When you come across possessive pronouns such as your, their, his, and hers, check to see whether they agree with other pronouns in the sentence. Most possessive pronouns are used messily in spoken language, so be careful to take special note when you see two pronouns in a sentence.

Incorrect: Some of you will have to bring their own beer.

Correct: Some of you will have to bring your own beer.

In this sentence, the possessive pronoun towards the end of the sentence should match the pronoun following "Some of". Because the first pronoun is "you", the possessive pronoun must be your, not their. "Their" would only be correct if the sentence began "Some of them will have to bring…"

Incorrect: If anyone comes over, take their name.

Correct: If anyone comes over, take his or her name.

The subject is anyone, which is singular, and which therefore requires a singular pronoun such as "his" or "her". This error has become common because of the demand for political correctness; instead of saying "his or her", people will often just say "their." Either "his" or "her" alone is technically correct, but writing "his or her," is also acceptable.

D. Singular and Plural Pronouns

F. Objects of to be verbs