7.1 名词性从句
四类名词性从句
在英语中，名词或名词短语主要充当四种成分：主语、宾语、表语和同位语。如果我们把句子当作名词来用，让它们分别在另一个句子中作主语、宾语、表语和同位语，那么充当这四种成分的句子就会构成对应的从句：主语从句、宾语从句、表语从句和同位语从句。 这四种从句在本质上相当于名词的作用，所以我们把它们统称为名词性从句。
主语从句
主语从句概述
简单句： The book is interesting.
主从复合句： What I am reading is interesting.
解释： 简单句中，book为名词作主语；主从复合句中，完整句子what I am reading作主语，因此称之为主语从句。该从句有自己的主语（I）和谓语（am reading），what在主语从句中作am reading的宾语。
主语从句：在复合句中充当主语的从句。
What we need is more time.
- that引导的主语从句。无词义也不作成分，只起单纯的连接作用，且通常不可以省。
- That Tom couldn’t control the model car was obvious.
- That he will join our team makes us very excited.
- 通常，that引导主语从句时用it做形式主语，把从句置于句尾。
- It was obvious that Tom couldn’t control the model car.
- It makes us very excited that he will join our team.
- whether引导主语从句，意为”是否“，只起连接作用，不充当任何成分。
- Whether the news is true is still a question.
- Whether Tom will join us is uncertain.
- 注意：置于句首时必须用whether引导，置于句尾时，也可用if。
- It is uncertain whether/if Tom will join us.
- 连词代词what，who，which，whose等引导主语从句，这些连接代词作用相当于代词，在从句中担当主语、宾语、表语、定语等。
- Who is responsible for the project is not yet clear.
- Which school you decide to go is an important matter.
- What he said yesterday made me upset.
- 连接副词when，where，why，how引导主语从句，这些连接副词相当于副词，在从句中充当状语。
- When my father will come back is still unknown.
- whatever，whoever，whomever，whenever，wherever等词引导主语从句，表示”无论什么“、”无论谁“、”无论何时“、”无论在（到）哪里“等。
- Whatever you gave me is in that box.
- Whoever comes is welcome.
宾语从句概述
简单句： I believe his words.
主从复合句： I believe what he said.
解释： 简单句中，his words作宾语；主从复合句中，完整句子what he said作宾语，因此为宾语从句。该从句有自己的主语（he）和谓语（said），what在宾语从句中作said的宾语。
表语从句概述
简单句： English is a useful tool.
主从复合句： The book is what I want.
解释： 简单句中，a useful tool作表语；主从复合句中，完整句子what I want作表语，因此称为表语从句。该从句有自己的主语（I）和谓语（want），what在表语从句中作want的宾语。
表语从句：在复合句中充当句子的表语成分。
The fact is that he doesn’t really try his best to complete it.
- that引导的表语从句。无词义也不作成分，只起单纯的引导作用。
- The trouble is that I cannot get in touch with him.
- My idea is that we should take action right now.
- whether引导表语从句，意为”是否“，只起连接作用，不充当任何成分。
- The question is whether the book is worth reading.
- The key is whether we can overcome the difficulties.
- 注意：whether可引导表语从句，但与之同意思的if却不能用于引导表语从句。
- 由as if/as though引导，意为”似乎，好像“。
- It was as though/as if she had known Tom for years.
- 连词代词what，who，which，whose等引导表主语从句。
- The problem is who we can get to replace her.
- What I wonder is which road we should take.
- 连接副词when，where，why，how引导表语从句。
- What we need to work out is how we can operate this machine.
- That is why she failed to pass the exam.
- My question is where they once lived.
- 连词because也可以引导表语从句。
- It’s just because the weather was bad.
- That’s because I love you too much.
- 注意：because可引导表语从句，但与之同意思的since，as，for等不能用于引导表语从句。
同位语从句概述
简单句： I like the book, Gone with the wind.
主从复合句： The mother must accept the fact that her baby is deaf.
解释： 简单句中，Gone with the wind 作the book的同位语；主从复合句中，完整句子that her baby is deaf作the fact的同位语，因此称为同位语从句。该从句有自己的主语（her baby）和谓语部分（is deaf），that在同位语从句中不作成分。