The Comma

A comma is used to separate parts of a sentence so that the reader can understand its meaning more accurately and quickly.   Using too few or too many commas can actually impair understanding.   These are rules that strike a balance in the use of commas.

Note: Definitions of grammatical words and expressions used in this discussion are provided at the end of this page.

1. When a date is is used alone, separate the day of the month from the year with a comma.   Also, separate days of the week from the date by a comma.

• June 7, 1942
• June to July, 1978
• Wednesday, June 7, 1942

2. When a date is used in a sentence, place a comma after the year.

• June 7, 1942, began the invasion of Europe.
• June to July, 1978, were hot months.

3. When the month and year are used alone, or when the day of the month precedes the month, as in military use, they need not be separated by a comma.

• June 1942
• 7 June 1942

4. When the month and year are used in a sentence, place a comma after the year.

• June 1942, marks an historical year.

5. Use a comma between the name of a city or village and the name of the state, county, or country.

• Buffalo, New York       Rochester, Monroe County       Paris, France

6. Use a comma to separate each item in an address that is part of a sentence.

• My address is 1234 Euclid Ave., Albany, NY 45678, the entire year.   (Note the absence of a comma between the state and zip code.)
• Baghdad, Iraq, is the scene of much fighting.

7. Use a comma after the salutation of a friendly letter and after the closing in a friendly or business letter.   Note: Use a colon after the salutation of a business letter.

• Dear Mary,       Your friend,       Sincerely,

8. Use a comma to set off company names.

• Microsoft, Inc., is a famous company.

9. Use a comma to set off a title, but not "Jr." when used at the end of the name.

• John Smith, D.D.S, has just arrived in town.
• Robert Smith Jr. was called to the office.
• Smith, Robert, Jr. was listed on the manifest.

10. Use commas to set off thousands (000s) in numerals.   Do NOT used commas in zip codes, phone numbers, years and house numbers.   Optional use: The comma may be omitted for numbers betweeen 1000 and 9999.

• The circumference of the earth is about 25,000 miles.
• Mr. John Smith, 3568 Euclid Ave., Villas, NJ 08251
• My phone number is 212 689 2131
• The distance between New York City and San Francisco is about 3,000 miles.
• The distance between New York City and San Francisco is about 3000 miles.

11. Use a comma to set off abbreviation, such as, i.e., e.g., viz., etc.

12. Use commas to set off words of direct address.

• Mary, will you please close the window?
• You cannot enter through that entrance, my friend, because it is locked.
• If, Sir, you refuse to cooperate, I cannot predict the consequences.

13. Use commas to set off a direct quotation from the rest of the sentence ending in a period, but not with questions or exclamations.   Note Do not use commas with indirect quotations.

• Jack's father said, "Go to college to get a good job."
• "I guess I will go to college," replied Tom.
• "But," said his mother, "don't spend all your time in the local saloons."
• "Get out!" cried his mother.
• "Is this the main entrance?" asked Larry.
• Jack's father said that Tom ought to attend college. (Indirect quotation.)

14. Use a comma to indicate words left out of a parallel word group.

• The corn was high; the wheat, golden.
• Mary is good at Science; Daniel, English.

15. Use a comma after all except the last element in a series consisting of 3 or more words, phrases, or clauses.   Note 1: When 1 or more of the elements contains a comma, use semicolons instead of commas.   Note 2: No commas separate the elements if all of them are joined by and, or, or nor.

• The Japanese, Chinese, and Korean writing systems are similar.
• New York City accents differ in the Bronx, in Manhattan, in Queens, in Brooklyn, and in Richmond.
• People say that Arabic is difficult to pronounce, that its alphabet is complicated to write, and that learning the language takes a long time.
• She listened and watched and sighed.

16. Use commas after the words, first, second, third, etc., when these words introduce elements in a series.   Use semicolons to separate elements of the list.

• My reasons for liking him are as the following: first, he is generous; second, second, he is educated; and third, he is clever.

