【摘要】名词性从句是高中学生学习英语语法的难点，也是高考的热点之一。名词性从句包括主语从句、宾语从句、表语从句和同位语从句。本文通过典型例句总结了主语从句的主要用法，同时也分析了主语从句的难点，旨在帮助年轻教师及学生教学语法之参考。 
　　【关键词】连接词 主语从句 形式主语 难点区别 
　　众所周知，引导名词性从句的连接词通常有三类，他们用法各不相同，现解释如下：连接词that，没有词义；不作句子成分；但在主语从句中不能省略；连接词if ＼whether，词义“是否”；不作句子成分，不能省略；在主语从句中只用whether；连接代词what，whatever，which，whichever，who，whoever，whom，whomever，whose 以及连接副词when，whenever，where，wherever，how，however，why，有词义；在主语从句中作主语、宾语、表语和状语；不能省略。 
　　一、主语从句概述 
　　在主从复合句中充当主语的一个句子就叫主语从句，例如：That the earth goes round the sun is well-known to everybody. 
　　Whether she will come to help us has not been known yet. 
　　When we will go to Beijing for visa to America is still a secret. 
　　二、主语从句中的主谓一致 
　　当主语从句作一个主从复合句的主语时，主句的谓语动词通常用单数，但what 引导的主语从句中谓语动词是need，want，require等的时候，主句谓语动词和表语保持一致，如： 
　　What I am most interested in is American movies. 
　　What I want is a large sum of money. 
　　What I need are a great many books. 
　　三、形式主语 
　　为了避免头重脚轻，通常用it作形式主语，把主语从句放在后面作真正主语，常用句式有： 
　　1.It + be + 形容词 + that-从句 
　　It is necessary that everybody should have a healthy diet and exercise regularly. 
　　2.It + be + 过去分词 + that-从句 
　　It is said that she is going to study abroad after he graduates from Lanzhou University. 
　　3.It + be + 名词 + that-从句 
　　It is a pity that such an educated and qualified graduate cannot find a job. 
　　4.其他含有it 作形式主义的句式： 
　　It makes no difference who will go to Shanghai for the conference with me. 
　　It remains to be seen whether she will join my research studio. 
　　四、名词性从句的难点及区别 
　　1.what引导主语从句时的理解：what 在从句中要充当主语、宾语或表语；what 经常译为“所…的东西”；what =the thing（s） that，如： 
　　What made him proud was that his students had been admitted to key universities.（作主语） 
　　What they want to do is to continue traveling abroad after retirement.（作宾语）
　　What she used to be is a secret to us all.（作表语） 
　　2.wh+ever 与 no matter + wh-的用法。引导让步状语从句可以换用，引导主语从句只能用wh+ever，如： 
　　Wherever you go and whatever you do，，I’ll be right here waiting for you. 
　　=No matter where you go and no matter what you do，I’ll be right here waiting for you. 
　　Whatever you said at the meeting is very useful and valuable. 
　　Whoever leaves the office last，please close the window. 
　　=No matter who leaves the office last，please close the window. 
　　Whoever leaves the office last must close the window. 
　　参考文献： 
　　[1]张道真.实用英语语法[M].外语教学与研究出版社.2002. 
　　[2]薄冰.英语语法[M].开明出版社.1998.