When a pronoun’s antecedent is part of a correlative
conjunction pair, there is sometimes confusion on whether to make the pronoun
singular or plural.
The general rule for this situation is the same as the rule
in the subject verb agreement situation: only the noun closest to the pronoun
counts. If the noun closest to the pronoun is singular, use the singular
pronoun. If it is plural, use the plural pronoun. For example, consider the
following sentence:
Not only the gorilla but
also the lions were given their food early.
In this example, the first noun, “gorilla”, is singular, but
the second noun, “lions” is plural. Since the noun closest to the pronoun (lions)
is plural, the pronoun, “their”, is plural (notice that the verb "were"
is also plural because the noun closest to it is plural). If the nouns,
“gorilla” and “lions”, switched places, the pronoun would be singular because
the noun closest to it would be singular.
Not only the lions but
also the gorilla was given its food early.