英語從句的詞性詳解

從句是構成一部分語句的一組詞，并包括一個主語和一個謂語。被當做詞類使用的從句也叫做分句。分句可以由關系或疑問代詞，關系或疑問副詞，以及從屬連詞引導。

關系代詞是who，which，what，that（=who或which），as，以及復合關系詞whoever，whichever，whatever等。
主要的關系副詞是where，whence，whither，wherever，when，whenever，while，before，after，till，until，since，as，how和why等。
疑問代詞是who，which和what等。
疑問副詞是where，when，whence，whither，how和why等。

最重要的從句連詞是because，since（=because），though，although，if，unless，that（in order that，so that），lest，as，as if，as though，than和whether等。

根據從句作為詞類的使用情況，可以將它們分為形容詞，副詞或名詞從句。

一、形容詞從句

修飾實詞的從句叫做形容詞從句。形容詞從句可以由關系代詞，地點或時間關系副詞引導。

{Able men | Men of ability | Men who show ability} can always find employment.
{Treeless spots | Spots without trees | Spots where no trees grew} were plainly visible.

每一組中的名詞（men，spots），分別被形容詞，形容詞短語，以及形容詞從句修飾。但整個語句的意思沒有改變。

二、副詞從句

被當做副詞修飾語使用的從句叫做副詞從句。副詞從句可以由關系副詞（when，where，before），從屬連詞（if，though，because），和關系或疑問代詞引導。

Jack spoke {thoughtlessly. | without thinking. | before he thought.}
The schoolhouse stands {there. | at the crossroads. | where the roads meet.}
We pay our rent {monthly. | on the first of every month. | when the first of the month comes.}

每一組中，動詞（spoke，stands，pay）被副詞，副詞短語，以及副詞從句修飾。

副詞從句通常修飾動詞，但它們也常用作形容詞和副詞的修飾語。

Angry because he had failed, he abandoned the undertaking. [從句修飾angry.]
I am uncertain which road I should take. [從句修飾uncertain.]
Farther than eye could see extended the waste of tossing waters. [從句修飾farther.]
Here, where the cliff was steepest, a low wall protected the path. [從句修飾here.]

使用that的副詞從句可以用于修飾動詞和形容詞。

He rejoiced that the victory was won.
I am glad that you are coming.
He was positive that no harm had been done.
They were unwilling that the case should be brought to trial.

應注意，這種用法等同于“because”或“as to the fact that。”這種從句可以被解釋為狀賓結構的名詞從句。應根據意思（place，time，cause，concession）分類副詞從句。

三、名詞（或實詞）從句

當做名詞使用的從句叫做名詞性從句。

{Agreement | To agree | That we should agree} seemed impossible.
{Victory | To win | That we should win} was out of the question.
The merchant feared {loss. | to lose. | that he might lose money.}
I expect {success. | to succeed. | that I shall succeed.}

每一組中，agreement和victory等名詞被不定式或名詞從句替代。在前兩個實例中，名詞從句是主語。后兩個例子，它是動詞（feared，expect）的賓語。

名詞從句可用于任何更重要的名詞結構，如主語，及物動詞的直接賓語，名詞的同位語，以及謂語主格。名詞從句可以由that，whether和if等從屬連詞，who，which和what等疑問代詞，以及where，whence，whither，how，why和when等疑問副詞引導。

That Milton was spared has often caused surprise. [主語]
Brutus said that Tom was a tyrant. [said的賓語]
Tom commanded that the prisoners should be spared. [賓語]
I wish that you would work harder. [賓語]
The traveller inquired where he could find the inn. [賓語]
He asked me what my name was. [asked的第二個賓語]
My fear that the bridge might fall proved groundless. [fear的同位語]
One fact is undoubted,—that the state of America has been kept in continual agitation.—Burke. [fact的同位語]
The old saying is that misery loves company. [謂語名詞]

名詞性從句經常被當做“of commmanding”，“of telling“，“of asking”，以及thinking，doubting和desiring等動詞的賓語使用，在感嘆詞it是語法上的主語時，帶that的名詞性從句經常出現在謂語中。

It was plain that war was at hand.
It was clear that this administration would last but a very short time.
It must be admitted that there were many extenuating circumstances.
It was by slow degrees that Fox became a brilliant and powerful debater.
It was under the command of a foreign general that the British had triumphed at Minden.

在這些句子中，名詞從句可以被視為it的同位語。此外，名詞從句還可以是介詞或副詞的賓語。