In which cases do we use the subjunctive form of a verb?
We use the subjunctive form of the verb when we refer to a situation that cannot happen anymore... or an impossible situation.
"If Jose Rizal WERE alive, he would have a lot to say about our present politicians." In this sentence, JR cannot live again.
"If Mary WERE a swan, she could have flown away." In this sentence, Mary can never be a swan.