1、一、It用作实词 表达以下概念:指代前文提到的事物，前文中的this,that；替代前文中的内容；指代一位性别不明的小孩或未知的人；指代未指明但谈话双方都知道的那件事；指代时间、天气、气候、距离等自然现象。二、It用作形式主语 替代作主语的从句、动词不定式、动名词，而把真正作主语的从句、动词不定式、动名词置于句尾。It 作形式主语的常见句型：1.代作主语的动词不定式，其句型为（1）It be adj.(for sb.)to do sth.（2）It be adj.of sb.to do sth.（3）It替代作主语的动名词的常见句型：Its no good/use doingIts(well)
2、worth doingIts(well)worth ones while doing/to doIts(well)worth while doing/to do 2.It替代作主语的从句常见句型 （1）It is+noun+从句 （2）.It is adj.+clauseIts surprising that(should)竟然Its a pity/shame that(should)竟然（3）It verb sb.+clause=It is v-ing+clauseIt+surprise/delight/interest/disappoint/worry/disturb/annoy/amaz
3、e/bother/concern/frighten/please/anger sb.that（4）It verb(to sb.)that=sb/sth verb to do(verb=appear,seem,come about,emerge,follow,chance,happen,occur,transpire,turn out,work out)（5）It is v-ed that=sb/sth is to do(verb=say,report,think,believe,hope,expect,agree,accept,decide,determine,intend,plan,unde
4、rstand,know）四、It 作形式宾语 用来替代作宾语的从句、动词不定式、动名词，而把真正作宾语的从句、动词不定式、动名词置于句尾。It 作形式宾语的常见句型：1.verb+it+adj./noun(for/of)to do/clause (verb=think,believe,suppose,consider,feel,make,keep)五、强调句型It is/was+被强调部分+that(who)强调句型用来强调谓语动词以外的任何句子成分。当被强调部分是人时也可以用who。在使用强调句型时需注意以下几点：1.请注意强调句型的特殊疑问句2.在强调原因状语从句时，只能强调由becaus
5、e所引导的从句。3.在强调not until结构时必须把not与until一起放到被强调的位置上。4.注意强调句型与定语从句的区别。六、It 常用的固定搭配1.make it(1).在口语当中相当于succeed,表示：成功、做到、说定、赶上、及时到达。1.It is+被强调部分+that.该句型是强调句型。将被强调的部分放在前面，其它部分置于that之后。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。It was about 600 years ago that t
6、he first clock with a face and an hour hand was made.It was they that(who)cleaned the classroom yesterday.It was in the street that I met her father.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
7、a famous film star.=Not until she took off her dark glasses did I realize she was a famous film star.=I didnt 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
8、very clear that hes round and tall like a tree.=That hes round and tall like a tree is very clear.4.It is important(necessary,right,strange,natural.)that.该句型和上一个同属一个句型。由于主句中的形容词不同，that 后的从句中要用虚拟语气（should+动词原形），should 可以省去。建议记住该句型中的形容词。It is important that we(should)learn English well.It is necessary
9、 that he(should)remember these words.5.It is said(reported,learned.)that.该句型中的it 仍是形式主语，真正主语是that 引导的主语从句。该结构常译为”据说（据报道，据悉）”。It is said that he has come to Beijing.It is reported that another earth satellite has been put into orbit.6.It is suggested(ordered.)that.该句型和上一个同属一个句型。主句中的过去分词是表示请求，建议，命令等词时
10、，that 后的从句要用虚拟语气（should+动词原形），should 可以省。常译为”据建议；有命令）It is suggested that the meeting(should)be put off.It was ordered that we(should)arrive there in two hours.7.It is a pity(a shame.)that.该句型中，that后的从句一般用虚拟语气（should+动词原形），should可省去表示出乎意料，常译为”竟然”。没有这种意义时，则不用虚拟语气。It is a pity that such a thing(should
