虛擬條件句的從句部分含有were, should, 或had時, 可省略if，再把were, should或had 移到從句的句首，實行倒裝。
例如：
Were they here now, they could help us. =If they were here now, they could help us.
他們現在在的話，就會幫助我們了。
Had you come earlier, you would have met him. =If you had come earlier, you would have met him.
你來得早一點，就碰到他了。
Should it rain, the crops would be saved. =Were it to rain, the crops would be saved.
假如下雨，莊稼就有救了。
注意：在虛擬語氣的從句中，動詞’be’的過去時態一律用』were』，不用was，即在從句中be用were代替。
例如：
If I were you, I would go to look for him. 如果我是你，就會去找他。
If he were here, everything would be all right. 如果他在這兒，一切都會好的。