Language morphs according to our needs. What was incorrect decades ago may now be correct.
Here’s one example of language in transition–pronoun-antecedent agreement. The following sentence is grammatically correct:
Everyone should bring his or her jacket to the game.
But if you utter this sentence, won’t you sound like a snooty reject from the English Honors Society? Yes. You will.
We say, “Everyone should bring their jacket to the game” because we’re talking, and we want to communicate–not stop and check whether or not our pronoun agrees in number with the antecedent noun.
But will your first-year writing college instructor deduct points if you write the second sentence instead of the first? Yes. Maybe. It depends.
Check out this talk by the Merriam Webster Word Nerds (my pet name for these language wizards). I love that these short videos focus on language in context–not on language as an absolute. Watch as Emily Brewster, Associate Editor at Merriam Webster, discusses “The Awkward Case of ‘His or Her.'”
My favorite illustration of language in transition occurs during Gentlemen Prefer Blonds, when the character played by Marilyn Monroe points to a poster with her name and says, “It is I.” If you’re like me, you hear that sentence and can’t believe it’s coming out of Marilyn’s mouth. But in the 1950s, this grammatically correct sentence sounded natural. No one sitting in a movie theater in the 1950s would have flinched. But when you answer the phone today, how often do you say, “It is I.” Again, echoes of that snooty English Honors Society outcast.