賓語從句根據引導詞可分為三種，一種是that引導的，第二種是if或whether引導的，第三種就是各種疑問詞引導的，第一種中的that沒有實在意義，只是一種統一的形式。

指的是that為賓語從句的引導詞。

賓語從句：置於動詞、介詞等詞性後面，在句子中起賓語作用的從句叫做賓語從句。

賓語從句分為三類：動詞的賓語從句，介詞的賓語從句和形容詞的賓語從句。”例句:I can’t tell him that his mother died.

that本身無詞義,在從句中不作任何成分,在口語中常常省略.例如:I guess somebody else has borrowed it.

省略：

that引導賓語從句，起連接主、從句的作用，本身無意義，在口語或非正式文體中常省略。

不省略：

1）從句的主語是that時，that不能省。

We know that that is an important meeting．

2）動詞後接多於兩個由that引導的賓語從句時，第一個that可省，但後面的that不可省。

He said (that) you were too young to understand the matter and that he was asked not to tell you.

3) that引導的賓語從句中緊跟複合句從句時，that不能省。

I think that if you have lost the library book, you must pay for it．

4) 當主句的謂語與賓語從句之間有插入語時，that不能省。

He says, in the newspaper, that English is getting more and more important．

5) 當that從句是雙賓語中的直接賓語時，that不可省。

I can’t tell him that his mother died.