It 作形式主语的四种结构
It作形式主语
It作形式主语和形式宾语，虽然是我们高中就学过的语法点，但在考研英语题型中，无论是在阅读还是翻译，常会考查该知识点。
一.it作形式主语。
英语中不定式、动名词、主语从句在作主语时主语往往显得很长，使整个句子看上去有点头重脚轻，这样就借助“it”来作形式上的主语，而把真正的主语移到句子后边去，使全句结构上前后平衡。
“it”并无实际意义。
It之后的谓语部分，可以是be+形容词，be+名词(词组)，或be+过去分词等。
it 作形式主语，主要分为下列三种情况：不定式作主语、动名词作主语和名词从句作主语。
具体分析如下：一、不定式作真正主语主要用于下列句型：1. It + is/was + adj./n.+ to do sth.A.名词作表语。
主要有a pity, a pleasure, an idea等。
It is a good idea to think this way. 这样考虑问题是个好办法除be外，其他动词也有跟名词的情况。
例如：It seems a pity to waste the food. 浪费这些食物真可惜。
B. 形容词或形容词短语作表语。
分两种情况：1.下列形容词；kind,good,nice,clever,wrong,right,foolish,wise,unwise,stupid,rude,careless,cruel,brave ,naughty,polite,selfish等词作表语时，不定式前常可加一个由of引起的短语，来说明不定式指的是谁的情况。
形容词表示不定式逻辑主语的特征，即形容词用来描述不定式行为者的性格、品行等。
例如：It was foolish of you to leave school.你中途退学，真是傻瓜。
2. 其他形容词作表语，常见的形容词有：necessary, hard，important, difficult, easy, possible，common等。
it作为形式主语
形式主语形式主语是动词不定式的一种,它也是逻辑主语, 可以把它归类到逻辑主语的第一种(不定式的逻辑主语) 用作宾语的不定式，用作目的状语，用作结果状语的不定式都是属于不定式的大概念里面的.形式主语： It +be+(the)+adj+for sb+to do sth.形式主语it作为形式主语的it并无实际语义，只是为满足语法上的需要，避免句子头重脚轻，它代替的是句子的逻辑主语，概括起来会有如下情况：1. 句子的逻辑主语为不定式如：It is very kind of you to give me a hand in time.It is my pleasure to address the meeting.It was pretty hard for him to bring up the child on his own.2. 句子的逻辑主语为从句如：It so happened that the tickets were sold out.It is extremely obvious that she has been lying about her identity.It suddenly occurred to me that the message must have been hiddenbetween the layers of the briefcase.3. 句子的逻辑主语为动名词短语这类句子远不如前面两种出现率高，主要在（no good, waste, useless, no use,dangerous）等词语的后面用如：It is no use reasoning with him.It is no good reading in dim light.作形式主语的代词只能用it ，不能用that，this等词。
例如:1) It is easier to lose friends than to make friends. 交朋友难而失去朋友比较容易。
“it”引导主语从句和“it”做形式主语还有强调句型的区别分别是什么？
“it”引导主语从句和“it”做形式主语还有强调句型的区别：it引导的主语从句，形式主语就是it，真正的主语在句子的后面，通常是to do的不定式短语。
而强调句的结构
it is/was+被强调部分+that/who+句子其余部分，结构词it is/was和that/ who都是没有实际意思的，只是构成句子结构的词而已。
这个强调句只能强调名词和代词，也就是主语和宾语，不能强调其他句子成分。
主语从句：It is kind of you to help me with my housework.
强调句：It is you who help me with my housework.
主语从句中it做形式主语的常见句型：It+be+形容词+主语从句，如：It is u ncertain whether he can come to Jenny’s birthday party or not. It + be + 名词词组+ 主语从句，这类名词有：a fact, a pity, a shame, an honour，a question等，如：
It’s a pity that you missed the exciting football match.
It remains a question whether he will come or not.
