Sometimes, there is confusion
on subject-verb agreement with correlative conjunctions. Let's look at the
example sentence from above again:
Not only the human caretaker
but also the monkey was rescued from the collapsed monkey
exhibit.
There are two nouns that the correlative conjunction is
pointing to; why not use the plural verb “were” instead of the singular verb
“was”? The answer is simple: only the noun closest to the verb counts. The
rule to follow here is: if the noun closest to the verb is singular, use the
singular verb; if it is plural, use the plural verb. In this case, the noun
closest to the verb is “monkey”, which is singular. Therefore, the verb is
singular.
This rule stands for all the correlative conjunction pairs
except one: “both-and”. Since this pair’s job is to specify that multiple
things are involved, the plural verb is always used. Consider the slight
variation of the above example sentence:
Both the human caretaker
and the monkey were rescued from the collapsed monkey exhibit.
Here, the correlative conjunction pair “both-and” is used,
so the verb, “were”, is plural.