Grammatically Correct: The writer's essential guide to punctuation ...

GRAMMAR
• Collective nouns are those that may be treated as either singulars
or plurals-but you must go one way or the other. If you have
decided to treat such a word as singular, you cannot then apply a
plural pronoun to it, or vice versa. The following sentences are
incorrect:
The committee was unable to get their report out by the deadline.
[should be its report]
Herfamilyaren'tusuallythatsupportive, but I! rallied round her this time.
[should be they rallied]
For more on this, see "Collective nouns" under "Agreement Between
Subject and Verb" on page 214.
• Writers are sometimes unsure which pronoun to use when there
is more than one antecedent. The rule is, use a plural pronoun if
the antecedents are joined with and (a compound subject): This
holds whether the antecedents are individually singular or plural. If
they are joined with or or nor (alternative subjects), have the pronoun
agree with whichever antecedent lies nearest to it.
Bayview High and Riverdale High will be holding their annual reunions
on the same night.
[compound subject, both antecedents singular]
The salesclerks and the store manager said that they had had enough.
[compound subject, one antecedent plural, one singular]
Either Ellis or Herb will bring his camera.
[alternative subject, both antecedents singular, pronoun singular]
Neither the tree nor the bushes should have their branches pruned
just yet.
[alternative subject, last antecedent is plural, pronoun plural]
Something was different: Either the paintings or the mirror had been
moved from its position.
[alternative subject, last antecedent is singular, pronoun singular]
Note that constructions such as the last two often look awkward;
thus, you may want to consider recasting them even though they
are grammatically correct.
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