一、it 作人稱(chēng)代詞的用法
1.指事物
作為人稱(chēng)代詞，it 可以除人以外的一切事物或動(dòng)物。如：
I dropped my watch and it broke.
我把手表掉在地上摔壞了。
It's hard work, but I enjoy it.
工作很辛苦，可是我樂(lè )意干。
“Where is the dog?”“It’s in the bedroom. ”
“狗在哪?”“在臥室里”。
2.指人
it 指人主要用于指不性別不明的嬰兒或用于確認某人的身份。如：
Is it a boy or a girl?
是男孩還是女孩?
There is a knock on the door. It must be the postman.
有人在敲門(mén)，一定是郵遞員。
【說(shuō)明】在答語(yǔ)中，常用來(lái)指本人，如說(shuō)It's me。
3.代替某些代詞
代詞it 還可用于代替指示代詞this, that 以及復合不定代詞 something, anything, nothing等。如：
“What's this?”“It's a new machine. ”
“這是什么?”“是一種新機器”。
Nothing is wrong, is it?
沒(méi)出什么問(wèn)題，是嗎?
二、it 作非人稱(chēng)代詞的用法
1.基本用法
it 作非人稱(chēng)代詞的用法，主要用于指時(shí)間、距離、價(jià)值、天氣、氣候及溫度等自然現象。如：
It's too late to go there now.
現在去那兒已經(jīng)太遲了。
It rained all day yesterday.
昨天下了一天的雨。
It can get very hot here.
這里有時(shí)會(huì )很熱。
2.用于某些句型
It's time for sth.
該做某事了。
It's time to do sth.
該做某事的時(shí)候了。
It's time for sb to do sth.
某人該干某事了。
It's (about / high) time + that-從句.
某人該做某事了。
(從句謂語(yǔ)用過(guò)去式，有時(shí)也用“should+動(dòng)詞原形”)
It's first (second) time + that-從句.
某人第幾次干某事。
(從句謂語(yǔ)用現在完成時(shí))
It's + 時(shí)間段 + since-從句.
自從……有一段時(shí)間了。
It's + 時(shí)間段 + before-從句.
過(guò)多長(cháng)的時(shí)間才……
三、it用作形式主語(yǔ)
一、主語(yǔ)從句是在復合句中充當主語(yǔ)的從句，通常放在主句謂語(yǔ)動(dòng)詞之前或由形式主語(yǔ)it代替，而本身放在句子末尾。
1. It 作形式主語(yǔ)和it引導強調句的比較：
It 作形式主語(yǔ)代替主語(yǔ)從句，主要是為了平衡句子結構，主語(yǔ)從句的連接詞沒(méi)有變化。而it引導的強調句則是對句子某一部分進(jìn)行強調，無(wú)論強調的是什么成分，都可用連詞that。被強調部分指人是也可用who/whom。例如：
It is a pity that you didn't go to see the film.
你沒(méi)有去看這個(gè)電影，多可惜��！
It doesn't interest me whether you succeed or not.
對于你是否成功，我并不感興趣。
It is in the morning that the murder took place.
兇殺案發(fā)生的時(shí)間是在早上。
It is John that broke the window.
打碎窗戶(hù)的是約翰。
2.用it 作形式主語(yǔ)的結構
(1)It is ＋名詞＋從句
It is a fact that … 事實(shí)是…
It is an honor that …非常榮幸
It is common knowledge that …是常識
It's a pity that you missed the exciting football match.
多么可惜啊，你錯過(guò)了一場(chǎng)精彩的足球比賽。
(2)it is ＋形容詞＋從句
It is natural that… 很自然…
It is strange that… 奇怪的是…
It is uncertain whether he can come to Jenny's birthday party or not.
他來(lái)不來(lái)參加簡(jiǎn)的生日派對，這個(gè)不確定。
(3)it is ＋不及物動(dòng)詞＋從句
It seems that… 似乎…
It happened that… 碰巧…
It seemed that he didn't tell the truth.
似乎他沒(méi)有講真話(huà)。
It happened that I was out when he called.
碰巧，他打電話(huà)的時(shí)候我在外面。
(4)it＋過(guò)去分詞＋從句
It is reported that… 據報道…
It has been proved that… 已證實(shí)…
It is reported that 16 people were killed in the earthquake.
據報道，在這場(chǎng)地震中，有16人遇難。
常用句型如下：
�。�1）It + be + 名詞+ that從句
It is common knowledge that 是常識
It is a surprise that 令人驚奇的是
It is a fact that 事實(shí)是
�。�2）It + be + 形容詞 + that從句
It is necessary that 有必要
It is important that 重要的是
It is obvious that 很明顯
�。�3）It + be + 動(dòng)詞的過(guò)去分詞+ that從句
It is believed that 人們相信
It is known to all that 眾所周知
It has been decided that 已決定
�。�4）It + 不及物動(dòng)詞 + that 從句
It appears that 似乎
It happens that 碰巧
It occurred to me that 我突然想起
另注意：在主語(yǔ)從句中用來(lái)表示驚奇、不相信、惋惜、理應如此等語(yǔ)氣時(shí)，謂語(yǔ)動(dòng)詞要用虛擬語(yǔ)氣“(should) +do”，常用的句型有：
It is necessary (important, natural, strange, etc.) that
It is suggested (requested, proposed, desired, etc.) that
