1、一名词性从句简介1、主语从句 作句子主语的从句叫主语从句。主语从句通常由连接词 that，whether，if; 连接代词what，whatever，who，whoever ，which; 连接副词 how，when ，where ，why 等词引导。例如：What he wants to tell us is not clear. / Who will win the match is still unknown. (1) 主语从句可以位于句首，但有时为避免句子头重脚轻，常用 it 代替主语从句作形式主语放于句首，而把主语从句置于句末。主语从句后的谓语动词一般用单数形式。That the e
2、arth is round is true. = It is true that the earth is round. Whether he will come hasnt been decided. = It hasnt been decided whether he will come. 常用句型如下： It + be + 名词/形容词+ that 从句 It is a pity that we cant go. It is clear that Tom has returned.It + be + 动词的过去分词 + that 从句 It is said / reported / be
3、lieved / known that It + 不及物动词 + that 从句另:在主语从句中用来表示惊奇、不相信、惋惜、理应如此等语气时，谓语动词要用虚拟语气“(should) +do ”，常用的句型有：It is necessary (important, natural, strange, etc.) that sb. should do sth.It is a pity (a shame, no wonder, etc.) that sb. should do sth.It is suggested (requested, proposed, advised, etc.) that
4、sb. should do sth.(2) 主语从句不可位于句首的五种情况： It is said /reported that结构中的主语从句不可提前。例如：It is said that President Jiang will visit our school next week. That President Jiang will visit our school next week is said. It happens/occurs结构中的主语从句不可提前。例如：It occurred to him that he failed in the examination. That h
5、e failed in the examination occurred to him. It doesnt matter how/whether 结构中的主语从句不可提前。例如：It doesnt matter whether he is wrong or not. Whether he is wrong or not doesnt matter. 含主语从句的复合句是疑问句时，主语从句不可提前。例如：Is it likely that it will rain in the evening? Is that it will rain in the evening likely? if 引导
6、的主语从句It is not clear to me if she likes the present. If she likes the present is not clear to me. 注意：(1)连词 that, whether 在主语从句中不担任句子成分，只起连接作用，不能省略。并且 whether 引导主语从句时不能用 if 代替。 (2)连接代词 who, which 和连接副词 how, when, where, why 在句中既保留自己的疑问含义、又起连接作用，在主语从句中充当主语，宾语，状语，不能省略。可以用形式主语 it 引导。(3)who, whom, which,
7、 what 等可以和 ever 构成合成词，引导主语从句和宾语从句。此类主语从句不能用 it 引导，引导词在句中担任句子成分，不能省略。 2、宾语从句 在复合句中用作宾语的从句是宾语从句;在句中可以作谓语动词或介词及非谓语动词的宾语。引导宾语从句的关联词与引导主语从句，表语从句的关联词大致一样。 1. 由连接词 that 引导的宾语从句连接词 that 引导宾语从句时，that 在句中不担任任何成分，在口语或非正式的文体中常被省去，但如从句是并列句时,第二个分句前的 that 不可省。例如：He has told me (that )he will go to Shanghai tomorro
8、w and that he has got everything ready.2. 用 who，whoever, whom, whose, which, whichever , what, whatever, when , where, why, how等关联词引导的宾语从句相当于特殊疑问句，应注意句子语序要用陈述语序。例如：She always thinks of how she can work well.She will give whoever needs help a warm support. 3. 用 whether 或 if 引导的宾语从句，其主语和谓语的顺序也不能颠倒，仍保持
9、陈述句语序。此外，whether 与 if 在作“是否”的意思讲时在下列情况下一般只能用 whether，不用 if：a. 引导主语从句并在句首时；b. 引导表语从句时；c . 引导从句作介词宾语时；d. 从句后有“or not”时； e. 后接动词不定式时。Whether there is life on the moon is an interesting question. The question is whether she should have a low opinion of the test.Everything depends on whether we have enou
10、gh money. I wonder whether he will come or not. Can you tell me whether to go or to stay?4. 注意宾语从句中的时态呼应，当主句动词是现在时，从句根据自身的句子情况，而使用不同时态。例如：I know (that)he studies English every day. （从句用一般现在时）I know (that)he studied English last term. （从句用一般过去时）I know (that) he will study English next year. （从句用一般将来时
11、）I know (that)he has studied English since 1998. （从句用现在完成时）当主句动词是过去时态（could, would 除外） ，从句则要用相应的过去时态，如一般过去时，过去进行时，过去将来时等；当从句表示的是客观真理，科学原理，自然现象，则从句仍用现在时态。例如： The teacher told us that Tom had left us for America 5. think, believe, expect , imagine, suppose 等动词引起的否定性宾语从句中，要把上述主句中的动词变为否定式，即将从句中的否定形式移到主句
12、中。例如：We dont think you are here. I dont believe he will do so. 3同位语从句 如果担任同位语的是个句子，则这个句子是同位语从句。同位语从句表示先行名词的具体内容，常见的能跟同位语从句的名词有 news、fact, problem , question、wish、hope 、idea、information、advice、suggestion、truth、word, promise、belief, doubt, demand、 message、order 、thought, reply, reason ,request、rumour、
13、等。引导同位语从句常用连词 that，它在句中不担任句子成分，没有词意。除 that 外，还有 whether, when, where, who, what, which, why, how 等。同位语从句与先行名词有时也可以分开。The news that we won the game is exciting. I have no idea when he will come back home. The thought came to him that Mary had probably fallen ill. They have no hope that he will recove
14、r. 注：同位语从句与定语从句的区别： （1）同位语从句的先行名词极为有限，而定语从句的先行词则不计其数。 （2）引导同位语从句的连词 that 没有实际意义，在句中不担任句子成分，一般不能省略。而引导定语从句的 that 则在从句中作主语，宾语等( 在从句中作宾语时可以省略；)。引导同位语从句的 wh 一词多具有疑问意义，而引导定语从句的 wh 一词则没有疑问意义。 I had no idea that you were here （that 引导同位语从句，不能省略）Have you got the idea（that）this book gives you of life in anci
15、ent Greece？（that 引导定语从句，作宾语，可以省略）（3）同位语从句与先行名词是等同关系，一个抽象，一个具体，两者常可以转述为主表关系，定语从句与先行词是修饰与被修饰关系。The news that our team won the game is true.= The news is that our team won the game. (同位语从句)The news that you have heard isnt true. (定语从句)（4）when 和 where 引导的同位语从句与定语从句的区别。when 和 where 前面的名词若是表示时间、地点的名词，则 wh
16、en 和 where 引导的是定语从句，否则为同位语从句。如：They put forward the question where they could get the money.( 同位语从句)This is the place where the accident happened.( 定语从句)4表语从句在句中作表语的从句叫表语从句。它常位于句中联系动词或是起联系动词作用的动词之后。引导表语从句的关联词与引导主语从句的关联词大致一样， The fact is that we have lost the game. Thats just what I want. This is whe
17、re our problem lies. The problem is where we can hold our meeting. That is why he didnt come to the meeting. seem, look, as if, because 等词均可引导表语从句：It seems that /looks as if it is going to rain. It was because I got up late. 注意:当主语是 reason 时，表语从句要用 that 引导而不是 because。例如：The reason why he was late was that (不能省略)he missed the train by one minute this morning.
