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，這叫做混郃條件句。 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 it had rained last night (過去), it would be very cold today (現在).