Basic Principle: Singular subjects need singular verbs; plural subjects need plural verbs. My brother is a nutritionist. My sisters are mathematicians.
See the section on Plurals for additional help with subject-verb agreement.
The indefinite pronouns anyone, everyone, someone, no one, nobody are always singular and, therefore, require singular verbs.
Everyone has done his or her homework.
Somebody has left her purse.
Some indefinite pronouns — such as all, some — are singular or plural depending on what they're referring to. (Is the thing referred to countable or not?) Be careful choosing a verb to accompany such pronouns.
Some of the beads are missing.
Some of the water is gone.
On the other hand, there is one indefinite pronoun, none, that can be either singular or plural; it often doesn't matter whether you use a singular or a plural verb — unless something else in the sentence determines its number. (Writers generally think of none as meaning not any and will choose a plural verb, as in "None of the engines are working," but when something else makes us regard none as meaning not one, we want a singular verb, as in "None of the food is fresh.")
None of you claims responsibility for this incident?
None of you claim responsibility for this incident?
None of the students have done their homework. (In this last example, the word their precludes the use of the singular verb.
Some indefinite pronouns are particularly troublesome Everyone and everybody (listed above, also) certainly feel like more than one person and, therefore, students are sometimes tempted to use a plural verb with them. They are always singular, though. Each is often followed by a prepositional phrase ending in a plural word (Each of the cars), thus confusing the verb choice. Each, too, is always singular and requires a singular verb.
Everyone has finished his or her homework.
You would always say, "Everybody is here." This means that the word is singular and nothing will change that.
Each of the students is responsible for doing his or her work in the library. Don't let the word "students" confuse you; the subject is each and each is always singular — Each is responsible.
Phrases such as together with, as well as, and along with are not the same as and. The phrase introduced by as well as or along with will modify the earlier word (mayor in this case), but it does not compound the subjects (as the word and would do).
The mayor as well as his brothers is going to prison.
The mayor and his brothers are going to jail.
The pronouns neither and either are singular and require singular verbs even though they seem to be referring, in a sense, to two things.
Neither of the two traffic lights is working.
Which shirt do you want for Christmas?
Either is fine with me.
In informal writing, neither and either sometimes take a plural verb when these pronouns are followed by a prepositional phrase beginning with of. This is particularly true of interrogative constructions: "Have either of you two clowns read the assignment?" "Are either of you taking this seriously?" Burchfield calls this "a clash between notional and actual agreement."*
The conjunction or does not conjoin (as and does): when nor or or is used the subject closer to the verb determines the number of the verb. Whether the subject comes before or after the verb doesn't matter; the proximity determines the number.
Either my father or my brothers are going to sell the house. Neither my brothers nor my father is going to sell the house. Are either my brothers or my father responsible?
Is either my father or my brothers responsible?
Because a sentence like "Neither my brothers nor my father is going to sell the house" sounds peculiar, it...