possive voice...

Passive voice的目的是指出事情的結果，不必要去提及行動者。
例如： The bank was robbed and some customers were injured. 銀行被打劫，有些顧客受了傷。若打劫者的身份仍未知，又或是你不想去透露主角是誰，句子便可用被動式。

I acknowledge that I made a mistake.
I acknowledge that a mistake was made.
第一句是說「我承認我犯了錯」，很清楚地交代是誰的錯。第二句就說「我承認有人犯了錯」，可能仍不知道誰犯了錯，又或者是否說話者並未願意承認自己的過失。

若動詞是to be + past participle，句子就是被動形。以下是一些例子：

Active: I told Mary a story.
Passive: Mary was told a story.

Active: I wanted to tell Mary a story.
Passive: Mary wanted to be told a story.

Active: I was going to tell Mary a story.
Passive: Mary was going to be told a story.

Active: I shall tell Mary a story.
Passive: Mary will be told a story.


什麼時候雖要用到被動語態
a. 當個不易說出動作的發出者既情況下, 如: someone. 又或唔知是誰做的.
My wallet was stolen (by someone). (主動: Someone stole my wallet.)
His car had already been damaged before that accident.

b. 當動作或狀態的承受者比發出者更為重要
My dog was killed by a speeding car.
(我的狗比那架車重要)

c. 當個動作發出者係人所共知, 不需要亦不重要去提及
Rice is grown in China (by farmer).

d. 當我們知道, 但不想提及這件事是誰做的
I was told that we might be able to leave early.
(主動: Someone told me that we might be able to leave early.)





被動語態 Passive Voice

英語之中，把動作敘述出來，可以用「主動語態」(Active Voice)，例如：

The dog bit the postman’s ankle.
(狗咬了郵差的足踝)

同一件事，另一個敘述法便是「被動語態」(Passive Voice)，例如：

The postman’s ankle was bitten by the dog. (郵差的足踝被狗咬了)

I eat an egg. (active voice) - the focus is on "I".
The egg is eaten by me (passive voice) - the focus is on "the egg".

Simple Present Tense

Active Voice: I teach him.
Passive Voice: He is taught by me.


Present Continuous Tense

Active Voice: I am teaching him.
Passive Voice: He is being taught by me.


Present Perfect Tense

Active Voice: I have taught him.
Passive Voice: He has been taught by me.


Present Perfect Continuous Tense

Active Voice: I have been teaching him for a week.
Passive Voice: N/A


Simple Past Tense

Active Voice: I taught him yesterday.
Passive Voice: He was taught by me yesterday.


Past Continuous Tense

Active Voice: I was teaching him when you came.
Passive Voice: He was being taught by me when you came.


Past Perfect Tense

Active Voice: I had taught him before you came.
Passive Voice: He had been taught by me before you came.


Past Perfect Continuous Tense

Active Voice: I had been teaching him an hour before you came.
Passive Voice: N/A


Simple Future Tense

Active Voice: I shall teach him tomorrow.
Passive Voice: He will be taught by me tomorrow.


Future Continuous Tense

Active Voice: I shall be teaching him when you come.
Passive Voice: N/A


Future Perfect Tense

Active Voice: I shall have taught him before the sun sets.
Passive Voice: He will have been taught by me before the sun sets.


Future Perfect Continuous Tense

Active Voice: I shall have been teaching him for an hour before the sun sets down.
Passive Voice: N/A

In sentences written in passive voice, the subject receives the action expressed in the verb; the subject is acted upon. The agent performing the action may appear in a "by the . . ." phrase or may be omitted.

Sometimes the use of passive voice can create awkward sentences, as in the last example above. Also, overuse of passive voice throughout an essay can cause your prose to seem flat and uninteresting. In scientific writing, however, passive voice is more readily accepted since using it allows one to write without using personal pronouns or the names of particular researchers as the subjects of sentences (see the third example above). This practice helps to create the appearance of an objective, fact-based discourse because writers can present research and conclusions without attributing them to particular agents. Instead, the writing appears to convey information that is not limited or biased by individual perspectives or personal interests.

You can recognize passive-voice expressions because the verb phrase will always include a form of be, such as am, is, was, were, are, or been. The presence of a be-verb, however, does not necessarily mean that the sentence is in passive voice. Another way to recognize passive-voice sentences is that they may include a "by the..." phrase after the verb; the agent performing the action, if named, is the object of the preposition in this phrase.

Choosing Passive Voice
While active voice helps to create clear and direct sentences, sometimes writers find that using an indirect expression is rhetorically effective in a given situation, so they choose passive voice. Also, as mentioned above, writers in the sciences conventionally use passive voice more often than writers in other discourses. Passive voice makes sense when the agent performing the action is obvious, unimportant, or unknown or when a writer wishes to postpone mentioning the agent until the last part of the sentence or to avoid mentioning the agent at all. The passive voice is effective in such circumstances because it highlights the action and what is acted upon rather than the agent performing the action.

Check this out for examples: http://owl.english.purdue.edu/handouts/grammar/g_actpass.html

2007-05-19 18:34:51 補充：
Here is a website if you want some practise:http://www.edict.com.hk/vlc/verbs/verbs5.htm