Verbs must agree in number with their subjects. Common rules for subject-verb agreement are given below.
Single subjects agree with single verbs; plural subjects agree with plural verbs.
The girl walks her dog.
The girls walk their dogs.
Compound subjects joined by and typically take a plural verb unless considered one item.
Correctness and precision are required for all good writing.
Macaroni and cheese makes a great snack for children.
My favorite is strawberries and apples.
My favorites are strawberries and apples.
Neither of the students is happy about the play.
Each of the many cars is on the grass.
Every one of the administrators speaks highly of Trevor.
Similarly, pronouns must agree with their antecedents (the words they replaced) in number; however, some pronouns also require gender agreement (him, her). Pronoun-antecedent agreement rules are given below.
Antecedents joined by and typically require a plural pronoun.
The children and their dogs enjoyed their day at the beach.
For compound antecedents joined by or, the pronoun agrees with the nearer or nearest antecedent.
Either the mice or the cat gets itself a meal of good leftovers.
When indefinite pronouns are used in a sentence, the pronoun must agree with the number of the indefinite pronoun.
Neither student finished his or her assignment.
Both students finished their assignments.
When each and every precede the antecedent, the pronoun agreement will be singular.
Every writer is attending his or her assigned lecture.
Because English does not have a nongendered singular pronoun, it’s common in everyday speech to treat they or their as singular. Still, using the “singular they” is not accepted by all grammarians, although there is considerable historical precedent for its use.
The bottom line is that while this issue is not usually tested, if you see it on an exam, use the technically correct response to be safe.
Common Usage: Every student should check their homework before turning it in.
Technically Correct: Every student should check his or her homework before turning it in.