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公共英语五级写作语法解析
引言：公共英语五级是全国公共英语等级考试(PETS)五个级别中的最高级，相当于我国大学英语专业二年级结束时的水平。针对备战公五的小伙伴们，小编教大家如何突破语法。
一、虚拟语气
1.概念
虚拟语气用来表示说话人的主观愿望或假想，所说的是一个条件，不一定是事实，或与事实相反。
2.在条件句中的应用
条件句可分为两类，一类为真实条件句，一类为非真实条件句。非真实条件句表示的是假设的或实际可能性不大的情况，故采用虚拟语气。
二、真实条件句
真实条件句用于陈述语气，假设的情况可能发生，其中if是“如果”的意思。
时态关系
句型：条件从句+主句 一般现在时：shall/will + 动词原形
If he comes, he will bring his violin.
典型例题
The volleyball match will be put off if it ___.
A. will rain B. rains C. rained D. is rained
答案B。真实条件句主句为将来时，从句用一般现在时。
注意：
1) 在真实条件句中，主句不能用be going to表示将来，该用shall, will.
(错) If you leave now, you are never going to regret it.
(对) If you leave now, you will never regret it.
2) 表示真理时，主句谓语动词便不用shall (will) +动词原形，而直接用一般现在时的动词形式。
三、非真实条件句
时态：可以表示过去，现在和将来的情况。它的基本特点是时态退后。
a.同现在事实相反的假设。
句型：条件从句+主句
一般过去时：should(would)+动词原形
If they were here, they would help you.
b.表示于过去事实相反的假设。
句型：条件从句+主句
过去完成时：should(would)have+ 过去分词
If she had worked harder, she would have succeeded.
The rice would not have been burnt if you had been more careful.
If my lawyer had been here last Saturday, he would have prevented me from going.
If he had come yesterday, I should / would have told him about it.
含义：He did not come yesterday, so I did not tell him about it.
If he had not been ill and missed many classes, he would have made greater progress.
含义： He was ill and missed many lessons, so he did not make greater progress.
c.表示对将来的假想
句型：条件从句+主句
一般过去时：should+动词原形/were+不定式/would+动词原形/should+ 动词原形
If you succeeded, everything would be all right.
If you should succeed, everything would be all right.
If you were to succeed, everything would be all right.
四、混合条件句
主句与从句的动作发生在不同的时间，这时主，从句谓语动词的虚拟语气形式因时间不同而不同，这叫做混合条件句。
If you had asked him yesterday, you would know what to do now.
(从句与过去事实相反，主句与现在事实相反。)
If it had rained last night (过去), it would be very cold today (现在).
五、虚拟条件句的倒装
虚拟条件句的从句部分如果含有were、should、或had可将if省略，再把were、should或had移到从句句首，实行倒装。
Were they here now, they could help us.
=If they were here now, they could help us. Had you come earlier, you would have met him
=If you had come earlier, you would have met him.
Should it rain, the crops would be saved.
=Were it to rain, the crops would be saved.
注意：
在虚拟语气的从句中，动词“be”的过去时态一律用“were”，不用was，即在从句中be用were代替。
If I were you, I would go to look for him.
如果我是你，就会去找他。
If he were here, everything would be all right.
如果他在这儿，一切都会好的。
典型例题
_____ to do the work, I should do it some other day.
A. If were I B. I were C. Were I D. Was I
答案C. 在虚拟条件状语中如果有were, should, had这三个词，通常将if省略，主语提前, 变成 were、should、had+主语的形式。但要注意，在虚拟条件状语从句中，省略连词的倒装形式的句首不能用动词的缩略形式。如我们可说 Were I not to do，而不能说 Weren’t I to do.
六、
besides
except
except for
except that
but
but for besides除t know Peter except that hes an Japanese.
Theres nothing but a chair in the room.
But for your help，I wouldnt have finished my homework.
注意：
(1)形容词最高级前要用the，而副词最高级前的the可省。
(2)下面这些词的比较等级可在后面加-er/-est或在前面加more/most构成。
cruel， often， able， clear， clever， correct， dear， free， friendly， happy， handsome， likely， lively， pleasant， right， simple， quiet， solid， strange， strict， stupid， wrong， etc.
形容词、副词比较等级常用的句型及用法：
类别 用法及意义 句型结构 例句
原级 没有比较 very / so / quite / too， etc. +原级 It was very warm yesterday.
二者比较程度相同 as+原级+as+比较对象 You are as clever as Mike.
一方是另一方的几倍 ...times as+原级+as+比较对象 This bridge is five times as long as that one.
二者比，程度不同 ...not as+原级+as+比较对象 You are not as tall as he.
二者比，前者不如后者 ...not so+原级+as+比较对象 Math isnt so hard as physics.
比 较 级 二者比，一方比另一方更re younger than Tom.
二者比，A比Bs much hotter today than it was yesterday.
A比B甚至还要s still stronger than Jack.