17. Use commas between adjectives of the same rank that modify the same noun, but not before the final adjective in a series if it is considered part of the noun.     Do not use commas to separate items of unequal rank in a series.   (Test for rank: Place an imaginary "and" between the word.   If it sounds normal and if the words can be reverse without changing the meaning, then the adjectives are of equal rank.)   Note 1: In general, no comma is required after numbers and after adjectives of size, shape, and age.   Note 2: If a word in a series modifies another word in the series, do not separate them with a comma.

• The cold, dark dungeon looked sinister.
• Beavers grow thick winter coats in winter.
• an old English castle         five small round holes
• Beavers wear thick, dark brown winter coats.

18. Use a comma after introductory words, mild interjections (use an exclamation point (!) for strong interjections), or adverbs at the beginning of a sentence.

• Yes, we have no bananas.
• Well, we had better start.
• Wait, I know where to find the key.
• However, he doesn't go to school any more.

19. Use a comma to to separate a statement from a tag question.

• I can go, can't I?

20. Use a commma to emphasize contrasts.

• The music was noisy, not melodious.

21. Use of a comma after words that have been moved to the beginning of a sentence from their normal position is optional.

• Normal order:       The play apparently was cancelled.
• Inverted order:     Apparently, the play was cancelled.
• Optional use:     Apparently the play was cancelled.

22. Use a comma to set off a parenthetical words and expression.   Note: When such words modify a word, they are an integral part of the sentence and are not set off by commas.

• John, after all, came back home.
• The play started late after all our hurrying to be there on time.
• The teacher, however, never arrived at the lecture.
• We must finish the report today however long it takes.

23. Do not use a comma before a parenthetical expression that immediately follows a coordinating conjunction that separates 2 independent clauses.

• My team was leading the league at the end of June, but of course, they always do well only in the early part of the season.

24. Use a comma to separate words and phrases that might be misread.   This can happen with the conjunction "for" is mistaken for prepositions used in prepositional phrases, which do not require commas.

• Bad:   The teacher beat the student with a whip.   (Who has the whip?)
• Good:   The teacher beat the student, with a whip.   (Teacher has the whip.)
• Good: The student was beaten by the teacher with a whip.   (No comma needed.)
  
  
• Bad:     We approved the bill for people were dying.
• Good:   We approved the bill, for people were dying.
  
  
• Bad:     While baking Jerry burned the bread.
• Good:   While baking, Jerry burned the bread.
  
  
• Bad:     Above the man watched for the sign of the lantern.
• Good:   Above, the man watched for the sign of the lantern.

25. Use a comma after a series of prepositional phrases at the beginning of a sentence.   Exception: A short prepositional phrase at the beginning of a sentence need not be followed by a comma unless it is required for clarity.

• From his seat in the audience, he could not hear the actors.
• Before the latest hit, Starwars was my favorite movie.
• On Sunday he plays tennis. (Comma not used.)
• In 1776 the colonies declared their independence. (Comma not used.)

26. Use a comma after introductory infinitive phrases and introductory participial phrases used as modifiers.   Infinitive phrases used as subjects need no comma.   (An inverted sentence.)

• To activate the alarm, pull the handle.   (infinite phrase as modifier)
• Erupting violently, Mt. St. Helens spewed ash for miles.   (participial phrase as mofifier)
• To live a good life was her only ambition.   (infinitive phrase as subject, i.e., inverted sentence)

27. Use a comma to set off an absolute phrase.

• His words dipped in honey, the actor mesmerized the crowd.
• The actor mesmerized the crowd, his words dipped in honey.

28. Use commas to set off nonessential (nonrestrictive) participles and participial phrases.

• Nonessential:     The customers, wishing to see the celebrity, came to the arena.
• Essential:         The customers wishing to see the celebrity should come to the arena.

29. Use commas to set off nonessential (nonrestrictive) appositives and appositive phrases   Note that some gerunds, gerund phrases, and noun clauses act as appositives and appositive phrases.

• Uranium, a heavy metal, is used in nuclear reactors.
• Brighton, a suburb of Rochester, has many beautiful homes.
• The student Aaron Butterfield was not at home.   (Student's name is essential to complete the meaning.)
• William the Conqueror invaded England.
• Nonessential:     February, the coldest month of the year in New York State, is the month in which I was born.
• Essential:         The poet Robert Frost is an American.
• Nonessential:     My new hobby, swimming, is taking much of my time.   (swimming is a gerund)

30. Use a comma before (not after) a coordinating conjunction that joins the two main (independent) clauses of a compound sentence.  

