tense - "If something was" vs "If something were"

Which of these sentences is correct, and why?

1. 
   

   "What if the Moon was a Disco ball?" or

   
   


2. 
   

   "What if the Moon were a Disco ball?"

   
   

Answer

We use the preterite (past tense form) when expressing a counterfactuality.

• If she loved me, I would change my job (but she doesn't love me).

But when it's a form of the verb to be, we can use "were" in place of it.

• What if the Moon was/were a Disco ball (but it's not).

This form is known as irrealis were. It isn't used for marking tense; it's a mood form indicating that it conveys a degree of remoteness from factuality.

The choice between were and was is a matter of style: were is somewhat more formal than was.

---

Huddleston and Pullum, A Student's Introduction to English Grammar