If you had come to class, you would have passed the exam. 如果你有來上課，你就會通過考試。 (你沒來上課, 也沒有通過考試)
If he hadn’t had his helmet on, he might have died. 如果他沒有戴安全帽，他可能會死掉。(因為他有戴安全帽,所以沒有死。)
if + 過去完成式表達一個在過去想像或假設的情況。可以在主要子句用would have, could have 或 might have + 過去分詞來表達某個想像情境的結果。
If you had talked to me when you saw me, you would have met my friend. 如果你在看到我的时候和我说话，你就会遇到我的朋友。
If she had taken her wallet, she could have bought what she wanted. 如果她帶了钱包，她就可以买到她想要的东西。
If the volunteers had found the missing person, they might have saved his life. 如果志愿者找到了失踪者，他们可能会挽救他的生命。
If I hadn’t married early, I wouldn’t have been miserable.
I wouldn’t have been miserable if I hadn’t married early.
在條件句子中也可以用 unless 來代表 if… (not)
I wouldn’t have stayed in the villa unless it had rained. – I wouldn’t have stayed in the villa if it hadn’t rained. 除非下雨，否则我不会呆在别墅里。
第三條件句 – 練習題