用在一般虛擬條件句中的虛擬語氣
(一)表示與現在、過去、將來事實相反的假設
1. 與現在事實相反的假設。
其句子結構為：
從句：if+主語+動詞的過去式(be變were)+其他
主句：主語+would(should, could, might)+動詞原形+其他
例：If I were you, I would go with him.
2. 與過去事實相反的假設。
其句子結構為：
從句：If+主語+過去完成時+其他
主句：主語+should(would, could, might)+現在完成時+其他。例：If you had studied harder last term, you could have passed exam.
3.表示對將來事實實現的可能性不大的假設。
其句子結構為：
從句：If+主語+should (were to )+動詞原形+其他
主句：主語+would (could, should, might)+動詞原形
例：If he were to go tomorrow. He might tell you.
(二)從句和主句要根據各自發所生的時間選用符合具體時間的虛擬語氣形式
1. 從句表示過去，主句表示現在。
If they had stared the early morning yesterday, they would be here now.
2. 從句表示將來，主句表示過去。
If I were not to make a preparation for my experiment this afternoon, I would have gone to see the film with you last night。
3. 從句表示過去，主句表示將來。
If we hadn’ t made adequate preparations, we shouldn’ t dare to do the experiment next week。
4.從句表示將來，主句表示現在。
If we shouldn’ t have an exam this afternoon. I would go shopping now.
