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名词性从句在句子中起名词作用的句子叫名词性从句。名词性从句的功能相当于名词词组,它在复合句中能担任主语、宾语、表语、同位语、介词宾语等,因此根据它在句中不同的语法功能,名词从句又可分为主语从句、宾语从句、表语从句和同位语从句。主语从句的用法一.主语从句在复合句中作主语,它可以位于句首,但常见的主语从句多放在句末,句首则用形式主语it。1.Thattheearthisroundistrue.=Itistruethattheearthisround.2.Whetherhewillcomehasn’tbeendecided.=Ithasn’tbeendecidedwhetherhewillcome.注意:连词that,whether在从句中不担任句子成分,只起连接作用,不能省略(注:if不可用来引导主语从句）二.用it作形式主语的结构(1)Itis＋名词＋从句Itisafactthat…事实是…Itisanhonorthat…非常荣幸Itiscommonknowledgethat…是常识(2)Itis＋形容词＋从句(多用should)Itisnaturalthat…很自然…Itisstrangethat…奇怪的是…(3)Itis＋不及物动词＋从句Itseemsthat…似乎…Ithappenedthat…碰巧…Itappearsthat…似乎…(4)Itis＋过去分词＋从句Itisreportedthat…据报道…Ithasbeenprovedthat…已证实…Itissaidthat…据说…it作形式主语和it引导强调句的比较it作形式主语代替主语从句,主要是为了平衡句子结构,主语从句的连接词有变化。而it引导的强调句则是对句子某一部分进行强调,无论强调的是什么成分,都可用连词that。被强调部分指人是也可用who/whom。例如:判断:Itisapitythatyoudidn’tgotoseethefilm.Itdoesn’tinterestmewhetheryousucceedornot.Itisinthemorningthatthemurdertookplace.ItisJohnthatbrokethewindow宾语从句的用法：句子结构：主句+连接词(引导词)+宾语从句连接词:从属连词that,whether,if连接代词Who,whom,whose,which,what连接副词where,how,why,when一.连词(引导词)1.当宾语从句是陈述句时(包括肯定句和否定句),连词由that引导,因为that在从句中不作任何成分,也没有任何具体意思,因此在口语或非正式文体中常省略。Janesaid(that)shewasn’tlateforthemeeting.2.当宾语从句是特殊疑问句时,由特殊疑问词充当连接词,因为该特殊疑问词(即连接词)在从句中担任一定的句子成分,具有一定的意义,所以不可以省略。Doyouknowwhathesaidjustnow?Idon’trememberwhenwearrived3.当宾语从句是一般疑问句时,由连词whether或if引导(口语中常用if),因为if/whether翻译成是否,具有一定的意义,所以不能省略。Lilywantedtoknowif/whetherhergrandmalikedthehandbag.Let’sseeif/whetherwecanfindoutsomeinformationaboutthatcity注意:①关联词只能用whether不能用if表示“是否”的情况如下：A)在表语从句和同位语从句中。如：Thequestioniswhetherthefilmisworthseeing.Thenewswhetherourteamhaswonthematchisunknown.B)在主语从句中，只有用it作形式主语时,whether和if都能引导主语从句,否则,也只能用whether。如:Whetherweshallattendthemeetinghasn’tbeendecidedyet.Ithasn’tbeendecidedwhether(if)weshallattendthemeeting.C)在介词之后。(介词往往可以省略)如:Italldepends(on)whethertheywillsupportus.D)后面直接跟动词不定式时。如：Hedoesn’tknowwhethertostayornot.E)后面紧接ornot时。如：Wedidn’tknowwhetherornotshewasready.②关联词if,whether均可使用的情况如下：A)引导宾语从句。如：Iwonderif(whether)thenewsistrueornot.B)在“be+形容词”之后。如：Hewasnotsurewhether(if)itisrightorwrong.宾语从句要注意的几个问题•1.时态呼应•2.否定转移:•3.形式宾语it的使用注:在think,believe,suppose,expect等动词之后,宾语从句中谓语的否定常转移到主句的谓语上。Idon’tthinkhewillseeyou.Idon’tbelievehewillgo.注:在接复合宾语的句子中(S+Vt+O+Oc),为了保持句子平衡,用it作形式宾语,将从句放于句尾,常接复合宾语的动词有:make,find,see,hear,feel,think...Ithinkitnecessarythatwetakeplentyofhotwatereveryday.Ithinkitapitytowastethefood表语从句的用法在复合句中用作表语的从句是表语从句,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,表语从句位于连系动词后,有时用asif引导。其基本结构为:主语+系动词+that从句。That’swhatweshoulddo.That’swhyIwanttoseeyou.1.be,seem,look等动词后均可跟表语从句：Mysuggestionisthatweshouldgoshopping.Itseemsthatitisgoingtorain.2.asif,because也可引导表语从句。Itlooksasifit’sgoingtorain.ItwasbecauseIgotuplate.3.在非正式文体中,引导表语从句的that可以省略。如:Thetroubleis(that)heisill.注意:在表语从句中,当reason做主语时,引导词只能用that,不能用because,如:他迟到的原因是因为他没有赶上早班车。Thereasonwhyhewaslatewasthathedidn’tcatchtheearlybus.同位语从句同位语从句一般跟在名词fact,news,promise,truth,belief,thought,idea,answer,information,knowledge,doubt,hope,law,opinion,plan,suggestion后面,用以说明或解释前面的名词.Thenewsthatourteamhaswonthematchistrue.Hisdelayisduetothefactthatthecarwentwronghalfway.注:1.that引导同位语从句与that引导定语从句的区别:引导同位语从句的that无实际意义,不作从句的任何成分,而引导定语从句的that从句的某个成分Hetoldmethenewsthatourteamwonthematch.Hetoldmethenewsthatwasveryexciting.Weareinterestedinthenewsthatsomeforeignerswouldvisitourschool.Weareinterestedinthenewsthathetoldus.2.在havenoidea之后常用wh-引导同位语从句.Ihavenoideawherehehasgone.Ihavenoideawhenhedidit.Ihavenoideawhathedid.