Conditional Mood: Speculative vs. Predictive

In a grammar class, I'm likely to ask, "Why are the following three sentences correct?":

1. If I knew you needed me, I would have helped.
2. If I were you, I would apply for the job.
3. If you have a question, I will answer it.

Notice the if-would combinations for sentences 1 and 2 but the if-will combination for sentence 3.

Most people in my class know the three sentences are grammatically correct but cannot explain why. The usual answer I get is, "Sentence 1 is in the past, sentence 2 is in the present, and sentence 3 is in the future, so we need will for the future." But these sentences have less to do with time, or tense, than they have to do with our state of mind, or mood. Here are the facts:

1. Sentence 1 cannot be in the past because it never happened (I did not know you needed me).
2. Sentence 2 is not in the present because it cannot be (I cannot be you).
3. Sentence 3 is a condition likely to happen in my mind (I will answer your question).

Sentences 1 and 2 have conditions that cannot be met, so we use the speculative if-would combination. The condition in sentence 3 is likely to happen, so we use the predictive if-will combination.