible that four people have one house, and that would be their house.

I think both card/cards are correct.
When we say "cards" we are thinking about individual cards.
When we say card we are thinking about the card itself, for which those individual cards are just costumized versions (each card has a different name on it but the format of all cards is the same).

[5jj]

All staff must wear their staff identity card/cards?

I know it's illogical, but the plural is more common.