This first section addresses subject-verb agreement errors. If the subject of a clause is singular, the corresponding verb must be singular; in other words, it must agree with the subject. If the subject is plural, the verb should be plural.
Keep in mind that although plural nouns usually end in s, verbs operate differently. An s ending on a verb signals a singular form.
4.1.1 Subjects That Appear to Be Plural But Are Not
Sometimes a subject appears to be plural when it is actually singular. In the following example, both the subject and the verb are plural.
Compound Subject • Verb
Hot dogs and cheeseburgers are my favorite foods.
The next example appears to be similar, but the subject is a single dish and is therefore singular.
Spaghetti and meatballs is my favorite food.
Because the subject is singular, the verb is singular, too.
Another type of singular subject that can falsely appear to be plural involves phrases such as along with or as well as. Consider these two examples:
Jill and Jack like reading the sports section.
Jill as well as Jack likes reading the sports section.
The sentences have very similar meanings, but the grammatical structures differ. In the first case, the subject — Jill and Jack — is plural, and so is the verb. In the second example, the subject is Jill alone, and as well as Jack is not grammatically part of the subject. Therefore, the subject takes the singular verb likes rather than the plural like.
The phrase along with works the same way. Thus, in the following sentence, both the subject and verb are singular:
An ineffective boss, along with dull work and long hours, is leading Peter to consider quitting.
The verb is unaffected by dull work or long hours.
4.1.2 Subjects and Prepositional Phrases
One thing to keep in mind is that the subject of a clause cannot be part of a prepositional phrase. Consider the following example:
The quality of their products has/have been deteriorating.
Has is a singular verb; have is plural. Which is the correct form in this sentence?
To answer that question, one should first identify the subject. Some people would mistakenly assume that the subject is products. However, products is the object in the prepositional phrase of their products, and therefore cannot be the subject of this sentence. Instead, the subject is quality, so the verb is singular: has.
Now, consider another example:
Every one of you has/have to contribute something.
What is the subject of the sentence? The subject cannot be you, because you is part of the prepositional phrase of you. Instead, the subject is the pronoun one, so the correct verb form is has.
4.1.3 The Word Number
Depending on the context, the word number can be singular or plural.
If it is used in combination with the indefinite article a, it should generally appear with a plural verb, as in:
A number of schools are closed today.
When used with the definite article the, however, number usually requires a singular verb, as in:
The number of schools is increasing.
4.1.4 Each, Neither, and Either
When appearing before the word of, the words each, neither, and either are all singular pronouns and therefore require singular verbs. However, these pronouns often appear with plural verbs — an error — because writers frequently mistake another word in the sentence for the subject.
Subject • Verb
Each of the volumes is fascinating.
Neither of you understands me.
4.1.5 Either/or and Neither/nor
The correlative conjunction pairs either/or and neither/nor create subject-verb agreement challenges for many people. Compare these two sentences:
Neither John nor the Smiths have arrived.
Neither the Smiths nor John has arrived.
This is an odd grammatical case where geography matters: it is the element of the subject that appears closest to the verb that determines the verb form. In the first example above, Smiths immediately precedes the verb, so the verb must be plural. In the second sentence, John appears next to the verb, so the verb is singular: has.
4.1.6 Plural Units, Singular Concepts
Sometimes units of time, distance, money, and so on appear plural but are in fact functioning as a singular amount. In such cases, a singular verb is required. For instance:
Five minutes is not enough time.
Six miles is too far.
Seven hundred dollars is a lot of money to lose gambling.
4.1.7 Verb Forms After Who
Relative clauses (see Section 3.1.6) are often culprits in agreement errors. In the following example, which contains no relative clause, one is the subject, and the verb must therefore be singular: has.
One of the employees has been reprimanded.
Now consider this sentence:
Carol is one of the employees who has/have been reprimanded.
Should the verb be has or have? To answer that question, we must first determine the antecedent for the pronoun who. Has only one employee been reprimanded, or have multiple employees been reprimanded?
The answer is multiple; Carol is merely one of them. The antecedent for who is employees, a plural noun, and thus the corresponding verb must also be plural. Have is the correct choice in this example.
4.1.8 Collective Nouns
In American English, collective nouns (see Section 1.1) are generally treated as singular, unless the members of the group are being considered individually. Compare these two sentences:
The couple is getting married next Sunday.
The couple are arguing with each other.
In the first sentence, the couple is acting in concert, so the subject and verb are both singular. In the second, they are acting as individuals, so the subject and verb are plural.
In contrast with American English, British English generally treats collective nouns as plurals.