(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**。
(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