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1、 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。 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Its up to sb. to do sth. 干是某人的职责或义务It is everyones duty to obey the law.遵守法律是每个人的义务。（ it作形式主
2、语, 代替不定式短语to obey the law）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作形式主语, 代替不定式短语to learn Chinese）It 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）It took them a year to build the bridge.建这座桥花了他们一
3、年的时间。（ it作形式主语, 代替不定式短语to build the bridge） It be + 形容词+ for sb. to do sth.与It be + 形容词+of sb. to do sth.：如果句型中的形容词描述的是sb.的品质、品格，在逻辑上可以作sb.的表语，则sb.前应用介词of，否则就用for。Its necessary for us to use a short-wave radio to pick up the programmes.我们用一台短波收音机收听这些节目是必要的。Its kind of you to help me.感谢你对我的帮助。（= You
4、are kind to help me. ）It was foolish of him to give up the job.他放弃那工作是愚蠢的。（= He was foolish to give up the job it代替动名词短语：动名词作主语用后置形式的情况远不及不定式那么普遍，常限于no good, no use, useless, waste等词的后面。 It is no good/ use having a car if you cant drive.如果你不会开车，有车也没用。( it作形式主语,代替动名词短语having a car)It is a waste of ti
5、me 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）It is no use asking him.问他没有用。（ it作形式主语,代替动名词短语asking him） 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。It was clear that they had no desire for peace.很清楚他们没有和平的诚意。（ it作形式主语,代替主语从句that they had no desire for peace）It is doubtful whether she will be
6、able to come.她能否来还很难说。（ it作形式主语,代替主语从句whether she will be able to come）It was clear enough what she meant.她的意思是够清楚的。（ it作形式主语,代替主语从句what she meant）用it作形式主语，把真正的主语从句移至后面的常见句型有： It is a pity/ a shame/ a fact/ an honour/ good news/ no wonder/ a wonder thatIt was a pity that the engineer couldnt come.可惜
7、工程师没能够来。It is a wonder that he continues to gamble when he always loses!令人惊讶的是他一直输还一直赌。 It is + 形容词（如： strange/ natural/ surprising/ obvious/ true/ fortunate/ wonderful/ funny/ possible/ impossible/ likely/ unlikely/ clear/ unusual/ certain/ important）that It is certain that he will win. 他一定会取胜。 It
8、seems/ happened/ turned out/ suddenly struck me/ occurred to methat It happened that I wasnt there that day. 恰好那天我不在那里。 It + be + 过去分词（如：said/ reported/ announced/ decided/ expected/ hoped/ known/ believed）thatIt is said that nothing has been done about it.据说至今对此没采取任何措施。It is reported that more than
9、 twenty people were killed in that bus accident.据报道在那次的公共汽车事故中有二十多人丧生。* 注意要在It is suggested/required/desired/ordered/proposedthat的主语从句中用虚拟语气： (should) + 动词原形It is requested that he give a performance at the party.有人请求他在聚会上表演一个节目。It is suggested that we should get everything ready by tonight.建议一切在今晚准
10、备好。 It doesnt matter +连接代词或副词It doesnt make too much difference +连接代词或副词It doesnt matter whether he comes or not.他来还是不来都没关系。It wont make much difference whether you go today or tomorrow.你今天去也好，明天去也好，关系不大。 it作形式宾语：it作形式宾语时，可以代替三种形式：不定式、动名词和宾语从句。it作形式宾语时，需具备两个条件： 真正的宾语是不定式、动名词或从句 有宾语补足语 具备了这两个条件，形式宾语i
11、t一定要用。 it代替不定式短语think/ find/ feel/ consider/ make/ regard+ it +形容词/名词 + 不定式短语I find it pleasant to work with him.(it 作形式宾语，代替不定式短语to work with him)我觉得和他一起工作很愉快。They felt it difficult to finish the work in such a short time.（ it 作形式宾语，代替不定式短语to finish the work in such a short time）他们认为在这么短的时间内完成这项工作是
12、困难的。All these noises made it impossible for me to go on with the work.（ it 作形式宾语，代替不定式短语to go on with the work）这些噪音使我无法继续工作。 it代替动名词短语( 这只限于少数句型，在多数情况下用不定式时更多一些)The professor considers it no good reading without understanding.这位教授认为阅读而不理解没有益处。He found it useless( no use) arguing with him.他发现和他辩论没有用。
13、He thought it absolutely senseless attempting the impossible.想做不可能的事情，他认为是完全没道理的。 it代替宾语从句：We all thought it a pity that the conference should have been cancelled.会议取消了我们都感到很遗憾。I took it for granted that they were not coming.我想他们准是不会来的了。Ill see to it that everything is ready in time.我负责使一切都按时准备好。 含i
14、t 的常用句型英语中有一些固定句型中含有it,应注意这些句型的使用。 It be + 被强调部分 + that/ who + 其他成分I met Peter in Japan last year. It was I who/that met Peter in Japan last year. It was Peter whom/that I met in Japan last year. It was in Japan that I met Peter last year. It was last year that I met Peter in Japan.* not until 也可用于强调句型例Mr Brown didnt come back until eleven oclock.可变为：It was not until eleven oclock thatMr Brown came back.* 强调句也可变为特殊疑问句例It was in 1949 that the PRC was founded.可变为：When was it that the PRC was founded? Its + 地点状语+ that（强调句） Its +地点名词+ where (定语从句
