逗号的使用方法是正确运用标点过程中最复杂，最易产生误解的问题之一。在一些情形中，存在着被广泛同意的使用方法。然而在另一些状况下，却有不仅一种使用方法。学生常常觉得，担忧标点的使用方法有点可笑：毕竟，法律剖析才是非常重要的呀。但，倘若一个人申请一份工作或向上级提交书面报告，没什么会比忽略标点运用基本规则更容易给人留下负面印象的了。毕竟，一位高级律师是决不会想去更正一位初级律师的逗号的使用方法的。
Comma usage is one of the most complex, and most misunderstood, questions of proper punctuation1. In some cases there are widely accepted rules governing comma usage; in a few cases, there is more than one acceptable approach. Students often think it's silly to worry about things such as punctuation: after all, isn't the legal analysis what really counts? However, when one applies for a job or submits written work to a supervisor2, nothing will leave a more negative impression than ignorance of the basic rules of punctuation. After all, the last thing a senior attorney wants to do is correct a junior attorney's comma usage.
1.
当你用一个短语或从属分句开始一个句子，并随后引入一个独立分句时，用逗号分隔。
When you begin a sentence with a phrase or dependent clause to introduce a subsequent independent clause, separate the clauses with a comma.
Incorrect: After many years as a criminal prosecutor3 she ascended4 to the bench.
Correct: After many years as a criminal prosecutor, she ascended to the bench.
Incorrect: Because the witness was unavailable the judge allowed the introduction of the testimony5 pursuant to an exception to the hearsay6 rule.
Correct: Because the witness was unavailable, the judge allowed the introduction of the testimony pursuant to an exception to the hearsay rule.
2. 用逗号分隔非限制性从句，但不要用逗号分隔非限制性从句。
非限制性从句对你说关于句子主语的某些事情，但并不对其含义进行限定；相反，限制性从句对主语的意思进行限定。
Use commas to set off a nonrestrictive clause in the middle of a sentence, but not to set off a restrictive clause. Nonrestrictive clauses tell you something about the subject of a sentence, but they do not limit, or restrict, the meaning. Restrictive clauses, on the other hand, limit the possible meaning of the subject.
ompare the following examples.
Correct Restrictive Use:
The suspect in the lineup who has red hair committed the crime.
Note how the subject suspect in this sentence is restricted in two ways: we know that this suspect is both in the lineup and has red hair. As a result, we know that the other suspects, who are not in the lineup, could not have committed the crime. Moreover, of those suspects in the lineup, we know that the one suspect in the lineup with red hair committed the crime. If there were more than one suspect in the lineup with red hair, the above usage would be incorrect because it implies a different meaning.
Correct Nonrestrictive Use:
The suspect in the lineup, who owns a red car, committed the crime.
In this example, the restrictive clause in the lineup tells us that of all possible suspects in the world, the one who committed the crime is in the lineup. However, while the nonrestrictive clause who owns a red car tells us something about the suspect, it does not foreclose the possibility that there are several different suspects in the lineup with red cars. The car color may tell us something useful, but it does not restrict us to only one possibility.
3.用两个逗号来分隔同位语或插入语。同位语是对它所跟随的名词进行描述的单词或短语，插入语告诉大家关于某个名词的一些事情，但对讲解该名词并无关紧要。
Use two commas to set off an appositive or an aside in the midst of a sentence. An appositive is a word or phrase that describes a noun it follows. An aside tells us something about the noun, but is not essential to defining the noun.
Correct Use with an Appositive:
The police chief, William A. Bendofsky, is an authority on the use of roadblocks to protect neighborhoods from drive-by shootings.
Correct Use with an Aside:
The pretrial phase of the litigation, like all pretrial work, lasted longer than the trial itself.
4. 用两个逗号，而不是一个，来分隔非限制性从句。
Use two commas, not one, to set off a nonrestrictive clause in the middle of a sentence.
Incorrect: The city, a polyglot7 of different races and religions provided many opportunities for cultural exchange.
Correct: The city, a polyglot of different races and religions, provided many opportunities for cultural exchange.
