(1) 与过去事实相反

例：If the man had pointed with his first finger while he was in Brunei, everyone would have thought that he was very rude. 在Brunei，如果那人用第一个手指指着的话，那人人都会认为他很不礼貌。

(2) 与现在事实相反

例：If I were in your position, I would call the police immediately.

如果我处在你的位置，我会立即打电话给警察。

(3) 与将来事实相反

例：If I had (should have) time tomorrow, I would certainly help you.

如果我明天有空的话，我当然会帮助你的。

(4) 虚拟条件句中的倒装：

例：Should it rain, the crops would grow better. 如果天下雨的话，庄稼会长得更好。

         Were I your father, I would not give you the money. 如果我是你父亲的话，我就不会给你那钱了。

         Had it not been for the captain, the ship would have sunk 如果不是那船长的话，那船就会沉没了。