• The meeting over the constitutional amendment adjourned until next month, and many of us were happy to know that the long evening had ended.

• Note 1: Do not use a comma if the main clauses are very short and are joined by the conjunctions and, but, so, or, or nor, but DO use a comma when the short clauses are separated by yet or for
  • The meeting adjourned and we headed for home.
  • The meeting adjourned, yet I remained in the room.
    
    
• Note 2: Do not confuse 2 main clauses, which contain 2 subjects and 2 predicates, with a compound predicate (1 subject and 2 predicates), which needs no comma.
  
  
• Mary was singing and smiling.
(1 subject, 2 verbs)
• Mary was singing, and she was smiling.
(2 subjects, 2 verbs)


• I could have danced for hours and stayed awake all night.
(1 subject, 2 verbs)
• I could have danced for hours, and I could have stayed awake all night.
(2 subjects, 2 verbs)


• Why don't you sit on the courch or sit on the floor?
• Why don't you sit on the couch or why don't you sit on the floor?
  
  
• Note 3: If the conjunction is missing, then the main clauses must be separated by a semicolon (;) or a period (.), which makes them into 2 sentences.
  
  
• Mary likes cake, but Tom likes pie.
• Mary likes cake; Tom likes pie.
• Mary likes cake. Tom likes pie.
  
  

31. When a sentence has 3 or more main clauses in a series, the clauses are usually separated by a semicolon.   However, if the clauses are short, a comma may be used to separate them.

32. A conjunctive adverb is preceded by a semicolon and followed by a comma.

• You are late; however, you must still take the exam.

33. Do NOT use commas between compound elements that are not main clauses.

• Mary still doesn't know that her illness is serious and that she will have to undergo an operation.   (Two subordinate clauses.)

34. Use commas to set off final nonessential (nonrestrictive) adjective clauses and nonessential (nonrestrictive) adverb clauses.   Note 1: which generally (but not always) introduces nonessential adjective clauses, while that introduces essential adjective clauses.   Note 2: The words although, even though, though, and whereas usually (but not always) introduce nonessential adverb clauses.

• Nonessential:     The District of Columbia, which I visited, is under the jurisdiction of Congress.
• Essential:         The District of Columbia that I visited is under the jurisdiction of Congress.

35. Use a comma to set off nonessential (nonrestrictive) adverb clauses that occur in the middle of a sentence.

• Clara, determined to become a physician, is currently studying honors biology.

36. Use a comma after an adverb clause precedes the main clause, but not when it follows the main clause and introduced by a subordinating conjunction.

• Although Tom works, he also attends night school.
• Tom attends night school although he works.
• Since Janet visited Paris, she has been interested in living there.
• Janet has been interested in living in Paris since she visited there.
• Because they are ignored, facts do not cease to exist.
• Facts do not cease to exist because they are ignored.
• As long as it happens to someone else, a joke is funny.
• A joke is funny as long as it happens to someone else.
• When you consider the alternative, old age isn't so bad.
• Old age isn't so bad when you consider the alternative.

37. Use a comma to set off an essential (restrictive) clause only to remove an ambiguity.

• I knew that the commissioner would resign that day, because my brother worked in his office and called me with the news of his indictment.   (Without the comma, the resignation might be construed to be the result of the brother's working in the office.)

A conjunction is a word that connects words, phrases, or clauses.   There are 3 kinds of conjunctions: coordinating, correlative, and subordinating.   Additionally, conjunctive adverbs function as conjunctions.

A coordinating conjunction joins words, phrases, and clauses of equal rank or function, such as 2 main (independent) clauses.   Examples: and, but, for, yet, nor, or, so, whereas.   Note the for is also used as a preposition.

• The cellar was dark, dank, cold, and smelly.
• Henry's action was brave, but the battle was lost
.

