Commas have a wide variety of uses, probably more than any other punctuation mark. This is undoubtedly one of the reasons that they are so often misused. By knowing the rules behind comma usage, you can overcome the uncertainty that often plagues writers when trying to determine when a comma should be used.
When two independent clauses (an independent clause is a clause that contains both a subject and a verb) are used in the same sentence without any punctuation to separate them, the sentence is called a run-on sentence. For example, the following is a run-on sentence because it is made up of two independent clauses that are run together without any punctuation: “This is a good place to work the benefits are great and the people are wonderful to work with.” There are several ways to fix run-on sentences.
One way to fix run-on sentences is to use a comma. A comma is used to separate two independent clauses that are separated by a coordinating conjunction. (For more information about coordinating conjunctions, refer to the article Conjunctions.
Jane directed the meeting, and Barbara took copious notes.
John was able to attend the meeting, but he had to leave early.
Do you want to meet at 9 a.m., or would you rather meet earlier if possible?
She could not be late for the meeting, so she took a cab.
Avoid using a comma between two independent clauses without a coordinating conjunction. This causes a comma splice.
They began the meeting fifteen minutes late, the director had still not arrived.
The secretary heard the good news, he was ecstatic.
Mary knew she had arrived early, she waited in the reception area.
They began the meeting fifteen minutes late, but the director had still not arrived.
The secretary heard the good news, and he was ecstatic.
Mary knew she had arrived early, so she waited in the reception area.
In some cases, when two short, related independent clauses are joined by a coordinating conjunction, the comma can be omitted.
They walked and we ran.
Matt dictated and John took notes.
Luisa sang but Kirk remained silent.
He waited yet no one arrived.
When in doubt about whether or not to use the comma in such instances, go ahead and use it. A comma in such cases is not incorrect even though it is not strictly necessary.
In addition to the possibilities mentioned above, some run-on sentences can also be fixed by adding an adverb or conjunction at the beginning of the sentence and using a comma between the two clauses.
After they began the meeting fifteen minutes late, the director decided to end early.
When the secretary heard the good news, he was ecstatic.
Because they enjoyed eating out so much, they were always short on cash.
Since Mary knew she had arrived early, she waited in the reception area.
Run-on sentences can also be remedied by using a semicolon in place of the comma, without the conjunction.
They began the meeting fifteen minutes late; the director had still not arrived.
The secretary heard the good news; he was ecstatic.
Mary knew she had arrived early; she waited in the reception area.
Semicolons should generally be used to separate two independent clauses only when the clauses are closely related, as in the examples above.
A comma is not used to separate an independent clause from a dependent clause (that is, a clause that can not function alone as a sentence but must be joined to a main clause).
Barbara listened to the discussion, and took notes.
John attended the meeting, but had to leave early.
Barbara listened to the discussion and took notes.
John attended the meeting but had to leave early.
Barbara listened to the discussion, and she took notes.
John attended the meeting, but he had to leave early.
(By including a subject in the second clause, it becomes an independent clause, and so a comma is used.)
You can also fix a run-on sentence by splitting it into two separate sentences. To do so, use a period instead of a semicolon, and capitalize the first word of the second sentence.
They began the meeting fifteen minutes late. The director had still not arrived.
The secretary heard the good news. He was ecstatic.
Mary knew she had arrived early. She waited in the reception area.
The decision of whether to use a comma and conjunction, semicolon, or period is largely one of style. Each method is correct, so choose which punctuation mark to use based on the rhythm that you want to achieve.
Use a comma to separate items in a series of three or more. Include a comma before the last item in the series (known as a serial comma or sometimes an Oxford comma).
At the seminar he learned about finding new customers, increasing capital, and investing returns.
They restocked their supply of binders, notepads, and blue pens.
Employee morale, overall productivity, and profits were all on the rise.
Though some writers omit the serial comma, careful writers will include it in order to preserve balance and to avoid possible ambiguity, as in the phrase “To my siblings, Alex and George” (in this example, we don’t know for sure if Alex and George are the siblings, or if they are in addition to the siblings).
