I would like to devote one last post to this topic in order to discuss a few more sentences that may pose a challenge: sentences where the subject is a collective noun or a word that indicates a portion; where two subjects are connected by "either... or" or "neither... nor"; or where there is a predicative expression that includes a noun.
Collective nouns are used to refer to a group of living beings or things. Depending on the sentence, they may take a singular or plural verb. If the members of the group are considered as a whole, the verb should be singular; if they are considered as individuals, the verb should be plural.
The jury has made a unanimous decision.
The cast are having trouble remembering their lines.
Words that indicate portions
To determine whether fractions and words such as percent, majority, all, none, and some must be followed by a singular or plural verb, look at the noun in the prepositional phrase that follows them. If the noun in the prepositional phrase (the object of the preposition) is singular, the verb should be singular. If the noun is plural, the verb should be plural.
Three quarters of the cake is gone.
Three quarters of the residents have voted.
"Either... or" and "Neither... nor"
When two singular subjects are connected by "either... or" or "neither... nor," the verb is singular.
Neither Jane nor I likes strawberries.
Yet when one of the subjects is plural, the number will depend on which subject is closest to the verb. If the nearest subject is singular, the verb will be singular. If the nearest subject is plural, the verb will be plural.
Either Robert or his siblings have to straighten that room today.
Neither his friends nor he knows how to get there.
A predicate nominal (noun) is part of a predicative expression. Predicative expressions describe or identify the subject and usually follow verbs such as "to be," "to seem," or "to appear." The problem arises when the subject is singular and the predicate noun is plural. In this case the verb must agree with the subject, not with the predicate noun, even if the sentence sounds a bit awkward. It is always possible to rewrite the sentence to get rid of the awkwardness.
What this essay needs is shorter paragraphs.