在句子中起名词作用的从句叫名词性从句(Noun Clauses)。名词性从句的功能相当于名词词组，它在复合句中能担任主语、宾语、表语、同位语、介词宾语等，因此根据它在句中不同的语法功能，名词从句又可分别称为主语从句、宾语从句、表语从句和同位语从句。

1. 主语从句

(1)三种连接词

①从属连词：that，whether等。

that引导主语从句只起引导作用，本身无实际意义，在主语从句中不充当任何成分，但不能省略。

That she left him cut him to the heart.

由whether及其他连词引导的主语从句放在句首，句后都可。

Whether it will please them is not easy to say.

②连接代词who，what，which，whatever，whichever，whoever。

What seems easy to some people seems difficult to others.

③连接副词when，where，how，why等。

Why he did it remains a mystery.

(2)位置：主语从句可以前置，也可以后置。用it作形式主语，而把主语从句放在句末，常用下面几种句型。

① It is still uncertain whether he is coming or not.

It + be + 表语 + 主语从句表语：(名词、形容词、过去分词)

② It seemed (happened, doesn’t matter, has turned out) that…

It doesn’t matter whether she will come or not.

It + 不及物动词 + 主语从句

③ It has been decided that the exhibition will not open on Sundays.

It is expected that the house price in Beijing will fall down.

It + 及物动词(被动语态)+ 主语从句

2.宾语从句

(1)由连接词that引导的宾语从句

(2)主语+及物动词+连接代词/连接副词引导的宾语从句

None of us knows where these new parts can be bought.

宾语从句的语序是陈述句语序，即：连接代词/副词+主语+谓语+其他成分。

(3)主语+及物动词+whether/if引导的宾语从句，宾语从句要用陈述句语序，whether与if引导宾语从句时一般可以互换使用。

Please let us know whether (if) they will come to our party.

在discuss，wonder，not sure和介词之后尽量用whether，if与whether含义容易混淆。

The board are discussing whether the fund should be allocated to that region.

(4)宾语从句中的否定转移

若主句主语是第一人称，谓语动词为think，consider，suppose，believe，expect，guess，imagine等，其后的宾语从句若含有否定意义，一般要把否定词转移到主句谓语上，从句谓语用肯定式。

I don’t think this dress fits you well. I don’t believe you will finish the work today.