A correlative conjunction functions like a coordinating conjunction, but they are always used in pairs.   They are as follows:

• both .... and
• either .... or
• neither .... nor
• not only .... but (also)
• whether .... or
  
  
• Example: Both Ann and Mary attended the concert.

A conjunctive adverb is used to connect independent clauses in the absence of a period (.) or comma (,).   Conjunctive adverbs are accordingly, also, besides, consequently, finally, furthermore, hence, however, indeed, moreover, nevertheless, otherwise, still, then, therefore, thus.   A conjunctive adverb is preceded by a semicolon (;) and followed by a comma (,).

• The play was extremely boring; nevertheless, we watched it without dozing.

A subordinating conjunction is a word that introduces a subordinate (dependent) clause.   Examples: as, after, as if, as long as, as soon as, although, because, before, how, in order that, so that, than, if, even if, even, even though, since, that, though, unless, until, when, where, wherever, whereas, while.

• Many students take a course in philosophy, although it is not requied.

A relative pronoun (who, whose, whosever, whom, whomever, which, whichever, and that) introduces a subordinate clause and relates it to a word in the main clause.

• Joe Louis was a prizefighter who became world champion for many years.

A parenthetical expression is a word or phrase inserted into a sentence as a comment or exclamation even though the sentence is complete without it.   Examples of such words are these: after all, by the way, of course, for instance, however, therefore, consequently, I believe, etc.   Note: however can also be used as an adverb.

• His behavior, after all, was uncalled for.
• Her credentials, by the way, are suspect.
• My admonition, however, went unheeded.

A phrase is a group of related word that does not have a subject and predicate.   It functions in a sentence as a single part of speech.   A phrase can appear at the beginning, the middle, or the end of a clause or sentence.   There are several types: appositive, prepositional, infinitive, participial, absolute, and gerund.

• An appositive is a noun or pronoun that renames and provides further information about a noun or pronoun.   An appositive is "in opposition" to to the noun or pronoun it renames and usually occurs directly after the word it modifies.   An appositive phrase is an appositive plus all its modifiers.   Appositives and appositive phrases are either essential or nonessential.   Note: Gerunds, gerund phrases, and noun clauses can be used as appositives.
  
  
• An essential (restrictive) appositive or appositive phrase must be included in the sentence to complete its meaning.
  
  
• My sister Kathy will attend college next year.   (I have 2 sisters, one named Kathy, so naming her is essential.)
• The comedian Woody Allen was born in New York City.
  
  
• A nonessential (nonrestrictive) appositive or appositive phrase may be excluded from the sentence to complete its meaning.
  
  
• My sister, Kathy, will attend college next year.   (I have 1 sister, so naming her is nonessential.)
• My new hobby, swimming, is taking much of my time.
• The highlight of my cruise, watching the sailboats compete, will never be forgotten.
• Woody Allen, a famous commedian, was born in New York City.
  
  
• A prepositional phrase consists of a preposition, its object, and any modifiers of its object.   There are 2 kinds of prepositional phrases: adjective, which modify nouns and pronouns, and adverb, which modify adjectives, verbs, and other adverbs.
  
  
• Comedian Woody Allen is a favorite of moviegoers
  
  .
• An adjective phrase is a prepositional phrase that functions as an adjective to a noun or pronoun.   It answer the questions, What kind of?, Which one?.   An adjective phrase is placed close to the noun or pronoun it modifies.
  
  
• Details about Woody Allen's private life are famous.
• Few of his movies are not funny.
  
  
• An adverb phrase functions as an adverb to modify adjectives, verbs, and adverbs.   It answers the questions, Where?, When?, How?, Why?, What?, To what extent or degree?, Under what conditions?   Unlike adjective phrases, adverb phrases can appear in different places in a sentence.
  
  
• The purloined letter was found on the table.
• The moon flight was successful beyond anyone's expectation.
• The fire engine sounded very loud in the early morning.
  
  
• An infinitive is the word "to" + the base form of a verb.   An infinitive phrase is a group of words made up of an infinitive, its modifiers, and its complements.   It is used as a noun, adjective, or adverb.   Sometimes the infinitive is used without the word "to".
  
