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(共43张PPT)
主语从句
一、主语从句的定义
定义：在复合句中充当主语的从句，称为主语从句。主语从句属于名词性从句，本质上是用一个句子替代简单句中的主语成分，通常位于句首（或用it作形式主语置于句首，从句后置）。
例句：
That he will come to the party is certain.
（他会来参加派对，这是确定的。——That引导的从句作主语）
What she said surprised everyone.
（她所说的话让所有人都惊讶。——What引导的从句作主语）
判断下列句子中划线部分是否为主语从句，是的打“√”，不是的打“×”，并说明理由。
She believes that he is honest.（ ）
Whether we can finish the task on time depends on our teamwork.（ ）
The news that he won the competition spread quickly.（ ）
How he solved the problem is still a mystery.（ ）
× 理由：划线部分为宾语从句，作谓语动词believes的宾语，而非主语。
√ 理由：划线部分为Whether引导的主语从句，在句中充当主语。
× 理由：划线部分为同位语从句，解释说明先行词the news的具体内容，主语是the news。
√ 理由：划线部分为How引导的主语从句，在句中充当主语。
二、主语从句的三要素
（一）语序
核心规则：主语从句必须使用陈述语序，即“引导词+主语+谓语+其他成分”，无论引导词是否为疑问词，都不能用疑问语序。
正确例句：When he will arrive is unknown.（他何时到达还不清楚。——陈述语序）
错误例句：When will he arrive is unknown.（疑问语序，需修正）
改正下列句子中的语序错误，使句子通顺。
What did she do yesterday is not important.
Whether will they go hiking tomorrow depends on the weather.
How can we improve our English quickly is a hot topic.
What she did yesterday is not important.（引导词What后接陈述语序，将did she do改为she did）
Whether they will go hiking tomorrow depends on the weather.（引导词Whether后接陈述语序，将will they改为they will）
How we can improve our English quickly is a hot topic.（引导词How后接陈述语序，将can we改为we can）
（二）引导词
主语从句的引导词分为三类，需根据从句的句意和成分选择，具体如下：
引导词类型 具体引导词 用法说明 例句
连词（无词义，不充当成分） That 引导陈述句作主语从句，不可省略；常用在it作形式主语的结构中 That he missed the train made his mother angry.
连词（有词义，不充当成分） Whether（是否） 引导不确定的疑问语气，不可用if替代（主语从句中只能用whether） Whether she will accept the invitation is uncertain.
连接代词（有词义，充当成分） What, Who, Whom, Whose, Which, Whatever, Whoever, Whichever 在从句中充当主语、宾语、定语、表语等成分 What he needs is a good rest.（What作从句宾语）
连接副词（有词义，充当成分） When, Where, Why, How, Whenever, Wherever, However 在从句中充当状语（时间、地点、原因、方式等） Why he resigned suddenly is a secret.（Why作从句原因状语）
选择合适的引导词填空，每空一词。
______ he said at the meeting moved all of us deeply.
______ we will hold the sports meeting hasn’t been decided yet.
______ broke the window last night is still under investigation.
______ you choose to live is your own business.
It’s important that ______ we do should be legal.
What 解析：从句中缺少宾语，结合句意“他在会议上说的话”，用连接代词What。
Whether 解析：从句表“是否举办运动会”，主语从句中表“是否”用Whether，不用if。
Who 解析：从句中缺少主语，结合句意“谁打破了窗户”，用连接代词Who。
Where 解析：从句中缺少地点状语，结合句意“你选择在哪里居住”，用连接副词Where。
whatever 解析：从句中缺少宾语，结合句意“我们做的任何事都应合法”，用连接代词whatever表泛指。
（三）主谓一致
核心规则：主语从句作主语时，谓语动词通常用单数形式；若从句表示两个或多个并列概念，谓语动词用复数形式。
补充要点：
单个主语从句作主语，谓语用单数：That she is a doctor is true.
并列主语从句（由and连接）表两个不同概念，谓语用复数：What he said and what he did are quite different.
