英语三大从句

复合句

【语法要点】

复合句是由一个主句加一个或几个从句所构成的句子。从句只用作句子的一个成分，不能独立。根据从句在句子中的作用，可分为名词性从句、定语从句和状语从句三类。

（一）名词性从句

名词性从句包括主语从句、表语从句、宾语从句、同位语从句。其关联词有连接词that、if、whether；疑问代词who、what、which和疑问副词when、where、how、why等。

1.名词性从句句法结构：

2.名词性从句的其它用法：

1）if不能引导表语从句。连接代词who、what、whose、which不能引导同位语从句。

2）有时as、as if/though、because也可以引导表语从句，能跟表语从句的谓语动词一般为系动词be、seem、look等。例如：

Things are not always as they seem to be.事情并不总是像表面上看来的那样。

It looks as if it were going to rain. It is because you eat too much.

3）介词宾语不可以用which来引导，而要用what来引导。例如：

We can learn what we did not know. He will talk to us about what he saw in the .

4）连词that引导的名词性从句除能用在except、but、in后之外很少作介词的宾语，。其它一些介词的宾语从句如果由连词that引导，则需用it先行一步作形式宾语。例如：He is a good student except that he is careless.

You may depend on it that they will support you.

5）若主句谓语动词是及物动词make、find、think、see、hear等，则把宾语从句置于宾语补足语之后，用it作形式宾语。例如：We find it necessary that we practise spoken-English every day.

6）某些作表语的形容词或过去分词后常接宾语从句，如sure、happy、glad、certain、pleased、afraid、surprised、satisfied等，连词that可省略，有的语法书称之为状语从句。例如：

I am sure that he will succeed.

I am afraid you don’t understand what I said.

Mother was very pleased her daughter had passed the exams.

7）连接代词whoever、whatever、whichever也可引导宾语从句。例如：

I will show you whatever you want to see.

You may choose whoever you like. I will take whichever fits the sockets.（插座）8）同位语从句一般跟在某些表示抽象概念的名词后面，用以说明名词所表示的具体内容。常跟同位语从句的名词主要有：idea、news、fact、promise、answer、belief、condition、doubt、fear、hope、order、problem、proof、question、reply、report、suggestion、thought、 truth等。

由连词that引导同位语从句既无语法功能，也无词汇意义，只是引导词；由连词whether引导同位语从句无语法功能，但有词汇意义“是否”；由连词when、where、how引导同位语从句在句中

分别作作时间、地点和方式状语。

注意→①关联词只能用whether不能用if表示“是否”的情况如下：

A)在表语从句和同位语从句中。例如：

The question is whether the film is worth seeing.

The news whether our team has won the match is unknown.

B)在主语从句中，只有it作形式主语时whether和if均可。否则，也只能用whether。例如：

Whether we shall attend the meeting hasn’t been decided yet.

It hasn’t been decided whether/if we shall attend the meeting.

C)在介词之后（介词往往可以省略）。例如：It all depends (on) whether they will support us.

D)后面直接跟动词不定式时。例如：He doesn’t know whether to stay or not.

E)与or not连用时。例如：We didn’t know whether or not she was ready.

②关联词if、whether均可使用的情况如下：

A)引导宾语从句，但当宾语从句是否定句时，一般用if引导。例如：

I wonder if/whether the news is true or not. I don’t care if it doesn’t rain.

B)在“be+形容词”之后。例如：He was not sure whether/if it is right or wrong.

③用if引导宾语从句如果会引起歧义，应避免使用if而用whether。试比较：

Please let me know if you want to go. Please let me know whether you want to go.

（if从句既可理解为宾语从句，也可理解为条件状语从句）

doubt作“怀疑”解接宾语从句时，主句为肯定句用whether或if，主句为否定句或疑问句用that。

10）it作形式主语

①that所引导的主语从句常由代词it作形式主语。且wh-系列引导词引导的从句均可。例如：

It makes everyone happy that the girl is still alive.

It doesn’t matter too much whether he’s coming or not.

It is still open to question who is to head the group. 谁领导这个小组还没定下来。

②常以it作形式主语的句型有：