一、虚拟条件句
条件状语从句是非真实情况，在这种情况下要用虚拟语气。
l-条件从句与现在事实不一致，句型为：If+主语十过去时，tiag+should (could，would，或might)+动词原形，例如：If l were you，1 would study hard.
2.条件从句与过去事实不一致，句型为：If+主语+had+过去分词，主语+should(could, would，或might)+have+过去分词，例如：If I had not studied hard.1would have failed in the exam last term
3.条件从句与将来事实不一致，句型为：lf+主语+should/were to+do，主语+should( could.)+原形do，例如：If l were to go to the moon one day,I could see itwith my own eyes.
注意：
1.If条件句中绝对不可出现“would”。
2-根据句中的时间状语，有时可能出现“混合虚拟”的情况，即主句可能是现在的情况，条件句也许是发生在过去的情况，但都遵守上述句型。
3.在条件句中如果出现were，had，should可省去if'
将这些词提前置于句首构成倒装，例如：w。re I to go tothe moon one clay,1 would see it with my own eyes.如果有一天我登上月球，我就可以亲眼目睹它的样子了。
二，名词性虚拟语气
在表示命令、建议、要求、惊叹的名词性从句中需用虚拟语气。基本句型为：主语+should+动词原形，例如：
1.Mother insisted that John (should) go to bed atnine o'clock(宾语从句)
2.It was required that the crops (should) be:harvested at once.(主语从句)
3.The suggestion that he (should) be invited wasrejected.(同位语从句)
4.That is their demand that their wages (should) bemcreased.(表语从句)
注意：在这种句子中绝不能出现“would”“must”
“could”等。
三、虚拟语气在一些特殊词中的使用或含蓄条件句
1.wish后的宾语从句。
与现在愿望不一致，用主语十过去时，例如：
I wi。hIwere you.
与过去愿望不一致，用主语+had+过去分词，例如：Iwish I had visited the White House whenI was in the States与将来愿望不一致，用主语+would (could)+原形。
2.It's time句型：当lt's tin】e后用that从句时应该为主i吾+should+动词原形或主语十过去时，例如：It，s time thatyou went to school.或It's time that you should go to schooL
3- If only引起的感叹句相当于“How I wish+宾语从句”。
(l)If only he could come.他要能来就好了。
(2)If only I had known the answer.我要早知道答案就好了。
4.WOuld rather，as if(though)引导的从句也需使用虚拟语气，表示过去的情况用过去完成时，表示现在与将来的情况用过去时，例如：
(l)I'd rather you posted the letter right away.
(2)She loves the children as if they were hers.
5.含蓄虚拟条件句含蓄条件句是指句中没有明显的虚拟条件句，而是利用其他手段来暗示存在虚拟条件。但是这类隐含式虚拟条件句往往都可以转化为if引导的条件句。常用来表示含蓄虚拟条件的手段有：
(1)介词或介词短语。如but for，but that，without,in case of, under more favorable condition等。
(2)连词。如so that, unless, in case, supposing,lest, provided(倘若……)，for fear that(唯恐)，in orderthat, on condition that, if only(要是……就好了)等。
注意：lest, for fear that和in case引起的从句中谓语动词多用should+动词原形，但也可以不用虚拟语气，而用动词的陈述语气形式。例如：The foreign teacher spokeslowly in case we misunderstood him这位外籍教师说得很慢以免我们误解。
(3)通过上下文及内在含义，句中往往有but,otherwise, unfortunately等类似转折词。
without, but. but for, otherwise引起的短语或句子常暗含着含蓄条件。例如：
①Without you,1 would never know him
②But for your oooperation, we wouldn't have done it
③But that she was afraid, she would have said no. .
④i would be most glad to help you, butI am busy now.
⑤I would have come to the party yesterday, but ljwas working.
⑥I am busy now, otherwise l would do you the favor!