現針對這一部分做詳細的講一、定語從句對前面的名詞具有修飾、限制或描述功能；同位語從句對前面的名詞具有補充、解釋、說明功能.如：The fact that she told us is believable.她對我們說的話是可信的.(that引導定語從句)The fact that he once joined the army is believable.他曾當過兵這一事實是可信的.(that引導同位語從句) 二、that在引導定語從句時,不光要起連接作用,還要在從句中作成分,若that在從句中作賓語,則that可以省略；而that引導同位語從句時,只起連接作用,不充當從句中的任何成分,且一般不能省略.如：Don’t you forget the promise (that) you made?難道你忘了你許下的諾言嗎?(that在定語從句中作賓語,可省略)He makes a promise that he will make you very rich if you work with him.他許下諾言：如果你和他一起干,他會使你很富有.(that在同位語從句中不作任何成分,且不省略) 三、when,where和why在引導定語從句和同位語從句時,它們的共同點是在這兩種從句中都可以充當狀語.但是,定語從句前有相應的先行詞,分別為表示時間、地點和原因狀語的名詞,而同位語從句前沒有相應的名詞.如：I still remember the day when (=on which) I first came to Beijing.我仍記得我第一次去北京的那一天.(when引導定語從句)I have no idea when she will be back.我不知道她何時才會回來.(when引導同位語從句) 四、定語從句前面的名詞既可以是具體名詞,也可以是抽象名詞；而同位語從句所修飾詞一般是少數抽象名詞,從句說明該名詞所指的具體內容,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.病人接受了醫(yī)生給他的建議.(定語從句限定advice)The patient accepted the advice that smoking should be given up.病人接受戒煙這一忠告.(同位語從句所表述的是advice的具體內容)This is the book that I bought yesterday.這是我昨天買的那本書.(先行詞為具體名詞) 五、what,whether和how不可以引導定語從句,但可以引導同位語從句.如：There is some doubt whether she will be dismissed from school.(whether引導同位語從句)她是否將被學校開除還有些懷疑.