if引导的虚拟语气主句使用什么时态

1. 当if后面接一般现在时的动词时,表示对将来的一种推测.
if sb do sth sb will/shall do sth.
If you go with me, you shall be rewarded.
2. 当if后面接一般过去时的动词时,则是一种虚拟语气.
if sb did sth sb would/should do sth.
If I didn't make that mistake, I would't have suffered such a failure.
3. 当if后面接什么时态都可以时，if为“是否”的意思，句子为宾语从句.
sb do sth if sb do sth.
He said if rain was stop.
由if引导的条件状语从句，时态应该是主将从现，就是说主句用一般将来时，而从句用一般现在时表示将来。
例如 If it doesn't rain tomorrow, I will visit my former school.
这里从句就用一般现在时。
当然if引导的从句也可以用虚拟语气
例如If I got up early in the morning, I wouldn't miss the train.

如果是对现在的虚拟, 从句用一般过去时, 主语用would/could/should +V 原形 如: If I were a bird, I could fly in the sky.

是的,从句往前推一个时态, 对现在虚拟,就用一般过去时,
If you didn't finish the work now, you would be punished by the teacher.
对过去虚拟,从句或者叫条件句就用过去完成时
If I had been there yesterday , I should have stopped him.

主将从现吧，主语将来时，从句现在时

表示与过去事实相反：if 从句用 had done （过去完成）

表示与现在事实相反： if 从句用 did/were