英语逗号的用法

逗号是英语文章中最常用的标点符号。当句子较长，难于一口气读完，往往就需要在适当的地方用逗号稍作停顿。逗号的另一个作用是便于读者看清句子结构，特别是在句子较长或容易产生误解的地方，作者常可借助逗号让读者能更好地理解所要表达的意思。

下面介绍逗号的主要用法：

1) 同位语
George's dog, Alan, was still sitting there waiting for him. 乔治的狗艾伦仍然蹲在那儿等他。
He is Lin Fei, one of my mother's old colleagues. 他是我妈的一位老同事林飞。

2) 插入成分
Computers, of course, can beat humans completely in certain areas. 当然，计算机在某些领域能完胜人类。
She must, I thought, have revised her first impression of me. 我想她一定已经改变了对我的最初印象。

3) 隔开句首的状语
位于句首的状语多数情况下会用逗号隔开，如:
Firstly, I must go over the price list. 首先，我必须看一下价格单。
Taken in time, the drug is very effective. 这种药如果及时服用的话会很有效。

4) 隔开句末不紧密依附于句子的状语，例如分词短语或复合结构等
She stood still by the window, watching the rain. 她一动不动地站在窗边，看到雨。
And there stood the minister, with his hand over his heart. 就在那儿，站着牧师，他一手捂着心口。
I don't think about my old home very much, only every now and then. 我并不非常想念老家，只是偶尔想想。

5) 分隔并列的句子成分或结构
War, famine, and flood are terrible. 战争, 饥荒和洪水都是很可怕的。
We had a long, hard, but interesting journey. 我们的旅途很长而且很累，但非常有意思。

6) 隔开状语从句，特别是当状语从句是位于句首时。
When he realized his mistake, he apologized to her sincerely. 当他认识到自己的错误时, 他真诚地向她道歉。
Although they look similar, these insects are actually quite different. 虽然这些昆虫看起来很相似,实际上它们是很不同的。

7) 隔开非限制性定语从句
They offered him some money, which he refused politely. 他们要给他一些钱，他婉言拒绝了。
The 9:30 train, which is usually very punctual, was late today. 九点半的那趟火车通常都很准时，但今天晚点了。

8) 隔开并列句
The dog's foot had been hurt, and the poor fellow could not walk on it. 那条狗有一只脚受伤了，可怜的东西无法用它来走路。
They've had three meetings, but still they haven't reached agreement. 他们已经开过三次会议,但还是未取得一致的意见。

9) 标出直接引语
He shouted, "Don't move, or I will shoot!" 他喊道：“不许动，不然我就开枪！”
"I do hope," said Michael, "they haven't taken all of them."
迈克尔说:“我真希望他们没有把所有的东西都拿走”

10) 感叹词后边也可以用逗号隔开，如：
Well, let's move on to the next question. 好了, 咱们转到下一个问题吧。

当然，当需要表达强烈的情感时，就需要用到感叹号, 如：
Ouch! That is really hurt. 哎哟！疼死我了。

以上总结了英语逗号的用法。在英语中可以用到逗号的地方还不只上面这些，而且在实际应用中，作者还可能因为其他原因（如感情色彩表达的需要，或担心句子太长读者看不清结构等）而使用逗号。另外有一点需要注意的是，汉语中有顿号，而英文中是没有的。汉语中的顿号在英文中要改用逗号来表示。