by Annette Lyon
It's subjunctive. (So is our first example above: the girl isn't home, but if she WERE, she could tell her mother the truth.)
A common rule of thumb people use is watching out for the keyword if, which often signals subjunctive.
Be wary about relying on if too much. There are plenty of cases where IF does NOT refer to something that’s contrary to fact, so the sentence isn’t subjunctive mood at all, and was is correct.
Yes, the sentence has if in it, but that doesn’t automatically make it subjunctive. In this instance, WAS is correct.
Subjunctive rule of thumb: When the statement is contrary to fact, use were.