5.在过渡性的副词前加逗号。比较常见的副词有accordingly, furthermore, however, moreover, therefore, 和 thus。
Place a comma after a transitional word that introduces a sentence. The following are examples of commonly used transitional words: accordingly, furthermore, however, moreover, therefore, and thus.
Incorrect: Accordingly he granted the motion to dismiss.
Correct: Accordingly, he granted the motion to dismiss.
Incorrect: Moreover she convinced the judge that her client had been out of state at the time of the burglary.
Correct: Moreover, she convinced the judge that her client had been out of state at the time of the burglary.
6. 当用逗号来分隔列举的项目时，在名单的最后一个项目之前前的连词前面加逗号。有很多人并不如此做，虽然这种使用方法经常见到，但这种方法在某些状况下或许会产生歧义。
When using commas to separate items in a list, place a comma before the conjunction that precedes the last separate item in the list, unless that last item is a compound term. Many people are taught not to place a comma before a conjunction preceding the last item in a list . However, while popular, this approach runs the risk of creating ambiguity8 in a number of situations. Consider the following.
Incorrect: The car was available in red, white, black and tan, and special-order colors.
上例中，假如车子有四种标准颜色可供选择，则逗号的使用方法不正确，由于这种使用方法使人以为车子还有一种复合颜色（black and tan）可供选择。但假如车子只有三种颜色可选，其中一种是复合颜色（black and tan），那样上述使用方法就是正确的。
If the car is available in four standard colors, then the above usage is incorrect, because it implies that black and tan is one, two-tone color option. However, if there are only three color options, one of which is black and tan, then the above usage is correct.
Correct: The car was available in red, white, black, and tan, and special-order colors.
上例中，放在连词and前的逗号使得读者非常了解，车子共有四种标准颜色的款式，防止了因为在连词and前不加逗号所产生的歧义。
The use of the comma before the first conjunction in this sentence makes it clear that there are four standard color options, avoiding the ambiguity created in the first example by the absence of a comma before and tan.
7. 假如有两个形容词一块修饰一个名词时，用逗号分隔这两个形容词。假如这两个形容词中的第一个形容词是用来修饰第二个形容词的，而不是修饰后面的名词，就不要用逗号分隔这两个形容词。
Use a comma to separate two adjectives that modify the same noun, but do not use a comma if the first of two adjectives modifies the second adjective, but not the noun. In considering this choice, ask yourself whether the two adjectives can be reversed. If they can, as in the first example below, separate them with a comma. If they can not, as in the second example below, do not use a comma.
Incorrect: The only approach to the city was by a long old highway.
Correct: The only approach to the city was by a long, old highway.
Incorrect: The suspect drove a light, blue truck.
Correct: The suspect drove a light blue truck.
In the second example, use of a comma would be incorrect, since light modifies blue, and is therefore not part of a series of commas that modify the word truck. However, on the off chance that the writer intended to write that the truck was light in weight as well as blue in color, then the first use would be correct. Thus, you can change the meaning of a sentence sometimes inadvertently by your use of commas.
8. 不要用逗号来替代引导词that。
Do not use a comma to replace the word that.
Incorrect: The court decided9, there is no constitutional right to a second appeal, except by means of a habeas petition.
Correct: The court decided that there is no constitutional right to a second appeal, except by means of a habeas petition.
Also Correct:
The court decided there is no constitutional right to a second appeal, except by means of a habeas petition.
In the second correct example, removing the word that from the sentence is acceptable because its absence does not confuse the reader. However, leave that in a sentence if removing it would create some doubt in the reader's mind concerning what the writer meant to convey.
9.不要用逗号分隔一个句子的并列谓语，除非不加逗号会让人费解或是并列谓语的第二部分需要强调。
As a general rule, do not use a comma to separate the parts of a double predicate, unless the sentence would be confusing without it, or the second part of the double predicate requires special emphasis. A double predicate exists where the sentence has one subject and two verbs related to that subject.
Incorrect: The customer finished his meal, and paid the check.
Correct: The customer finished his meal and paid the check.
用逗号分隔并列谓语来强调的例子：
Correct Use of Comma to Create Emphasis:
The defendant10 had been employed as a cashier for twenty years, and never once was accused of stealing money from the register.
