主句與從句的動作發生在不同的時間，這時主，從句謂語動詞的虛擬語氣形式因時間不同而不同，這叫做混合條件句。
If you had asked him yesterday, you would know what to do now.
（從句與過去事實相反，主句與現在事實相反。）
If you hadn’t stayed up so late, you wouldn’t be so sleepy now.
意味著：因為你熬夜了，所以現在這麼困。
If it had rained last night (過去), it would be very cold today (現在).
練習：
1. If you had listened to the doctor, you____(well) now.
你要是聽了醫生的話，現在都好了。
2. You ought to have come last night if you_____(interest) in Beijing opera.
如果你真的對京劇感興趣，昨晚你就應該來。