初中英语基本有三种句法：陈述句（含肯定、否定、疑问、感叹）、祈使句、虚拟句。示例如下：
陈述语气:用来陈述一个事实，或提出一种看法，有肯定否定疑问感叹等形式。
There are two sides to every question.每个问题都有两个方面。
I'm not interested in what you said. 我对你说的话不感兴趣。
Have you ever been to France? 你去过法国吗？
（感叹句主要是指由what和how引导的感叹句）
How beautiful you are!你是多么美丽啊！
What a splendid palace(it is)! 多么华丽的宫殿啊!
祈使语气：用来表示请求、命令、警告等。(一般主语是you，但无需主语)
Stand up；Follow me；
Let’s have a talk. 我们谈谈吧。
Don’t jump in the queue. 不要插队。
虚拟语气：(虚拟句)就是一种说法，一种带有情感色彩的说法，是说话人的主观愿望或假想，不是客观存在的事实。它具有特殊的谓语结构。例如：
If I were you, I would study hard. 如果我是你，我会努力学习。
I wish I were a bird.我希望我是一只鸟。
虚拟句的用途:可用于表达假设、愿望、建议、要求或责备等情感类话语。多用于各类从句中。一般情况下，虚拟句的应用往往是伴随着一些特定的单词，例如： If、wish、Were、would、would rather、only if、advise、suggestion、inportant…等，可以归纳十余种句型。我们平时如果见到would，should，或were，if，wish等虚拟词，那可能就是虚拟句了。学习时要结合具体例句去认识规律，进行理解和记忆。
怎样理解虚拟语气：虚拟句主要就是通过谓语动词和情态动词的特定形式来表达的。也是由if、wish等具有特定意义的单词来构造而成的。在这类复合句中，主句和从句都有特定的动词形式，以体现不同的时间和条件。下面我们详细总结一下。
虚拟句一般都是复合句，其中从句的时态，要按“后退一步法”来确定，就是要将时态后退一步，《现在时退一步是过去时；过去时退一步是过去完成时；将来时退一步可认为是过去将来时》。主句的时态也要根据实情有特别规定。所谓的与事实相反，就是说主句所表达的愿望与事实相反。
▲举一例：在一个多云的天气，小明没带伞就步行去了海边钓鱼，突然下雨了，小明打电话给小亮，要他赶快开车来接他回家，电话中小亮抱怨小明说：“如果是我，我就带把伞。”（If it were me, I would take an umbrella）这就是虚拟句。主句表达的愿望是带把伞，这就是与小明没带伞的事实相反。另外，通话时就相当于“现在”，所以按后退一步法处理从句时态，从句的谓语动词就要用过去式did（be用were），因主句和从句的时态一致，主句的谓语要用would (could, should, might) +do。
▲请注意常规约定：用do表示相关动词的现在式（原形）；did表示动词的过去式；done表示动词的过去分词；括弧内的英文表示可以省略；▲为警示注意要点。
一、IF条件状语从句中
这共有三种情况：与现在事实相反；与过去事实相反；与将来事实可能相反。
1、与现在事实相反：
从句谓语：did（或were） 。主句谓语：would (could, should, might) +do。
If I were you, I would take an umbrella. 如果我是你，我会带把伞。(现在没带伞)
If I knew her number I could ring her up. 要是我知道她的电话号码，我就可以给她打电话了。
If he were here, everything would be all right.如果他在这儿，一切都会好的。
2、与过去事实相反：
从句谓语： had done 。主句谓语：would (could, should, might) +have done。
If I'd left sooner，I'd have been on time. 要是我早点动身，我就准时到了。（没准时到）
If I had got there earlier, I should(或could) have met her. 如果我早到那儿，我就会见到她。
3、与将来事实可能相反：
从句谓语：did； should ＋do；were to＋do。主句谓语：would (could, should, might) +do。
If he went，would you go too? 如果他去，你也去吗? （不想去）
If it were fine tomorrow,I would plant trees. 如果明天天气好，我就种树。
If it were to rain,I would not go out. 如果下雨，我就不出去了。
If I were to go to the moon one day, I could see it with my own eyes.
