Agreement helps readers understand the relations between elements in a sentence. Subjects and verbs agree in number and person.
Most subject-verb agreement problems arise when endings are omitted from subjects or verbs or when the relation between sentence parts is uncertain.
An -s or -es ending makes a noun plural, but it makes
a present-tense verb singular.
The dog eats bones.(singular subject, singular verb)
The dogs eat bones.(plural subject, plural verb)
Subject and verb should agree even when other words come between them.
A catalogue of courses and requirements often baffles students.
The president, as well as the deans, has agreed to revise the catalog.
Subjects joined by and usually take plural verbs.
Frost and Roethke were contemporaries.
Momaday, Silko, and Vizenor write novels with American Indian characters.
When parts of a subject are joined by "or" or "nor," the verb agrees
with the nearer subject.
Either the painters or the carpenter knows the cost.
Neither the cabinet nor the bookcases are too costly.
With an indefinite pronoun, use a singular or plural verb as appropriate.
Both are correct.
Several were invited.
All of the money is for emergencies.
Collective nouns take singular or plural verbs depending on meaning.
The group agrees that action is necessary.
(The group is acting as a single entity, so a singular verb is required.)
A number of people are in debt.
(Number includes many people who all have individual debts, so a plural verb is required.)