Applicants should be proficient in word processing, transcription, taking minutes, filing and reading reports.
I gave gifts to my brothers, Pat and Bill. (Without the serial comma, we assume that the names of the brothers are Pat and Bill.)
He likes to jog, travel, golf, read and eat exotic foods. (For a moment, readers might think that he likes to read exotic foods.)
Applicants should be proficient in word processing, transcription, taking minutes, filing, and reading reports.
I gave the gifts to my brothers, Pat, and Bill. (When the serial comma is used, then we realize that the person gave gifts to her brothers, to Pat, and to Bill.)
He likes to jog, travel, golf, read, and eat exotic foods.
When a series concludes with and so forth, and the like, or etc., a comma generally precedes, and sometimes follows, such expressions.
He brought chips, dip, crackers, veggies, and so forth to the party.
Jan enjoys painting watercolors, portraits, etc., in order to relax.
The speaker distributed handouts, legal pads, pens, and similar items before the meeting started.
When the last item in the series consists of two entities joined by and, a comma still comes before the and that precedes the last item (but not before the and that is part of the last item).
He likes to eat egg salad, tuna fish, and peanut butter, and jelly sandwiches for lunch.
We participated in three segments: a discussion panel, a workshop, and an eat, and meet.
He likes to eat egg salad, tuna fish, and peanut butter and jelly sandwiches for lunch.
We participated in three segments: a discussion panel, a workshop, and an eat and meet.
To preserve parallel structure in a series, use words that fulfill the same grammatical function.
The new employee enjoys talking, restaurants, chess, and to go to sleep.
She is intelligent, hardworking, and going to make something of herself.
He likes to visit historical sites, museums, and to go to antique stores.
The new employee enjoys talking, eating at fine restaurants, playing chess, and sleeping.
She is intelligent, hardworking, and ambitious.
He likes to visit historical sites and museums and to go to antique stores.
To learn more about parallel structure in writing, see the article entitled “Parallelism.”
Serial commas are not needed when all items in the sentence are joined by conjunctions.
He enjoys running and fishing and skiing.
She has visited Oregon and California and Texas.
Was it Chaucer or Milton or Shakespeare who wrote that book?
He will be home tomorrow or Wednesday or Thursday.
However, commas can be used if the elements in the series are long or if the sentence might be misread without them.
You could earn a bachelor’s degree in four years, or a master’s degree in five years, or a doctorate in just over seven years.
He wanted to buy some needed office supplies, and go to the department store to pick up his suit, and run to the bank before it closed to deposit a check.
When the items within the series themselves have commas or are long and complex, semicolons should be used.
He picked up notepads, pens, and binders for the meeting; stopped by his office for a moment; and then continued on to the conference room.
Mary invited two of her co-workers, Liz and John, to accompany her; she made the travel arrangements; and then she prepared her speech.
Before he made the public announcement, he talked to all of the shareholders involved, including Mr. Douglas and Mr. Johnson; he called a meeting of all of the senior advisers at headquarters; and he told all of the employees in his department.
Don’t use a comma before the first item in a series or after the last item in a series unless the construction of the sentence requires it.
His new laptop computer is, red, white, and blue.
They talked about purchasing new desktop computers, filing cabinets, and ergonomic chairs, for the new offices.
His new desktop computer is red, white, and blue.
They talked about purchasing new desktop computers, filing cabinets, and ergonomic chairs for the new offices.
They talked about purchasing new desktop computers, filing cabinets, and ergonomic chairs, for the new offices must be furnished with top-quality equipment.
(In this last example, a comma is used after the series to separate it from the clause that follows it.)
When an ampersand is used to set off the last item in a series (as in company names, for example), a comma does not precede it.
He works for Smith, Jones & Jefferson.
The law firm of Jensen, Jensen & Wilson is one of the best in the country.
Do not use an ampersand in a regular series. Use and with the serial comma, instead.
He coughed, wheezed & sneezed all night.
