名词性从句中的What和That的区别，详解

在名词性从句里面，首先，你要知道的是what是要做成分的，它必然是主语，宾语，表语，还有同位语里的主宾表之类的成分，也就是说，它是有实在的意思，一般可以理解为"什么”的意思，而that仅仅是起到一个定位的作用，也就是它并不做任何有实在意义的成分。我举两个例子
I want to know what he has told you. 显然这里what指的是“什么，东西”的意思，
The thought came to him that Mary had probably fallen ill.显然从句里不缺任何成分，that就像胶布，连接主句从句

一that 引导的名词性从句，连接代词that除引导第一个宾语从句时可以省略外,引导其他各类名词性从句皆不能省略例如：① It is required in the regulations that you should not tell other people the password of your e-mail account.
② ---- Don’t you think it necessary that he go home at once?---- but the problem is that there is no car.
③ There is much chance that Bill will recover from his injury in time for the race.
④ Our English teacher told us (that) we all did very well in the examination and that ten of us got full mark.
以上四个句子中,that 分别引导主语从句,表语从句,同位语从句和宾语从句,除在第四个例句中第一个that 可以省略外,其他的that 均不可省略.其次,在引导名词性从句时,that不作句子中的任何成分.that 在引导名词性从句时具有三大特点：不可省略,不作成分,没有词义.

二． what引导的名词性从句
首先,what 引导名词性从句时,what 在句中不省略.这一用法与that引导名词性从句时的用法不尽相同.
① He spoke proudly of his part in the game,without mentioning what his teammates had done.what 在该句中引导宾语从句,what 不可省略.
② Great changes have taken place in that school.It is no longer what it was 20 years ago,when it was so poorly equipped.what在该句中引导表语从句,但在句中不可省略.其次,what 引导名词性从句时,具有词汇意义.这是what 与that 引导名词性从句的重要区别之一,What 一般指“----的东西/事情/人/时间/地点等”.
述综上所述综上所述,what 在引导名词性从句时具有三大特点：不可省略,作成分有词义.

记得采纳~

What 连接代词

That是连接词

例如：what I said makes me happy   ，what作said的宾语

That I buy an apple makes me happy

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that 不做从句的成份
而what一般做从句的主语