In the preceding example, the writer creates a greater emphasis on the defendant's innocence11 by setting off the second part of the double predicate with a comma. Without the comma, the second thought seems like an afterthought.
用逗号分隔句子防止歧义的例子：
Correct Use of Comma to Avoid Confusion:
The judge ruled that suppression of the evidence was required because it had been obtained illegally, and ordered the defendant released from prison.
In this example, the writer avoids confusion by using a comma to introduce the second in the series of compound verbs; without the comma, one might not be sure whether the verb ordered related to the subject it or the subject the judge. By contrast, in the sentence above about the restaurant customer, the comma is not needed, because it is a simple sentence.
10. 当用连词连接两个独立从句时，在连词前加逗号。连词包含and, but, or, nor, 和 yet。
When joining two independent clauses with a conjunction, place a comma before the conjunction. Conjunctions include the words and, but, or, nor, and yet.
Incorrect: The customer ate every piece of the apple pie and the waitress brought another pie.
Correct: The customer ate every piece of the apple pie, and the waitress brought another pie.
In the incorrect example, the reader may at first think the customer ate the pie and the waitress. In the correct example, the comma before the conjunction tells the reader, STOP, another independent clause with its own subject is about to begin.
11. 一般，在which前面加逗号，但不要在that前面加逗号。虽然有些作者习惯于用which来引入限制性从句，传统使用方法是用that来引入限制性从句，用which来引入非限制性从句。在引入限制性从句时，在that前不要加逗号，在引入非限制性从句时，在which前必须要加逗号。
Generally, use a comma before which but not before that. Although some writers use which to introduce a restrictive clause, the traditional practice is to use that to introduce a restrictive clause and which to introduce a nonrestrictive clause. When writing a restrictive clause, do not place a comma before that. When writing a nonrestrictive clause, do place a comma before which.
Correct Restrictive Use:
The store honored the complaints that were less than 60 days old.
Correct Nonrestrictive Use:
The store honored the complaints, which were less than 60 days old.
These sentences have different meanings as well as different punctuation. In the restrictive sentence, the store honored only those complaints less than 60 days old, but not those over 60 days old. In the nonrestrictive sentence, the store honored all the complaints, all of which were less than 60 days old.
12. 在引号内加入逗号，不要在引号外面加，不论逗号是不是是其所引用的引语的组成部分。普通的规则是，逗号，句号一直放在引号内，而其他标点，如问号，冒号，分号和感叹号都要放在引号外面，除非他们原来就是所引用的引语的组成部分。
Place commas inside, not outside, quotation12 marks. Follow this practice whether or not the comma is part of the original quotation. The general rule is that commas and periods should be inside the quotation marks at all times, while all other forms of punctuation, such as question marks, colons13, 百度竞价推广icolons, and exclamation14 points, should be outside the quotation marks, unless they were contained in the original quotation.
Incorrect: The court held that physical injury is not a required element of a sexual harassment15 claim, and the plaintiff went on to win her case.
Correct: The court held that physical injury is not a required element of a sexual harassment claim, and the plaintiff went on to win her case.
13. 用两个逗号来分隔日期和地址。表述详细日期（年月日）时，或详细的地点（如国家，州，城市）时，在最后的项现在后加两个逗号。
Use two commas when setting off dates and places. When using a full date or multi-part geographical16 designation , use two commas around the last part of the designation.
Incorrect: On June 28, 1974 Judge Hayes took her seat on the Supreme17 Court.
Correct: On June 28, 1974, Judge Hayes took her seat on the Supreme Court.
However: In June 1974 Judge Hayes took her seat on the Supreme Court.
Incorrect: Laredo, Texas was host for the 1994 World Rodeo Championship.
Correct: Laredo, Texas, was host for the 1994 World Rodeo Championship.
Incorrect: We arrived in Tokyo, Japan for the meeting of the G-7 leaders.
Correct: We arrived in Tokyo, Japan, for the meeting of the G-7 leaders.
参考：从属从句和短语；限制性从句和非限制性从句
Cross References: Dependent Clauses and Phrases; Clauses Restrictive and Nonrestrictive