She likes bananas, apples & pears.
He coughed, wheezed, and sneezed all night.
She likes bananas, apples, and pears.
Inverted Sentence Order
In the natural structure of a sentence, the subject and any modifiers come before the predicate and its modifiers.
The senior vice president and his assistants decided to inquire into the matter when they heard about the possible merger.
Mr. Miller’s secretary had already left before we could reach her.
When the sentence order is inverted so that the adverbial clause that modifies the predicate comes first, a comma follows the predicate.
When they heard about the possible merger, the senior vice president and his advisors decided to inquire into the matter.
Before we could reach her, Mr. Miller’s secretary had already left.
Commas are used to separate multiple adjectives when the order of the adjectives could be reversed and still be logical.
The manager wore a neatly pressed, stylish suit.
He works in a small, cluttered office.
She has a clear, commanding voice.
If the order could not be logically reversed, commas are omitted.
He wore new suede shoes on his first day of work. (You would not generally say “He wore suede new shoes on his first day of work,” for example.)
Ms. Tucker bought an old desktop computer for her children.
Last week my colleague brought a delicious Hawaiian dessert to the company social.
Commas are also often used to distinguish phrases that express contrast.
I said I wanted to arrive early, not just on time.
He was a good person, but very outspoken.
Your integrity, not your bottom line, should be your main focus.
She decided not to read but merely to take a nap.
Constructions with Not Only
Constructions that include not only are often, though not always, set off by commas. Usually either two commas or no commas are used.
They asked to speak to the director, not only to make a complaint, but also hoping to change the policy.
She was furious, not only because of the problem, but because no one was able to offer a plausible solution.
They were prepared not only to strike but also to quit if their demands weren’t met.
The man disliked not only his co-workers but his boss as well.
The More, the Less, and Similar Constructions
A comma is generally used between the elements of a comparison, such as the more...the more and similar expressions, unless they are very short.
The more I read about the author, the more I like her.
The louder Mike became, the angrier he felt.
The more you read, the better you’ll understand.
The more the merrier.
The sooner the better.
Independent Expressions and Transitional Phrases
Yes, no, indeed, and similar words, which are sometimes referred to as independent expressions, are also followed by a comma when they come at the beginning of a sentence or when they appear in the middle of a sentence if they cause an interruption in the normal sentence flow.
No, we will not be attending the conference.
Well, I don’t believe that he has arrived yet, but I’m sure he will arrive soon.
Marian feels that, indeed, we should continue the discussion.
Phrases such as consequently, however, of course, as a result, and the like, which are sometimes referred to as transitional phrases, should also be set off by commas.
Nevertheless, she is still the best figure skater in the county.
The CEO will be delayed, however.
I have several friends, for example, who worked there years ago.
Similarly, expressions such as for example, that is, or (in the sense of “in other words”), and the like are generally followed by a comma. They are also often preceded by either a comma, an em dash, or a semicolon, or sometimes the entire phrase they introduce is set off by parentheses or em dashes. If the abbreviations e.g. or i.e. are used (for example or that is, respectively), these abbreviations are not italicized. Such abbreviations should not be used in formal writing.
The board members—that is, the more vocal ones—did not agree with the recommendation.
Please bring all personal essentials (e.g., toothbrush and tooth paste, comb or brush, soap, shampoo, shaving needs, etc.) with you when you come.
Janet was finally able to put the incident behind her; that is, she was at least able to stop talking about it.
The console, or keyboard, was very complicated.
Restrictive and Nonrestrictive Phrases and Clauses
Clauses that are not essential to the meaning of a sentence are called nonrestrictive clauses, while clauses that are essential to the meaning of the sentence are called restrictive clauses. Do not use commas to set off a phrase or clause if taking out the particular phrase or clause would affect the meaning of the sentence.
Mary’s manager, whose name was Bob, was gone all week.
(By using commas, we let the reader know that Mary only has one manager, and we indicate that the name of her manager is not essential information.)
Mr. Willis’s promotion, which happened just last week, was rather unexpected.
