英语从句的词性详解

从句是构成一部分语句的一组词，并包括一个主语和一个谓语。被当做词类使用的从句也叫做分句。分句可以由关系或疑问代词，关系或疑问副词，以及从属连词引导。

• 关系代词是who，which，what，that（=who或which），as，以及复合关系词whoever，whichever，whatever等。
• 主要的关系副词是where，whence，whither，wherever，when，whenever，while，before，after，till，until，since，as，how和why等。
• 疑问代词是who，which和what等。
• 疑问副词是where，when，whence，whither，how和why等。

最重要的从句连词是because，since（=because），though，although，if，unless，that（in order that，so that），lest，as，as if，as though，than和whether等。

根据从句作为词类的使用情况，可以将它们分为形容词，副词或名词从句。

一、形容词从句

修饰实词的从句叫做形容词从句。形容词从句可以由关系代词，地点或时间关系副词引导。

• {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.

每一组中的名词（men，spots），分别被形容词，形容词短语，以及形容词从句修饰。但整个语句的意思没有改变。

二、副词从句

被当做副词修饰语使用的从句叫做副词从句。副词从句可以由关系副词（when，where，before），从属连词（if，though，because），和关系或疑问代词引导。

• 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.}

每一组中，动词（spoke，stands，pay）被副词，副词短语，以及副词从句修饰。

副词从句通常修饰动词，但它们也常用作形容词和副词的修饰语。

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

使用that的副词从句可以用于修饰动词和形容词。

• 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.

应注意，这种用法等同于“because”或“as to the fact that。”这种从句可以被解释为状宾结构的名词从句。应根据意思（place，time，cause，concession）分类副词从句。

三、名词（或实词）从句

当做名词使用的从句叫做名词性从句。

• {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.}

每一组中，agreement和victory等名词被不定式或名词从句替代。在前两个实例中，名词从句是主语。后两个例子，它是动词（feared，expect）的宾语。

名词从句可用于任何更重要的名词结构，如主语，及物动词的直接宾语，名词的同位语，以及谓语主格。名词从句可以由that，whether和if等从属连词，who，which和what等疑问代词，以及where，whence，whither，how，why和when等疑问副词引导。

• That Milton was spared has often caused surprise. [主语]
• Brutus said that Tom was a tyrant. [said的宾语]
• Tom commanded that the prisoners should be spared. [宾语]
• I wish that you would work harder. [宾语]
• The traveller inquired where he could find the inn. [宾语]
• He asked me what my name was. [asked的第二个宾语]
• My fear that the bridge might fall proved groundless. [fear的同位语]
• One fact is undoubted,—that the state of America has been kept in continual agitation.—Burke. [fact的同位语]
• The old saying is that misery loves company. [谓语名词]

名词性从句经常被当做“of commmanding”，“of telling“，“of asking”，以及thinking，doubting和desiring等动词的宾语使用，在感叹词it是语法上的主语时，带that的名词性从句经常出现在谓语中。

• 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.

在这些句子中，名词从句可以被视为it的同位语。此外，名词从句还可以是介词或副词的宾语。