It：英语句子里最忙的'临时工'

英语中，当真正的主语太长时，通常用 it 占住句首，把不定式、动名词或主语从句"丢"到句尾——这就是形式主语的核心逻辑。

1

一、四大类型全解

类型一：It + be + 形容词/名词 + to do sth.

初高中最高频句型。真正主语是不定式短语。

It is important to learn English well.

学好英语很重要。

It was a mistake to trust him.

信任他是一个错误。

It is necessary for us to have some exercise every day.

我们每天有必要进行一些锻炼。（for us 是不定式的逻辑主语）

必背形容词：important, necessary, difficult, easy, hard, possible, impossible, useful, dangerous

类型二：It + be + 形容词/名词 + doing sth.

动名词作真正主语，频率低于不定式，但有固定搭配必须掌握。

It is no use crying over spilt milk.

覆水难收。

It is a waste of time arguing further.

继续争论是浪费时间。

It is dangerous playing with fire.

玩火是危险的。

✦ 必背搭配：no use / no good / useless / worth / worthwhile / dangerous / a waste of time + doing

◈ 类型三：It + be + 形容词/名词/过去分词 + that从句

主语从句作真正主语，考试中结构最复杂。

① It is + 形容词 + that 从句

It is obvious that the strength of a country's economy is directly bound up with the efficiency of its agriculture and industry.

显而易见的是，一个国家的经济实力与其工农业生产效率密切相关。

② It is + 名词 + that 从句

It is a fact that English is being accepted as an international language.

英语正被接受为国际语言，这是一个事实。

③ It is + 过去分词 + that 从句（"据说/据报道"类）

It is reported that a severe storm hit that area last week.

据报道，上周暴风雨袭击了那个地区。

It has been proved that what you said is right.

已经证明你说的是对的。

必背过去分词：said, reported, believed, thought, known, proved, suggested, estimated

◈ 类型四：It + 不及物动词 + that从句 / It takes/costs + sb. + 时间/金钱 + to do

① It + 不及物动词 + that 从句

It so happened that I had no money that day.

碰巧那天我没带钱。

It turned out that he had passed the exam.

结果他通过了考试。

It seems that he knows the truth.

似乎他知道真相。

✦ 必背不及物动词：happen, seem, appear, turn out, occur, follow

② It takes/costs + sb. + 时间/金钱 + to do sth.

It took her three hours to mend her bicycle.

她修自行车花了三个小时。

It cost us $500 to buy the bed.

我们买那张床花了500美元。

二、特别补充：find/think/consider + it + 形容词/名词 + to do（形式宾语，与形式主语对照）

这是初高中极易混淆的考点。区别在于：

✦ 形式主语：it 在句首，真正主语在后面。结构：It is + adj. + to do / that...

✦ 形式宾语：it 在动词后，真正宾语在后面。结构：主语 + find/think/make/consider + it + adj./n. + to do / that...

真题例句：

I find it difficult to learn English well.

我发现学好英语很难。

（it 是形式宾语，真正宾语是 to learn English well）

We think it our duty to protect the environment.

我们认为保护环境是我们的责任。

（it 是形式宾语，真正宾语是 to protect the environment）

He made it clear that he would not give up.

他明确表示他不会放弃。

（it 是形式宾语，真正宾语是 that 从句）

必背动词：find, think, make, consider, feel, believe, regard, take

三、考点与易错点

✦ 考点一：识别真正主语/宾语。

看到 it 在句首或动词后，立刻问：真正的主语/宾语在哪？往往在句尾。

✦ 考点二：for sb. vs. of sb. 的区别。

It is important for sb. to do 中 important 描述事情；It is kind of sb. to do 中 kind 描述人的品质。

✦ 考点三：虚拟语气。

It is necessary/important/essential + that 从句时，从句谓语用 (should) + 动词原形。

✦ 易错点一：和强调句混淆。

黄金检验法——去掉 It is…that，剩余部分若完整，是强调句；不完整，是形式主语。

例：It is obvious that he is lying. → 去掉后 "Obvious he is lying" 不完整 → 形式主语

例：It was in the library that I met him. → 去掉后 "I met him in the library" 完整 → 强调句

✦ 易错点二：形式主语 vs. 形式宾语。

it 在句首是形式主语；it 在动词后是形式宾语。切勿混淆。

✦易错点三：that 不能换成 what/which。

主语从句引导词只能用 that，且 that 不可省略（正式写作中）。

✦ 易错点四：It is the first time that... 中的 it 不是形式主语，而是指时间的人称代词，that 引导定语从句。

✦ 易错点五：It is no use doing 中只能用 doing，不能用 to do。

类似还有 no good / useless / worth / worthwhile。

四、真题实战 10 道

第1题 Does ______ matter if he can't finish the job on time?

A. this　B. that　C. he　D. it

答案 D。 it 作形式主语，真正主语是 if he can't finish the job on time 这个从句。matter 是谓语，"有关系/要紧"。

第2题 ______ is a fact that English is being accepted as an international language.

A. There　B. This　C. That　D. It

答案 D。 形式主语 it 代替 that 引导的主语从句。There be 句型不能这样用。

第3题 In fact ______ is a hard job for the police to keep order in an important football match.

A. this　B. that　C. there　D. it

答案 D。 形式主语 it，真正主语是 to keep order...。for the police 是不定式的逻辑主语。

第4题 ______ is no good reading without full understanding.

A. Now　B. That　C. This　D. It

答案 D。 形式主语 it 代替动名词短语 reading without full understanding。no good + doing 是固定搭配。

第5题 ______ took us several hours to clear the snows and open the road to traffic.

A. They　B. All　C. He　D. It

答案 D。 It takes sb. some time to do sth. 句型，it 作形式主语。

第6题 I find ______ difficult to work with him.

A. that　B. this　C. it　D. him

答案 C。 这是形式宾语！find + it + adj. + to do。it 是形式宾语，真正宾语是 to work with him。句意：我发现和他一起工作很难。

第7题 ______ is known to everybody that the moon travels round the earth once every month.

A. It　B. As　C. That　D. What

答案 A。 形式主语 it 代替 that 从句。注意对比：As is known to everybody, the moon...（As 引导非限制性定语从句）才是另一个正确结构，但本题空后直接跟 is，只能用 It。

第8题 ______ is suggested that you read some meaningful books and do some physical exercise.

A. This　B. It　C. That　D. What

答案 B。 It is suggested that... 是典型的形式主语 + 过去分词 + that 从句结构，意为"有人建议……"。

第9题 We consider ______ our duty to help those in need.

A. that　B. this　C. it　D. one

答案 C。 形式宾语！consider + it + n. + to do。it 是形式宾语，真正宾语是 to help those in need。句意：我们认为帮助有需要的人是我们的责任。

第10题 It is not obvious ______ the capacity to visualize objects suits one to answer questions.

A. what　B. that　C. how　D. which

答案 C。 it 是形式主语，真正的主语是 how 引导的主语从句。句意：这种想象物体的能力如何让人回答某些问题，这一点并不明显。