用在一般虚拟条件句中的虚拟语气
(一)表示与现在、过去、将来事实相反的假设
1. 与现在事实相反的假设。
其句子结构为：
从句：if+主语+动词的过去式(be变were)+其他
主句：主语+would(should, could, might)+动词原形+其他
例：If I were you, I would go with him.
2. 与过去事实相反的假设。
其句子结构为：
从句：If+主语+过去完成时+其他
主句：主语+should(would, could, might)+现在完成时+其他。例：If you had studied harder last term, you could have passed exam.
3.表示对将来事实实现的可能性不大的假设。
其句子结构为：
从句：If+主语+should (were to )+动词原形+其他
主句：主语+would (could, should, might)+动词原形
例：If he were to go tomorrow. He might tell you.
(二)从句和主句要根据各自发所生的时间选用符合具体时间的虚拟语气形式
1. 从句表示过去，主句表示现在。
If they had stared the early morning yesterday, they would be here now.
2. 从句表示将来，主句表示过去。
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. 从句表示过去，主句表示将来。
If we hadn’ t made adequate preparations, we shouldn’ t dare to do the experiment next week。
4.从句表示将来，主句表示现在。
If we shouldn’ t have an exam this afternoon. I would go shopping now.