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1、名词性从句在复合句中起词名词作用的句子叫名词性从句 (Noun Clauses）。 名词性从句的功能相当于名词，可分别作主句的主语、表语、宾语和同位语。因此，名词性从句可分为主语从句、表语从句、宾语从句和同位从句。（一）引导名词性从句的连接词1）连接代词： who, whose, whom, what, which有词义，在从句中必须充当句子成分，如主语、表语、宾语或定语等。2）连接副词： when, where, why, how有词义，在从句中必须充当成分，只能作状语。3）连接词： that, whether, if, as if that 无词义，在从句中不充当成分，做宾语时可省略；if
2、 ，whether，as if虽有词义，但在从句中不担任成分。注意：连接代词与连接副词在句中不再是疑问词，因而从句中谓语不用疑问式。连接代词与连接副词在从句充当句子成分，连接词whether 和if（是否），as if（好象）在从句中不充当句子成分，只起连接作用。根据句义，如果连接代词与连接副词，whether、if 和as if都用不上时，才用that作连接词（that本身无任何含义）。 4）连接代词：whatever, whoever, whomever, whichever 5）语序名词性从句都必须与陈述句语序相同，即“主语谓语”。（二）主语从句:在复合句中其语法作用是主语的句中，叫主语
3、从句。1）主语从句位于句首e.g. （1）That he finished writing the composition in such a short time surprised us all.（2）Whether we will go for an outing tomorrow remains unknown.(注意：不能把whether改为if， 因为if不能引导主语从句)（3）Whatever you did is right. （4）Who will be our monitor hasnt been decided yet.（5）What caused the acciden
4、t remains unknown.（6）Which of the two is better remains to be seen.（7）When we will start the work is important.2）为了避免句子头重脚轻，用it作形式主语，主语从句放在句末。e.g. （1）It doesnt matter so much whether you will come or not. （2）It is true that he has made a very important discovery in chemistry.（3）It is a pity that we
5、wont be able to go to the south to spend our summer vacation.（4）Is it likely that it will rain in the evening ? 3）it 作形式主语的主语从句有时为了考虑句子平衡，通常在主语从句处使用形式主语it，而将真正的主语从句移至句末。这分四种情况：(1) 对于以连词that引导的主语从句，通常用形式主语it替代主语从句： It is + 名词 + 从句 It is a fact that 事实是； It is good news that 是好消息；It is a question that
6、 是个问题； It is common knowledge that 是常识类似的名词还有：a pity；a wonder；a good thing； no wonder； surprise等。It is a mystery to me how it all happened. It is common knowledge that the whale is not a fish.It is no surprise that Bob should have won the game. It is +形容词 + 从句It is necessary that 有必要； It is clear th
7、at 很清楚；It is likely that 很可能； It is important that 重要的是 类似的形容词还有：strange; natural; obvious; true; good; wonderful; possible; unlikely; unusual; certain; evident; surprising; interesting; astonishing, etc.It is doubtful whether she will be able to come.It seems obvious that we can not go on like this
8、.It is necessary that you（should）master the computer. 需要注意的是这类主语从句中，谓语动词很多为“（should）动词原形”，即要用虚拟语气。 It is +过去分词 + 从句 It is said that 据说； It is reported that 据报道；It has been proved that 已证明； It must be proved that 必须指出类似的过去分词还有：known; expected; believed; thought; hoped; required; suggested; demanded;
9、etc.例如：It is said that honesty is the best policy.It is said that thirteen is an unlucky number.It is reported that over 300 million people in China are suffering from near-sightedness.It is known to all that the earth is round. 高考题链接：1. It never occurred to me_you could succeed in persuading him to
10、 change his mind.(陕西高考)Awhich Bwhat Cthat Dif2. Its obvious to the students_they should get well prepared for their future.(天津卷)Aas Bthat Cwhich Dwhether3. _some people regard as a drawback is seen as a plug by many others.( 北京) AWhether BWhat CThat DHow4. It is uncertain_side effect the medicine wi
11、ll bring about，although about two thousand patients have taken it.(浙江)Athat Bhow Cwhat Dwhether（三）表语从句：在复合句中作表语的完整句子，位于be动词或系动词之后，说明主语是什么或者怎么样。e.g. （1）The question was who could go there. （2）He has become what he wanted to be ten years ago. （3）She has remained where I stood yesterday for an hour. （4
12、）His suggestion is that we should stay calm.（5）It seems as if it is going to rain.（6）The question is whether the enemy is marching towards us. (注意：不能把whether改为if， 因为if不能引导表语从句)（7）What she couldnt understand was why fewer and fewer students showed interest in her lessons.（四）宾语从句：宾语从句在复合句中作宾语，引导宾语从句的连
13、词that一般可省略。e.g. I hope (that) everything is all right.1）介词之后的宾语从句，不可用which或if连接，要分别用what或 whether。e.g. Im interested in whether youve finished the work. Im interested in what youve said. 2）whether与if都可以引导宾语从句，常可互换，但下面情况不能互换。 宾语从句是否定句时，只用if，不用whether。e.g. I wonder if it doesnt rain.宾语从句中的whether 与or
14、not直接连用，就不能换成if。e.g. I dont know whether the report is true or not.注意：介词后的宾语从句要用whether引导，whether 可与不定式连用。whether也可引导主语从句、表语从句、同位语从句，以上均不能换成if。但引导条件从句时，只能用if，而不能用whether。e.g. It depends on whether we have enough time.They dont know whether to go there. Please come to see me if you have time. （五）同位语从句：在复合句中作某一抽象名词的同位语，一般位于该名词之后。（如：promise，message，doubt，belief，reason，possibility，conclusion，thought，order，question，problem，report，rumor，hope，truth，news，fact，idea，suggestion，evidence等）e.g. I have no idea when he will be back.The fact that he had not said anything surprised everybody.Ive com
