在考研英語的文章中，同位語從句和定語從句都放在被修飾詞的后邊，從形式上來看，它們十分相似，很多同學(xué)搞不清楚涉及到定語從句和同位語從句的相關(guān)知識點。為了減少大家在讀文章時的相關(guān)障礙，老師現(xiàn)就同位語從句和定語從句的相關(guān)區(qū)別給大家做一個講解。

（一）連接詞作用不同。

以that為例，連接定語從句的that一定會在從句中充當(dāng)一定的成分；而連接同位語從句的that只起連接作用，不在從句中擔(dān)任任何句子成分。whether 和 how 可以引導(dǎo)同位語從句，但不能引導(dǎo)定語從句。關(guān)系代詞和關(guān)系副詞除了連接從句的作用外，還在定語從句中充當(dāng)一定的句子成分，如主語、賓語、定語、表語等。引導(dǎo)定語從句的連接詞是關(guān)系詞，常見的關(guān)系代詞和關(guān)系副詞有that , which , who , whose , whom , when , where , why , as，than, but等

The fact that we talked about is very important.

The fact that he succeeded in the experiment pleased everybody.

（二）先行詞不同。

定語從句先行詞既可以是人，也可以是物。相當(dāng)于形容詞。

The moon is a satellite that goes round the earth.

The few points that the president stressed in his report are very important.

同位語從句進(jìn)一步說明的是具有抽象概念的詞，其作用相當(dāng)于名詞，對前面的名詞進(jìn)行補(bǔ)充說明。如fact, result, discovery，belief , doubt , fact , hope , idea , news , possibility , thought , order , suggestion , wish , answer , information , conclusion , decision , discovery , knowledge , law , opinion , problem , promise , proof , question , report , truth , risk等等。

He has an idea that he can make the scientific instrument in a better way.

He expressed the hope that he would come to China.

（三）從引導(dǎo)詞來看

如果引導(dǎo)從句的詞為when表示時間，where表示地點，why表示原因，how怎么樣，表示方式，而它前面的詞分別表示時間，地點，原因，方式等意義，那它們就是關(guān)系副詞，引導(dǎo)的是定語從句。

I’ll never forget the day when I saw the Great Wall.

This is the room where LuXun once lived.

The question when we will start the work is not decided.

You have no idea how worried I was.