从句子成分的角度来说, 从句就是用一个句子取代一个简单句中的某一个成分, 于是变成了对应的从句.
比如:
我们用一个句子取代主语, 那这个句子就成了一个主语从句;
同样的, 如果一个句子取代了宾语的位置, 那它就是一个宾语从句;
如果一个句子取代了状语的位置, 那它就成为了一个状语从句.
如果要用一句话来定义名词性从句, 我们可以将其概括为: 在句子中起名词作用的句子就是名词性从句.
名词性从句的功能相当于名词词组, 它在复合句中能担任主语、宾语、表语、同位语、介词宾语等, 因此根据它在居中不同的语法功能, 名词性从句又可分别称主语从句、宾语从句、表语从句、同位语从句、补语从句.
You make me sad.
You make me who l am.
第二个句子当中用了一个句子what l am watching, 是一个疑问句改造成的王语从句, 注意特殊疑问句作句子成分时要变成陈述语序.
1) 位于句首
如:
What Jack wanted to tell us was not clear.
Who will win the game is still unknown.
Where the meeting will be held has not yet been announced.
2) 位于句尾, 使用it作形式主语, 而把主语放在句末
很多时候是为了避免句子头重脚轻, 所以常用形式主语it代替主语从句作形式主语放于句首, 而把主语从句置于句末. 注意此时主语从句后的谓语动词一般用单数形式.
常用的结构有以下几个:
a) lt be +名词+that从句
lt’s a great pity that they didn’t get married.
lt 's a good thing that you have a witness.
b) lt be +形容词+that从句
lt is great that l have such a smart brother like you.
lt’s strange that there are no lights on.
c) lt be +动词的过去分词+that从句
lt’s said/known that he has been there many times.
lt has been decided that the gallery will not open on Sundays.
d) lt seems/happens + that从句
lt seemed certain that he would win the prize.
lt happens that they were absent.
当用陈述句、一般问句和特殊问句这三种句子类型充当另外一个句子的宾语时, 就构成了宾语从句.
把"that+陈述句"这一结构放在宾语的位置即构成宾语从句.
可跟that从句做宾语的动词包括say, think, insist, wish, hope, demand, imagine,wonder, know, suppose, see,believe, agree, admit, deny, expect, explain,order, command, feel, dream, suggest, hear, mean, notice, prefer,request,require, propose, declare, report等.
如:
He told me (that) he had to leave.
l think (that) my life will be very different in te