One of the most fundamental skills in writing is the ability to make the elements of a sentence agree. If your subject is singular but your verb is plural, it is a problem.
General Rule: Singular subjects require singular verbs, while plural subjects require plural verbs.
This rule is easy to work with when the subject and verb in the sentence are clear. For example, consider the following sentences where finding the errors is not difficult:
There is no question that these sentences are incorrect as written. However, when modifiers and prepositional phrases are added to the sentences, the problems with subject-verb agreement may become harder to spot. Consider the sentences again:
Now that the subject and the verb are separated from each other it becomes somewhat tougher to spot the problems in subject-verb agreement. However, by analyzing the sentence and breaking it down to a subject and a verb, the error becomes apparent again.
Some sentences have more than one verb and every verb in a sentence has a subject. In terms of analysis, the task is still the same to isolate the verbs and their subjects and ignore the modifiers and prepositional phrases that obscure the relationship between the subject and the verb. For example, in this sentence:
There is a main subject, developments, and its verb, are challenging. But the prepositional phrase about how people process information also has a verb, process. The subject of this verb is people.
Compound subjects use conjunctions such as and, neither…nor and either…or . Singular subjects joined by the word and are always plural. When using neither…nor or either…or , the verb must agree with the noun closest to the verb.
Collective nouns treat entities made up of many parts as a single unit and therefore, they are singular. Examples of collective nouns include: the jury, the corporation, and the team. Some words that end in s appear to be plural but are actually collective nouns. For example, Mathematics is singular.
Indefinite pronouns refer to an unknown or unidentified person or thing. Indefinite pronouns include: everyone, anyone, anybody, everything, nothing, somebody, someone, and each. Most indefinite pronouns are singular. There are only a handful of plural indefinite pronouns.
These are: both, few, many, and several. Some indefinite pronouns may be either singular or plural. These include: all, any, more, most, none, and some. These are singular when the noun they refer to is singular and plural when the noun they refer to is plural.