大牙有必要做全瓷牙吗:过去分词是什么意思？

就是在现在完成式中特有的一种动词的表现方式。
如：I have had lunch.
此句中，had就是过去分词

在现在完成时中特有的是过去分词
在正在完成时中特有的是现在分词

一、过去分词作定语

1.过去分词作定语,作用相当于一个定语从句.如:

What\'s the language spoken (= that is spoken)in that area?那个地区讲的是什么语言?

Is there anything planned ( = that has been planned) for tonight?今晚安排了什么活动没有?

2.过去分词短语还可以作非限制性定语,作用相当于一个非限制性定语从句.如:

The book, written ( = which was written) in 1957, tells the struggle of the miners.这本书是1957年写的,讲的是关于矿工斗争的故事.

3.单个过去分词作定语常放在所修饰的名词之前,也可放在其后.如:

Do you know the number of books ordered?订了多少书,你知道吗?

They decided to change the used material.他们决定改变所用材料.

4.过去分词常表示动作发生的时间早于谓语动词,或者没有时间性,只表示被动关系.如:

The question discussed is very important.被讨论过的问题是很重要的.(既表被动又表完成)

I don\'t like to see letters written in pencil.我不喜欢看用铅笔写的信.(没有一定的时间性,只表被动)

5.注意过去分词与其它非谓语形式作定语的区别:现在分词(doing)作定语,表示一个主动的、正在进行的动作;现在分词的被动语态(being done)表示一个被动的、正在进行的动作;不定式(to do)作定语表示一个将要发生的动作.如:

The meeting being held(which is being held) now is very important.正在召开的这个会议很重要.

The meeting held(which was held) yesterday is very important.昨天召开的会议很重要.

The meeting to be held(which will be held) tomorrow is very important.明天将要召开的会议很重要
二、过去分词作状语

1.作原因状语.

相当于as, since, because引导的从句,这类状语多放在句子前半部分.如:

Given advice by the famous detective, the young lady was no longer afraid. (Since/ As she was given by the famous detective...)有了著名的侦探的指点,姑娘不再害怕了.

Frightened by the noise in the night, the girl didn\'t dare to sleep in her room. (Because she was frightened by the noise...)姑娘被夜里的响声吓坏了,不敢在自己的屋里睡觉了.

Written very well, the novel is worth reading.书写工整的小说值得一看.

Done in a hurry, his homework was full of mistakes.他匆忙做的作业错误百出.

2.作时间状语.

相当于when引导的状语从句.如果两个动作同时发生,可在分词前用when, while等使其时间意义更明确.如:

When heated, water can be changed into steam.水加热后可以变成蒸汽.

注意:作时间状语时,过去分词如果同时表被动和动作完成,常可换用现在分词的被动完成式;过去分词如果只表被动,不表完成,则不可与现在分词的被动完成式换用.如:

Discussed(Having been discussed) many times, the problems were settled at last.在讨论了多次之后,问题终于解决了.(过去分词既表被动又表完成)

Seen from the hill, the park looks very beautiful.从山上看这个公园非常漂亮.(过去分词只表被动)

3.作条件和假设状语.

相当于if, unless引导的从句.如:

Given more attention(If they had been given more attention), the cabbages could have grown better.如果再精心一些,这些大白菜还可以长得更好.

Compared with you, we still have a long way to go.和你相比,我们还有很大的差距.

4.作方式或伴随情况状语.

The hunter left his house , followed by his dog.猎人离开了屋子,后面跟着他的狗.

She sat by the window, lost in thought.她坐在窗前,陷于沉思.

作状语表示方式或伴随情况时,过去分词可用并列句代替.如:

The hunter left his house, followed by his dog. (= He was followed by the dog. )

5.用分词短语作状语时,它逻辑上的主语要与句子的主语保持一致,否则分词短语就要有自己的逻辑主语(用名词或代词的主格来表示).这种结构称为独立主格结构.

All our savings gone,we started looking for jobs.积蓄全部用完了,我们就开始找工作.(All our savings gone是过去分词的独立主格结构)

He rushed into the room, his face covered with sweat.他满脸是汗冲进屋内.(his face covered with sweat是过去分词的独立主格结构)