To avoid confusion, use commas to separate words and word groups with a series of three or more.
My $10 million estate is to be split among my husband, daughter, son, and nephew.
Use a comma to separate two adjectives when the word and can be inserted between them.
He is a strong, healthy man.
We stayed at an expensive summer resort.
You would not say expensive and summer resort, so no comma.
Use a comma when an -ly adjective is used with other adjectives.
To test whether an -ly word is an adjective, see if it can be used alone with the noun. If it can, use the comma.
Felix was a lonely, young boy.
I get headaches in brightly lit rooms.
Brightly is not an adjective because it cannot be used alone with rooms; therefore, no comma is used between brightly and lit.
Use commas before or surrounding the name or title of a person directly addressed.
Will you, Aisha, do that assignment for me? 你，艾莎，做我给你的事吗？
Yes, Doctor, I will. 是的，医生，我会的。
Capitalize a title when directly addressing someone.
Use a comma to separate the day of the month from the year and after the year.
Kathleen met her husband on December 5, 2003, in Mill Valley, California.
If any part of the date is omitted, leave out the comma.
They met in December 2003 in Mill Valley.
Use a comma to separate the city from the state and after the state in a document. If you use the two-letter capitalized form of a state in a document, you do not need a comma after the state.
NOTE: With addresses on envelopes mailed via the post office, do not use any punctuation.
I lived in San Francisco, California, for 20 years.
I lived in San Francisco, CA for 20 years.
Use commas to surround degrees or titles used with names. Commas are no longer required around Jr. and Sr. Commas never set off II, III, and so forth.
Al Mooney, M.D., knew Sam Sunny Jr. and Charles Starr III.
Use commas to set off expressions that interrupt sentence flow.
I am, as you have probably noticed, very nervous about this. 正如你可能注意到的那样，我很紧张。
When starting a sentence with a weak clause, use a comma after it. Conversely, do not use a comma when the sentence starts with a strong clause followed by a weak clause.
If you are not sure about this, let me know now. 如果你对此不太肯定，现在就告诉我。
Let me know now if you are not sure about this. （注意这两句话的区别，后句强调告诉我！）
Use a comma after phrases of more than three words that begin a sentence. If the phrase has fewer than three words, the comma is optional.
To apply for this job, you must have previous experience. 要申请这份工作，你必须要有经验。
On February 14 many couples give each other candy or flowers. 2月14日，许多夫妇互相送糖果或鲜花。
On February 14, many couples give each other candy or flowers.
If something or someone is sufficiently identified, the description following it is considered nonessential and should be surrounded by commas.
Freddy, who has a limp, was in an auto accident.
Freddy is named, so the description is not essential.
The boy who has a limp was in an auto accident.
We do not know which boy is being referred to without further description; therefore, no commas are used.
Use a comma to separate two strong clauses joined by a coordinating conjunction--and, or, but, for, nor. You can omit the comma if the clauses are both short.
I have painted the entire house, but he is still working on sanding the doors. 我已粉刷了整个房子，但他仍在打磨门窗。
I paint and he writes. 我画画，他写字。
Use the comma to separate two sentences if it will help avoid confusion.
I chose the colors red and green, and blue was his first choice. 我选择了红色和绿色，蓝色是他的首选。
A comma splice is an error caused by joining two strong clauses with only a comma instead of separating the clauses with a conjunction, a semicolon, or a period. A run-on sentence, which is incorrect, is created by joining two strong clauses without any punctuation.
Time flies when we are having fun, we are always having fun. (Comma splice)
Time flies when we are having fun we are always having fun.(Run-on sentence)
Time flies when we are having fun; we are always having fun.
Time flies when we are having fun, and we are always having fun. (Comma is optional because both strong clauses are short.)
Time flies when we are having fun. We are always having fun.
Use commas to introduce or interrupt direct quotations shorter than three lines.
He actually said, "I do not care." 他居然说：“我不关心”。
"Why," I asked, "do you always forget to do it?" “为什么，” 我问？“你总是忘记做这件事吗？”
Use a comma to separate a statement from a question.
I can go, can't I? 我可以去，不是吗？
Use a comma to separate contrasting parts of a sentence.
That is my money, not yours. 那是我的钱，不是你的。
Use a comma when beginning sentences with introductory words such aswell, now, or yes.
Yes, I do need that report. 是的，我确实需要那份报告。
Well, I never thought I'd live to see the day . 恩，我从没想过我会活到今天。
Use commas surrounding words such as therefore and however when they are used as interrupters.
I would, therefore, like a response. 因此，我想得要一个回应。
I would be happy, however, to volunteer for the Red Cross. 然而，我愿意为红十字会志愿工作。