You and ye used to be the plural forms of the second person pronoun. You was the accusative form, and ye was the nominative form.

Because of this, you still conjugates verbs in the plural form even when it is singular; that is, you are is correct even if you is only referring to one person.

Thee and thou used to be the singular forms. Thou was the nominative form, and thee was the accusative form. Thy and thine were the genetive forms, and their use followed the same rules as a and an.