小米一箩筐
一、 定语从句是形容词从句，其作用相当于一个形容词，是用来修饰前面的名词或代词的；同位语从句是名词从句，其作用相当于一个名词，是对前面的名词作进一步解释的。例如： 1． We heard the news that he had told her. 我们听到他对她说的消息。 2． We heard the news that he had won the game. 我们听到消息他赢得了比赛。 例1中的that从句的作用相当于一个形容词，其作用是修饰the news；例2中的that从句的作用相当于一个名词，是对the news的进一步说明。 二、定语从句的引导词在从句中充当一定的成分，可作主语、宾语、状语等；而同位语从句中的引导词在从句只起连接作用，不作任何句子成分。例如： 1. A plane is a machine that can fly. 飞机是一种能飞的机器。 2. The fact that they didn't finish the work has to be faced. 必须面对事实，他们没有完成工作。 例1中的引导词that在从句中充当句子成分，作从句的主语，故为定语从句；例2中的that只起连接作用，引导从句解释fact的内容，不作任何句子成分，故为同位语从句。 三、引导定语从句的关联词在从句中作宾语或状语时，可以省略或被其他词代替；而同位语从句的引导词一般不能省略，更不能被代替。例如： 1. The news that she heard is true. 她听到的消息是真的。 2. The news that she will go abroad is true. 她将出国这消息是真的。 例1是定语从句，that可省略；例2是同位语从句，that不能省略。 3. The reason why he was chosen remains unknown. 他为什么被选上的原因还是不清楚。 4. The idea why he was chosen attracted our attention. 他为什么会被选上，这一想法引起我们的注意。 例3中why引导的是定语从句，why可以被 for which或 that 代替；例4中 why引导的是同位语从句，why 不能省去，也不能被其它词代替。 四、同位语从句与其所修饰的名词之间是一种同位关系，二者之间存在逻辑上的系表关系，可用“主+系+表”结构来表示。例如： The news that he won the first place is true. 他赢得冠军的那个消息是真的。 上句若用“主+系+表”结构来表示，则是： The news is that he won the first place. 消息是他赢得了冠军。 意思合理，系表结构成立，故为同位语从句。 五、定语从句所修饰、限定的先行词可以是各类名词，可以有复数形式；而同位语从句一般都与抽象名词同位，一般没有复数形式。例如： 1. The possibilities that she was offered seemed very great.她得到的可能性似乎大些。 2. Her mother was worried about the possibility that her daughter dislike to go to school. 她的母亲很担心，她女儿有可能不喜欢上学。 例1中的possibilities是定语从句的先行词，可用复数形式；例2中的possibility是抽象名词，后接的是同位语从句，一般不用复数形式。 六、由when, why, where引导的定语从句分别修饰或说明表示时间、原因或地点的词，但它们引导的同位语从句一般不和表示时间或地点的词同位。例如： 1. I still remember the day when I first came to Beijing. 我仍然记得初次来北京的那天。 2. I have no idea when she will be back. 我不知道她何时回来。 3. This is the house where I lived two years ago. 这是我两年前住的房子。 4. The question where we shall have a meeting hasn't decided. 我们到什么地方去开会，这个问题没有决定。 例1、3中的when和 where引导的是定语从句，day 和house分别表示时间和地点；例2、4中的when和 where引导的是同位语从句。 如果在定语从句与同位语从句的学习中能把握住上述几种区别，那么在阅读文章时，就会迎刃而解，收到更好的效果。 谢谢 祝你学习进步
顺其自然0012
在定语从句中，that 关系代词（在句中作主语、宾语或定语）1.只能用that作为定语从句的关系代词的情况a) 在不定代词，如：anything, nothing, everything, all, much, few, any, little等作先行词时，只用that，不用which。 All that is needed is a supply of oil. Finally, the thief handed everything that he had stolen to the police. b) 先行词有the only, the very, the just修饰时，只用that。 He is the very man that helped the girl out of the water . c) 先行词为序数词(the last)、数词、形容词最高级时，只用that。. The first English book that I read was “The Prince and the Pauper” by Mark Twin . d) 先行词既有人，又有物时。 He talked about the teachers and schools that he visited . e)当主句是以who 或which 开始的特殊疑问句时，用that 以避免重复。 Who is the person that is standing at the gate . f)关系代词在从句中做表语 He is not the man that he used to be . 1）不用that的情况a) 在引导非限定性定语从句时 b) 介词后不能用
顺宏冷暖-MISS冯
That可以引导名词性从句，状语从句和强调句。
It was exactly what I needed是表语从句，是"主句+表语从句"构成的主从复合句,其中表语是由"what"引导的是表语从句来充当.这里"it" 作代词,当然"it"也可替代后面的名词从句放在句首作形式主语,但这里却不成。
that名词性从句。
①引导宾语从句。及物动词后的引导词that可省略。
I didn't expect (that) he could win the championship.
The teacher pointed out that Tom was not working hard enough.
② 引导主语从句。通常采用it作形式主语的句型。
That the earth goes around the sun is known to everyone.
（It is known to everyone that the earth goes around the sun.）
③引导表语从句。
The trouble is that we are short of money.
④引导同位语从句。
引导同位语从句的that和引导定语从句的that是不同的。前者只起语法作用，在从句中不作任何成分；而后者在定语从句中作主语、宾语或表语。举例说明：
The news that he resigned from office surprised us.
The idea that he holds is very common nowadays on campus.
扩展资料：
与that 有关的常见重要短语。
1、in that，意为“既然、因为”。
Criticism and self-criticism is necessary in that it helps us correct our mistakes.
