在複合句中充當同位語的名詞性從句稱為同位語從句。
一 同位語從句的位置
1 同位語從句常跟在某些抽象名詞（如idea, news, fact, promise, hope, message等）後面。如
The news that our women volleyball team had won the championship encouraged us all greatly.
我們女排贏得冠軍的消息大大地鼓舞了我們所有人。
2有時同位語從句不緊跟在它所修飾的名詞後，而被別的詞隔開，在語法上叫做分隔式同位語從句。如
The thought came to her that maybe she had left the
door open whenshe left home. 她突然想起可能在她離開家時沒把門關上。
二 同位語從句前面的名詞通常用單數，且往往帶有限定詞加以修飾（word除外)。如：
Where did you get the idea that I could not come?
你在哪兒聽說我不能來？
Word came that China launched its first manned spaceship on Oct 15, 2003.消息傳來，中國於2003年10月15日首次成功發射了載人宇宙飛船。
三 同位語從句連接詞有that, who, whether, how, when, where等
They were all very much worried over the fact that you were sick.
對你生病這件事，他們都很擔心。
注意：名詞doubt「懷疑」後面的同位語從句用whether連接；在no doubt 「不懷疑」後的同位語從句用that連接。如
We have some doubt whether they can complete the task on time.
我們懷疑他們是否準時完成任務。
There is no doubt that Zhang Wei will keep his promise.
我們相信張偉會遵守諾言的。
1 以下名詞常用that引導
advice, announcement, argument, belief, claim, conclusion, decision, evidence, explanation, fact, feeling, hope, idea, impression, information, knowledge, message, news,opinion, order, probability, promise, proposal, remark, reply, report, reason, saying, statement, suggestion, thought, treat, warning, wish, word,
2 Whether可以引導同位語從句，不能引導定語從句
He hasn』t made the decision whether he will go there.
他還沒有決定是否去那裡。
3 What可以引導同位語從句，不能引導定語從句
I have no idea what he is doing now.我不知道他現在在幹什麼。
4 how可以引導同位語從句，不能引導定語從句
It』s a question how he did it. 他如何做了此事，那是一個問題。
5 who,whom，which, when, where, why都可以引導同位語從句
She raised the question where we could get the fund.她提出這個問題：我們到哪兒能獲得這筆獎金。
四 同位語從句中的語氣
在suggestion, advice, request, order等意為「建議，命令，要求」的名詞後，同位語從句中的謂語動詞常用「should+動詞原形」的虛擬語氣，should可以省略。如
Our teacher gave us some advice how we (should) use the computer. 老師給我們提出了一些任何使用電腦的建議。
五 同位語從句和定語從句的區別
1同位語從句和先行詞是同等的關係；而定語從句是修飾先行詞。
2 that在同位語從句中無詞義，不充當句子成分；而在定語從句中充當主語賓語等句子成分。
3 whether, how, what可以引導同位語從句，不能引導定語從句.
4 who, whom, which, when,where,why用來引導可以引導同位語從句，保持原來疑問詞的含義，而他們引導定語從句時，不具有疑問詞的含義。
習題
1 There is much chance ____ Bill will recover from his injury for the race. A that B. which C. until D. if
答案 A 比爾的傷將恢復並能及時參加比賽的可能性很大。
2 Nobody believed his reason for being absent from the class ______ he had to meet his uncle in the airport.
A why B. that C where D. because
答案 B 他沒來上課，因為他到機場接他叔叔，這個理由沒人相信。
先行詞是reason。
3 Some researchers believe that there is no doubt ______ a cure for AIDS will be found.
A which B. that C. what D. whether
答案B 一些研究者認為， 毫無疑問將會找到醫療愛滋病的方法。
4 We should consider the students』request _____ the school library provide more books on popular science.
A that B. when C. which D. where
答案 A 我們應該考慮學生的要求，即學校圖書館應該多提供一些大眾科學方面的書籍。
5 There』s little doubt _____ our team will beat yours.
A which B. whether C. if D. that
答案 D 幾乎可以肯定，我們隊會戰勝你們隊。
6 Do you have any idea ______ his cousin will go abroad for further study or not?
Ａ that B if C. whether D. why
答案 C 你知道他表弟是否去國外深造？
7 Information has been put forward ______ more middle school graduates will be admitted into universities.
答案 B 更多中學畢業生將被大學錄取，這一消息已被放出。
8 -It』s thirty years since we last meet.
-But I still remember the story, believe it or not, ______ we get lost on a rainy night.
A whose B. that C what D. when
答案 B 「三十多年沒見面了。」
「信不信由你，但是我依然記得我們在雨夜迷路的事。」先行詞是story。