Rhetoric and Composition/Lack of agreement between noun and pronoun

Rules

Pronouns (words such as it, her, them, this, someone, who, him, they, themselves, herself, etc.) replace specific nouns (persons, places, or things) so you don't have to keep repeating them. Like subjects and verbs, pronouns and nouns need to agree in "number": in whether they are singular or plural. They also need to agree in gender: masculine, feminine, or inclusive (both).

Errors in noun-pronoun agreement usually simply result from writing quickly and not editing closely enough. Three specific instances, though, can cause problems:

1. The nouns each, and one are all singular and take singular pronouns; either or neither is singular unless it specifically refers to plural alternatives.
2. When using singular nouns that refer to both sexes or for which the gender is not known, use both masculine and feminine pronouns together (him or her, he or she, himself or herself, his or her) or rewrite the sentence to make the noun and the pronoun both plural. (If all of the members of a group are of one gender, it is acceptable to use the male or female pronoun, as in "Each member of the football team will take his gear onto the bus.")
3. Some nouns can be either singular or plural: audience, group, team, unit, class, and others. Use a singular pronoun if the group is acting as a unit, as in "The audience expressed its appreciation with loud applause." Use a plural pronoun if the group is acting as individual members, as in "The team went their separate ways, some showering, some leaving the stadium, some drinking champagne, and some going home to sleep." [In the second example, it's a good idea to write "team members" to be clear.]
4. The words "They" and "Their" are third-person plural personal pronouns in Modern English. The "singular" they and their is used as a gender-neutral singular rather than as a plural pronoun, but the correctness of this usage is disputed.

Examples

• Every one of the studies indicated their its methodology.
• Neither Jackson nor Juarez believed they he had been represented unfairly.
• Each researcher included a control group with their his his or her test group.
• By 1999, the lacrosse team had outgrown their its space.
• Neither a crocodile nor a lion are is a suitable pet.
• Either Ed or Bill are is a plumber.

But --

• Neither crocodiles nor lions is are suitable pets.
• Either Ed and Bill or Ted and Jeff is are plumbers.