1、虚拟语气用于条件状语从句中
（1）表示与现在事实相反的假设，条件状语从句中的谓语动词用“过去式（be动词的过去式用were）”，而主句中的谓语动词用“would / should/ could / might + 动词原形”。如：
If I were a boy, I would join the army.
If the had time, she should go with you.
（2）表示与过去的事实相反，条件状语从句中的谓语动词用过去完成时，主句中的谓语动词则用“would / should / might / could + have +过去分词”。如：
