虚拟语气是假想，是愿望，不是事实。
if条件句
If it had not rained last week, we might have run out of drinking water. 要是上周没下雨，我们可能连吃的水都没了。
If I were you, I would study harder now. 如果我是你，我会更加努力得学习。
What would you buy if you were to win the lottery? 如果你中了大奖，你会买啥？
含蓄条件句 otherwise, with, without, but for
We could not have made such a great achievement without your help. 没有你的帮忙我们不可能取得如此成就。
He was busy yesterday. Otherwise, He should have attended the meeting. 他昨天很忙。否则，他应该参加那次回忆了。
If被省略的情况， 倒装句, were/had/should提前
Had you not helped us, we could not have made such a great achievement. 如果你之前没有帮我们，我们不可能取得如此成就。
Had they known the the sixth price will bring disasters, they might have had him killed. 如果他们之前知道
insist, command, order, demand, requist, require, suggest, advise, propose, recommend ，should加动词原型，should可省略
I suggest that you (should) follow your father's advice. 我建议你听从你爸的意见
I insist that he should change his strategy. 我坚持他应该改变战略。
It is required that she marry the old man. 她被要求嫁给老男人。
My suggestion is that you be there on time. 我的建议是你准时到那里。
suggest意思不是建议而是表明，暗示时，不虚拟
Are you suggesting that I am lying? 你在表明我说谎呢？
insist意思不是坚持做而是坚持说时，不虚拟
He insisted that he did not cheat, 他一直坚称自己没作弊。
与过去事实相反，表对过去事情的遗憾，用had done
I wish I had brought a house earlier. 我真希望自己早一些买房！
与现在事实相反，从句did/were
I wish he would answer my email. 我希望他回我的电子邮件。
将来的主观愿望，从句would do
I wish the economy would get better. 我希望经济将来会变好。
I wish you be quiet. 我希望你安静点。
If only she didn't drive so fast. 如果他没有开那么快就好了。
as if/as though有时不是虚拟
He acts as if he knew you. 他表现得好像他知道你。
Don't treat the baby as if he was made of steel. 别把孩子像铁孩子一样粗鲁的对待。
It sounds as if she has been really ill. 不是虚拟
would rather 表将来或现在，谓语动词过去时；表过去，谓语动词用过去完成时
I would rather he came tomorrow 我希望他明天到
I would rather he had been here yesterday. 我宁愿他昨天就到了。
it's time+从句
it's (high/about) time+that从句, that可省略，从句一般用一般过去时或should+动词原型
It's time that you should leave here. 到时间了，你该离开这里了。
it is +形容词
It is strange that we could be good friends. 很奇怪的是，我们成了好朋友
