Could anyone please tell me what is the difference between the following expressions?
#1 the friends and family of users.
#2 the friends and families of users.
Actually, #1 is a line of an article, which is
Facebook said on Wednesday that it planned to make a series of changes to its news feed algorithm so that it will more favorably promote content posted by the friends and family of users.
I believe what is happening is created by the fact that group nouns can be understood as plural nouns by some English speakers. This is less common nowadays, though I believe it persists in the UK to some extent:
Usually this means that the group noun is considered to be composed of multiple members, rather than there being many of that noun.
However, in the case of "friends and family of users" a singular reading doesn't work. I believe that we instead process a plural reading with the understanding of what is plural widened in scope: instead of the group being plural because there are multiple members, we understand it to be plural because there's more than one of them.
You can see this phenomenon in other, less stereotypical phrases:
You can use cows' branding to identify the farms and herd of cows.
I know that the protecting the identity of users is important.
You know the genre of band of musicians by the music they play.
There's no appreciable difference beyond the the fact that we're forcing a widened plural reading onto family in "friends and family of users".
"Family" should be plural here because they are talking about more than one family. Presumably all Facebook users are not part of the same family. So they should say "the families of users". "Family of users" implies that there is only one family for all users.
This has nothing to do with whether collective nouns are singular or plural. There is more than one family under discussion, therefore it should be plural.
