一、同位語從句的定義和特點

在主從復(fù)合句中作同位語的從句稱為同位語從句。

同位語從句一般用that, whether，what, which, who, when, where, why, how 等詞引導(dǎo)，常放在fact, news, idea, truth, hope, problem, information, wish,promise, answer, evidence, report, explanation, suggestion, conclusion等抽象名詞后面，說明該名詞的具體內(nèi)容。換言之，同位語從句和所修飾的名詞在內(nèi)容上為同一關(guān)系，對其內(nèi)容作進(jìn)一步說明。

例：The news that they had won the game soon spread over the whole school.
他們比賽獲勝的消息很快傳遍了整個學(xué)校。
析：they had won the game說明The news的全部內(nèi)容，因此該句為同位語從句。

二、正確運用同位語從句的引導(dǎo)詞，準(zhǔn)確把握同位語從句

引導(dǎo)同位語從句的連接詞

?

 功能 例詞
從屬 連詞 ?? 只起連接作用，不充當(dāng)從句中的任何成分。 that, whether
連接 代詞 既起連接作用，又在從句中擔(dān)任成分（主語、賓語、表語或定語）。 who,? what? ，whose, which
連接 副詞 既起連接作用，又在從句中擔(dān)任成分（狀語）。 when,? where, why, how ???
復(fù)合代詞 & 復(fù)合副詞 既起連接作用，又在從句中擔(dān)任成分（主語、賓語、表語或定語、狀語）。 ?whoever, whatever, whichever, whenever, wherever, however

1.如同位語從句意義完整，應(yīng)用that引導(dǎo)同位語從句。（即that 不充當(dāng)任何成分，只起連接作用，不可省略）

例：The general gave the order that the soldiers should cross the river at once.
將軍下達(dá)了戰(zhàn)士們立即過河的命令。
析：the soldiers should cross the river at once是the order的全部內(nèi)容，且意義完整，因此應(yīng)用that引導(dǎo)同位語從句。

2.如同位語從句意義不完整，需增加"是否"的含義，應(yīng)用whether引導(dǎo)同位語從句。（if不能引導(dǎo)同位語從句）

例：We'll discuss the problem whether the sports meeting will be held on time.
我們將討論運動會是否會如期舉行的問題。
析：the sports meeting will be held on time意義不完整，應(yīng)加"是否"的含義才能表達(dá)the problem的全部內(nèi)容，因此應(yīng)用whether引導(dǎo)同位語從句。

3.如同位語從句意義不完整，需增加"什么時候"、"什么地點"、"什么方式"等含義，應(yīng)用when, where, how等詞引導(dǎo)同位語從句。

例1：I have no idea when he will be back.
析：he will be back意義不完整，應(yīng)加"什么時候"的含義才能表達(dá)idea的全部內(nèi)容，因此應(yīng)用when引導(dǎo)同位語從句。

例2：I have no impression how he went home, perhaps by bike.
析：he went home意義不完整，應(yīng)加"如何"的含義才能表達(dá)impression的全部內(nèi)容，因此應(yīng)用how引導(dǎo)同位語從句。

4.當(dāng)主句的謂語較短，而同位語從句較長時，同位語從句常后置。
如：The thought came to him that maybe the enemy had fled the city.

三、把握同位語從句和定語從句的區(qū)別，明確同位語從句和相似從句的界限

同位語從句和定語從句相似，都放在某一名詞或代詞后面，但同位語從句不同于定語從句。同位語從句對名詞加以補充說明，是名詞全部內(nèi)容的體現(xiàn)，且名詞和同位語從句的引導(dǎo)詞均不在從句中作成分；定語從句說明先行詞的性質(zhì)與特征，與先行詞是修飾與被修飾的關(guān)系，且名詞和定語從句的引導(dǎo)詞均在從句中作成分。

區(qū)分時可以在先行詞與從句之間加一個系動詞be,使之構(gòu)成一個新句子，如果句子通順且符合邏輯，則為同位語從句，反之，則為定語從句。

如：The report that he was going to resign was false.
因為the report was that he was going to resign 句意通順，所以，that he was going to resign 是同位語從句。

四、典型例題

1. Some researchers believe that there is no doubt____ a cure for AIDS will be found.
A. which B. that C. what D. whether

2. A warm thought suddenly came to me ____ I might use the pocket money to buy some flowers for my mother's birthday．
A. if B. when C. that D. which

3. Nobody believed his reason for being absent from the class ________ he had to meet his uncle at the airport.
A. why? B. that　C. where D. because

4. Along with the letter was his promise _______ he would visit me this coming Christmas.
A. which B. that C. what D. whether

5. Danby left a word with my secretary ____________ he would call again in the afternoon.
A. who B. that C. as D. which