一、同位語從句的定義和特點
在主從復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，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容。換言之，同位語從句和所修飾的名詞在內容上為同一關系，對其內容作進一步說明。
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校。
析：they had won the game說明The news的全部內容，因此該句為同位語從句。
二、正確運用同位語從句的引導詞，準確把握同位語從句
引導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，又在從句中擔任成分(狀語)。when, where, why, how
復合代詞 & 復合副詞既起連接作用，又在從句中擔任成分(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，應用that引導同位語從句。(即that 不充當任何成分，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.
將軍下達了戰士們立即過河的命令。
析：the soldiers should cross the river at once是the order的全部內容，且意義完整，因此應用that引導同位語從句。
2.如同位語從句意義不完整，需增加"是否"的含義，應用whether引導同位語從句。(if不能引導同位語從句)
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，應加"是否"的含義才能表達the problem的全部內容，因此應用whether引導同位語從句。
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，應用when, where, how等詞引導同位語從句。
例1：I have no idea when he will be back.
析：he will be back意義不完整，應加"什么時候"的含義才能表達idea的全部內容，因此應用when引導同位語從句。
例2：I have no impression how he went home, perhaps by bike.
析：he went home意義不完整，應加"如何"的含義才能表達impression的全部內容，因此應用how引導同位語從句。
4.當主句的謂語較短，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，是名詞全部內容的體現，且名詞和同位語從句的引導詞均不在從句中作成分;定語從句說明先行詞的性質與特征，與先行詞是修飾與被修飾的關系，且名詞和定語從句的引導詞均在從句中作成分。
區分時可以在先行詞與從句之間加一個系動詞be,使之構成一個新句子，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. thatC. 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
（兼職編輯：張博）