The Teicherts of Milwaukee are related to us.
The client who arrived here at eight this morning missed his appointment.
(By not using commas, we indicate that the information of when the client arrived identifies him, and in this case it is essential to the meaning of the sentence in order to set him apart from other clients who arrived this morning.)
The car that we bought two years ago has never had a problem.
The Teicherts, of Milwaukee, are related to us.
See the article “Nonrestrictive and Restrictive Phrases and Clauses” for additional reading.
Parenthetical elements add explanatory or supplementary information. Because they are not essential to the meaning of a sentence, they too should be set off by commas.
Atlanta, where my daughter is from, is the capital of Georgia.
That company, first founded in 1977, has been around for more than 30 years.
A parenthetical element that follows a coordinating conjunction used to separate two independent clauses, on the other hand, should not be preceded by a comma.
He said he would be here on time, but honestly I don’t see how he can make it now.
She did a great job, and while she is a dedicated employee, she’s still pretty new to the team.
I believe that on Monday I saw him, and at the time, he seemed to be doing well.
A comma is generally not required after an adverb that begins a sentence, though it would not be incorrect.
Hurriedly he walked down the street.
Repeatedly he thanked them for their kindness.
Unabashedly she went up to the stand and took the mike.
However, when the adverb is used to modify the whole sentence, then a comma should be used.
Fortunately, we were able to postpone the luncheon.
Incredibly, we were able to make it to the show on time.
Sadly, the building will have to be razed.
Adverbial Clauses and Phrases
As mentioned above, when a sentence begins with an adverbial clause (a dependent clause that begins with a subordinating conjunction and answers the question of when, where, how, or why), a comma is used to separate it from the rest of the sentence.
When she stepped off the train, the cab was waiting for her.
After the meeting began, the board members took turns sharing their ideas.
However, a comma is not used after an introductory adverbial phrase that immediately precedes the verb it modifies.
Singing in high soprano is Miss Olivia Blair.
Walking beside me is my wife, Liz.
A comma is likewise not used when the adverbial clause follows the main clause (which it does in the natural order of a sentence), unless it is needed to avoid misreading. In the first two examples below, the sentences are in the natural order, so no comma is used.
He was uncertain because he did not know what the outcome would be.
Martha was upset when she heard her favorite team had lost.
In the next two examples, a comma is used to avoid misreading.
She seemed to be in pain, because her breathing was very shallow.
I knew that the meeting would be held tomorrow, when Jane arrived back in town. (Compare to “I knew that the meeting would be held tomorrow when Jane arrived back in town.”)
A participle (a verb form that can be used as an adjective) when used as an introductory element should be set off with a comma.
Relieved, he quickly went to tell his wife the good news.
Intrigued, she turned to see who had been calling her name.
Running, we were barely able to reach the bus in time.
Cheering, the crowd rushed in to congratulate their team.
A participial phrase (a phrase made up of a past or present participle and any objects, modifiers, or complements that go with it) that begins a sentence is always separated from the main clause by a comma.
Arriving late, he dashed down the hall to the conference room.
Unprepared to answer, Michael could only stammer out a jumbled response.
Running to catch her bus, the woman lost her shoe.
However, a comma is not used after an introductory participial phrase that immediately precedes the verb it modifies.
Out of the complex came the man we were searching for.
Around the corner stormed the angry woman.
Take care not to confuse a participial phrase with a gerund phrase (a phrase containing a gerund and any of its modifiers, objects, or complements). If a gerund phrase is used as the subject of the sentence, then a comma is not used.
Running in the rain is one of her favorite hobbies.
Talking quietly is to your advantage around here.
To speak with clarity and confidence is a great accomplishment.
Moreover, as with the nonrestrictive and restrictive clauses mentioned above, if the participial phrase is essential, then do not use commas.
The man talking very loud is my brother.
The woman directing the program is named Jill.
However, do set off a participial phrase with commas if it is not essential to the meaning of the sentence. For example, participial phrases that modify a proper noun are not essential because the noun is already strongly identified, so commas should be used to set off the participial phrase.
