虚拟语气(Subjunctive Mood)这一语法项目是各类英语考试中心测试的重点之一。虚拟语气是一种特殊的动词形式，用来表示说话人所说的话并不是事实，而是一种假设、愿望、怀疑或推测。判断是真实条件句还是非真实条件句。只有在非真实条件句中才使用虚拟语气。通过句子意思，看假设的条件是否能够实现，能够实现是真实条件句，不能使用虚拟语气；假设的条件不能实现则是非真实条件句，要用虚拟语气.判断这个假设是与哪个事实相反。通常有三种情况：①与过去事实相反。②与现在事实相反。③与将来事实可能相反
I: 最基本的虚拟语气句型:
1. 虚拟现在时表示与现在事实相反的假设，其if 从句的谓语形式用动词的过去式(be 一般用were)，主句用would/ should/ could/ might 动词原形。If places were a like, there would be little need for geographers.如果各个地方都一样，就不需要地理学家了。
2. 虚拟过去时是表示与过去事实相反的假设，if 从句的谓语形式用过去完成时即had＋过去分词，主句用would / should / could / might have 过去分词。If he had known your address yesterday,he would have telephoned you.
3. 虚拟将来时是表示对将来实现的可能性很小的或不确定的假设。If从句的谓语形式用一般过去式或用were to / should 动词原形，主句用would / should/could/ might 动词原形。If he were to leave today, he would get there by Friday
4. 省略if 采用倒装语序的条件句。有时可以把含有助动词、情态动词、be或have的虚拟条件句中的连词if省去，而将had , should, were 等词提到主语之前，即用倒装结构。Had he worked harder, he would have got through the exams.Were he to leave today, he would get there by Friday.Were I in your place, I wouldn’t do that.

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