一、虚拟语气用于主语从句中
在It is (was)important (necessary, desirable, imperative, advisable, incredible, urgent, possible, essential, natural, preferable, insistent, crucial, better, best, ridiculous, vital) that…能及It is (was) a pity (shame, wonder, must, suggestion, proposal, requirement, request, desire, order, recommendation) that….,It is (was)desired (arranged, decided, ordered, proposed, requested, recommended, suggested, settled) that…等句型的主语从句中，其谓语用“should+动词原形(其中should可以省略)”来构成虚拟语气。
例：It is important that we (should)speak politely.
我们说话要有礼貌，这是很重要的。
例：It is essential that she these application forms be sent back as early as possible.
将这些申请表格尽快地反馈回来是很必要的。
二、 虚拟语气用于宾语从句中
当动词ask, arrange, beg, advise, command, deserve, direct,desire, demand,determine, move, prefer, propose, intend, request, require, suppose 等后面接宾语从句时，从句的谓语用”should+动词原形” 来表示虚拟语气。
例: The judge ordered that the prisoner(should) be remanded.
法官命令被告还押。
Mr.Chairman, I move that the money____for library books.
主席先生，我提议把那笔钱用来购买图书馆书籍。