名词性从句中的What和That的区别,详解.

一that 引导的名词性从句
首先,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.
例如：① Nobody believed his reason for being absent from the class that he had to meet his uncle at the airport.该句中,that引导同位语从句,但在句中不作任何成分.
② It is our belief that improvements in health care will lead to a stronger,more prosperous economy.该句中,it 是形式主语,that引导的主语从句才是整个句子的真正主语,that在句中不作任何成分.最后,在引导名词性从句时,that没有任何词汇意义.
① A warm thought suddenly came to me that I might use the pocket money to buy some flowers for my mother’s birthday.
② Danby left word with my secretary that he would call again in the afternoon.在以上两个考例中,that仅起引导同位语从句的作用,没有任何词汇意义.综上所述,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”.
例如：① Do you have any idea what is actually going on in the classroom?what在该句中引导同位语从句并作这个同位语从句的主语,词义为“----的东西、事情”,整个句子的汉语意思是“你知道教室里到底发生了什么事”.
② It is what you do rather than what you say that matters.这是一个强调句型,被强调的部分是由what引导的两个主语从句,what在句中的词义为“----的东西、事情”,整个句子的汉语意思是“关键要看你做什么而不是说什么”.最后,what 引导名词性从句时不仅只起引导作用,同时还要作句中的某个句法成分.这一点是what 在引导名词性从句时与that 用法区别的关键所在.
① I just wonder_________ that makes him so excited.A.why it does B.what he does C.how it is D.what it is 这一题的正确答案是D,是一个强调句型作宾语的典型考例,被强调的成分what 在句中不仅只起引导宾语从句的作用,同时在宾语从句中作makes 的主语.
② A modern city has been set up in what was a wasteland ten years ago.在这个句子中,what 引导的从句作了介词in 的宾语,同时what 又在宾语从句中充当主语,意思是“……的地方”.值得注意的是,在引导名词性从句时,that 引导的句子一般不作介词的宾语,相反,由what 引导的句子作介词宾语的情况显得更为常见.
例如：③ The other day,my brother drove his car down the street at what I thought was a dangerous speed.本题中,介词at后面用了what引导的宾语从句,what在宾语从句中作主语,而that不可以这样使用.综上所述综上所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.