“It” 既是高中英語教學重難點,也是近幾年高考的熱點語法。它的用法極其廣泛,既可以作人稱代詞,也可以作非人稱代詞,表示時間、距離、氣候等；既可以充當形式主語和形式賓語,也可以用於強調句結構中;它還常常用在某些動詞或特殊詞類之後,構成習慣用語。下面就其使用的重點及難點,分門別類地加以總結。
一 作人稱代詞,可以用來代替人、物或事；亦作非人稱代詞，表示時間、天氣、季節、距離等
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.(就這麼回事)
4 It's fine today.
5 It's only half an hour's walk from my home to the school.
二 指無生命的東西，性別不詳或性別無關緊要時，可用“It”來指動物，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.他們生了一個十磅重的嬰孩。
三 作形式主語
英語中不定式、動名詞、主語從句在作主語時，主語往往顯得很長，使整個句子看上去有點頭重腳輕，這時就需要藉助“It”作形式上的主語，而把整個句子的主語移到句子後邊去，使句子看上去平穩一些。
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.
（註：句中劃線部分為真正的主語）
四 作形式賓語
這種情況通常只用於能帶以名詞或形容詞作賓語補足語的動詞後面，這類動詞可以是think/believe/feel/make/consider/find/---。而真正的賓語可以是動詞不定式、動名詞或從句。
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.
（註：句中劃線部分為真正的賓語）
五 用於強調句型中
一） 為了強調句子的某一成分，通常把引導詞“It”用在句首，被強調部分可以是句子的主語、賓語或狀語。其句型是“It is/was+被強調部分+that---”。如果被強調主語是人，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 +被強調部分+that---”也是強調巨型，主要用來強調時間狀語。可譯為“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 用於幾種特殊句式中
一）在“It is time(about time, high time) that ---”句式中，that從句中常用一般過去時態，表示“該是……的時候了”。that有時可以省略。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從句中常用完成時態。如果主句中的謂語動詞是一般現在時，則從句中的謂語動詞用現在完成時；如果主句中的謂語動詞是一般過去時，則從句中的謂語動詞用過去完成時。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+一段時間+since---”句式中，主句中以時間段做表語，從句中謂語動詞通常是瞬間動詞的一般過去時態；當從句中的謂語動詞是延續性動詞時，若該動詞用一般過去時，則表示該動作的結束距離現在的時間；若該動詞用完成時，則表示該動作的發生距離現在的時間。
It is(has been)five years since I left here. 我離開這兒有五年了。
It is (has been)five years since I smoked. =I smoked five years ago.我戒煙有五年了。
It is(has been) 5 years since I have smoked.=I have smoked for 5 years.我吸煙有五年了。
四）在“It is---when---”句式中，when引導的是一個時間狀語從句，主句中的it指時間，表語由表示具體時間點的詞語來充當。
It was five o'clock when he got home.
五）在“It is---before---”句式中，主句中的it指時間，謂語動詞的時態是一般將來時或一般過去時。主句中的表語多是long, not long, three days, two weeks等表示時間段的詞語。
It was three days before he went to Beijing. 3天後，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無意義，引導一個表語從句。表示“看起來好象……”如果與事實不符，則從句中謂語動詞用虛擬語氣。
It looks/seems as if he is ill.(真的病了)
It looks/seems as if he were ill.(沒有生病)
七 用在某些由名詞轉化來的動詞之後，構成習慣性動詞短語，it無實義.
一）某些原表示人、動物或事物名稱的名詞轉化的動詞；如：to dog it 打扮起來，擺闊氣; to pig it 像豬一樣生活，過困苦的生活; to king it 做帝王，稱王稱霸; to hotel it 投宿旅館.
We had better chance it. 我們最好去碰碰運氣。
She should not lord it like that. 她不該這樣擺臭架子。
二）某些原表示人或動物身體部位的名詞轉化的動詞；
Let's face it.面對現實吧。（或：鼓起勇氣來）
There won't be any bus and we have to foot it in the rain. 不會有公共汽車了，我們只好在雨中步行。
We'd better leg it or we'll be late for work.我們最好著去，否則我們就要遲到了。
You should shoulder it. 你應該承擔責任。
She lost all her money and had to pad it home. 她把錢丟光了，只得拖著腳步回家。
三）某些原表示交通工具的名詞轉化的動詞。
to boat it 乘船去; to bus it 坐公共汽車; to taxi it 坐出租汽車去; to tube it 坐地鐵去;
As the bridge has been damaged by the flood, we have to boat it.由於橋被洪水沖壞，我們只得乘船去。
Why not taxi it here? 為什麼不坐計程車去呢？
You had better bus it, otherwise you will be late. 你最好坐公共汽車，否則會遲到的。
八 用在某些由形容詞轉化來的動詞之後，構成習慣性動詞短語，it無實義.
To cool it 放鬆下來，平靜下來; to brave it 拚命干; to rough it 生活簡單，過艱苦生活
She cooled it at a table for a while. 她在桌子旁邊冷靜了一會兒。
The explorers had to rough it when they got into the jungle.勘探隊員進入叢林後，只得過艱苦生活。
九 用於某些動詞的後面，構成習慣用語。
To fight it out 決一雌雄，爭辯個明白; to keep at it 別鬆勁，幹下去; to get it 理解，明白; to have it 占上風; to get it alone 單幹; to call it a day 今天就到此為止吧。
You will catch it! 你可小心點（警告用語）
You are in for it. 這下你可得干到底了。（或：這下你肯定要倒霉了）
She will have it out with Mike. 她要和邁克爭個高低。
That's more like it. 這才像話。
You ask for it. 你活該。
You can't make it to the other shore in this weather. 天氣這麼惡劣，你可到不了對岸。
A: Shall we meet next week? 下星期我們碰一次頭好嗎？
B: Yes, let's make it next Sunday. 讓我們約定下星期日碰頭吧。
一 作人稱代詞,可以用來代替人、物或事；亦作非人稱代詞，表示時間、天氣、季節、距離等
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.(就這麼回事)
4 It's fine today.
5 It's only half an hour's walk from my home to the school.
二 指無生命的東西，性別不詳或性別無關緊要時，可用“It”來指動物，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.他們生了一個十磅重的嬰孩。
三 作形式主語
英語中不定式、動名詞、主語從句在作主語時，主語往往顯得很長，使整個句子看上去有點頭重腳輕，這時就需要藉助“It”作形式上的主語，而把整個句子的主語移到句子後邊去，使句子看上去平穩一些。
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.