11、)happen in your class.这种事竟然发生在你们班上，真是遗憾！It is a pity that he is ill.他生病了，真遗憾！8.It is time(about time,high time)that.该句型中that 后的从句应该用虚拟语气，值得注意的是 常用过去时态表示虚拟 有时也用should+动词原形，should 不能省。常译为”是（正是）的时侯”。It is time that children should go to bed.=It is time that children went to bed.9.It is the first(second
12、.)time that.该句型要和上一个句型区别开来。该句型中的that 从句不用虚拟语气，而用完成时态。至于用什么完成时态，由主句的谓语动词的时态决定。如果是一般现在时，后面从句用现在完成时态；如果是一般过去时，后面从句则用过去完成时态。该结构中 that 可以省去；it有时用 this 替换常译为”是第一（二）次”。It is the first time I have been here.=This is the first time I have been here.10.It is.since.该句型主要用作处理瞬间动词的完成时，又要和表示一段时间的时间状语连用的问题。主句中是时间作
13、表语，其时态是现在时或完成时，since 引导的从句通常是一般过去时态，而且是瞬间动词。如果主句是一般过去时，从句则用过去完成时。It is(has been)5 years since his father died.11.It is.when.该句型中的 when 引导的是一个时间状语从句，主句中的 it 指时间，表语由具体的时间充当。常译为”当的时候，是”。It was 5 oclock when he came here.12.It be.before.该句型主句中的 it 指时间,主句中的时态常是将来一般时 或过去时两种时态主句中的表语多是long,not long,3 days,2
14、 weeks 等表示时间段的词或短语。常译为”之后”。It was 3 days before he went to Beijing.It will be not long before he finishes his job.13.It happens(seems,looks,appears)that.该句型中it是形式主语，that 引导的是主语从句，主句中的happen,seem等词是不及物动词 It happened(so happened)that he met his teacher in the street.碰巧 It seems that he will be back in
15、 a few days.看来 14.It takes sb.to do sth.该句型中的不定式是真正的主语，it是形式主语，句型中的直接宾语是时间。常译为”做要花费某人”。It took thousands of people many years to build the Great Wall.15.It is no good(use)doing sth.该句型中的真正主语是动名词短语，主句中的表语可以是no good,(not any good),no use,(not any use)。It is no good learning English without speaking En
16、glish.16.It doesnt matter whether(if).该句型中whether(if)引导的从句是真正主语，该句型常译为”不论（是否）没关系。It doesnt matter if they are old.17.It is kind(of sb.)to do sth.该句型中的不定式短语是真正主语，如果不定式的逻辑主语是由 of引起，主句中的形容词必须是能表示逻辑主语特征的形容词。常见的有：bad,brave,careless,clever,cruel,foolish,good（好心的）,honest,horrible,kind,lazy,modest,naughty,n
17、ice（有教养的）,polite,rude,silly,stupid,wise,wrong（错误的）等。这个句型可以改写为：sb.is kind to do sth.It is kind of you to say so.=You are kind to say so.18.It is necessary(for sb.)to do sth.该句型与上一个同属一个句型。如果不定式的逻辑主语是由for引起，主句中的形容词通常是表示重要性，紧迫性，频繁程度，难易，安全等情况的形容词。常见的形容词有：important,necessary,natural easy,safe,common,norma
18、l,hard,difficult,dangerous,unusual,rare,impossible,pleasant等。在中的形容词作表语可以用从句改写，如：It is important for her to come to the party.=It is important that she(should)come to the party 19.It looks(seems)as if.该句型中it无意义。as if 引导一个状语从句。常译为，”看起来好象”如果与事实不相符合，则用虚拟语气 It looks as if he is ill.（真的病了）It looks as if h
19、e were ill.（没有生病）It seemed as if he were dying.20.We think it important to learn a foreign language.该句型中的it 作形式宾语。为了记忆方便我们可称该句型为6123结构。6指主句中常用的动词：think,believe,make,find,consider,feel；1指的是形式宾语it；2指的是宾补的两种形式：形容词或名词；3指的是真正宾语的三种形式：不定式短语，动名词短语或that引导的宾语从句。We think it our duty to clean our classroom every day.He felt it important learning English well.They found it difficult that they would finish their work in two days.
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