It + be + 过去分词+ 主语从句，这类过去分词有：announced, believed, expected, hoped, decided, reported, said, shown等，如：It is reporte that 16 people were killed in the earthquake.。
it作形式主语和宾语的几种结构
“It”作形式主语和宾语It作形式主语和形式宾语用法，是中学阶段英语学习的主要语法项目之一。
纵观历届高考题，无论是单项选择，还是完形填空，it用法始终是反复考查的重、热点之一。
现将it在特殊句型中作形式主语和形式宾语用法，进行如下归纳分析。
一、It 用作形式主语当不定式（短语）、动名词（短语）或从句在某个句子中作主语时，为保持句子结构前后平衡，避免头重脚轻，因此常用it作形式主语置于句首，而将真正的主语放在句尾。
此时it只起先行引导作用，本身无词义。
e.g. It is wrong to tell a lie.(说谎是错误的。
) 〔It为to tell a lie的形式主语〕It is no use arguing about it.(争吵是没用的。
) 〔It为arguing about it的形式主语〕It is uncertain who will come.(谁要来还不确定。
) 〔It为who will come的形式主语〕It 作形式主语的常见句型：① It + be + 形容词+ to do sth. / doing / that ….e.g. It is very important to learn a foreign language.(学一门外语非常重要。
)It is useless crying over the spilt milk.(覆水难收。
)It was really surprising that she married a man like that.(她嫁给那样的男士真让人惊讶。
)② It + be +名词词组+ doing / that ….e.g. It is no good telling lies.(撒谎没好处。
)It is a pity that you didn’t go to see the film yesterday.(你昨天没看成那部电影真遗憾。
it做形式主语用法大全含练习及答案
It作形式主语常见句型动词不定式，动名词或主语从句作主语时，通常把它们放在谓语动词前，而用it作形式主语，放到句首，常见句型有：1. It + be + 形容词+主语从句，如：It is uncertain whether he can come to Jenny’s birthday party or not.2. It + be + 名词词组+ 主语从句，这类名词有：a fact, a pity, a shame, an honour，a question等，如：It’s a pity that you missed the exciting football match.It remains a question whether he will come or not.3. It + be + 过去分词+ 主语从句，这类过去分词有：announced, believed, expected, hoped, decided, reported, said, shown等，如：It is reported that 16 people were killed in the earthquake.It is not decided who will give the operation to the patient.4. It + 不及物动词(seem, appear, happen等) + 主语从句, 这类不及物动词有：appear, happen, seem等，如：It seemed that he didn’t tell the truth.It happened that I was out when he called.5. It + be + 形容词+ for sb.）+ 动词不定式这类句型常用形容词easy, difficult, hard, important, possible，wise等作表语，有时候为了强调不定式动作的执行者，常在不定式前加for sb，如：It’s necessary for the young to master two foreign language.It is unwise to give the children whatever they want.这类形容词有：easy, difficult, hard, important, possible，wise6. It + be + 形容词+ of sb. + 动词不定式，这类形容词常是表示心理品质,性格特征的形容词，如：kind, nice stupid, clever, foolish, polite, impolite, silly, selfish, considerate等。
it做形式主语的19个句型
1.It is/was + 被强调部分 + that/who ...之巴公井开创作该句型是强调句型。
被强调部分可以是主语，宾语，表语或状语。
强调的主语如果是人，that 可以由 who 换用。
如果把这种句型结构划掉后，应该是一个完整无缺的句子。
这也是判断强调句型与其它从句的方法。
2. It is not until + 被强调部分 + that ...该句型也是强调句型。
主要用于强凋时间状语，译成汉语“直到……才……”，可以说是 not ... until ... 的强调形式。
It was not until she took off her dark glasses that I realized she was a famous film star.= Not until she took off her dark glasses did I realize she was a famous film star.= I didn't realize she was a famous film star until she took off her dark glasses.3. It is clear /obvious/true/possible/cer tain… that …该句型中it 是形式主语，真正的主语是 that 引导的主语从句，常译为“清楚（显然，真的，肯定……）”是主语从句最罕见的一种结构。
It is very clear that he's round and tall like a tree. = That he's round and tall like a tree is very clear.4. It is important /necessary/right/strange/natural... that ...+(should) do该句型和上一个同属一个句型。
it作形式主语的典型句型
fast. 你
是很 的。
4. It be + 名词（形容词）+ doing sth.
it代替真正的主语----- 动名词（短 语 ），可
用于这类句型的名词或形容词有dangerous,
nice, foolish, worth, waste, no good, not any
good, no use,not any use等。例 如 ：
make frie n d s .失去朋友比交朋友更容易。
2. It be + 形 容 词 + of sb. + 动词不定式
(短语）
it代 替 真 正 的 主 语 — 动 词 不 定 式 （短
语)。动词不定式的逻辑主语是由介词of引起
的 ，形容词必须是能表示逻辑主语性格特点
的词。常见的有bad, brave,careless,clever,
unusual, rare,impossible, pleasant等。例 如 ：
① It is important for her to come to
the party. 能
很重 。
" I t is difficult for him to do the math
problem.
是 的。
③ It’s very dangerous for you to run so
。
" I t is wrong of me to pick up your
umbrella.
