1. 目的状语从句中的虚拟语气
(1) 在for fear that, in case, lest引导的目的状语从句中，若用虚拟语气时，从句谓语为： should + 动词原形。并且 should不能省略
She examined the door again for fear that a thief should come in. 她又把门检查了一遍，以防盗贼的进入。
He started out earlier lest he should be late. 他很早就出发了以防迟到。
(2) 在so that, in order that所引导的目的状语从句中，从句中的谓语为： can / may / could / might / will / would / should + 动词原形。如(from www.yygrammar.com)：
He goes closer to the speaker so that he can hear him clearer. 他走近说话的人以便能挺得更清楚。
He read the letter carefully in order that he should not miss a word. 他把信读得很仔细以便不漏掉一个单词。
2. 让步状语从句中的虚拟语气
(1) 在even if, even though 所引导的让步状语从句中，可用虚拟语气，主句、从句的结构与if所引导的条件从句结构相同。如：
Even if he were here himself, he should not know what to do. 即使他亲自来也不知该怎么办。
Nobody could save him even though Hua Tuo should come here. 即使华佗在世也救不了他。
(2) 在whatever， whichever，whenever，whoever, wherever，however, no matter wh-word 等引导的让步状语从句中，从句虚拟语气结构为：
① may +动词原形(指现在或将来)。如：
We will finish it on time no matter what / whatever may happen. 不管发生什么事，我们都要按时完成。
We will find him wherever / no matter where he may be. 无论他在哪里，我们都要找到他。
I will wait for him no matter how late he may come. 不管他来的多么晚，我都会等他。
② may +完成式(指过去) ，主句结构不限。如：
You mustn’t be proud whatever / no matter what great progress you may have made. 不管你取得了多么大的进步，你也不能骄傲(from www.yygrammar.com)。
We must respect him no matter what / whatever mistakes he may have made. 不管他翻过什么错误，我们必须尊敬他。
(3) 在though, although等引导的让步状语从句中，从句虚拟语气结构为 should +动词原形，主句结构不限。如：
Although / Though he should often be late, he is a good student. 尽管他经常迟到，他还是个好学生。
Although / Though he should be secretary, he must obey the rules. 尽管他是书记，他也必须遵守规定。
3. 方式状语从句中的虚拟语气
as if, as though引导的方式状语从句常用虚拟语气。虚拟语气的结构为：
表示所发生的时间虚拟语气结构
发生在主句动作之前had + 过去分词
与主句动作同时发生过去时(be 用were )
发生在主句动作之后would / could / might / should+原形动词
例如：
They began to talk warmly as if they had known each other for long. 他们开始热烈的谈论起来就好像他们已相互认识很久了。
He coughed twice as if someone should come. 他咳嗽两声就好像有人要来了。
4. 原因状语从句中的虚拟语气
amazed, angry, annoyed, astonished, disappointed, frightened, happy, pleased, proud, sorry, surprised, upset等后面的状语从句中常用虚拟语气。其虚拟语气的结构为：
① should + 原形动词(指现在或将来)。如：
He was angry that you should call him by name. 他很生气，你竟然对他直呼其名。
I was astonished that he should not answer such an easy question. 我很惊讶他竟答不出如此简单的问题。
② should + 完成式, 指过去。如：
I’m very sorry that you should have failed the exam. 我很遗憾，你这次考试竟然失败了。
I was very surprised that Father should have known what I did yesterday. 我很吃惊，父亲竟指导我昨天所作的事情(from www.yygrammar.com)。
From:https://www.zgghmh.com/CET-6/20007556.asp