如果有一天我去月球，我可以亲眼看到它。
If it should rain tomorrow, we would stay at home. 如果明天下雨，我们就呆在家里。
If I should see him, I would tell him. 万一我见到他，我就告诉他。
▲注意：要表达与将来事实可能相反的情况，从句谓语可用三种情况： did或were to+do或should+do。但did应用较少，did主要用于与现在事实相反的情况。应用较多的是其它两种句法，要表达与将来情况相反，were to与should都可译为“万一”或“如果”，它俩作用相似，有时可相互替代，但也有区别，were to 一般用于与实际完全相反的假设，多译为如果，而should较委婉一些，多译为万一，should用的较多，它还可用于其他的虚拟句中，它还有表示责备和遗憾的用法。
▲注：If虚拟句的从句中绝对不能出现would。在If虚拟句中主句谓语一般都用would+do或would+had+done，如果主句有情态意义，可把would改为could, might, should。（would=将要；could=能；might=可以；should=应该）
▲当从句中有“should+do”时，主句也可用陈述语气或祈使语气。如：
If I should see him, I will tell him. 万一我见到他，我就告诉他。
If it should rain tomorrow, don’t expect me. 万一明天下雨，就别等我了。
▲当IF从句部分含有were, should, 或had, 可将if省略，再把were, should或had 移到从句句首，形成倒装。
If they were here now, they could help us.= Were they here now, they could help us.如果他们现在在这里，他们可以帮助我们。
If you had come earlier, you would have met him.=Had you come earlier, you would have met him.如果你来得早一点，你就会见到他了。
If it Should rain, the crops would be saved.=Should it rain, the crops would be saved.如果下雨，庄稼就会得救。
▲真实条件句中没有should和would，只可有shall或will，如：If you go now, you will see him. 如果你现在去，你将见到他。其中，从句是一般现在时，主句是将来时。（非虚拟句）
二、wish 后宾语从句中（虚拟语气中可省略that，非虚拟时不可省略)
与事实相反(不同)，这里要看从句，因为是宾语从句，主句包含着从句。
1、表示与现在事实相反的愿望，从句谓语：did 。
I wish（that）I had your brains.我希望我有你那样的头脑。
I wish I were as tall as you.我希望和你一样高。
2、表示与过去事实相反的愿望，从句谓语：had+done或would(could)＋have＋done。
I wish I had known the truth of the matter. 我希望我那时就知道这件事情的真相。
He wished he hadn't said that. 他希望他没讲那样的话。
I wish you could have come to my birthday party. 我真希望你能来参加过我的生日聚会。
3、表示将来难以实现的愿望，从句谓语：would(could,might,should)+do
I wish I should have a chance again.我希望我还能有一次这样的机会。
I wish it would rain tomorrow. 我希望明天下雨就好了。
（wish可按当时时态，从句的时态只与从句所指的时间有关，与wish的时态无关。)
三、名词性从句中：（主语从句，宾语从句，表语从句，同位语从句）注意：如下这些从句中的虚拟语气中不应有would,must, could等。在表示命令、建议、要求、惊叹时的名词性从句中需用虚拟语气。当不特别强调情感时，从句可以用陈述语气。
1、主语从句中的虚拟句：主要有三种情况。
①句型：It is+形容词+ that …。从句谓语：should＋do。should可省。
It is important that we should speak politely.我们说话要有礼貌，这是很重要的。（形容词）
It is a surprise that he should not come. 很奇怪,他竟没有来。（名词）
用于此句型的形容词或名词有：necessary, desirable, imperative, good, right, wrong, better等。
②句型：It's +过去分词+ that …。从句谓语：should＋do。Should不可省。
It is desired that this rule should be brought to the attention of the staff.