  
• World Airlines Flight 107 will be ready to board in 1 hour.
• To run moderately, is an excellent form of exercise.
• You should try to obtain a seat near the window..
• To live a good life was her only ambition.
• Tom did not darequestion his father's admonition.
  
  
• A participle is a verb form that is used as an adjective.   (A participle can also be used as a verb.)   A present or past participial phrase is a participle, its modifiers, and its complements.   It is always an adjective.   A participial phrase is either essential or nonessential.
  
  
• An essential (restrictive) participial phrase is required to complete the meaning of the sentence.
  
  
• The president sent an encouraging letter to the new employee.
• The encouraged student wrote often.
• Encouraged, the student wrote often.
• John submitted his completed completed report on Monday.
  
  
• A nonessential (nonrestrictive) participial phrases is not required to comple the meaning of the sentence.
  
  
• Having been encouraged, the employee worked hard.
• Driven into the corner by a dog, the cat hissed violently.
• Waiting anxiously for her supervisor's reaction, Paula could not sleep.
• The teacher, having received the student's essay, correctly it immediately.
  
  
• An absolute phrase is composed of a noun or pronoun plus a participle or participial phrase.   The absolute phrase modifies an independent clause or sentence, not just one word, by indicatiang time, place, or circumstances.
  
  
• Our meeting finished, we headed for the spa.
• His car having been stolen, he called the police.
• The criminal answered the sergeant's questions, his eyes showing much fear.
  
  
• A gerund is an -ing form of a verb used as a noun.   A gerund phrase is composed of a gerund, its modifiers, and its complements.
  
  
  • Fast driving is a dangerous activity.
  • Before leaving, the finished her report.
  • Eating a good breakfast in the morning is a good habit.
  • A loud rumbling of motorcycles indicated that the gang had arrived.
  • My new hobby, swimming, is taking much of my time.
  • The highlight of my cruise, watching the sailboats compete, will never be forgotten.
    
    

A clause is a group of words that contain a subject and verb.   There are two kinds of clauses: main (independent) and subordinate (dependent).

• A main clause can stand alone as a sentence because it expresses a complete thought.   Main clauses are joined by coordinating conjunctions.
  
  
• The prisoner escaped from prison, but the police arrested him later.   (Two independent clauses.)
  
  
• A subordinate clause cannot stand alone as a sentence because it does not express a complete thought.   Subordinate clauses are joined to main clauses by subordinating conjuntions or relative pronouns to form sentences.   A subordinate clause can appear at the beginning, the middle, or the end of the main clause.   There are three kinds of subordinate clauses: adjective, adverb, and noun.
  
  
• An adjective clause modifies a noun or a pronoun.   They are essential (restrictive) and nonessential (nonrestrictive):
  
  
• An essential adjective clause is required to make the meaning of the sentence complete.
  
  
• I cut down all the trees that were 6 feet tall.   (Of all the trees avaiable, only those at least 6 feet tall were cut.
• People who are blind develop sensitive hearing.
  
  
• A nonessential adjective clause is not required to make the meaning of the sentence complete.
  
  
• I cut down all the trees, which were 6 fee tall.   (All the trees available were cut down; they were all at least 6 feet tall.
• My roommate spoke German, which I did not understand.
  
  
• An adverb clause is used as an adverb to modify a verb, adjective, or adverb.   They are essential (restrictive) or nonessential (nonrestrictive).
  
  
• An essential adverb clause is required to make the meaning of the sentence complete.
  
  
• The sale of movie tickets has decreased since the price was increased.
• Don't visit the seashore in the summer unless you book reservations far in advance.
• Mark carries his water bottle wherever he goes.
  
  
• A nonessential adverb clause is not required to make the meaning of the sentence complete.
  
  
• Joan wants to take a course in AP physics, since she wants to become an astronaut.
• The speech seemed to last a short time, although the clock showed that it took 1 hour.
  
  
• A noun clause is used as a noun.
  
  
• The belief that unicorns exist is a myth.
  
  
• An infinitive clause consists of an infinitive, its subject, its modifiers, and its complements.
  
  
• The patient waited for the dentist to tell her the results of the X-rays.