英语语法精讲（名词性从句和定语从句）
英语语言的基本句式就四种---主谓句式，主谓宾句式，主系表句式和There be...句式。一个无论结构多么复杂的英语语句，也不过是主句中附带了多个不同类型的从句。主句和所有的从句都是上边的四种句式。要准确地理解语句的意义，就要将主句及所有的从句的相互修饰关系整理清楚。
英语的从句是不可能单独使用的，它必须附属于主句。英语的从句有以下几种类型：名词性从句，定语从句，状语从句。
名词性从句
顾名思义，名词性从句是在语句中作为名词功能使用的。名词可以作主语，宾语，表语，同位语以及定语，因此，名词性从句可以在语句中作主语，称为主语从句；作宾语，称之为宾语从句；作同位语，称之为同位语从句。很显然，这是依照名词性从句的功能来划分的，但名词性从句不能作定语，定语从句是另外一个类别的从句。
✬主语从句✬
主语从句的位置可以在句首，也可以在句首使用形式主语‘It’，然后将过于厚重的主语从句置于句尾，让语句不至于头重脚轻，例句：
What is the priority in life is troublesome to every one of us.
Where and how he can rest his restless heart has long been troubling himself. Who will be elected as chairman of the board draws lots of attention.
That seek for ease and comfort at our young age shrinks our lifelong happiness is a lesson to learn.
以上例句可以使用形式主语，肯好地表述为：
It is troublesome to every one of us what is the priority in life.
It has long been troubling himself where and how he can rest his restless heart. It draws lots of attention who will be elected as chairman of the board.
It is a lesson to learn that seek for ease and comfort at our young age shrinks our lifelong happiness.
✬宾语从句✬
在句子中作谓语动词的宾语，例句：
He dares to question what is taught in books and lessons.
He follows whoever takes the leading position in the company.
We are looking forward to what is to come next.
They don’t doubt that Chinese national power and strength is growing at a fantastic speed.
✬表语从句✬
在主系表句式句子中作表语，例句：
The top concern in our life has been how we should explore ourselves,sometimes but not always,to strengthen our ability to expand wealth.
Our question is why we have to go to our greatest length at our young age to study
and learn and avoid some of the pleasure life has been offering us.
特别提示：带有表语从句的特殊句式‘It seems that...’和‘It looks/seems as though/if...’，例句：
It seems that he covers a larger range of books in his reading than those of his age.
It looks as if we are gaining our leading position in the fierce competition. ✬同位语从句✬
同位语是紧跟在名词或者代词之后，补充说明这个被修饰对象的一些信息，它就是这个对象本身。同位语从句即是解释被修饰对象本身的信息内容，可以为了英语句子结构的紧凑性，不直接跟在被修饰对象后边。例句：
The concern is bothering most people in western countries whether the Covid-19 health crisis will be put under control sometime soon.
He is losing his patience to seek for an answer to the question what has been the working measure to expand his own range of reputation in the materialistic world. They have chosen to ignore the fact that their move to reopen working places in such a widespread severe infectious disease is costing more citizens’ lives.
以上是名词性从句按照功能的分类，它还可以按照从句的构成分为两类：由‘that’构成的名词性从句和由疑问词构成的名词性从句。
▲‘that’构成的名词性从句：
‘that’在从句中没有表达任何意义，也不担任任何句子成分，构成主语从句和同位语从句的‘that’不能省略。当然美式英语中，尤其是非正式语言场景中，这条规则被忽略。
跟在谓语动词之后的‘that’构成的宾语从句中的‘that’可以省掉，但是，如果一个谓语动词后边跟两个以上的‘that’构成的宾语从句，从第二个从句开始，‘that’不能省掉。
▲疑问词构成的名词性从句：
这类名词性从句中要特别注意，从句虽然表达的是疑问意义，但从句本身不是独立的句子，不能使用疑问句式，例句：
Where and when an effective cure to the Covid-19 will come out is still vague. 为了更好的语句工整性，表述为：
It is still unclear where and when an effective cure to the Covid-19 will come out.
He raised a question at the conference whether the funding for the project would be accomplished on their own.
✬定语从句✬
在汉语和英语语言中，做定语的既可以是形容词，也可以是名词，但是英语语言的定语从句是独立于名词性从句的另外一个类别的从句，定语从句是个形容词性的语言结构。
