有点时间，我回答一下吧！

这是一个好问题！你提的三个问题我认为是一个问题，可以一并作答。

真实条件句的类型有6种，交代一下背景，以便与非真实条件句分开。

will表“意愿”的条件分句中，主句用的是will和shall（I和We作主语），其实这就是属于我们常说的Type 1真实条件句，也叫开放条件句。

If you will wait a moment, I'll see if Mr. Jones is free.

I shall be grateful if you will reply promptly.

If you will let me have this report back when you next come in, I shall be grateful.

这样的例子很多：从句是前提，说话人认为前提很大可能会实现，主句就会发生，否则不会发生。

Would表“意愿”的条件分句中，情况有不同，主句除了能用will外，还能用would，should ，could ，might。这样的表述方式一般都比较委婉和礼貌，多用在口语中，比如：

I would/should be very grateful if you would …

I would appreciate it if you would …

I should be very grateful if you would let me know if you have any vacancies.

If you would accept a compromise, we could end this disagreement now.

If you would just wait here for a moment, I'll see if she's free.

If you would take a seat for a moment, I'll see if Mr Turner is in.

If you would all follow me, I'll show you to your rooms.

If you would like to come I will get a ticket for you.

If you would write me a letter about it , I will attend to it at once.

If you would write me a letter about it , I would/should be most grateful.

You might do me a great favour if you would......(用的比较少)

“爱学习的小明 ”网友提出的问题是说，为啥will表示“意愿”却不能像would表示“意愿”那样在主句中使用would/should /could/might，我觉得最可能的解释是would表示意愿的委婉和礼貌用法实际上在很早以前的语法书上被认为是虚拟语气，而will表示意愿的用法是陈述语气，不能瞎用。

I shall do this, if you will let me.    （陈述语气）

I should do this, if you would let me. (虚拟语气)

这样看的话就好理解很多了：

I shall be grateful if you would reply promptly.  （错误）

I shall be grateful if you will reply promptly.     （正确）

I should be grateful if you would reply promptly.  （正确）

（引自A Dictionary of Good English A Guide to Current Usage，P105）

注意一下，你看的那本章振邦的书我没有，我看的是“新编高级英语语法”这本，你的那本可能是有点旧了，在我看的这本书上章振邦认为你提出的这个用法属于真实条件句的其中一类，而且跟你看的书上有些区别，你的那本书上说：从句用表意愿的would，主句可以用will/shall，我觉得不对，我认为：主句能用will/would/should /could/might，不能用shall（与人称无关），且用might很少见。