Marty, whistling a happy tune, showed up with three suitcases and a large carryon.
The Mountain High School Eagles, concerned with winning the game, never saw the antics of the fans.
Participial phrases that modify nouns that are strongly identified in other ways should likewise be set off by commas.
The youngest member of our family, determined to win some day, never gives up when we wrestle.
Our most recent hire, talking incessantly while she walked, almost ran into the wall.
Finally, when using participial phrases, make sure that they correctly modify the part of the sentence that they are supposed to so that they do not create a dangling modifier.
Jogging around the corner, a large dog got right in my path.
As I was jogging around the corner, a large dog got right in my path.
For a discussion of dangling modifiers, see the article entitled “Dangling and Misplaced Modifiers.”
Appositives are nouns or noun substitutes that rename and could take the place of another noun immediately before them. Like adverbial clauses (discussed above), they should not be set off by commas if they are essential to the meaning of the sentence.
The poet Walt Whitman is one of my favorite writers.
(If commas were put around “Walt Whitman,” then we would suggest that Walt Whitman were the only poet, which of course is not true.)
The movie The Princess Bride is one of my favorites.
(Again, the use of commas would suggest that The Princess Bride is the only movie.)
When the appositive is not necessary to the meaning of the sentence, then commas should be used.
Her favorite movie, Gone with the Wind, is a Civil War–era classic.
(She presumably has only one favorite movie, so the appositive with the title is helpful information, but not necessary to the sentence. If it were, we would write “Gone with the Wind, her favorite movie, is a Civil War–era classic.)
The comedian of our house, Mike, loves to tell jokes and do tricks.
(In this sentence, the name Mike isn’t strictly necessary to the meaning of the sentence.)
The symposium, a much-anticipated yearly event, will begin next Thursday.
(Here, again, the information between the commas is not essential to the sentence.)
An appositive that follows a proper noun is always nonessential and should be set off by commas.
The Eiffel Tower, one of my favorite tourist spots, is beautiful at night.
Lewis Tucker, the president of the company, will be visiting here tomorrow.
To determine whether an appositive is restrictive (essential) or nonrestrictive (not essential), try leaving it out and see if the sentence still makes sense.
My dad, Mark Rogers, lived there years ago.
The law firm Jensen & Williams is one of the best in town.
My dad lived there years ago.
The law firm is one of the best in town.
In the first example, the name Mark Rogers is not essential to the meaning of the sentence, as the speaker only has one dad. In the second example, Jensen & Williams is necessary in order to identify the law firm being discussed. If we had said That law firm, instead, then the name would have become nonessential, and we would use commas to set if off.
An infinitive phrase at the beginning of the sentence is always followed by a comma unless the infinitive is the subject of the sentence. To determine the function of the infinitive, first determine if the phrase could come at the end of the sentence. If it can, then it is not acting as the subject of the sentence.
To reach our deadline on time, we will have to put in some overtime.
We will have to put in some overtime to reach our deadline on time.
To receive the best advice possible, you should talk with Jan.
You should talk with Jan to receive the best advice possible.
If the introductory phrase is very short, the comma can be omitted as long as the meaning will still be clear without it. (However, keeping the comma would not be incorrect.)
To understand you must begin to truly listen.
To win you will have to work very hard.
An infinitive phrase used as the subject of a sentence is in its natural location and should not be followed by a comma.
To win the bid will take a great deal of effort.
To be more punctual is one of their primary goals.
Very short prepositional phrases (phrases containing a preposition and a noun or pronoun and its modifiers) that come at the beginning of a sentence do not need to be followed by a comma.
At the beach we played sand volleyball.
In the boardroom the executives discussed the matter carefully.
Similarly, a comma is not needed when the introductory prepositional phrase is very short and does not contain any verb forms, cannot be misunderstood, and is necessary to the meaning of the sentence, such as when indicating the time that something occurred or will occur.
On Friday our meeting will begin half an hour early.