并列主语从句表同一概念（如“衣食住行”类固定搭配），谓语用单数：What he eats and drinks is good for his health.
根据句意，用括号内动词的适当形式填空。
That he will attend the meeting ______（be）certain.
What he told me and what I saw ______（be）two different things.
How to solve the problem ______（be）a difficult task for us.
Whether they will come and when they will arrive ______（not be）clear yet.
What the teacher said ______（have）great influence on us.
is 解析：单个主语从句作主语，谓语用单数，时态为一般现在时。
are 解析：两个并列主语从句表不同概念，谓语用复数。
is 解析：“疑问词+不定式”结构作主语，视为单数，谓语用is。
are not 解析：两个并列主语从句表不同疑问，谓语用复数，结合yet用一般现在时。
has 解析：单个主语从句作主语，谓语用单数，have的第三人称单数形式为has。
三、主语从句的用法
主语从句主要有两种用法，核心区别在于从句的位置：
（一）直接位于句首作主语
从句直接放在句首，后面接谓语动词，适用于从句较短、句意简洁的情况。
例句：Who will be our new monitor is to be decided by the class.
（二）用it作形式主语，从句后置
当主语从句较长时，为避免句子头重脚轻，常用it作形式主语，将真正的主语从句置于句末。（详细内容见第四部分）
1. 将下列句首主语从句改写为“it作形式主语”的结构。
That we should protect the environment is everyone’s duty.
2. 判断下列句子的用法是否正确，错误的改正。
It is a pity that he failed the exam is true.
It is everyone’s duty that we should protect the environment. 解析：将较长的主语从句后置，用it作形式主语，使句子结构平衡。
错误，改正为：It is a pity that he failed the exam. 或 That he failed the exam is a pity. 解析：原句重复了主语结构（It和that从句均表主语），需删除其一，保持句式正确。
四、it作形式主语的主语从句
核心用法：it是形式主语，无实际语义，真正的主语是后置的从句，常见句式有4类：
It + be + 形容词 + that从句（形容词多为描述态度、评价的词，如important, necessary, clear, certain等）
It + be + 名词短语 + that从句（名词短语如a pity, a fact, a secret, an honor等）
It + be + 动词的被动语态 + that从句（常见动词如say, report, believe, know等）
It + 不及物动词 + that从句（常见动词如happen, occur, seem, appear等）
例句：
It is important that we should study hard.（我们应该努力学习，这很重要。）
It is a pity that you can’t come with us.（你不能和我们一起去，真遗憾。）
It is reported that the city will hold an international festival.（据报道，这座城市将举办国际节日。）
It happened that I met my old friend yesterday.（我昨天碰巧遇到了我的老朋友。）
1. 用it作形式主语改写句子：That he passed the driving test made his parents happy.
2. 根据句意，补全下列“it作形式主语”的句子。
It is necessary that we ______（finish）the work before Friday.
It ______（report）that the temperature will drop sharply tomorrow.
It seems that she ______（know）the truth already.
It made his parents happy that he passed the driving test. 解析：将主语从句后置，it作形式主语，保持句意不变，句式更平衡。
（should）finish 解析：在It is necessary that...结构中，从句谓语用“should+动词原形”，should可省略，表虚拟语气。
is reported 解析：固定句式It is reported that...，表“据报道”，用一般现在时的被动语态。
knows 解析：It seems that...从句用一般现在时，主语she为第三人称单数，谓语用knows。
五、主语从句的注意事项
注意事项1：whether与if的区别
主语从句中，表“是否”只能用whether，不能用if；if仅可引导宾语从句、条件状语从句。
正确：Whether he will come is unknown. 错误：If he will come is unknown.
注意事项2：that的不可省略性
主语从句位于句首时，引导词that不可省略；若用it作形式主语，that从句后置时，that可省略（但正式文体中建议保留）。
正确：That she is late is unusual. / It is unusual（that）she is late.
