一、定義：

A. 表語從句就是用一個(gè)句子作為表語。說明主語是什么或者怎么樣，由名詞、形容詞或相當(dāng)于名詞或形容詞的詞或短語充當(dāng)，和連系動(dòng)詞一起構(gòu)成謂語。

例句：The problem is when we can get a pay rise. 問題是，當(dāng)我們可以得到加薪。

B. 連接表語從句的連接詞有：that, what, who, when, where, which, why。例句：

He has become what he wanted to be ten years ago.
他已經(jīng)成為了他10年前想成為的。

She has remained where I stood yesterday for an hour.
她一直在我昨天站的地方站了一個(gè)小時(shí)。

His suggestion is that we should stay calm.
他的建議是，我們應(yīng)該保持冷靜。

The question is when he can arrive at the hotel.
問題是，他什么時(shí)候可以到達(dá)酒店。

二、注意：

A. 表語從句一定要用陳述語序。

False: The question is when can he arrive at the hotel.
Right: The question is when he can arrive at the hotel.

B. 不可以用if，而用whether連接表語從句（as if 例外）；
引導(dǎo)賓語從句時(shí)可以互換if/whether，位于介詞后要用whether；
位于句首時(shí)要用whether；
引導(dǎo)表語從句，主語從句，同位語從句時(shí)要用whether。

False: The question is if the enemy is marching towards us.
Right: The question is whether the enemy is marching towards us.
Right: It looked as if he had understood this question.

C. 不像賓語從句，在有表語從句的復(fù)合句中，主句時(shí)態(tài)和從句時(shí)態(tài)可以不一致。

Right: The question is who will travel with me to Beijing tomorrow.
Right: The question is why he cried yesterday.

D. that在表語從句中不可以省掉。

表語從句的基本用法

表語從句只能置于主句之后，而主句的動(dòng)詞只能是聯(lián)系動(dòng)詞。

名詞性從句在be等系動(dòng)詞后作表語時(shí)被稱為表語從句，例如：

The problem is how we can get the things we need. 問題是我們怎樣能弄到我們需要的東西。(how 在表語從句中充當(dāng)方式狀語)

The scissors are not what I need. 這把剪刀不是我所需要的。(what在表語從句中充當(dāng)賓語)

What I told him was that I would find him a good play. 我告訴他的是我會(huì)給他找個(gè)好劇本。(what在主語從句中作直接賓語，that作為表語從句的引導(dǎo)詞在該表語從句中不充當(dāng)句子成分，不能省略)

That is what I want to tell you. 那就是我想要對你講的。(what在表語從句中充當(dāng)直接賓語)

That is why she failed to pass the exam. 那就是她考試不及格的原因。(why在表語從句中充當(dāng)原因狀語)

注意：“That is why...”是常用句型，意為“這就是……的原因/因此……”，其中why引導(dǎo)的名詞性從句在句中作表語，該句型通常用于針對前面已經(jīng)說明過的原因進(jìn)行總結(jié)，又如：That is why you see this old woman before you know, Jeanne. 珍妮，這就是現(xiàn)在這個(gè)老太婆出現(xiàn)在你面前的原因。(前文提到Jeanne對老婦人顯得蒼老憔悴深感詫異，說話人對她講述了其中的原因之后，用這一句來進(jìn)行概括)。

下面是兩個(gè)與“That is why...”形式相似的結(jié)構(gòu)，它們與“That is why...”結(jié)構(gòu)之間的關(guān)系要能夠辨析清楚：

(1)“That is why...”與“That is the reason why...”同義，只不過從語法結(jié)構(gòu)上講，“That is the reason why...”中why引導(dǎo)的是—個(gè)定語從句，將其中的the reason去掉則與“That is why...”結(jié)構(gòu)一樣，例如：

That is (the reason) why I cannot agree. 這就是我不能同意的理由。

(2)“That is because...”句型中從屬連詞because引導(dǎo)的名詞性從句在此作表語，這也是個(gè)常用句型，意為“這就是為什么……/因?yàn)椤薄！癟hat is because...”與“That is why...”之間的不同在于“That is because...”指原因或理由，“That is why...”則指由于各種原因所造成的后果， 例如：

He did not see the film last night. That is because he had to help his little sister with her homework. 昨天晚上他沒有去看電影，那是因?yàn)樗脦椭拿妹米鲎鳂I(yè)。(第一句話說明結(jié)果， 第二句話說明原因)

He had seen the film before. That is why he did not see it last night. 他以前曾看過那部電影，因此他昨天晚上沒有去看。(第一句話說明原因，第二句話說明結(jié)果)