你的 , 是 的不 。
常用it作形式主语的句型结构
常用it作形式主语的句型结构◇It + be +形容词+ that-从句可用于此句型的形容词有: wonderful,true，good，right，wrong，（un）important，useless，surprising，clear，unusual，lucky，certain, necessary等。
如：①It is quite certain that he will be at the meeting.②It is surprising that he came late to school this morning.③It is important that we(should)study hard注意: 该句型中的形容词是（un）important, necessary等时，从句应为(should )+动词原形。
◇It + be + -ed 分词+ that-从句适用该句型的过去分词主要有: said,reported,announced,hoped,thought，told，believed，expected，decided，suggested,known等。
如：①It is hoped that one day they will have enough animals to set them free②It is well known that the earth goes around the sun.③It is suggested that the sports meeting (should ) be put off until next week. 注意: 该句型的过去分词是suggested时，从句应为(should )+动词原形。
◇It + be +名词+ that-从句适用该句型的名词（词组）有: a pity，an honor，a good thing，a fact，a surprise，good news, one’s duty等。
“It”作形式主语和形式宾语的用法详解
it作形式主语和形式宾语一、it作形式主语：当不定式（短语）、动名词（短语）或从句在某个句子中作主语时，为保持句子结构前后平衡，避免头重脚轻，因此常用it作形式主语置于句首，而将真正的主语放在句尾。
此时it只起先行引导作用，本身无词义。
it作形式主语时，可以代替三种形式：不定式、动名词和主语从句。
1. it代替不定式短语常用于下列句型中：如：It is everyone’s duty to obey the law.遵守法律是每个人的义务。
It is difficult for a foreigner to learn Chinese.对于一个外国人来说，学习汉语是困难的。
It took them a year to build the bridge.建这座桥花了他们一年的时间。
It is bad manners to stare at people.瞪着眼睛看人是不礼貌的。
It is up to us to help those in need.帮助那些有困难的人是我们的责任。
eg. It’s important for us to learn English well.学好英语对我们来说是重要的。
It’s kind of you to help me.感谢你对我的帮助。
⒉ it代替动名词短语：It’s no good/use/useless/a waste of time doing sth.做某事没有用/浪费时间①It is no good/ use having a car if you can’t drive.如果你不会开车，有车也没用。
②It is a waste of time watching TV.看电视是浪费时间。
（it作形式主语,代替动名词短语watching TV）⒊ it代替主语从句：这个主语从句可以用连词that引导，也可以用连接代词或连接副词引导。
如：①It was clear that they had no desire for peace.很清楚他们没有和平的诚意。
it做形式主语的19个句型
It作形式主语常见句型is/was + 被强调部分+ that/who ...该句型是强调句型。
被强调部分可以是主语，宾语，表语或状语。
强调的主语如果是人，that 可以由who 换用。
如果把这种句型结构划掉后，应该是一个完整无缺的句子。
这也是判断强调句型与其它从句的方法。
2. It is not until + 被强调部分+ that ...该句型也是强调句型。
主要用于强凋时间状语，译成汉语“直到……才……”，可以说是not ... until ... 的强调形式。
It was not until she took off her dark glasses that I realized she was a famous film star.= Not until she took off her dark glasses did I realize she was a famous film star.= I didn't realize she was a famous film star until she took off her dark glasses.3. It is clear /obvious/true/possible/certain… that …该句型中it 是形式主语，真正的主语是that 引导的主语从句，常译为“ 清楚（显然，真的，肯定……）”是主语从句最常见的一种结构。
It is very clear that he's round and tall like a tree.= That he's round and tall like a tree is very clear.4. It is important /necessary/ right/strange/natural... that ...+(should) do该句型和上一个同属一个句型。
it作形式主语和宾语的几种结构
B. 动词+ it + that从句。常见于like, take, have, put等少数动词之后（it相当于that从句的同位语）。
I take it that they will succeed sooner or later.
我认为他们迟早会成功的。
The newspapers have it that some Japanese firms have gone bankrupt.
（他们发现与我们中国人一起工作很愉快。）
I don’t feel it difficult to understand the Special English.
（我觉得理解英语特别节目并不难。）
He makes it a rule never to borrow money.
（他立志决不向别人借钱。）
(我花了一些时间才读完那段阅读材料。)
It took him fourteen hours to go to New Zealand from Shanghai by plane.
(从上海乘飞机去新西兰花了他14小时。)
How long does it take you to go to Beijing from Qingdao by train?
(据说他们发明了一种新型电脑。)
It is believed that China will become one of the strongest countries in the world.
