(一) 概念
一般来说，在主从复合句中,用作同位语的从句叫同位语从句。它通常跟在某些名词之后，用以说明或解释该名词表示的具体内容。可以跟同位语从句的名词通常有：advice, decision, fact, hope, idea, information, message, news, promise, proposal, reply, report, suggestion, word（消息），problem， question, doubt, thought等。例如：
They were delighted at the news that their team had won.
当听到他们队获胜的消息时，他们欣喜若狂。
Where did you get the idea that I could not come？你从哪儿听说我不能来？
有时同位语从句可以不紧跟在被说明的名词后面，而被别的词隔开。 如：
The thought came to him that Tom might have returned the book.
他突然想起汤姆可能已经还了书了。
（二）引导词
[寻规找矩] 请仔细观察下列句子，注意从句引导词的用法。
1. The news that Mr. Li will be our new English teacher is true.
2. He hasn’t made the decision whether he will go there.
3. The question who should do the work is being discussed at the meeting.
4. I have no idea what the boy is doing in the next room now.
5. We haven’t yet settled the question where we are going to spend our summer vacation this year.
6. I have no idea how I can get to the railway station.
7. I have no idea when he will be back．
[小结归纳]
① that引导同位语从句时无词义，也不充当任何成分，但通常不可以省略，如句1；
② whether引导同位语从句时意为“是否”，通常不能用if来代替,如句2;
③ 连接代词who, what等可以引导同位语从句，如句3， 4；
④ 连接副词where, how, when等可以引导同位语从句， 如句5，6，7。
(三) that 引导的同位语从句和定语从句
① 意义不同：同位语从句用来进一步说明前面名词的内容；而定语从句用来修饰、限定前面的先行词。试比较：
1. The news that our team has won the final match is encouraging.
2. The news that you told us is really encouraging.
[分析] 句1中that引导同位语从句，说明“news”的内容：我们队取得了决赛胜利。
句2中that引导定语从句，对“news”加以限定：是你告诉我们的，而非来自其他渠道。
② that的功能不同：that引导同位语从句时是一个纯连词，不充当任何成分；而引导定语从句时，不仅起连接作用，而且还指代先行词并在从句中充当主语、宾语等成分。试比较：
1. Dad made a promise that he would buy me a CD player if I passed the English test.
2. Dad made a promise that excited all his children.
[分析] 句1中 that引导 同位语从句，其中that无词义，也不充当任何成分；
句2中that引导定语从句，that指代promise，又在从句中充当主语，且that可以用which替换。
③ 可否省略：that在引导同位语从句时，通常不可省略。在引导定语从句时，若在从句中作宾语，通常可以省略，若作主语则不可以省略。
[即学即用]
I． 请用适当的词填空，使下列句子意思完整。
1. They expressed the hope _______ they would come over to China soon.
2. The fact _______ he didn’t see Tom this morning is true.
3. Word has come _______ some American guests will come to our college for a visit next week.
4. He can’t answer the question _______ he got the money from his home yesterday.
5. Do you have any idea _______ is actually going on in the classroom?
6. The problem _______ we should have the meeting in the hall now must be decided at once.
II. 下列各句中均有一处错误，请改正。
1. Our team has won the game, that made us very happy.
2. I’ve come with a message from Mr Wang how he won’t be able to see you this afternoon.
3. He must answer the question if he agrees with what she said or not.
4. I’ve read the book where you gave me the day before yesterday.
5. One of the men held the pinion when what the book said was right.
III． 把下列句子翻译成英语。
1. 我向他许诺说我一到北京就给他写信。
2. 他经常问我这个问题，那就是这个工作是否值得做。
3. 他什么也不说，这一事实使大家都感到惊奇。
4. 在我看来，他刚才告诉我的这个消息是真实的。
5. 他突然想起他本来应该去接儿子的。
Key:
I. 1. that 2. that 3. that 4. how 5. what
6. whether
II. 1 that→which 2. how→that 3. if→whether
4. where→that / which或省略where
5. when→that 6. that→how
III. 1. I made a promise that I would write to him as soon as I got to Beijing.
2. He often asked me the question whether the work was worth doing.
3. The fact that he had not said anything surprised everybody.
4. In my opinion, the news (that / which) he told me just now is true．
5. A thought suddenly came to him that he should have picked up his son.