现在分词的结构和时态
1. 现在分词独立结构
现在分词可有其独立的逻辑主语。这种主语常常是名词或代词主语，置于现在分词之前，二者构成一种分词独立结构。现在分词独立结构常用作状语，置于句首或句末，偶尔也置于句中。分句独立结构多用在书面语中。
(1) 表时间。如：
The bell ringing, the children all stopped talking.
铃声一响，孩子们都不说话了。
The dark clouds having dispersed, the sun shone again.
乌云已散去，太阳又普照大地了。
The question being settled, we went home.
问题解决之后，我们就回家了。
(2) 表原因。如：
It being a holiday, I went fishing.
那天放假，我钓鱼去了。
The night being dark, she was afraid to go there.
天黑，她不敢去那儿。
The river having risen in the night, the crossing was impossible.
夜里河水上涨，渡河不可能了。
(3) 表条件。如：
Weather permitting, we'll have an outing tomorrow.
要是天气许可的话，我们明天就去郊游。
Other things being equal, I would buy the black dress not the white one.
其他方面若都相同，我将买那件黑的衣服，不买那件白的。
(4) 表方式或伴随情况。如：
The teacher came in, his hand carrying a book.
老师手中拿着书进来了。
Their room was on the third floor, its window overlooking the sports ground.
他们的房间在三层楼上，窗户俯视着操场。
He guiding her, they stumbled through the street.
他引着她，两个人蹒跚着穿过那条街。
(5) 现在分词独立结构有时可由介词with或without引导。如：
She came without anyone accompanying her.
她来了，没有任何人陪着她。
2. 现在分词的否定结构
现在分词的否定式由 “not+现在分词” 构成。如：
Not knowing where to go, she went to the police for help.
她不知道该往哪儿走，就去请警察帮助。(现在分词一般式的否定结构)
Not seeing John, I asked where he was.
我看不见约翰，于是问他在何处。（现在分词一般式的否定结构）
Not being seen by anyone, the thief escaped.
那个贼趁无人看见时逃跑了。（现在分词被动式的否定结构）
Not having done it right, I tried again.
我由于没有做对，所以又试了试。（现在分词完成式的否定结构）
3. 现在分词的一般式
(1) 现在分词的一般式通常表示其动作与谓语动词的动作同时发生。如：
She sat there reading a novel.
她坐在那里看小说。
A little child learning to walk often falls.
学走路的小孩常常跌跤。
(2) 现在分词的一般式所表示的动作有时在谓语动词的动作之前发生。如：
Going into the room, he shut the door.
走进房间，他就关上了门。
4. 现在分词的完成式
现在分词的完成式表示其动作在谓语动词的动作之前完成。
Having finished her homework, the little girl began to watch TV.
做完作业后，这个小女孩开始看电视。
Having lived in Beijing for many years, Carter knew the city well.
因为在北京住了多年，卡特对这个城市很熟悉。
5. 现在分词的被动式
现在分词的被动式表示其逻辑主语为现在分词动作的承受者。
(1) 现在分词的一般被动式。如：
The building being built is our library.
正在建的那栋楼是我们的图书馆。
The question being discussed is of great importance.
正在讨论的问题非常重要。
(2) 现在分词的完成被动式。如：
Having been warned by the teacher, the students didn't make such mistakes.
老师警告他们之后，学生们不再犯这样的错误了。
Having been told many times , he still did not know how to do it.
（人家）已经告诉他多少次了，他还是不知道怎么做。
6. 垂悬现在分词
现在分词作状语时，其逻辑主语应该与句子的主语一致，但有时现在分词的主语与其所在句中的主语并不一致，这种现在分词即所谓的垂悬现在分词。垂悬现在分词容易使句意模糊，甚至造成歧义，因而通常被认为是不合规范或错误的用法。
Searching along the deck, it had taken him some time to find a doctor.
他沿着甲板找了好久才找到一名医生。（searching的逻辑主语是句中的him）
Walking or sleeping, this subject was always in my mind.
不论是走路或睡觉，我总是在想着这个问题。
（walking or sleeping 的逻辑主语是句中的 my）