（註：句中劃線部分為真正的主語）
四 作形式賓語
這種情況通常只用於能帶以名詞或形容詞作賓語補足語的動詞後面，這類動詞可以是think/believe/feel/make/consider/find/---。而真正的賓語可以是動詞不定式、動名詞或從句。
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.
（註：句中劃線部分為真正的賓語）
五 用於強調句型中
一） 為了強調句子的某一成分，通常把引導詞“It”用在句首，被強調部分可以是句子的主語、賓語或狀語。其句型是“It is/was+被強調部分+that---”。如果被強調主語是人，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 +被強調部分+that---”也是強調巨型，主要用來強調時間狀語。可譯為“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 用於幾種特殊句式中
一）在“It is time(about time, high time) that ---”句式中，that從句中常用一般過去時態，表示“該是……的時候了”。that有時可以省略。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從句中常用完成時態。如果主句中的謂語動詞是一般現在時，則從句中的謂語動詞用現在完成時；如果主句中的謂語動詞是一般過去時，則從句中的謂語動詞用過去完成時。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+一段時間+since---”句式中，主句中以時間段做表語，從句中謂語動詞通常是瞬間動詞的一般過去時態；當從句中的謂語動詞是延續性動詞時，若該動詞用一般過去時，則表示該動作的結束距離現在的時間；若該動詞用完成時，則表示該動作的發生距離現在的時間。
It is(has been)five years since I left here. 我離開這兒有五年了。
It is (has been)five years since I smoked. =I smoked five years ago.我戒煙有五年了。
It is(has been) 5 years since I have smoked.=I have smoked for 5 years.我吸煙有五年了。
四）在“It is---when---”句式中，when引導的是一個時間狀語從句，主句中的it指時間，表語由表示具體時間點的詞語來充當。
It was five o'clock when he got home.
五）在“It is---before---”句式中，主句中的it指時間，謂語動詞的時態是一般將來時或一般過去時。主句中的表語多是long, not long, three days, two weeks等表示時間段的詞語。
It was three days before he went to Beijing. 3天後，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無意義，引導一個表語從句。表示“看起來好象……”如果與事實不符，則從句中謂語動詞用虛擬語氣。
It looks/seems as if he is ill.(真的病了)
It looks/seems as if he were ill.(沒有生病)
七 用在某些由名詞轉化來的動詞之後，構成習慣性動詞短語，it無實義.
一）某些原表示人、動物或事物名稱的名詞轉化的動詞；如：to dog it 打扮起來，擺闊氣; to pig it 像豬一樣生活，過困苦的生活; to king it 做帝王，稱王稱霸; to hotel it 投宿旅館.
We had better chance it. 我們最好去碰碰運氣。
She should not lord it like that. 她不該這樣擺臭架子。
二）某些原表示人或動物身體部位的名詞轉化的動詞；
Let's face it.面對現實吧。（或：鼓起勇氣來）
There won't be any bus and we have to foot it in the rain. 不會有公共汽車了，我們只好在雨中步行。
We'd better leg it or we'll be late for work.我們最好著去，否則我們就要遲到了。
You should shoulder it. 你應該承擔責任。
She lost all her money and had to pad it home. 她把錢丟光了，只得拖著腳步回家。
三）某些原表示交通工具的名詞轉化的動詞。
to boat it 乘船去; to bus it 坐公共汽車; to taxi it 坐出租汽車去; to tube it 坐地鐵去;
As the bridge has been damaged by the flood, we have to boat it.由於橋被洪水沖壞，我們只得乘船去。
Why not taxi it here? 為什麼不坐計程車去呢？
You had better bus it, otherwise you will be late. 你最好坐公共汽車，否則會遲到的。
八 用在某些由形容詞轉化來的動詞之後，構成習慣性動詞短語，it無實義.
To cool it 放鬆下來，平靜下來; to brave it 拚命干; to rough it 生活簡單，過艱苦生活
She cooled it at a table for a while. 她在桌子旁邊冷靜了一會兒。
The explorers had to rough it when they got into the jungle.勘探隊員進入叢林後，只得過艱苦生活。
九 用於某些動詞的後面，構成習慣用語。
To fight it out 決一雌雄，爭辯個明白; to keep at it 別鬆勁，幹下去; to get it 理解，明白; to have it 占上風; to get it alone 單幹; to call it a day 今天就到此為止吧。
You will catch it! 你可小心點（警告用語）
You are in for it. 這下你可得干到底了。（或：這下你肯定要倒霉了）
She will have it out with Mike. 她要和邁克爭個高低。
That's more like it. 這才像話。
You ask for it. 你活該。
You can't make it to the other shore in this weather. 天氣這麼惡劣，你可到不了對岸。
A: Shall we meet next week? 下星期我們碰一次頭好嗎？
B: Yes, let's make it next Sunday. 讓我們約定下星期日碰頭吧。
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