注意事项3：虚拟语气的使用
在It is important/necessary/strange/adviseable that...结构中，主语从句的谓语用“should+动词原形”，should可省略，表虚拟语气。
例句：It is strange that he（should）be absent from class.
改正下列句子中的错误。
If we can go abroad depends on our grades.
She said that he would come is a lie.
It is important that we must finish the task on time.
That he is a good student is known to all of us.
将If改为Whether 解析：主语从句中表“是否”只能用Whether，不能用if。
在She said后加that，即She said that that he would come is a lie. 或改为That he would come, she said, is a lie. 解析：原句为复合句嵌套，主句谓语said后需接宾语从句，第二个that引导主语从句，不可省略，需补充第一个that使句式清晰。
将must改为（should） 解析：It is important that...结构中，从句用虚拟语气，谓语为“should+动词原形”，should可省略，不能用must。
正确 解析：主语从句位于句首，that不可省略，句式和语义均正确。
六、易混淆从句类型辨析
主语从句常与同位语从句、定语从句、表语从句混淆，核心区别在于从句的功能（充当主语/同位语/定语/表语）和引导词的作用。
从句类型 核心功能 引导词特点 例句对比
主语从句 充当句子主语 that无词义不充成分；连接代词/副词有词义充成分 That he won the prize surprised us.（主语）
同位语从句 解释说明先行词（名词） 先行词多为抽象名词（news, fact, idea等），that无词义不充成分 The news that he won the prize surprised us.（解释news）
定语从句 修饰先行词（名词/代词） 引导词（关系词）在从句中充成分，可指代先行词 The news that he told me surprised us.（that指代news，作从句宾语）
表语从句 充当系动词后的表语 与主语从句引导词用法一致，位于系动词后 The surprise is that he won the prize.（表语）
判断下列句子中划线从句的类型（主语从句/同位语从句/定语从句/表语从句）。
The fact that she has passed the exam makes her family proud.
What he wants is a new computer.
I have no idea whether he will come or not.
The book that I borrowed from the library is very interesting.
My hope is that we can travel together next year.
主语从句 解析：划线从句充当句子主语，the fact并非先行词（若为同位语从句，the fact需是独立主语，从句仅解释说明）。
主语从句 解析：划线从句充当句子主语，What在从句中作宾语。
同位语从句 解析：划线从句解释说明先行词idea的具体内容，that无词义不充成分。
定语从句 解析：划线从句修饰先行词the book，that指代the book，在从句中作宾语。
表语从句 解析：划线从句位于系动词is后，充当表语。
用适当的引导词、动词形式填空，每空1词。
______ he will go to college depends on his grades.
It is a fact ______ English is widely used in the world.
What he said ______（be）very meaningful for us.
It is important that we ______（learn）from our mistakes.
______ broke the glass is still a mystery.
It is reported that a new bridge ______（build）next year.
How we can get there ______（not decide）yet.
______ you like the movie or not is none of my business.
It happened that I ______（meet）my teacher in the street yesterday.
Whatever you ______（do）, you should stick to it.
Whether/That 2. that 3. is 4.（should）learn 5. Who 6. will be built 7. hasn’t been decided 8. Whether 9. met 10. do
下列句子均有一处错误，请找出并改正。
If we will have a picnic tomorrow is not decided.
That she is late for school is because she missed the bus.
It is necessary that he must finish the work today.
What he told me and what I heard was different.
It is strange that she is absent from the meeting.
If→Whether 2. because→why 3. must→（should） 4. was→were
5. is→（should）be
按要求改写句子，保持句意不变。
That he didn’t attend the meeting made the manager angry.（改为it作形式主语）
We don’t know when we will start the project.（改为主语从句作主语）
It is a pity that you can’t join us.（改为句首主语从句）
Whether they will help us is uncertain.（改为it作形式主语）
He will come to the party. It is certain.（合并为主语从句）
答案
It made the manager angry that he didn’t attend the meeting.
When we will start the project is unknown to us.
That you can’t join us is a pity.
It is uncertain whether they will help us.
That he will come to the party is certain. / It is certain that he will come to the party.
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