A pronoun must agree with its antecedent in number (singular or plural) and gender (masculine or feminine).
In this sentence, Galen is the antecedent of his, he'd, and his.
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Galen, after saying goodbye to his family, discovered he'd lost his wallet.
In the following sentence, Garcias is the antecedent of they, even though it follows the pronoun.
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Until they buy the house, the Garcias are staying in a hotel.
Look at the next example. Here, Mark and Mancini is a compound antecedent, which requires the plural pronoun their.
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Mark and Mancini took their cue from the senator.
Agreement problems with indefinite pronouns
Indefinite pronouns cause many agreement problems. Some pronouns ( several, few, both, and many) are clearly plural and take plural verbs and plural pronouns.
Several are expected to give up their rooms.
Both brothers told their parents the truth.
Some pronouns may “feel” plural, but are actually singular and take singular verbs and pronouns: each, either, neither, everyone, everybody, no one, nobody, anyone, anybody, someone, and somebody.
Each is responsible for his or her (not their) own ticket.
Everyone wants to get his or her (not their) name in the paper.
When the use of a singular form would lead to a statement that doesn't make sense, you should use a plural form. For example, in the sentence Everyone left the lecture because he thought it was boring, they would be a better choice than he for the pronoun. However, the general rule is to use singular forms of verbs and pronouns with these indefinite pronouns.
Some indefinite pronouns ( none, any, some, all, most) fall into an “either/or” category, taking singular or plural verbs and pronouns, depending on the intended meaning. Sometimes the distinction is subtle.
None of the men was hurt. ( not one = singular)
None of the men were hurt. ( no men = plural)
Some is better than none. ( some = a quantity = singular)
Some were delicious. ( some = a number of things = plural)
All is well. ( all = the sum of all things = singular)
All are well. ( all = a number of people = plural)
If a plural meaning is not clear from the context, use singular verbs and pronouns.
Pronouns with collective nouns
Collective nouns can require either singular or plural verbs and singular or plural pronouns, depending on meaning.
The team plays according to its schedule. (emphasizes the unit = singular)
The team couldn't agree on their goals. (emphasizes individuals = plural)
If you are uncertain, choose a singular verb and a singular pronoun, or reword the sentence to make it clearly plural.
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The team members couldn't agree on their goals.