I know to use 'is' for singular and 'are' for plurals.
I was recently listening to a song and it reminded me of a 'rule' a teacher once told me about.
The chorus repeats: Line 1: BIG GIRLS CRY WHEN THEIR HEARTS ARE BREAKING.
Normally, this is what i would write because it is talking about multiple gorls and it is not a collective noun (i dont think it is?). But then the song continues with....
Line 2: BIG GIRLS CRY WHEN THEIR HEART IS BREAKING.
This is what a teacher had once told me would also be correct and his justification was, although there is more than one girl, it would be incorrect to say 'hearts' as you are describing more than one girl who each has only one heart. So in other words, if we are talking about a group of people and describing for example a body part that there is only one of, it would be correct to word it the same way as Line 2.
Now my boyfriends mother who is also very good at grammar seems to disagree so i am right back to being confused again! Can anyone clarify please?? Thanks in advance.