Outside of a few specific exceptions, when you are writing with proper subject-verb agreement, any singular subject--a person, place or thing that performs the action--must have a singular verb, while any plural subject must have a plural verb. The challenge is to identify a singular subject properly and then use the correct singular form of the verb to maintain subject-verb agreement.
As a rule, the subject and the verb of a sentence must always agree in number. If one person, place or thing performs an action, then the verb or action will always be singular.
In most cases, the singular form of a verb ends with the letter "s," while the plural form usually does not. The opposite is true of nouns, which typically add an "s" to show plural form.
Use caution when your subject can be singular or plural depending on the context of the sentence--examples are indefinite pronouns, such as everybody, others and most, and collective nouns, such as committee, group or team.
Finding the Subject
The key is to locate the performer of the action that the sentence describes. In the sentence, "Sally always calls her mother at 3 p.m.," Sally is performing the action. Because Sally is one person, or singular, you would use the verb "to call" in its singular form: calls.
Once you identify the subject by asking yourself who or what, it is easier to identify which form of the verb to use for proper subject-verb agreement.
A compound subject occurs when your sentence has more than one subject, or more than one person or thing performing the action. In most sentences with multiple subjects, the plural form of the verb is the correct choice for subject-verb agreement.
The Center for Writing at the University of Minnesota notes that native English speakers usually can choose the proper form of the verb intuitively in these cases. However, many people, even native English speakers, can find it difficult to maintain subject-verb agreement when "and" joins a singular and a plural subject. In such a case, use the plural form of the verb so the subjects and verb agree. In the sentence "The boys and their dad jog every day," the verb "jog" is used in its plural form, despite its proximity to the noun "dad."
With compound subjects, it is important to notice the word or words that join the multiple subjects, called conjunctions. A few basic rules govern proper subject-verb agreement, depending upon the conjunction used.
According to the Purdue Online Writing Lab, when "and" joins the subjects, use the verb’s plural form. For example, “Sherry and Paula jog every Tuesday.” However, when "or" or "nor" join two subjects, use a singular verb. For example, “Sherry or Paula jogs every Tuesday.”
When "or" or "nor" join a compound subject containing both a singular and a plural noun, apply the proximity rule. For example, “Neither Sherry nor her sisters jog every Tuesday.”
Words between Subject and Verb
The Purdue Online Writing Lab cautions against confusion by words written between the subject and the verb. Remember that the subject must agree with the verb; avoid matching the action word to the person, place or thing that is mentioned in the phrase. In the sentence, “The old woman with all the cats walks past my house,” it may be tempting to use the verb "walk" because the noun "cats" is plural. However, the subject is "woman," and the verb that agrees is singular.
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