it用法探究
“It” 既是高中英语教学重难点,也是近几年高考的热点语法。它的用法极其广泛,既可以作人称代词,也可以作非人称代词,表示时间、距离、气候等；既可以充当形式主语和形式宾语,也可以用于强调句结构中;它还常常用在某些动词或特殊词类之后,构成习惯用语。下面就其使用的重点及难点,分门别类地加以总结。
一 作人称代词,可以用来代替人、物或事；亦作非人称代词，表示时间、天气、季节、距离等
1 ----Who is it?
-----It's me, Mike.
2 Did you see my pen? I put it on the desk this morning.
3 That's it.(就这么回事)
4 It's fine today.
5 It's only half an hour's walk from my home to the school.
二 指无生命的东西，性别不详或性别无关紧要时，可用“It”来指动物，幼童等。
1 I threw the little dog to him and he caught it.
2 They got a baby and it was a ten-pounder.他们生了一个十磅重的婴孩。
三 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，这时就需要借助“It”作形式上的主语，而把整个句子的主语移到句子后边去，使句子看上去平稳一些。
1 It is fun for him to study, but it is difficult to study and work at the same time.
2 It is very clear that the elephant's leg is round and tall like a tree.
3 It will be no good learning without practice.
4 It is said that he put forward a new question at the meeting.
5 It is suggested that we (should) arrive there in 2 hours.
6 It's a pity that our teacher can't take part in our party.
7 It took thousands of people many years to build the Great Wall.
（注：句中划线部分为真正的主语）
四 作形式宾语
这种情况通常只用于能带以名词或形容词作宾语补足语的动词后面，这类动词可以是think/believe/feel/make/consider/find/---。而真正的宾语可以是动词不定式、动名词或从句。
1 In the 1870s, when Marx was already in his fifties, he found it important to study the situation in Russia, so he began to learn Russian.
2 He felt it useful learning English well.
3 They found it difficult that they would finish their work in two days.
4 I felt it a surprise that they were all unfriendly to me.
（注：句中划线部分为真正的宾语）
五 用于强调句型中
一） 为了强调句子的某一成分，通常把引导词“It”用在句首，被强调部分可以是句子的主语、宾语或状语。其句型是“It is/was+被强调部分+that---”。如果被强调主语是人，可用who替代that。
1 It was about 600 years ago that the first clock with a face and an hour hand was made.
2 It was last night that I met Mike.
3 It was I that/who met Mike last night.
4 It was Mike that I met last night.
二） “It is/was not until +被强调部分+that---”也是强调巨型，主要用来强调时间状语。可译为“直到……才……”
I didn't realize she was a famous film star until she took off her dark glasses.
→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.
六 用于几种特殊句式中
一）在“It is time(about time, high time) that ---”句式中，that从句中常用一般过去时态，表示“该是……的时候了”。that有时可以省略。it用法探究
It's time (that) you went to bed.
二）在“It is/was the first/second/--- time that---”句式中，that从句中常用完成时态。如果主句中的谓语动词是一般现在时，则从句中的谓语动词用现在完成时；如果主句中的谓语动词是一般过去时，则从句中的谓语动词用过去完成时。表示“某人第…次…”。
It is the first time that I have been to Beijing.
=This is the first time that I have been to Beijing.
It was the first time that I had been to Beijing.
三）在“It is/was/has been+一段时间+since---”句式中，主句中以时间段做表语，从句中谓语动词通常是瞬间动词的一般过去时态；当从句中的谓语动词是延续性动词时，若该动词用一般过去时，则表示该动作的结束距离现在的时间；若该动词用完成时，则表示该动作的发生距离现在的时间。
It is(has been)five years since I left here. 我离开这儿有五年了。
It is (has been)five years since I smoked. =I smoked five years ago.我戒烟有五年了。
It is(has been) 5 years since I have smoked.=I have smoked for 5 years.我吸烟有五年了。
四）在“It is---when---”句式中，when引导的是一个时间状语从句，主句中的it指时间，表语由表示具体时间点的词语来充当。
It was five o'clock when he got home.
五）在“It is---before---”句式中，主句中的it指时间，谓语动词的时态是一般将来时或一般过去时。主句中的表语多是long, not long, three days, two weeks等表示时间段的词语。
It was three days before he went to Beijing. 3天后，他去了北京。
It will be not long before he finishes his job.不久他就把他的工作做完了。
六）在“It looks/seems as if---”句式中，it无意义，引导一个表语从句。表示“看起来好象……”如果与事实不符，则从句中谓语动词用虚拟语气。
It looks/seems as if he is ill.(真的病了)
It looks/seems as if he were ill.(没有生病)
七 用在某些由名词转化来的动词之后，构成习惯性动词短语，it无实义.
一）某些原表示人、动物或事物名称的名词转化的动词；如：to dog it 打扮起来，摆阔气; to pig it 像猪一样生活，过困苦的生活; to king it 做帝王，称王称霸; to hotel it 投宿旅馆.
We had better chance it. 我们最好去碰碰运气。
She should not lord it like that. 她不该这样摆臭架子。
二）某些原表示人或动物身体部位的名词转化的动词；
Let's face it.面对现实吧。（或：鼓起勇气来）
There won't be any bus and we have to foot it in the rain. 不会有公共汽车了，我们只好在雨中步行。
We'd better leg it or we'll be late for work.我们最好着去，否则我们就要迟到了。
You should shoulder it. 你应该承担责任。
She lost all her money and had to pad it home. 她把钱丢光了，只得拖着脚步回家。
三）某些原表示交通工具的名词转化的动词。
to boat it 乘船去; to bus it 坐公共汽车; to taxi it 坐出租汽车去; to tube it 坐地铁去;
As the bridge has been damaged by the flood, we have to boat it.由于桥被洪水冲坏，我们只得乘船去。
Why not taxi it here? 为什么不坐出租车去呢？
You had better bus it, otherwise you will be late. 你最好坐公共汽车，否则会迟到的。
八 用在某些由形容词转化来的动词之后，构成习惯性动词短语，it无实义.
To cool it 放松下来，平静下来; to brave it 拼命干; to rough it 生活简单，过艰苦生活
She cooled it at a table for a while. 她在桌子旁边冷静了一会儿。
The explorers had to rough it when they got into the jungle.勘探队员进入丛林后，只得过艰苦生活。
九 用于某些动词的后面，构成习惯用语。
To fight it out 决一雌雄，争辩个明白; to keep at it 别松劲，干下去; to get it 理解，明白; to have it 占上风; to get it alone 单干; to call it a day 今天就到此为止吧。
You will catch it! 你可小心点（警告用语）
You are in for it. 这下你可得干到底了。（或：这下你肯定要倒霉了）
She will have it out with Mike. 她要和迈克争个高低。
That's more like it. 这才像话。
You ask for it. 你活该。
You can't make it to the other shore in this weather. 天气这么恶劣，你可到不了对岸。
A: Shall we meet next week? 下星期我们碰一次头好吗？
B: Yes, let's make it next Sunday. 让我们约定下星期日碰头吧。