虚拟语气表示说话人的愿望、假设、猜测或建议,而不表示客观存在的事实。虚拟语气通过谓语动词的特殊形式来表示。下面分别介绍虚拟语气在各种句式中的用法。

　　虚拟语气用于表语从句、同位语从句做advice, idea, order, demand, plan, proposal, suggestion, request 等名词的表语从句和同位语从句,其谓语动词要用虚拟语气的结构"(should)+动词原形"。

　　例如:

　　We all agreed to his suggestion that we (should)go to Beijing for sightseeing.

　　My idea is that he (should) do exercises first.

　　虚拟语气用于以as if(as though)引导的表语从句或状语从句

　　如果从句表示与现在事实相反,谓语动词用一般过去时;表示与过去事实相反,谓语动词用"had+过去分词";表示与将来事实相反,谓语动词用"would(might, could )+动词原形"。例如:

　　He looked at me as if I were mad.

　　He speaks English so fluently as if he had studied English in England.

　　It looks as if it might rain.

　　但as if(as though)后的从句也常用陈述语气,这是因为从句中的情况往往是可能发生的或可能被设想为真实的。例如:

　　It looks as if our side is going to win.

　　虚拟语气用于主语从句

　　在主语从句中,谓语动词的虚拟语气结构用"should+动词原形"的结构,表示惊奇、不相信、惋惜、理应如此等。例如:

　　It is necessary (important, natural, desirable, advisable, strange, etc.) that we should clean the room every day.

　　It was a pity (a shame, no wonder, etc.) that you should be so careless.

　　It will be desired (suggested, decided, ordered, requested, proposed, etc.) that she should finish her homework this afternoon.

　　在上述主语从句中,should意为"应该"、"竟然",可以省去,但不可换用would。主句所用动词的时态不限。

　　注意:这种从句表示的是事实。如果说话人对这种事实表示惊奇,就可用虚拟语气。反之,如果不表示惊奇,that从句也可用陈述语气。例如:

　　It is strange that he did not come yesterday.

　　It is a pity that you can't swim.