逗号是最常见的标点符号。可是，我们都用对了吗？看看琐碎的规定吧。再次声明，此文内容摘录翻译自《美国大学英语写作》。一起学习吧~
三 逗号
1 分割一系列个体
例如：
The street vendor sole watches, necklaces, and earrings.
The pitcher adjusted his cap, pawed the ground, and peered over his shoulder.
The exercise instructor told us to inhale, exhale, and relax.
Joe speed into the hot, still-smoking engine.
注意：
A 在列举一系列个体的时候，最后一个逗号（and的之前）的可有可无，但一般是要写上的。
B 如果列举的两的个体，加不加逗号要靠语感来判断（靠！！！）。如果加了and读起来顺，那么这块就需要加逗号，比如：Joe speed into the hot and still-smoking engine。如果加了and独立来不顺，就不能加逗号，比如：Tony wore a pale green tuxedo。
（这条太坑爹了~我的理解，如果这两个罗列的部分是都直接修饰后面的名词的，则需要加逗号；如果是前一个修饰 后一个的，则不需要。这样就可以解释为什么用and来判断了。都是修饰后面名词的，它们是并列的，可用and；如果是前面后面修饰的，则不存在并列关 系，and则不合适呢。）
2 置于状语或从句之后。
例如：
Just in time, Sherry applied the brakes and avoided a car accident.
Although he had been first in the checkout line, Deion let an elderly woman go ahead of him.
注意：
如果这些修饰成分放在句子主干的后面，则不需要加逗号。尤其是从句，放在主句后面不需要逗号分割。如果修饰成分很短，放在句子主干前面也可以省略。
3 分割插入成分
例如：
The vinyl car sent, sticky from the heat, clung to my skin.
Marty’s computer, which his wife got him as a birthday gift, occupies all of his space time.
The hallway, dingy and dark, was illuminated by a bare bulb hanging form a wire.
注意：
分 割成分有我们熟悉的插入语，也包括一些从句。是否需要逗号如何判断呢？如果此处删除不影响整句基本表达，则需要逗号分开。比如：Sue Dodd, who goes to aerobics class with me, was in a serious car accident。这句话就需要用逗号把这个从句隔开。但是这句：The woman who goes to aerobics class with me was in a serious car accident则不需要隔开，因为删掉从句后句子基本表意受到影响。
4 连接并列句
并列句可以用的连词包括：and，but，for，or，nor，so，yet。
例如：
Sam closed all the windows, but the predicted thunderstorm never arrived.
I like warning comfortable clothing, so I buy oversize shirts and sweaters.
Peggy does not envy the skinny models in magazines, for she is happy with her own well-rounded body.
（提示：为什么for表示原因只能放在句子的后部而不能放在句子的开头呢？因为此时的for是连词。）
注意：
如果两个并列句比较短，逗号可以省略。
The Ferris wheel started and Wilson closed his eyes.
Many people left but the band played on.
I made a wrong turn so I doubled back.
逗号在此只能分割两个独立句子，就是有独立的主语和谓语的句子。如果两个动词共同组成谓语部分，则不可以用逗号分开。
The doctor stared over his bifocals and lectured me about smoking.
Dean switched the lamp on and off and then tapped it with his fingers.
5 在直接引语中使用
用逗号把直接引语部分同整个句子分割开。（中文会使用分号和句号，注意区别）
例如：
The carnival baker cried, “Step right up and win a prize!”
“Now is the time to yield to temptation,” my horoscope read.
“I’m sorry,” said the restaurant hostess. “You’ll have to wait.”
“For my first writing assignment,” said Scott, “I have to turn in a five-hundred-word description of a store.”
注意：在引号结尾出，逗号、句号等标点要放在引号内部。
6 分割常见名词
1）对话人名
If you’re the last to leave, Paul, please switch off the lights.
2）日期
June 30, 2008, is the day I make the last payment on my car.
3）地址
I buy discount children’s clothing from Issacs Baby Wear Factory, Box 900, Chicago, Illinois 60614. （注意：邮编前不加逗号）
4）信件的开头和结尾
Dear Santa,
Sincerely yours,
（注意：在正式邮件中，开头使用冒号，如：Dear Sir:）
5）数字
The insurance agent sold me a $50,000 term life insurance policy.
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