First, here’s a link to an excellent web article on the subject if you’d rather not read my ramblings.
My usual explanation of subjunctive mood involves “Fiddler on the Roof.” Tevye sings about what he would do if he were rich. Not if he was rich. It’s an impossible dream (which is a totally different musical, I know) he can never achieve, so he uses the subjunctive mood. Well, maybe not Tevye, but the lyricist. Thank you, Sheldon Harnick.
People get confused, though, and think that every time they use “if” they need to use “were.” That’s simply not how it works. “If I was older I would be eligible for more discounts.” I will be older, eventually. There’s nothing hopeful or impossible in that situation. I will be older, and I will get more discounts when I am. “If I was dead, I wouldn’t have to worry about grammar.” Nothing hopeful or impossible there, either. I will be dead someday, and when I am, I won’t have to worry about grammar anymore.
If I were vacationing in Greece . . . Now THAT is both hopeful and impossible, so I use the subjunctive mood to indicate it.
What about a character whose aunt is in the hospital? Frank didn’t know how his aunt was faring. If she (was / were) dead, someone would have called by now, wouldn’t they?
It’s possible she IS dead. He doesn’t know. Use the usual verb form, “was,” to show that it’s possible. If she was dead, someone would have called him.
It’s just as legitimate to recast the sentence to avoid confusion about need for the subjunctive. Frank didn’t know how his aunt was faring. If she had died, someone would have called by now, wouldn’t they?
Suggestions and commands often take the subjunctive.
I demand he go along with us. (Normally you would say “he goes.” However, for the subjunctive form you use “go,” the root verb. The root is the infinitive form without “to.” It’s the word you look up in the dictionary.)
It is essential that the plans be completed by July 15. (Normally you would say “plans are completed.” The subjunctive takes the root verb, “be.”)
We use common wording that contains the subjunctive. “If I were you.” “Heaven forbid.” “God save the queen.” All of those are subjunctive; if they were not, they would be “If I was you,” “heaven forbids,” and “God saves the queen.”
A professional editor will be able to correct misuse (or omission) of the subjunctive. Don’t be afraid to attempt using it. If you’re right, your editor will likely praise your skills. If you’re not, your editor will at the least correct the issue without comment; she might even attempt to teach you what you did wrong. Either way, the result will be correct. It’s a vanishing usage, but in my professional opinion it’s one worth saving–at least in print.