希望这条规则引起全体职员的注意。（动词过去分词）
用于此句型的动词过去分词有：suggested, settled, proposed, requested等等。
③句型：It's a pity that …。从句谓语：should＋do；should＋have+done。Should一般不省。
It is a pity that she should fare so badly. 她的遭遇如此糟糕，真可惜。
It's a pity that he should have failed the exam. 他考试竟没及格，真是遗憾。
It's a pity that he failed the exam. 他考试没及格，很遗憾。(也可用陈述句，非虚拟无情感)。
2、宾语从句中的虚拟句：（wish后的宾语从句略）
在表示坚持、命令、建议、要求等几类动词后的宾语从句要用虚拟语气。从句的谓语都是：should+do。should可省。
这四类动词有人归纳为：一个坚持(insist)；两个命令(order, command)；三个建议(advise, suggest, propose)；四个要求(demand, require, request, ask)。示例如下：
He insisted that I (should) go with them. 他坚持要我同他们一起去。
He ordered that it (should) be sent back. 他命令把它送回去。
The doctor advised that he (should) not smoke. 医生建议他不要抽烟。
He asked that I (should) appear.他要求我出场。
I propose that we should hold a meeting tonight. 我建议我们今晚开个会。
Mother insisted that John (should) go to bed at 9 o’clock. 母亲坚持要约翰九点钟上床睡觉。
3、同位语从句中的虚拟句：谓语动词： should+do。Should可省。
某些名词后的同位语从句：如decision决定, demand要求, desire愿望, insistence坚持, order顺序, suggestion建议, recommendation, request等名词，需要用虚拟语气。
The suggestion that he (should) be invited was rejected. 邀请他的建议被拒绝了。
4、表语从句中的虚拟句：
①在advise忠告、decision决定、demand要求、idea想法、plan、necessity等名词做主语时（主+系+that表），表语从句常用虚拟句。谓语动词：should+do。should可省。
Their demand is that their wages (should) be increased. 他们的要求是增加工资。
②as if／as though好像（可互换）引导的表语从句：从句谓语：did；had+done。例如：
He looks as if he were old. 他看起来好像老了。
I felt as if he had been tired yesterday. 我觉得他昨天好像很累。
It looks as if we will be late.我们似乎要迟到了。（当今英语as if也可用于陈述句。）
▲注意：在名词性从句中绝不可以出现would,must, could等；上述名词性从句中的should大都可以省略，只有在主语从句的②③类型中，should不可省略。在名词性从句的虚拟语气中That不能省略。
四、定语从句中：虚拟句仅此一种形式：It is time(about time，high time)that …。从句谓语：did；should+do。（Should不可省）。（定语从句中的that多可省略）
例如：
It is time I went home now.；It is time I should go home now.我该回家了。
time前有时有about和high修饰：例如：It’s high time we left.我们早该动身了。
▲若变（It is time I went home now. 我该回家了。）为陈述句如下：
可使用现在时：It is time I go home now.或使用将来时：It is time I will go home now.
五、部分状语等从句及常见应用中：（以下为阅读）
1、would rather(宁愿)此为常用结构，可引导宾语状语从句等：从句谓语：did；had+done。
即：现在与将来的情况用did，过去的情况用had+done。（I would rather=I’d rather）。
I would rather you did this instead of me. 我宁愿你做这件事而不是我。
I’d rather you posted the letter right away. 我宁愿你马上把这封信寄出去。
I’d rather you had returned the book yesterday. 我宁愿你昨天就还书了。
I would rather watch TV at home than go to the cinema.
我宁可在家看电视而不愿去看电影。（would rather…than用于比较）
也可直接使用：I would rather stay at home.我宁愿呆在家里。
He’d rather work in the countryside.他宁可到农村去工作。（非虚拟句would rather do）
2、介词Without（没有）引导的条件状语从句。主要用于表达与事实相反的假设。
主句谓语：（现在、将来）would（could，should，might）do；（过去）would (not) have done。
Without air, man couldn’t exist on the earth.没有空气，人类就不能在地球上生存。
Without your help, I would have failed the exam.如果没有你的帮助，我就不能通过考试。
3、副词otherwise（否则）引导条件状语从句。主句谓语：would（could，should，might）do。
I am not you, otherwise I would take the job.我不是你，否则我会接受这份工作。
4、before（早于）引导的时间状语从句也可虚拟。（表示：宁可…也不…）主句谓语：would+do。
He would die before he lied. 他宁死也不会撒谎。
5、Even if（即使）引导的条件状语从句：从句谓语：had+done；主句谓语：would +have+done。
Even if he had been ill, he would have gone to his office. 即使生了病，他都去办公室。
6、as if／as though（好像）引导的方式状语从句：从句谓语：did；had+done。例如：
He acts as if he knew me. 他显得认识我似的。（与as though可互换）
He talks as if he had been abroad. 他说起话来好像曾经出过国。（过去用had+done）
7、in order that或so that（以便）引导目的状语从句：从句谓语：could（might，should）+do
Mr green spoke slowly so that his students could (might) hear clearly.
