现针对这一部分做详细的讲一、定语从句对前面的名词具有修饰、限制或描述功能；同位语从句对前面的名词具有补充、解释、说明功能.如：The fact that she told us is believable.她对我们说的话是可信的.(that引导定语从句)The fact that he once joined the army is believable.他曾当过兵这一事实是可信的.(that引导同位语从句) 二、that在引导定语从句时,不光要起连接作用,还要在从句中作成分,若that在从句中作宾语,则that可以省略；而that引导同位语从句时,只起连接作用,不充当从句中的任何成分,且一般不能省略.如：Don’t you forget the promise (that) you made?难道你忘了你许下的诺言吗?(that在定语从句中作宾语,可省略)He makes a promise that he will make you very rich if you work with him.他许下诺言：如果你和他一起干,他会使你很富有.(that在同位语从句中不作任何成分,且不省略) 三、when,where和why在引导定语从句和同位语从句时,它们的共同点是在这两种从句中都可以充当状语.但是,定语从句前有相应的先行词,分别为表示时间、地点和原因状语的名词,而同位语从句前没有相应的名词.如：I still remember the day when (=on which) I first came to Beijing.我仍记得我第一次去北京的那一天.(when引导定语从句)I have no idea when she will be back.我不知道她何时才会回来.(when引导同位语从句) 四、定语从句前面的名词既可以是具体名词,也可以是抽象名词；而同位语从句所修饰词一般是少数抽象名词,从句说明该名词所指的具体内容,如：advice,answer,belief,doubt,fact,hope,idea,information,message,news,order,promise,proposal,possibility,story,suggestion,thought,truth,view,word等.The patient accepted the advice that the doctor gave him.病人接受了医生给他的建议.(定语从句限定advice)The patient accepted the advice that smoking should be given up.病人接受戒烟这一忠告.(同位语从句所表述的是advice的具体内容)This is the book that I bought yesterday.这是我昨天买的那本书.(先行词为具体名词) 五、what,whether和how不可以引导定语从句,但可以引导同位语从句.如：There is some doubt whether she will be dismissed from school.(whether引导同位语从句)她是否将被学校开除还有些怀疑.