Hes far older than you.
表越来越s getting fatter and fatter.
A比B(高，长s getting healthier and stronger than his brother.
表比s less rich than he.
表与其说，不如s more than a teacher.
Shes more than tired.
表并不比某某s no taller than you.
最高级 三者或三者以上比较某某最s one of the best students in this class.
第几大/长s a letter for you.
用于指初次提到某人/物 She has a dog.
指某类物或人中的任何一个 A horse runs fast.
用在不可数名词前表一次/场/或一个/种人或物 I would like a coffee.
用于时间、度量衡名词前表每一 He has two meals a day.
用于某些习惯用语或固定词组中 as a result，have a rest
have a chat，in a hurry
have a word with sb.
a little，a lot，a pair of
a cup of，a great deal of.
七、Your boyfriend told you.
过去将来时态 should+v.原/would+v.原表过去预计将要发生的动作或存在的状态。常用于从句或引语中 常用于状语从句、名词性从句或间接引语中。 She said she would vote for me.
She said she wouldnt vote for me.
were/was going to+v.原表过去即将发生或打算要做 She said it was going to rain soon.
was/were+v.-ing表过去的计划，安排 I wondered when the plane was arriving.
was/were about to+v. 原表过去即将，就要 I was about to go out when the phone rang.
was/were to+v.原表过去的计划决定，要求命令等 He told us they were to hold a meeting the next day.
现在进行时态 说话时正进行的动作 now， at present， these days，
this morning / week / month， during this season， Look! Listen! etc.
always， constantly， frequently， all the time He is playing basketball now.
现阶段正进行的动作 Im writing a book these days.
表计划安排好的将来动作 Shes flying to Paris tomorrow.
八、名词性从句
概念
在句子中起名词作用的句子叫名词从句 (Noun Clauses)。 名词从句的功能相当于名词词组, 它在复合句中能担任主语、宾语、表语、同位语、介词宾语等，因此根据它在句中不同的语法功能，名词从句又可分别称为主语从句、宾语从句、表语从句和同位语从句。
引导名词性从句的连接词 引导名词性从句的连接词可分为三类：
连接词：that、whether、if不充当从句的任何成分)
连接代词：what、whatever、who、whoever、whom、whose、which.
连接副词：when、where、how、why
不可省略的连词
1. 介词后的连词
2. 引导主语从句和同位语从句的连词不可省略。
That she was chosen made us very happy.
We heard the news that our team had won.
比较：whether与if 均为“是否”的意思。 但在下列情况下，whether不能被if 取代：
1. whether引导主语从句并在句首
2. 引导表语从句
3. whether从句作介词宾语
4. 从句后有“or not”
Whether he will come is not clear.
大部分连接词引导的主语从句都可以置于句末，用it充当形式主语。
It is not important who will go.
It is still unknown which team will win the match.
九、名词性that-从句
1)由从属连词that引导的从句叫做名词性that-从句。That只起连接主句和从句的作用，在从句中不担任任何成分，本身也没有词义。名词性that-从句在句中能充当主语、宾语、表语、同位语和形容词宾语，例如：
主语：That he is still alive is sheer luck.他还活着全靠运气。
宾语：John said that he was leaving for London on Wednesday.约翰说他星期三要到伦敦去。
表语：The fact is that he has not been seen recently.事实是近来谁也没有见过他。
同位语：The fact that he has not been seen recently disturbs everyone in his office.
近来谁也没有见过他，这一事实令办公室所有的人不安。
形容词宾语：I am glad that you are satisfied with your job. 你对工作满意我感到很高兴。
2)That-从句作主语通常用it作先行词，而将that-从句置于句末，例如：
It is quite clear that the whole project is doomed to failure.很清楚，整个计划注定要失败。
It’s a pity that you should have to leave.你非走不可真是件憾事。
用it作形式主语的that-从句有以下四种不同的搭配关系：
a.It + be +形容词+ that-从句
It is necessary that... 有必要……
It is important that... 重要的是……
It is obvious that... 很明显……
b. It + be + -ed分词+ that-从句
It is believed that... 人们相信……
It is known to all that... 从所周知……
It has been decided that... 已决定……
c. It + be +名词+ that-从句
It is common knowledge that... ……是常识
It is a surprise that... 令人惊奇的是……
It is a fact that... 事实是……
d. It +不及物动词+ that-分句
It appears that... 似乎……
It happens that... 碰巧……
It occurred to me that... 我突然想起……
十、名词性wh-从句
由wh-词引导的名词从句叫做名词性wh-从句。Wh-词包括who、whom、whose、whoever、what、whatever、which、whichever等连接代词和where、when、how、why等连接副词。
Wh-从句的语法功能除了和that-从句一样外，还可充当介词宾语、宾语补语和间接宾语等，例如：
主语： How the book will sell depends on its author.书销售如何取决于作者本人。
直接宾语：In one’s own home one can do what one likes.在自己家里可以随心所欲
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