The indefinite pronouns anyone, anybody, everyone, everybody, someone, somebody, no one, and nobody are always singular. This is sometimes perplexing to writers who feel that everyone and everybody (especially) are referring to more than one person. The same is true of either and neither, which are always singular even though they seem to be referring to two things.
The need for pronoun-antecedent agreement can create gender problems. If one were to write, for instance, "A student must see his counselor before the end of the semester," when there are female students about, nothing but grief will follow. One can pluralize, in this situation, to avoid the problem:
Students must see their counselor before the end of the semester.
Or, one could say
A student must see his or her counselor. . . .
f there is more than one possible antecedent for a personal pronoun in a sentence, make sure that the pronoun refers only to one of them:
[WRONG] Jerry found a gun in the trousers which he wore.
"Which he wore" could modify "trousers" or "gun."
[WRONG] Jerry called Steve twelve times while he was in Reno.
The pronoun "he" could refer either to "Jerry" or to "Steve."