In July they attended a seminar in Florida.
Note: If a word or short phrase that is not a prepositional phrase is used at the beginning of a sentence to designate when, the comma should still be omitted. (See the section on adverbs above.)
Yesterday they decided to postpone the conference.
Next week they will make the final decision.
On the other hand, prepositional phrases that are longer than three or four words should generally be followed by a comma when they come at the beginning of a sentence.
During his interview with the Doe Company, he was asked many thought-provoking questions.
After making all of the arrangements for his trip, Lance was finally able to relax.
Prepositional phrases that contain a verb form (a gerund or a participle) and come at the beginning of a sentence should likewise be followed by a comma.
After discussing the matter, we decided not to go.
Before making a decision, they consulted their attorney.
Also use commas if the prepositional phrase is parenthetical (that is, if it does not provide any essential information).
They determined, after reading the report, that the changes were possible.
Dina, before accepting the position, thoroughly researched the company.
Commas should likewise be used when necessary to avoid misreading.
Before beginning, the meeting coordinator called the off-site employees.
Dates, Addresses, and Place Names
A comma should follow the month and day when they are followed by the year. This is the format generally used by writers in the United States.
My son was born on June 20, 2003.
The letter was dated May 3, 1987.
If the sentence continues after the date, then a comma should likewise follow the year.
On November 20, 2009, we will open the new plant.
Beginning July 24, 2011, all personnel will be able to telecommute.
When the day precedes the month (as in 8 August 2008), no comma should be used.
The scheduled day of the meeting was 9 April 2004.
According to the meeting minutes of 3 October 2008, the decision was made to revisit the issue in 6 months.
When both a city name and the state, province, or country name are identified, the state, province, or country name should be preceded and followed by a comma (unless it comes at the end of the sentence).
We visited Denver, Colorado, over the holiday.
Chicago, Illinois, is known as the Windy City.
My mother is originally from Paris, France.
The plane should arrive in Montreal, Canada, by 8 p.m.
When the state, province, or country name is used in the possessive form, however, the second comma is dropped.
Calgary, Canada’s bid for the Olympics was accepted.
Tallahassee, Florida’s commerce and industry are continually expanding.
Furthermore, when the state, province, or country name becomes part of a compound structure, the second comma is likewise omitted.
The Boston, Massachusetts-based company was established in 1902.
That Denver, Colorado-headquartered firm was originally founded by Dennis Johnson himself.
A comma is sometimes used to indicate that one or more words have been omitted from a sentence when the omitted text is not necessary for meaning.
One meeting is scheduled for this afternoon, the other for tomorrow morning.
One employee is good at planning, another at organizing, and a third at following through.
The comma can occasionally be omitted if the sentence is clear without it.
John misses her and she him.
In longer constructions, a semicolon is often used to separate the larger sentence parts and a comma is used to separate the smaller parts.
In Boston there are 20 branches; in New York, 35; and in Memphis, 12.
Last year we sold 374 such models; this year, none.
A comma is often used to separate the rest of the sentence from a quotation or statement.
“Let’s plan to meet at one,” she said.
Someone once declared, “A foolish consistency is the hobgoblin of little minds.”
“Don’t forget to stop at the store,” he reminded.
When the quotation is broken up in the middle of the sentence, two commas should be used—one before the interruption, and one after.
“When you get to the light,” John stated, “don’t forget to turn right.”
“The longer you’ve lived,” I thought, “the happier you can be.”
For quotations that are used in more formal contexts or that are longer than one sentence, a colon is used in place of a comma to separate the quotation from the introduction.
In his analysis, Mr. Swensen reported: “Last year our profits fell by 12 percent. In order to curb this trend, we will have to cut our production costs and improve our marketing strategy.”
In the preface, the author states: “The more important thing you can do is to gain and maintain customer loyalty.”
When the word that is used or when a quotation is not preceded or followed by such phrases as she said, they declared, and the like, a comma (or colon) should not come before or after the quoted material, and the quote itself should generally begin with a lowercase letter in order to fit the sentence structure, whether or not the original text or statement was capitalized.
