名词性从句：主语从句、表语从句、宾语从句和同位语从句，它们在复合句中的功用相当于名词，因此称为名词性从句，在句中分别作主语、表语、宾语和同位语。
1．When
he will come
is still unknown.
2．I
don’t know who has watered the fields.
3．The
problem is that we need more money.
4．Have
you heard the news that our team won
the game?
1． 主语从句：在复合句中作句子主语的从句。
引导词：连词that、whether;疑问代词who,
what, which;
疑问副词when,
where, how, why
(1)
连词that（无词意）,
whether(是否),
在从句中不担任句子成分，只起连接作用;
whether能引导主语从句，而if不能。
That
you don’t like him has nothing
to do with me.
Whether
John will do this experiment
remains a question.
（2）疑问代词who,
what, which,
在从句中既作连接词又充当主语、宾语、表语、定语等。
Who
will be sent abroad to further his studies is not
announced.
What
surprised me most
was that such a little girl could play the violin so well.
Which
school
will win the prize
is not known.
Whose
dictionary has not been found
is still unknown.
Whichever
you take will be yours.
Whoever
wants
this book may
take it.
Whatever
was said
here must be
kept secret.
(3)疑问副词when,
where, how, why在从句中充当时间状语、地点状语、方式状语、原因状语
When
they will start
hasn’t been decided
yet.
Where
the heroine went
is not mentioned at the end of the story.
How
he managed to finish the composition in
such a short time is still a mystery.
Why
he often comes here is known to
us all.
(4)用it作形式主语的主语从句常用的句型有：
It’s said that…
It is certain that…
It seems/ happens
that…
It’s possible/
important/ necessary/ clear that…,该句型从句的谓语动词使用虚拟语气形式：should+动词原形。
It is necessary that
we should learn some English grammar.
2.表语从句：在复合句中作句子表语的从句
引导词有that,
whether, what, which, who, whom, whose, when, where, why, how,
because等
（1）
引导表语从句的that不省略，that仅起连接作用，在从句中不充当任何成分，无任何意义
The impression he
makes on me is that he is a reliable
person.
(2)
the
reason后面的表语从句只能用that引导，我们学生易犯“the
reason is because…”的错误
The
reason why
the little actress has been such a success
is
that she is both clever and hard-working.
(3)
在表示命令order等，建议suggestion,
advice等的名词后的表语从句中，谓语动词要用虚拟语气：
should+动词原形，should可省略
His suggestion is
that we (should) hold another meeting
to discuss the problem.
(4)
whether可引导表语从句，表“是否”，它在从句中不充当成分，if不能引导表语从句。
The question is
whether we can rely on him.
(5)
连接代词what,
which, who, whom, whose除起连接作用外，还在从句中做主语、宾语、表语和定语。
That’s
what he is worried about.（在从句作中宾语）
The problem is
who can do the work.（在从句中作主语）
（6）连接副词when,
where, why, how起连接作用外，还在从句中作状语。
That’s why I was
late.
That is where he was
born.
That is how he did
it.
(6)
连词because引导表语从句，只用在
That/This/It is
because…结构中
That is because
she often works hard.
3．宾语从句：从句在句中充当宾语的成分。宾语从句可作谓语动词的宾语，也可作介词的宾语，也可作动词不定式等非谓语动词形式的宾语，还可作某些形容词的宾语从句。
Jenny thought
(that) her teacher was unfair.
I’d like to know
which one is your husband.
I am sure
(that) he won’t mind.
It all depends on
whether they will support us.
4.同位语从句：一般跟在某些名词后面，用以解释或说明前面的名词的内容。经常带同位语从句的名词有fact,
news, message, doubt, possibility, idea, reason, belief, hope,
thought, promise, suggestion, question等。
引导词有连词that,
whether；连接代词who,
which, what和连接副词where,
when, why, how等
（1）
that,
whether只起连接作用，不在从句中作任何成分。
The idea
that England stands for fish& chips…is past.
There is no doubt
that the price of cars will
go down.
The problem
whether we should continue to
do the experiment has been solved.(不能用if)
(2)连接代词who,
which, what和连接副词where,
when, why, how在从句中作相应成分。
He can’t answer the
question how he got the money.
The question
who should go abroad requires
consideration.
I have no idea
which one I should choose.
I’ve got a pretty
good idea why they left early.
The question
where we should go has not been
discussed.
I have no idea
when Jack will be back.
同位语从句与定语从句的区别：
We expressed the
hope (that) they had expressed.
我们表达了他们曾经表达过的那种希望。（定语从句）
We expressed the
hope that they would come to visit
China again.
我们表示希望他们再来中国访问。（同位语从句）
1）
从语法角度上看，引导同位语从句的that是连词，只起连接作用，在从句中不作任何句子成分；而引导定语从句的that是关系代词，除起连接作用外，还在从句中作主语或宾语等句子成分。
2）
从语义角度上看，同位语从句与前面的名词hope是同位关系，表示hope的内容是they
would come to visit China again。因而同位语从句是名词性的，其功能是对名词作补充说明；而定语从句与它前面的名词是所属关系，表示“…的”（他们曾经表示过的），起修饰作用，因此定语从句是形容词性的，其功能是修饰先行词。
3）
同位语从句的连词that不能省略，而定语从句的关系代词that，当其在从句中作宾语中，可省略，作主语也不可省略。
I’ve heard the
news that he visited our factory.
I’ve heard the
news that he told you the other day.
The news
that the plane would take off on time
made everybody happy.
The news
that is spreading around the airport
is that a heavy storm is coming.
The suggestion
that students should learn something
practical is worth considering.
The suggestion
that they are considering is
that students should learn something practical.
