Is it either is or are?

Either is (not either are) is grammatically correct because “either” is a singular indefinite pronoun (e.g., “Either (option) is fine”).

However, in informal English, we sometimes say “either of X are” (e.g., “I don’t think either of those options are acceptable,” “I don’t think either of them are acceptable”) and “either X or Y are” (e.g., “Either Paula or Sasha are going to do it”).

Deciding if is or are is the correct choice with indefinite pronouns can be difficult. Why not use QuillBot’s free Grammar Checker to help you check the subject-verb agreement in your sentences?