Certain indefinite pronouns are always singular—even though plurality is implied— it always takes a singular verb.
— The Writer's Digest Writing Clinic
Pronouns referring to one or more unspecified beings, objects, or places are called indefinite pronouns. Some examples include: another, each, either, everyone, nothing, and someone. They may refer to a group, but a singular verb is used. For instance:
- Everyone on the soccer team gets a new jersey for the season.
- Someone is knocking at the door.
If you are trying to achieve gender neutrality, this rule needs to be considered. Phrases such as, "Everyone is entitled to their own opinion" is incorrect. Instead, it should be, "Everyone is entitled to his or her own opinion."