1. 在 lest ，for fear that( 以免) ,in case(以防)引导的目的状语从句中的虚拟语气
She walked quietly lest she (should)wake up her roommates. 她走得很轻以免吵醒她的室友。
2. 表应当做 值得做 一类动词后的宾语从句
建议advise, suggest, propose, recommend命令order, command
请求ask, demand, require, request指示direct
督促urge提议move, vote
希望desire坚持insist
打算intend安排arrange
例如：
I insisted that he (should)stay. 我坚持要他留下。
He urged that they go to Europe. 他督促他们到欧洲去。
He suggested that we shouldleave early. 他建议我们早点动身。
He ordered that it (should)be sent back. 他命令把它送回去。
I ask that he leave. 我要求他走开。
He requires that I (should)appear. 他要求我出场。
I move that we accept the proposal. 我提议通过这项提案。
He arranged that I should go abroad. 他安排我去国外。
She desires that he do it. 她希望他做此事。
The general directed that the prisoners should be set free. 将军指示释放那些俘虏。
*suggest表“暗示”insist表“坚持说”时不用虚拟语气
比较：
He insisted that Ihad read his letter. 他坚持说我看过他的信。
He insisted that I should read his letter. 他坚持要我看他的信。
He suggested that we (should) stay for dinner. 他建议我们留下吃饭。
I suggested that you had a secret understanding with him. 我觉得你与他心照不宣。
3. order,suggestion,idea,plan, proposal, advice, demand等名词后的表语从句或同位语从句
Our suggestion is that you（ should）be the first to go． 我们的建议是你应该第一个去。
4.*advice, agreement, command, decision, decree, demand, determination, indication, insistence, order, preference, proposal, request, requirement, stipulation, suggestion, idea, plan, order
l “It is (was) 紧急 重要-- 带感情色彩
上述demand/suggest等动词过去分词 或
important,natural,strange ,necessary，surprised, appropriate等形容词 后的主语从句
1. It is ordered that the army (should) get there by 4 .
2. It is necessary that she (should) be sent there at once.
注：*It is necessary，important，strange，natural， advisable, anxious, compulsory, crucial, desirable, eager, essential, fitting, imperative(绝对必要), impossible, improper, obligatory, possible, preferable, probable, recommended, urgent, vital etc. ；it is a pity；It is requested/suggested/desired/proposed
虚拟语气三个基本句型
1、提出将来会发生的事：主句：主语＋would/should/might/could＋动词原形；
从句：should＋动词原形/were to＋动词原形；
2、提出现在的条件： 主句：主语＋would/should/might/could＋动词原形；
从句：动词过去式；
例句：If he studied at this school, he would know the enviornment around the school very much.
3、提出过去的未发生的条件：主句：主语＋would/should/might/could have＋动词过去分词
从句：had＋动词过去分词
例句： If I had read the book, I would have told you about ：
与现在事实相反：If I were you, I would go there tomorrow.
与现在事实相反：If he came to the party, I wouldnt come.
与过去事实相反：If she had been there, she would have met Jack.
与将来事实相反：If it were to rain tomorrow, they couldnt go for an outing.
与将来事实相反：If they should attend the meeting, we might get more support from them.
参考资料来源：百度百科-虚拟语气
虚拟语气顺口溜解释
虚拟语气顺口溜：一坚持，二命令，三建议，四要求。这些情况下，虚拟语气中的should可以省略。if条件从句虚拟语气 口诀：过去了，就原了；过完了，就完了；过去了，也原了 与现在相反：从句用过去时态，主句用would，should，could，might 动原。 口诀：过去了，就原了。 与过去相反：从句用过去完成时态，主句用would，should，could，might have PP。 口诀：过完了，就完了。 与将来相反：从句用过去时态，主句用would,should,could,might 动原。 口诀：过去了，也原了。 说明：原指用动词原形；完指用动词完成时态。 虚拟语气省略should 口诀：一坚持，二命令，三建议，四要求 口诀解释： 一坚持指的是insist， 二命令指的是order、command， 三建议指的是suggest、advise、recommend， 四要求指的是ask、demand、request、require。
