过去分词（短语）作状语及定语是非谓语动词的重要用法，现分析如下：

I. 过去分词（短语）作状语

过去分词（短语）作状语时表示的动作是主语动作的一部分，与谓语表示的动作或状态几乎是同时发生，或是先于谓语动词的动作发生，它的逻辑主语与句子的主语一致。过去分词作状语一般都用逗号同其它成分隔开，常表时间，条件，原因，方式，伴随，让步等含义，相当于一个状语从句。

1．作时间状语相当于when引导的从句，通常放于句首。例如：

Seen from the top of the hill (= When the city is seen from the top of the hill), the city looks more beautiful.

Accepted by the Party, he decided to devote his life to the cause of the Party.入党以后，他决定献身于党的事业。

2． 作条件状语相当于if, unless引导的从句，一般放在句首。例如：

Given more attention (= If it is given more attention), the accident could have been avoided.

Given another chance, he will do better.再给他一次机会，他会做得更好。
Compared with your brother, you should make greater efforts to study English.和你哥哥相比，你应该更加努力学习英语。
If heated, water can be turned into steam.水如果被加热，会变成水蒸气。

3． 作原因状语相当于because, as, since引导的从句，多放于句首。例如：

Scolded (=As she was scolded) by the teacher, the girl sat there without lifting her head.

Encouraged by the speech, the young people made up their minds to take up the struggle. 受到了讲演的鼓舞，年轻人决定起来从事斗争。

4．作方式或伴随状语时，一般不能用状语从句替换，但可以转换成并列分句或非限制性定语从句，可位于句首或句尾。例如：

Surrounded by his students, the professor sat there cheerfully. (= The professor was surrounded by his students and sat there cheerfully.)

The old man went into the room, supported by his wife.那个老人在他的妻子的搀扶下走进了房间。
Seated at the table, my father and I were talking about my job.  我和父亲坐在桌子旁边讨论着我的工作问题。

5． 作让步状语相当于though, if引导的从句，常放在句首。例如：

Tired(= Though he was tired), the worker went on working.

Exhausted by the running, they went on running after the robber. 尽管已经跑得筋疲力尽，他们还是继续追赶着那个强盗。
    Laughed at by many people, he continued his study.尽管被许多人嘲笑，他还是继续他的研究。

6．过去分词（短语）作状语时，有时为了强调，前面可带连词when, while, if, though, as if, unless, until等，以便使句意更清楚。例如：

If given more time, they would have done it better.

II. 过去分词（短语）作定语

过去分词作定语时，表示完成和被动的意义。

过去分词作定语的位置：

1．单个的过去分词作定语，绝大部分情况下放在所修饰的名词前。例如：

an excited boy; boiled water.但有时为了强调，也可放在所修饰的名词后。例如：

I want to change the material used.

2．过去分词短语作定语时放在所修饰的名词后，作用相当于定语从句。例如：

He is reading a novel written (= which was written) by Lu Xun.

Some of the people invited (= who have been invited) to the party can’t come.

过去分词作定语也可用作非限制性定语，前后用逗号隔开。如：
The books, written by Lu Xun, are popular with many Chinese people.这些书是鲁迅写的，受到了许多中国人民的喜爱。
The meeting, attended by one thousand students, was a success.  这次会议获得很大的成功，共有一千个学生出席了。

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)

过去分词短语作定语有三种时态：表示动作已发生；表示动作将要发生；表示动作正在发生。对比以下三句：

The building built last year is very beautiful.

The building being built will be completed next month.

The building to be built will be a hospital.

III、过去分词作表语 
    过去分词作表语，表示主语的性质、特征或状态。 
    用作表语的过去分词，被动意味很弱，主要表示动作的完成和状态。此时的过去分词相当于一个形容词，其后常不跟 by 短语。如： 
    The glass is broken. 玻璃破了。 
    Our classroom is crowded. 我们的教室很拥挤。 
    The ground is covered with snow. 地上覆盖着雪。 
    注：被动语态的过去分词，动作意义很强，句子主语为动作的承受者，后常跟“ by+ 施动者”。如： 
    The glass was broken by Jack. 玻璃是杰克打破的。 
    The windows were closed by Li Ming last night. 昨天夜里是李明关的窗。 
    表示感觉的一些过去分词 (surprised, disappointed, excited, pleased 等 ) 及其他一些过去分词（ dressed, drunk, devoted, lost, known, married, bent, recovered, separated 等）常可用作表语，表示状态。其中有些只表状态，毫无被动意义。如： 
    I found that I was lost. 我发现我迷路了。 
    Those days are passed and gone 那些日子一去不复返了。 
    He is dead drunk. 他喝得烂醉。