虚拟语气用来表达与事实相反、愿望、建议、假设、不确定或主观态度。
17.1 与现在事实相反
结构：
If + 主语 + 过去式, 主语 + would/could/might + 动词原形例句：
If I were you, I would accept the offer.
如果我是你，我会接受这个机会。这里说话人不是“你”，所以是假设。
注意：正式英语中，be 动词常用 were。
If he were here, he would help us.
如果他在这里，他会帮我们。17.2 与过去事实相反
结构：
If + 主语 + had done, 主语 + would/could/might have done例句：
If I had studied harder, I would have passed the exam.
如果我当时更努力学习，我就通过考试了。实际情况是：当时没有更努力，也没有通过考试。
17.3 与将来可能性很小的情况相反或假设
结构：
If + 主语 + were to do/should do/过去式, 主语 + would + 动词原形例句：
If it were to rain tomorrow, the match would be canceled.
如果明天下雨，比赛就会取消。17.4 wish 后的虚拟
对现在的愿望：
I wish I knew the answer.
我希望我知道答案。对过去的遗憾：
I wish I had told her the truth.
我希望我当时告诉了她真相。对将来的愿望或不满：
I wish he would stop complaining.
我希望他别再抱怨了。17.5 建议、要求、命令后的虚拟
在某些表示建议、要求、命令的词后，从句谓语常用：
should + 动词原形其中 should 可省略。
常见词：
suggest, recommend, demand, request, insist, order, propose例句：
The teacher suggested that he should read more.
The teacher suggested that he read more.
老师建议他多读书。