What are the rules about using 'half of' with plural nouns?

Question

Here are some sentences with 'half of' and plural nouns that I consider to be well-formed: >Half of all films are a waste of celluloid. >Half of users surveyed said they preferred the old product. >Half of the women here are your ex-girlfriends. >Half of Americans are uninsured. Here are some sentences with 'half of' and plural nouns that don't feel well-formed to me: > Half of people are women. > Half of books are hardback. > Half of dogs are neutered. > Half of fruits are citrus. To me, the above require 'all' before the noun or some other form of modification to sound correct or at least less awkward. (In fact, part of my problem is deciding whether these sentences sound wrong because of grammar or semantics.) I'd appreciate either: 1. To be told my second set of examples are actually fine (preferably with links to similar examples). 2. A clear rule for when one can use 'half of' with a plural noun. It can't be just about modification if the 'Half of Americans' sentence is well-formed.

Answer 1

You raise an interesting question. I suspect your statement about it not being about modification, though, relies upon a faulty assumption about how the term "Americans" works. Grammatically, "Americans" is a substantive adjective (implying, American citizens/residents/etc.). For that reason, "Americans" is modifying an implied noun. Another example may counter the modifier hypothesis, but I don't think the one you provided is such an example.