He said that “there never was a better place than this.”
Mary reminded us to always “do the very best you can” in order to achieve your dreams.
Was it Shakespeare who said that “a rose by any other name would smell as sweet”?
The director said she would want to “receive a full report of our findings within a month’s time.”
When a quote ends in a question mark, exclamation point, or dash and the sentence continues, no comma should precede (or follow) the closing quotation mark.
“Should we break the news?” John asked.
“You better be there this afternoon!” I cried.
“I plan to be back in time for the seminar—” she began.
For more information about the use of quotation marks with other punctuation, refer to the article “Quotation Marks.”
Commas with Direct and Indirect Questions
A question included as part of a longer sentence is usually preceded by a comma. The first word does not need to be capitalized, but if the question is long or has external punctuation, an initial cap may be helpful.
Silently she wondered, where have they been?
The question, what can we do about it? was foremost on his mind.
The directors had to ask themselves, Is this course of action the best one for the shareholders, or is there something different we should be doing?
Indirect questions, on the other hand, are not preceded by a comma and are not followed by a question mark.
What to do was the question they confronted.
Bianca wondered how she could complete the acquisition.
Maxims and Mottoes
As with appositives, clauses, and the like, commas are used to set off maxims, mottoes, proverbs, and similar expressions only when they are not essential to the meaning of the sentence.
The phrase “All’s well that end’s well” was her favorite saying.
The company motto, “All for one and all for all,” appeared on all their letterhead.
I don’t believe that the early bird always gets the worm.
Commas are used before and after a word or phrase of direct address.
I want you to know, Ms. Roberts, that we really appreciate your hard work.
Jeff, could you help me draft a proposal?
If you’ll follow me, sir, I’ll show you the way to the conference room.
An absolute phrase is a phrase that contains a subject and an adjective phrase (usually a participial phrase) and, unlike many other types of phrases, modifies an entire clause or sentence.
Its hunger satiated, the lion turned its interest to other things.
Her meeting finished, Jan could finally sit down and relax.
Tag questions, which generally verify the veracity of something, should be preceded by a comma.
You are coming to the summer social, aren’t you?
They make athletic shoes, right?
Titles in Names (II, III, Jr., Sr., and the Like)
Name designations such as II, III, and so forth should not be preceded by a comma.
I believe she will be married to John Hampton Douglas III.
Have you heard the history of Henry VIII?
Similarly, titles such as Jr. and Sr. no longer need to be preceded by a comma (though a comma would not technically be wrong).
Let me introduce you to Daniel Morgan Jr.
Jeffrey M. Danzie Sr. will be your new supervisor.
Inc., Ltd., and the Like
Words such as Inc., Ltd., L.L.C., and the like are not required to be set off by commas when used as part of a company name. However, if commas are used, they should appear both before and after the word when the name is used in running text.
Last week I applied for a job at Milton & Milton Inc.
The vice president of sales at Banzer Products, Ltd., just resigned.
Parentheses and Brackets
When the context of a sentence calls for a comma at the end of material enclosed within parentheses or brackets, the comma should follow the closing parenthesis or bracket. comma never precedes a closing parenthesis.
When they purchased the equipment (which was last Saturday), they had no idea that they would need it so quickly.
They bought a large, expensive (though not brand new), black bookcase.
“After they talked to the witness [Jonathan Talway], they decided to reexamine the matter.”
Maintain Grammatical Function
As with all punctuation, commas are used because they fulfill a particular grammatical function. Therefore, a comma should not be used simply to reflect or designate a pause in speech.
I told them that, we no longer required their marketing services.
The best thing I ever did was, to go back to school.
I told them that we no longer required their marketing services.
The best thing I ever did was to go back to school.
Such pauses in speech do not need to be mirrored in written text. However, if it is necessary to reflect a pause in writing, use ellipses (three spaced periods) instead.
I told them that...we no longer required their marketing services.
The best thing I ever did was...to go back to school.