格林先生说得很慢,好让学生听清楚。
8、某些过去分词短语引起虚拟。从句谓语：done；主句谓语：would have done。
Given more time, I would have done it better. 如果给我更多的时间，我会做得更好。
9、非真实条件状语形成的虚拟。从句谓语：had done；主句谓语：would have done。
He would have given you more help, but he had been so busy.
他本来会给你更多的帮助，但他太忙了。
10、对过去的事表示责备引起虚拟。主句谓语：should have done。
You should have been here five minutes ago. 你五分钟前就该来了。
11、but, but for, but that, 引起的短语或句子常暗含着虚拟条件。
I would be most glad to help you, but I am busy now. 我很乐意帮助你，但是我现在很忙。
But for your cooperation， I couldn't have done it. 如果没有你的合作，我是做不到的。
But that she was afraid, she would have said no. 如果不是她害怕，她会说不。
12、（若不是）If it were not for；If it had not been for；but for；without，引导虚拟四者意义相同，可以互相替代，后面的主句也需虚拟。
If it were not for his help, I wouldn’t go home now. 如果没有他的帮助，我现在不会回家。
but for his help, I wouldn’t go home now. 要不是他的帮助，我现在不会回家。
六、部分日常习惯的虚拟含蓄条件句：
1、有些虚拟条件隐藏在短语或连词中；或隐藏在上下文中；或已成为习惯说法；或用于简单句。
What would I have done without you? 如没有你，我会怎么办呢？
It would be easier to do it this way. 这样做会比较容易。
You might stay her forever.你可以永远待在这儿。
We would have succeeded.我们本来是会成功的。
You wouldn’t know.你不会知道。
I would like to come.我愿意来。
I wouldn’t have dreamed of it. 这是我做梦也不会想到的。
2、由Lest以免，In case以防，For fear that生怕，引导的目的状语从句，是虚拟句，都有为了“避免”的意思，虽意义略有差别，但用法相似。从句谓语： should +do 。should可省。
He started out earlier lest he should be late.他很早就出发了以防迟到。
Keep quiet in case you interrupt him.安静点，免得打扰他。
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。
3、①某些习惯表达（建议告诫愿望do）；②意外，惊异；③句首may+do表示祝愿，但愿；④动词原形也可表达虚拟；⑤有时用would并非虚拟句，只为礼貌。
①You'd better set off now.你最好现在就出发。
①I'd rather not tell you the secret.我情愿不告诉你这个秘密。
①It would be better for you not to stay up too late.你最好别熬夜到很晚。
②Why should you be so late today?你今天怎么会迟到呢？
②How should I know?我怎么知道呢？
②Why should it matter to you?这跟你有啥关系？
③May good luck be yours!祝你好运！
③May you be happy!祝你快乐！ （may+do）
③May you do even better!祝你取得更大成就！
④Long live the people! 人民万岁！(动词原形)
④“God bless you,” said the priest.牧师说：“愿上帝保佑你！”
⑤Would you show me the way to the post office? 你能告诉我去邮局的路吗？
▲在初中英语虚拟句中，would通常表示一种假设或愿望，而不是过去式的will。
would多出现于主句中。在虚拟语气中，should通常用于第一人称，would可用于任何人称，同时也可根据意思用情态动词could（表示可以），might（表示可能），should（表示应该）。
should和would的使用有一定的规律。一般来说，should多用于从句，表示一种道德上的义务或建议；而would则多用于主句，表示一种可能性或结果。