英语语法精讲：语态被动有方
英语动词有主动语态(the active voice)和被动语态(the passivevoice)两种形式。如果主语是谓语动词的主宰，这就是主动语态;如果宾语成为动作的执行者，这就是被动语态。
在下列两个句子中，(a)是主动语态，(b)是被动语态。
① a. I have just bought a new book.
b. A new book has just been bought by me.
② a. Tom will invite you to dinner.
b. You will be invited to dinner by Tom.
主动转被动语态的步骤
从主动语态转换为被动语态时，必须按照下列步骤进行：
⒈把谓语动词后头的宾语移到句首当主语。如果没有宾语或者不是宾语的句子成分， 就没有新主语;这句话也就不能有被动语态了。
⒉如果有两个宾语(即直接宾语和间接宾语)，只要把其中一个变成主语即可， 其他一个保留在原位。
⒊用助动词“be + 过去分词”的动词形式，并和主语的人称、数目配合;动词时态也要和主动语态里的配合。
⒋如果主动语态中有语气动词(如：must, can, should)等，就以这个语气动词和“be + 过去分词”连用。
⒌把主动语态里的主语移到句末， 但要在它前面加上介词“by ”。通常，这个“by + 主语”的短语，都被省略了。
⒍如果谓语动词是片语动词(the phrasal verb)的话， 就要把片语动词当一个单位处理。例如：
③ a. We must do the work.
b. The work must be done (by us)。
④ a. John gave Anne a pen.
b. Anne was given a pen by John 或 A pen was given to Anne by John.
⑤ a. They have put off the meeting.
b. They meeting has been put off.
使用被动语态的情况
一般上说，我们用主动语态的时候多，用被动语态的时候少。然而，如果我们不知道谁是动作的执行者，我们只有被动语态这条路可走：
⑥ A cat was knocked down.
⑦ Electricity is widely used in all cities.
⑧ The annual sports meet may be held in three months.
此外，在下列情况下，也最好用被动语态：
⒈宾语比主语重要，必须突出，如：
⑨ A thief was arrested.
⑩ The waste paper has been burnt.
如果把⑨和⑩改为主动语态，就平淡乏味了：
△The police arrested a thief.
△Someone has burnt the waste paper.
⒉不方便提到主语;在此情况下， 常用“it”来引导，如：
11. It is said that the government will raise the income tax.
⒊有些动词多以被动语态出现，如：
12. All are expected to come early.
13. The report was based on the findings of a survey.
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