英语语法 虚拟语气的时态If that be so,we shall take action at once.从句时现在

英语语法 虚拟语气的时态
If that be so,we shall take action at once.
从句时现在,主句用将来.
Only that it rains today,I would go.
前半句是虚拟,I would go只是表示可能性.
John would do it if you asked him.
与现在发生的事实成反比.
If I were in your shoes,I'd accept the terms.
同上
If we had left earlier,we wouldn't have missed the train.
与过去发生的事实成反比.
You would laugh if I told you.
同现在反比
We wouldn't have seen her if it hadn't been for him.
同过去反比
It is necessary that we should do following ourselves schedule.
同现在反比
It is strange that she should have done it
同过去反比
以上的我的理解都对吗?那么“与将来发生的事实成反比”和“与现在发生的事实成反比”我感觉上没区别,看语法书上也是,两者形式一样,