一、概说
it 看似简单，但用法却并不简单。它不仅可以指人也可以指物，不仅可以指时间和距离也可指自然现象和自然环境，不仅可用作形式主语也可用作形式宾语，等。现将其主要用法分述如下。
二、用作人称代词
1. 用于指事物
it用作人称代词最基本的用法就是代替前面已提到过的事物，以避免重复：
This is my watch, it’s a Swiss one. 这是我的手表，它是瑞士制的。
I cannot find my watch; I must have lost it. 我找不到手表，我一定把它给丢了。
2. 用于指动物或婴儿
除用于指代事物外，还可指动物或性别不详的婴儿：
“Where is the cat?” “It’s under the bed.” “ 猫在哪儿?”“在床下。”
They got a baby and it was very lovely. 他们生了个孩子，很可爱。
3. 用于上文提到的情况
He smokes in bed and I don’t like it. 他在床上抽烟，我不喜欢他这样。
Her mother kept telling her not to go out at night, but it didn’t help. 她母亲老叫她晚上不要出去，但是没用。
4. 用于指人
it用于指人主要用确定未知人的身份：
“Who is it?” “It’s me.” “是谁啊?”“是我。”
“Listen. Someone is crying.” “Oh, it must be Mary.” “听，有人在哭。”“噢，一定是玛丽。”
Someone must have been here. But we have no idea who it was. 一定有人来过，但我们不知道是谁。
5. 指人时与he和she的区别
当it用于指人时，主要用于确定未知的或者是身份不明的人，若是指已知的或身份明确的人，则应根据情况使用he或she。比较：
I hear a knock at the door. It must be the postman. 我听见有人在敲门，一定是邮递员来了。
Jim is at the door. He wants to see you. 吉姆在门口，他想见你。
A tall man stood up and shook hands with her. It was the general manager. 一个高个子站起来同她握了手，他是总经理。
The general manager just called. He told us to wait for him at the gate. 总经理刚来过电话，他叫我们在门口等他。
6. 指物时与one的区别
两者均可代替前面提到的事物，区别是：it指的是与前面已提到的事物为同一物，此时的it等于“the (this, that, my...) 名词”；而one 指的是与前面已提到的事物为同一类物，此时的one等于“a 名词”。比较：
I have a dictionary but I’ve lent it to Mary. 我有一本词典，但把它借给玛丽了。
I haven’t a dictionary; can you lend me one? 我没有词典，你能借我一本吗?
三、用作虚主语或虚宾语
1. 用于指时间
It’s still early. 时间还早。
It’s already nine o’clock. 已是9点了。
It’s three years since he left here. 他离开这儿已有3年了。
2. 用于指距离
It’s a long way from here. 从这儿去很远。
How far is it from here to the station? 从这儿去车站有多远?
3. 用于指环境
It’s noisy in here. 这里面很嘈杂。
It was very quiet in the garden. 花园里很安静。
4. 用于指天气等自然现象
It’s very cold today. 今天很冷。
It is raining. 正在下雨。
It’s 37℃ today. 今天气温是摄氏37度。
5. 用于笼统地谈论某情况
I cannot help it. 没办法了。
"How’s it going?" "Well, not so good." “情况如何?”“不是很好。”
6. 用于某些习语
(1) make it 及时赶到；成功，办成：
You can make it if you hurry. 如果你赶快还可以及时赶到。
He wants to make it as a writer. 他想作一名作家而一举成名。
You needn’t worry; he will make it. 你不必担心，他会办成的。
(2) catch it 被责骂，受处罚(www.hxen.com)：
If I come home late I’ll catch it from my mother. 如果我回家晚了，我妈妈会骂我。
四、用作形式主语
1. 基本用法
当不定式、动名词、从句等用作主语时，避免头重脚轻，通常在句首使用形式主语it，而把真正的主语放在句子末尾：
Is it necessary to tell his father everything? 有必要把这一切都告诉他父亲吗?
It’s no good sitting up too late. 熬夜没有好处。
It is quite clear that he has read the book. 很显然，他读过这本书。
It doesn’t matter what he says. 他说什么没关系。
2. 几种特殊的形式主语
(1) 用作动词look, seem, appear, happen, occur, follow等的主语(后接that从句或as if从句)：
It seems as if it is going to rain. 看来要下雨了。
It seems that he knows everything. 他好像什么都知道。
It (so) happened that I had no money with me. 碰巧我没带钱。
From this witness it follows that he must be guilty. 根据该证人的证词判断，他一定有罪。
(2) 当系表结构后接有if 或when引出的状语从句时，通常在系表结构前使用形式主语表示说话人对某情况的看法：
It was a great surprise to me when he did a thing like that. 他这样做使我很吃惊。
It would be a tragedy if anything went wrong. 如果出了什么事就是一个悲剧。
(3) 用于其他固定句型，如if it were not for…(若不是因为)，it’s time that…(该…了)等。
3. 误用形式主语的几种情形
(1) 在该用it作形式主语的地方而误用其他词：
Is ______ necessary to tell his father everything?
