虚拟语气用于表示非真实的情况，通常包括以下几种情况：
与现在事实相反
If I were you, I would take an umbrella.
If there were no air, people would die.
与过去事实相反
If I had got there earlier, I should/would have met her.
If he had taken my advice, he would not have made such a mistake.
与将来事实相反
If he should come here tomorrow, I would talk to him.
If there were a heavy snow next Sunday, we would go skating.
错综条件句
If I had worked hard at school, I would be an engineer now.
If they had informed us, we would not come here now.
省略句
He would have finished it.
You could have passed this exam.
含蓄条件句
But for his help, we would be working now.
Without your instruction, I would not have made such great progress.
命令或请求
Please come over here.
Would you be so kind as to lend me a hand？
这些例子展示了虚拟语气在不同情境下的应用，包括表达假设、愿望、建议以及与现实不符的情况。虚拟语气的使用需要根据句子所表达的具体意义来选择合适的结构和动词形式。