I'm not an expert on all aspects of the subjunctive -- if I were, I'd explain all of it -- but there's one part I feel I understand pretty well.

If you have a counterfactual hypothetical, always use the subjunctive.

What is a counterfactual hypothetical? It's a hypothesis known to be false (at least from the speaker's point of view.) The phrase I use to remember is "If I were a rich man..."

"I wish I were taller." (Obviously, I am not taller, or I would not wish it.)

"If I were you..." (I am not you.)

Now, in hypotheticals that are not known to be false, you do not have to use the subjunctive.

"Even if he was rich, he's not any more." (He might have been rich in the past, so it's not a counterfactual hypothetical.)

To show the difference:

"If she were hiding in the woods, we would see her." (She is not hiding in the woods. Counterfactual hypothetical.)

"If she is hiding in the woods, we will see her." (She may or may not be hiding in the woods. Not a counterfactual hypothetical.)

Compare the following two versions:

1. "You say your fiance is rich? If he were rich, then he could afford to buy you a bigger ring than that."

2. "You say your fiance is rich? If he is rich, then he could afford to buy you a bigger ring than that."

quote:

---

"Even if he was rich, he's not any more." (He might have been rich in the past, so it's not a counterfactual hypothetical.)

---

I would still use the subjunctive here, at least some of the time, because there's doubt about it.

quote:

---

2. "You say your fiance is rich? If he is rich, then he could afford to buy you a bigger ring than that."

---

I would use "can" in place of "could"; could in present tense expresses a doubt that isn't really compatible with the use of "is" in this sentence.

On this subject, I think the primary reason why there's so much confusion about the subjunctive is that teachers seem to avoid talking about it, at least until you get to a level where it's too late for the vast majority of people to actually understand it.
There is a tendency in modern education to oversimplify things to a ridiculous level. For instance, from a web site aimed at providing resources for schools teaching English:

quote:

---

For present unreal events, we put the verb in the condition clause one step back — into the past:
[...]
If he were a good friend, he would buy them for me.

---

The same page later provides an explanation of the subjunctive -- but I think if you're going to do that, you need to avoid using it before you've introduced it.