A. it B. that C. what D. he
此题的正确答案应是A(it用作形式主语)，而不能选D。
(2) 在不该用形式主语的地方而误用形式主语：
______ must be something wrong with the machine.
A. There B. It C. He D. That
此题应选A，为there be句型与情态动词must连用的情形。
比较以下两组句子：
______ is known to us all, the earth turns around the sun.
______ is known to us all that the earth turns around the sun.
A. It B. Which C. As D. That
前一句填C，as用以引导一个非限制性定语从句；后一句填A，it为形式主语，真正的主语是其后的that从句。
______ is difficult to persuade her to stay.
______ is difficult is to persuade her to stay.(www.hxen.com)
A. It B. What C. He D. That
前一句填A，it为形式主语；后一句填B，what用以引导主语从句。注意后一句比前一句在不定式前多了个is。
五、用作形式宾语
1. 基本用法
当不定式、动名词、从句等用作宾语且其后跟有宾语补足语时，就应在宾语补足语前使用形式宾语，而将真正的宾语移至句末：
We found it difficult to persuade her. 我们发现很难说服她。
He makes it a rule to get up before dawn. 他习惯于天亮前起床。
I think it very strange that he goes out walking almost every night. 我认为他几乎每晚都出去散步是很奇怪的。
2. 几种特殊的形式宾语
通常意义的形式宾语主要见于真正宾语为不定式、动名词、从句等且其后跟有宾语补足语时的情形，即用于“动词 it 宾语补足语 真正的宾语”这样的结构，但以下两类形式宾语却比较特殊，其后没有宾语补足语：
(1) 由于介词后通常不能直接跟that从句作宾语，有个别特殊结构就在介词后先接it作形式宾语，再跟that从句：
You may depend on it that he will turn up in time. 你可以相信他会及时赶到的。
I can’t answer for it that the boy is honest. 我不能保证这个男孩是诚实的。
I’ll see to it that all these letters will be sent to the post before twelve. 我将注意让所有的信件在12点以前送到邮局。
【注】① 在其他情况下解决介词后跟that从句的办法是借用the fact作宾语：
They were worried over the fact that you were sick. 他们为你生病发愁。
② 个别介词(主要是but和except)也可接that从句作宾语：
I know nothing about him except that he lives next door. 我只知道他住在隔壁，其他的就不知道了。
(2) 有的动词由于通常只用作及物动词，当它们后接if从句或when从句，通常应先在动词后接it作形式宾语：
She won’t like it if you arrive late. 她不喜欢你迟到。
He hates it when people use his bike. 他讨厌别人用他的自行车。
I hate it if you say such things in public. 我讨厌你在大庭广众之下说那样的事。
I’d prefer it if I didn’t have to do so much work. 要是我不必做那么多工作，那就太好了。
I would appreciate it very much if you would help me with it. 如果你能帮助我做这事，我会十分感激。
【注】能这样用的动词不多，主要的有enjoy, like, dislike, love, hate, prefer, appreciate等表示情绪的动词。而且高考对此也有所考查，请看一道高考真题(答案选A)：
I hate ______ when people talk with their mouths full.
A. it B. that C. these D. them
(3) 用于 have it that(说，认为)，take it that(认为)等个别固定表达中：
I take it (that) you agree. 我以为你同意了(www.hxen.com)。
Report has it that about 30 people were killed in the accident. 据报道，在这次事故中大约有30人丧命。
六、用于强调句型
1. 基本句型结构
it用于强调句的基本句型结构是：It be 被强调部分 that(who) 其他部分。请看用例：
It was in the Japan that he died. 他是死于日本。
It was yesterday that he got married. 他是昨天结婚的。
It was a computer that he bought last week. 他上个星期买的是一台电脑。
2. 使用强调句型应注意的几点
(1) 强调主语时，that后谓语动词的数应与被强调的主语保持一致：
It is I who am right. 是我对。
It was you that were wrong. 是你错了。
(2) 不要想当然地用he, she, that等代替强调句中的it：
_____ was in this room that he was killed.
A. It B. That C. He D. Who
此题答案应选A。该句还原成非强调句为He was killed in this room.
【注】有关强调句型的其他用法说明，参见本讲义“强调句型”。
七、重点考点精练
1. Luckily, _____ happened to be a foreign teacher there.
A. it B. there C. they D. that
2. _____ is said to be no life on the moon.
A. It B. There C. That D. He
3. You should make _____ a rule to leave things where you can find them again.
A. it B. that C. you D. this
4. _____ is known to everybody, the moon travels round the earth once every month.
A. It B. As C. That D. What
5. I want very much to buy a color TV set, but I can’t afford _____.
A. it B. one C. this D. that
6. I should prefer _____ if you didn’t go there alone.
A. it B. that C. you D. which
7. He is always really rude, ______ is why people tend to avoid him.
A. that B. it C. this D. which
8. Having a trip abroad is certainly good for the old couple, but _____ remains to be seen whether they will enjoy it.
A. that B. it C. this D. which
9. Dear me! Just look at the time! I had no idea _____ was so late.
A. it B. as C. that D. what
10. _____ is hard is to do good all one’s life and never do anything bad.
A. He B. It C. That D. What
11. _____ is hard to do good all one’s life and never do anything bad.
A. He B. It C. That D. What
12. ____ doesn’t seem to have been much difficulty in solving the problem.
A. It B. That C. There D. He
13. I can’t remember a Christmas when _____ snowed so much.
A. it B. that C. what D. the weather
14. _____ was when she was about to go to bed that the telephone rang.
A. It B. That C. There D. He
15. Who was _____ that saved the drowning girl?(www.hxen.com)
A. that B. it C. what D. he
【参考答案】1—5 BAABB 6—10 ADBAD 11—15 BCAAB
