Given the following sentences that use will in the if clause (which is seldom with if-clauses and therefore, I'm not sure they all are even grammatical or not).
- If you will/would kindly lend me your book, I will be thankful to you.
- If you will not/would not mind lending me your book, I will be thankful to you.
- If you will/would wait for a while, I will check it for you.
- If you will use it, you can have it
- If you will not arrive before six o'clock, I cannot meet you.
What if the last sentence is modified as follows?
If you will not be arriving before six o'clock, I cannot meet you.
Once upon a time, it was found in a grammar book.
If the play will not be finished until ten o'clock, I will have to spend the night at your place.
Can the following version of this sentence have a different meaning (or no meaning at all — a wrong sense)?
If the play is not going to be finished until ten o'clock, I will have to spend the night at your place.
After all, the question is when is will used in if-clauses as the title implies?
Moreover, both the following sentences appear to indicate a probable condition.
- If he came, I should help him.
- If he came, I would help him.
Using should and would interchangeably in such contexts implies a significant difference in meaning?