定语从句中的 that 在定语从句中充当主语时不可省略，做定语从句中的主语是必须用，但作为宾语时可以省略。
如：
1、This is the book (that ）（代指前面的the book）I bought yesterday.
2、I like the book that （同上）is intrersting.
扩展资料
定语从句，一个句子跟在一名词或代词（先行词）后进行修饰限定，就叫做定语从句。通俗来讲，从句在整个句子中做定语，这个从句就叫做定语从句。从句在主句中充当定语成分。被修饰的词叫先行词。定语从句不同于单词作定语的情况，它通常只能放在被修饰的词（即先行词）之后。
定语 从句由关系词（关系代词、关系副词）引导，关系代词、关系副词位于定语从句句首。
参考资料：百度百科——定语从句
1．用作代词，代替前面所指的事物，常见于表示比较关系的状语从句中，例如：
It is warmer in the south than ( that of )the south.
She said ( that ) she would come.
I suggested ( that )we ( should ) go home.
Can I have the records ( that ) I lent you?
He is just the man ( that ) you talked about.
4．在 way （意为 manner ）后面，that 意思为 in which，例如：
Do it the way ( that ) I showed you.
5．在表示个人对事物反应、表示重要性或迫切性的adj后所接的从句中，例如：
I am glad ( that ) you are right.
It is obvious ( that ) they are happy together.
6．so that, so…that, such…that, 结构中，例如：
I came to see you so ( that ) you would know the truth.
She had so many children ( that ) she didn’t know what to do.
I was having such a nice time ( that ) I didn’t to leave.
7．用于表示时间的词后面，整个短语相当于when，例如：
I joined the army the year/month ( that ) my father died.
I thought her nice and honest the first time ( that ) I met her.
= I though her nice and honest when I met her.
8．如果定语从句中的谓语是 there is，作主语的关系代词 that 也常省略，例如：
This is the fastest train ( that ) there is to Beijing.
扩展资料：
定语用来限定、修饰名词或代词，是对名词或代词起修饰、限定作用的词、短语（动词不定式短语、分词短语）汉语中常用“……的”表示。主要由形容词担任，此外，名词、代词、数词、分词、副词、不定式以及介词短语也可以来担任，也可以由一个句子来担任。
单词作定语时通常放在它所修饰的词之前，作前置定语。短语、从句作定语时则放在所修饰的词之后，作后置定语。
被定语从句修饰的名词、代词称为先行词。如“the girl”，“the book”
如:She is the girl who likes singing. 她就是那个喜欢唱歌的女孩。
这就是一个定语从句。
关系副词在句中作状语
关系副词=介词+关系代词
why=for which
where=in/ at/ on/to which（介词同先行词搭配）
when=during/ on/ in/at which
1. “where”是关系副词，当然也不用“that”引导。
By the time when you arrived in London, we had stayed there for two weeks. 当你到达伦敦的时候，我们在那里已经待了两个星期。
I still remember the place where I met her for the first time. 我仍然记得我第一次见到她的地方。
Each time when he goes to business trip, he brings a lot of living necessities, such as towels, soap, toothbrush etc. 他每次出差都带着生活必需品，如毛巾，肥皂，牙刷等其他东西。
2.当从句的逻辑主语是some, any, no, somebody, anybody, nobody, something, anything, everything或nothing时，常用“there is”开头。
There is somebody here who wants to talk to you. 这里有人要和你说话。
分作进一步说明，通常是引导词和先行词之间用逗号隔开，将从句拿掉后其他部分仍可成立。
本回答被网友采纳that 常用作指示代词，不管作哪种句子成份，一般不省略，但在下列情况下有时可以省略：
1．用作代词，代替前面所指的事物，常见于表示比较关系的状语从句中，例如：
It is warmer in the south than ( that of )the south.
2．引导名词性从句作宾语，即宾语从句，例如：
She said ( that ) she would come.
I suggested ( that )we ( should ) go home.
3．作关系代词，在定语从句中作表语或宾语，例如：
Can I have the records ( that ) I lent you?
He is just the man ( that ) you talked about.
4．在 way （意为 manner ）后面，that 意思为 in which，例如：
Do it the way ( that ) I showed you.
扩展资料
that代替关系副词
that可以用于表示时间、地点、方式、理由的名词后取代when, where, why和"介词+ which"引导的定语从 句，在非正式文体中that常被省略（正式文体中不可省略），例如：
His father died the year (that / when / in which) he was born.
他父亲在他出生那年逝世了。
He is unlikely to find the place (that / where / in which) he lived forty years ago.
他不大可能找到他四十 年前居住过的地方。
定语从句，一个句子跟在一名词或代词（先行词）后进行修饰限定，就叫做定语从句。通俗来讲，从句在整个句子中做定语，这个从句就叫做定语从句。从句在主句中充当定语成分。被修饰的词叫先行词。定语从句不同于单词作定语的情况，它通常只能放在被修饰的词（即先行词）之后。
参考资料定语从句_百度百科
本回答被网友采纳1．用作代词，代替前面所指的事物，常见于表示比较关系的状语从句中，例如：
It is warmer in the south than ( that of )the south.
2．引导名词性从句作宾语，即宾语从句，例如：
She said ( that ) she would come.
I suggested ( that )we ( should ) go home.
3．作关系代词，在定语从句中作表语或宾语，例如：
Can I have the records ( that ) I lent you?
He is just the man ( that ) you talked about.
4．在 way （意为 manner ）后面，that 意思为 in which，例如：
Do it the way ( that ) I showed you.
5．在表示个人对事物反应、表示重要性或迫切性的adj后所接的从句中，例如：
I am glad ( that ) you are right.
It is obvious ( that ) they are happy together.
6．so that, so…that, such…that, 结构中，例如：
I came to see you so ( that ) you would know the truth.
She had so many children ( that ) she didn’t know what to do.
I was having such a nice time ( that ) I didn’t to leave.
7．用于表示时间的词后面，整个短语相当于when，例如：
I joined the army the year/month ( that ) my father died.
Mac came to see me the week ( that ) we went camping.
The time ( that ) you knocked at the door, my telephone rang.
I thought her nice and honest the first time ( that ) I met her.
= I though her nice and honest when I met her.
8．如果定语从句中的谓语是 there is，作主语的关系代词 that 也常省略，例如：
This is the fastest train ( that ) there is to Beijing.本回答被网友采纳
非限制性定语从句不能省略，只有在限制性定语从句中可以省略。因为非限制性从句如果省略就不是一个句子了。例如：I like eating fruit, which helps me keep healthy. 如果省略了，就变成了I like eating fruit, helps me keep healthy. 这句话出现了两个谓语，不是一个句子。
限制性定语从句可以省略的情况：
关系代词在从句中作宾语
Medical advances have reduced suffering(that） we experinced before. we experience suffering ， that 指的是suffering，作宾语，可以省略。
关系代词在从句中作表语
He is not the boy he used to be.
还存在其他情况，但不建议使用省略。