Question

虚拟语气从句怎么用？

Answer 1

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 alike, 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