(大家都相信中国将会步入世界强国之列。)
It was reported that more than 170 thousand people died in the 2004 tsunami.
it作形式主语和形式宾语
it作形式主语和形式宾语it既可作人称代词，用来表示动物或无生命的物体等，也可以作无人称代词，在句中作主语，表示“时间”、“距离”、“天气”等。
它还可以引导强调句，使语气得以加强。
此外，it在句中能作引导词，充当句子中的形式上的成分，如形式主语、形式宾语等。
㈠ it作形式主语：it作形式主语时没有具体的意义，而只是帮助把真正的主语移到句子后部去，使句子显得平稳一些。
it作形式主语时，可以代替三种形式：不定式、动名词和主语从句。
⒈ it代替不定式短语常用于下列句型中：It + be +形容词+ (for/of sb.) to do sth.It + be + 名词 + to do sth.It takes sb. some time to do sth. 干…花了某人…时间It’s up to sb. to do sth. 干…是某人的职责或义务如：①It is everyone’s duty to obey the law.遵守法律是每个人的义务。
（ it作形式主语, 代替不定式短语to obey the law）②It is difficult for a foreigner to learn Chinese.对于一个外国人来说，学习汉语是困难的。
（ it作形式主语, 代替不定式短语to learn Chinese）③It is not right to use these places as rubbish dumps.把这些地方用来倒垃圾是不对的。
（it作形式主语, 代替不定式短语to use these places as rubbish dumps）④It took them a year to build the bridge.建这座桥花了他们一年的时间。
（ it作形式主语, 代替不定式短语to build the bridge）⑤It is bad manners to stare at people.瞪着眼睛看人是不礼貌的。
常用it作形式主语地句型结构
常用it作形式主语的句型结构◇It + be +形容词+ that-从句可用于此句型的形容词有: wonderful,true，good，right，wrong，（un）important，useless，surprising，clear，unusual，lucky，certain, necessary等。
如：①It is quite certain that he will be at the meeting.②It is surprising that he came late to school this morning.③It is important that we(should)study hard注意: 该句型中的形容词是（un）important, necessary等时，从句应为(should )+动词原形。
◇It + be + -ed 分词+ that-从句适用该句型的过去分词主要有: said,reported,announced,hoped,thought，told，believed，expected，decided，suggested,known等。
如：①It is hoped that one day they will have enough animals to set them f ree②It is well known that the earth goes around the sun.③It is suggested that the sports meeting (should ) be put off until next week.注意: 该句型的过去分词是suggested时，从句应为(should )+动词原形。
◇It + be +名词+ that-从句适用该句型的名词（词组）有: a pity，an honor，a good thing，a fact，a surprise，good news, one’s duty等。
It的特殊用法
It的特殊用法一、作形式主语1．（1）It’s + adj.+ to do sth.It’s important to study English well.(2 ) It’s + adj. +that…It’s important/ necessary/ likely/ possible/ certain/…that…It’s likely that he will win the game.It’s certain that he will come this afternoon.2. It’s + v-ed + that…(1) It’s said/ thought/ believed/ supposed/ reported/ proved/ known…that…It’s known that the earth travels round the sun.= As is known to everybody, the earth travels the sun.= What is known to everybody is that the earth travels the sun.(2) It’s suggested/ advised/ proposed/ requested/ required/ insisted/commanded/ demanded/ ordered/…that…It’s suggested that she（should）finish her homework this afternoon.It’s required that I (should) go at once.3. (1) It’s + 名+that…常见的名词有：a pity, a fact, an idea, an honor, no wonder等It’s a pity that he can’t come to the party.It’s a fact that he didn’t pass the exam.It’s a good idea that we’ll go outing.It’s an honor that I was invited to the meeting.(It’s)no wonder (that) he always takes the first place in the exams.(2) It’s + 名+doing常见的名词有：use, goodIt’s no use crying.It’s no good crying over spilt milk.【谚语】牛奶溢了，哭也没用。
It构成的句型小结
It构成的句型小结一、It作形式主语的句型为使句子平衡，往往把it置于句首作形式主语，而把真正的主语（通常是不定式短语、动名词短语或主语从句）移至句末。
It 作形式主语的句型有：㈠it 代指不定式短语的句型1. It takes + (sb.) + sometime / some money + to do sth.做某事花去某人多长时间Just a minute, it won't take me long to change. 等一下,我很快就可以换好衣服。
It takes five minutes to walk there. 走到那里需要5分钟。
It took me three days to prepare for the examination. 我花了三天准备那次考试。
It takes a lot of money to buy a house like that. 买那样一幢房子需要很多钱。
2.It takes + 名词+ (for sb.) to do sth. 某人做某事需要… …It took great imagination as well as patience for Annie to teach me to speak.对安妮来说，教我说话需要极大的信心和想象力。
It takes time for them to prepare for the great changes that take place in space.他们需要很多时间准备应付太空中所发生的巨大变化。
3.It is + 形容词+ (for / of sb.) to do sth. 某人做某事是… …的for sb. 的句型常用于表示事物的特征特点，表示客观形式的形容词，如easy, difficult, hard, important, possible, impossible, comfortable, necessary, better等。