Singular and Plural Pronoun Antecedents:

An antecedent is a word that appears early in a sentence or paragraph, one that later words may refer to or replace. Pronouns should have a noun or another pronoun that serves as their antecedent.

For instance, in the following sentence, the noun carpenter is an antecedent for the pronoun his.

The carpenter needs his tools.

We could theoretically write, "The carpenter needs the carpenter's tools," but that creates a lot of clutter. The pronoun stands in the place of carpenter so we don't have to keep repeating the word. Since in this sentence the subject is a single carpenter, the pronoun must be singular to match the singular noun in the sentence above. The verb needs is a singular verb also, matching the number of the noun. However, if the sentence contained multiple carpenters, the plural antecedent would require a plural pronoun.

The seven carpenters need their tools.

Now, the antecedent carpenters is plural, so it must take a plural pronoun. The verb need is a plural verb here, also matching the number of the noun. The material above seems simple enough, but three tricky areas can cause problems.

First, there are indefinite pronouns that do not refer a specific person or object--some of them are considered singular and others are considered plural. You can read about them here. Second, a writer can shift between pronouns. You can read about this problem here. Finally, a sloppy writer can confuse the reader by creating sentences in which it is unclear who or what the pronoun refers to. You can read about that problem here.