2、now that，意为“既然、由于”。
Now that they have taken matters into their hands, the pace of events has quickened.
3、see (to it) that，意为“注意、务必做到、保证”。
We will see to it that she gets home early.
See to it that you are not late again.
4、seeing that，意为“鉴于、由于”。
Seeing that it is 8 o'clock, we'll wait no longer.
Seeing that he was busy with his work, I didn't disturb him.
参考资料：that-百度百科
gell墨脱
that在定语从句中做主语、表语或宾语,作宾语时可省略.必须用that的情况：先行词有人又有物先行词有形容词最高级修饰先行词是不定代词先行词有不定代词修饰以who,which开头的问句先行词有the very, the same ,the last等词修饰先行词有序数词,数词修饰时.关系词在定语从句中做表语时不能用that的情况：介词+关系词非限定性定语从句举例：Is this the book that you borrowed in the library?这是你在图书馆借的那本书吗?Who that break the window should be punished． 谁打碎了窗户都要受到惩罚． All that is needed is a supply of oil. 所需的只是供油问题. Finally, the thief handed everything that he had stolen to the police. 那贼最终把偷的全部东西交给了警察.
摇滚喵喵
that从句用法如下：
一、引导名词性从句
即引导主语从句、宾语从句、表语从句和同位语从句，that没有任何意义，也不作任何句子成分，只起引导作用。
1. 引导主语从句
由于中英语言文化的差异，汉语没有主语从句。如，“英语很重要不是人人都认同的。”汉语语法认为，“英语很重要”是主位词组做句子的主语。
而英语句子“That English is of vital importance is not acknowledged by all.”中，That English is of vital importance是主语从句。虽然that没有任何意义，也不作任何句子成分，只起引导作用，但是却不能省略。如：
That English teacher can speak fluent English is a fundamental requirement.
2. 引导宾语从句
引导宾语从句的that一般可以省略，但在以下六种情况下，一般不能省略。
（1）两个以上的宾语从句并列时，从第二个从句开始，that 不能省略。如：
Jack was informed（that）he had been enrolled in Sun Yat-sen University，and that he should register by August.
（2）介词后引导宾语从句的that 不能省略。如：
His parents expected him nothing but/except that he can make a living by himself after graduation.
（3）主句的谓语动词与that引导的宾语从句之间有插入语时，that不可省略。如：
The head teacher told Jack， after a short hesitation， that he could have a day off on condition that he could make up for the missing lessons.
（4）形容词后引导宾语从句的that一般不省略。如：
Marys parents are very content that their daughter has made such great progress in the final examination.
（5）在 it（形式宾语）+ adj.（补足语）+ that（宾语从句）结构中， that不能省略。如：
Everyone believes it strange that he could pass the driving test.
（6）在直接引语中，that引导的宾语从句与主句隔开时，that不能省略。如：
“Im sorry to say，” he said， “that you are not the suitable person for the work.”
3. 引导表语从句
表语从句位于连系动词后，引导表语从句的that一般不能省略。如：
My advice is that everyone be punctual for the appointment.
特别注意：下列句式中的that一般不能用because代替。
The reason why he was late for school is that he missed the early bus.
4. 引导同位从句
同位语从句就是在news， information， fact， word， idea等抽象名词之后，说明其具体内容的从句。引导同位语从句的that一般不能省略。如：
Based on the fact that you are enthusiastic about Chinese culture， Im writing to invite you to get involved in it.
二、引导定语从句
that常被用来代替关系代词which或who，引导定语从句。以下几种情况，多用that而不用which或who。
1. 当先行词是表示事物的all， any， anything， everything， nothing或被all， any， every等修饰时。如：
Do you have anything that you are puzzled with？
All that can be done must be done.
2. 当先行词被形容词的最高级或序数词修饰时。如：
It is one of the most touching movies that have been shown this month.
The first thing that we should do is to get some food.
3. 当先行词有the only， the very， the same， the last 等修饰时。如：
The only thing that is impressive is his unforgettable experience in Beijing.
4. 当主句以who或which开头的疑问句时。如：
Who is the girl that is delivering a speech over there？
5. 当先行词既有人又有物时。如：
The writer and his novel that you have just talked about are really well known.
三、引导状语从句
1. that 可引导目的状语从句和结果状语从句，that一般不省略。如：
The story is so touching that we will bear in our mind for a long period.
An English Speech Contest will be organized so that/ in order that students can improve their oral English.
sjloveyuliqin
That可以引导定语从句 、名词性从句 、状语从句 。
that是表语从句。
技巧：判断是什么从句，就是看从句在整个句子中做什么成分，显然是在整个句子“It was exactly
某某”中做was的表语。当然，是what引导从句，在从句中充当宾语成分，为need的宾语。
扩展资料：
1、(引导名词性从句)
He expressed the hope that we would keep in touch with his firm.他表示希望我们与他的公司保持联系。
My idea is that we should act on his suggestion.我的意见是我们应当按照他的建议去办。
That she is still alive is a relief. 她还活着,这是令人感到宽慰的。
2、(引导状语从句,表示原因或理由)因为,由于
We are glad that we have accomplished another arduous task. 我们都感到高兴因为又完成了一项艰巨的任务。
3、(引导状语从句,表示目的或结果)为了,以至于
He is working hard that he can catch up with the class. 他努力用功,以便赶上班上同学。
4、(引导表示愿望,感叹的从句,主句常省略)
ThatI could stay at home today! 今天要是我能呆在家里多好呀!
参考资料：百度百科——that
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