在复合句中充当同位语的名词性从句称为同位语从句。
一 同位语从句的位置
1 同位语从句常跟在某些抽象名词（如idea, news, fact, promise, hope, message等）后面。如
The news that our women volleyball team had won the championship encouraged us all greatly.
我们女排赢得冠军的消息大大地鼓舞了我们所有人。
2有时同位语从句不紧跟在它所修饰的名词后，而被别的词隔开，在语法上叫做分隔式同位语从句。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离开家时没把门关上。
二 同位语从句前面的名词通常用单数，且往往带有限定词加以修饰（word除外)。如：
Where did you get the idea that I could not come?
你在哪儿听说我不能来？
Word came that China launched its first manned spaceship on Oct 15, 2003.消息传来，中国于2003年10月15日首次成功发射了载人宇宙飞船。
三 同位语从句连接词有that, who, whether, how, when, where等
They were all very much worried over the fact that you were sick.
对你生病这件事，他们都很担心。
注意：名词doubt“怀疑”后面的同位语从句用whether连接；在no doubt “不怀疑”后的同位语从句用that连接。如
We have some doubt whether they can complete the task on time.
我们怀疑他们是否准时完成任务。
There is no doubt that Zhang Wei will keep his promise.
我们相信张伟会遵守诺言的。
1 以下名词常用that引导
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可以引导同位语从句，不能引导定语从句
He hasn’t made the decision whether he will go there.
他还没有决定是否去那里。
3 What可以引导同位语从句，不能引导定语从句
I have no idea what he is doing now.我不知道他现在在干什么。
4 how可以引导同位语从句，不能引导定语从句
It’s a question how he did it. 他如何做了此事，那是一个问题。
5 who,whom，which, when, where, why都可以引导同位语从句
She raised the question where we could get the fund.她提出这个问题：我们到哪儿能获得这笔奖金。
四 同位语从句中的语气
在suggestion, advice, request, order等意为“建议，命令，要求”的名词后，同位语从句中的谓语动词常用“should+动词原形”的虚拟语气，should可以省略。如
Our teacher gave us some advice how we (should) use the computer. 老师给我们提出了一些任何使用电脑的建议。
五 同位语从句和定语从句的区别
1同位语从句和先行词是同等的关系；而定语从句是修饰先行词。
2 that在同位语从句中无词义，不充当句子成分；而在定语从句中充当主语宾语等句子成分。
3 whether, how, what可以引导同位语从句，不能引导定语从句.
4 who, whom, which, when,where,why用来引导可以引导同位语从句，保持原来疑问词的含义，而他们引导定语从句时，不具有疑问词的含义。
习题
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 比尔的伤将恢复并能及时参加比赛的可能性很大。
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 他没来上课，因为他到机场接他叔叔，这个理由没人相信。
先行词是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 一些研究者认为， 毫无疑问将会找到医疗艾滋病的方法。
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 我们应该考虑学生的要求，即学校图书馆应该多提供一些大众科学方面的书籍。
5 There’s little doubt _____ our team will beat yours.
A which B. whether C. if D. that
答案 D 几乎可以肯定，我们队会战胜你们队。
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国外深造？
7 Information has been put forward ______ more middle school graduates will be admitted into universities.
答案 B 更多中学毕业生将被大学录取，这一消息已被放出。
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 “三十多年没见面了。”
“信不信由你，但是我依然记得我们在雨夜迷路的事。”先行词是story。
