Commas: There are many different places in writing when commas have to be used in a sentence, so this section will review the rules regarding comma use.

Commas as Coordinator
    The words And or But are coordinating conjunctions, or coordinators for short. Other coordinators are so, for, yet, or,  and nor. Each of the two statements is true independently of the other. A comma is also used if  it joins together two statements or clauses that have a subject and verb.

  Examples: The thin look was in, and yogurt sales soared.
                          Jogging is fine, but walking is healthier.
                          Aerobics became monotonous, so many turned to yoga.
                          Warming up is important, for the body dislikes sudden stress.
                          Doctors warn against diet fads, yet miracle diets keep appearing.
                          Supplements need to be monitored, or they may cause problems.
                          There is no magic bullet, nor do we expect one.
Put the comma before--and not after--the and or but.

Links like and and but also have other uses. Use no comma when they simply link two words or phrases--not two clauses, each with subject and verb.

   No Comma:  Executives are protected by stock options and golden parachutes.
                            We called his number several times but without success.

Comma for Subordinator
    Words like if, unless, because and whereas are subordinators (short for subordinating conjunctions). They introduce material that tells us when, where, why, or how. The words if  or because change a self-sufficient, independent clause to a dependent clause, which normally cannot stand by itself.

Dependent: Home buyers profit if interest rates go down.
                         Rate changes affect everyone, because they raise the cost of money.

    Punctuation with subordinators depends on how essential the added clause is to the overall meaning of the sentence. Does it make all the difference? Or is it only added optional information?

Comma for although/whereas. Use a comma when the main sentence is true, no matter what you add.

    Comma: He kept charging to his card, although his account was overdrawn. (he kept charging regardless)
                     Interest on loans was low, whereas interest on card balances was high. (it was low regardless)
                     They kept the family farm, no matter how unprofitable it became.
    Because follows a comma if the reason it introduces is added optional explanation. But sometimes the added reason is the whole point of the sentence- NO COMMA.

Comma: Many new immigrants were Asian, because racial quotas were lifted.
                Many immigrants came because the old country had offered them no future.

Rules regarding use of commas with subordinators.
     Subordinators (subordinating conjunctions) signal relationships like the following. The ones in the first group usually introduce essential, restrictive information.

Time:   when, whenever, while, before, after, since, until, as soon as, as long as

Place:  where, wherever

Condition: if, unless, provided

Intention: so that, in order that

Reason: because, since

The words in the second group usually introduce nonessential, nonrestrictive information.

Comma

Comparison: as, as though, as if

Contrast: though, although, whereas, no matter how, even though

Note a special use of however as a subordinator starting a nonessential, nonrestrictive clause. Use it with a comma:

Comma: Traffic fines have to be paid, however unreasonable they may seem.

     Who (whom, whose), which, and that bring in added material. They tell us which one or what kind: the runner who tripped; drugs that kill pain. They fill in background material: Madonna, whose road trips earn millions. Who, which, and that are relative pronouns, and the clauses they bring into a sentence are relative clauses. They may appear at different positions in the main clause:

    People who know how to talk can buy on credit.
                                                                              --Creole proverb

    Cajuns spoke Creole, which was a local French dialect.

To punctuate relative clauses, you need to ask: Comma or no comma?

Restrictive who/that Do not set off restrictive relative clauses. Clauses are restrictive when we need to know which one or what kind. Such relative clauses narrow the possibilities.

No comma: Ex-convicts who carry guns....
                A mole is a spy who infiltrates the enemy's bureaucracy.
                   In an emergency, call the lawyer whose name appears on this card.
                   The number that he gave us was no longer in service.
Tip: The pronoun that almost always introduces a restrictive clause. Shortened relative clauses with a pronoun like that or whom left out are always restrictive.

No Comma: The reviews [that] we sent were lost in the mail.
                     The lawyer [whom] the firm retained charged large fees.

COMMA:  The bill targeted illegal aliens, who lack proper documentation. (all do)
                    Sharks differ from whales, which surface to breathe. (applies to all)
                    We drove down Pennsylvania Avenue, which leads past the White House. (We've already focused on the street.)

    Use no punctuation when the place of a noun is taken by a clause-within-a-clause. Clauses replacing a noun are called noun clauses. They start with words like that, why, how, where, who, and which: tell me that you understand; explain why it failed; ask them where they live. Other words that might start a noun clause are whoever and whatever: take whatever is available.

NOUN:                               The mayor announced her plans.
NOUN CLAUSE:               The mayor announced that she would run for re-election.

NOUN:                            The paper never revealed the source.
NOUN CLAUSE:            The paper never revealed who had leaked the news.

Take out commas used mistakenly to set off noun clauses:

                                                                        found that excessive force
WRONG COMMA: The police review board found, that excessive force had been used.

COMMAS for MODIFIERS

Know when to set off modifiers in a sentence.

    Modifiers come into a bare-bones sentence to add information or fill in detail. Many such modifiers are prepositional phrases, starting with words like on, at, by, from, as with, without, during, before, after, behind, across and around. These phrases usually blend into the sentence without a break.

NO COMMAS: Many immigrants perished during the trek across the deserts and mountains of the West.
                          The trail from St. Louis to the Northwest became known as the Oregon Trail.

Many other modifiers building up detail in a sentence are verbals. They are forms of verbs that don't serve as the complete verb but serve some other purpose in the sentence. Look for -ing forms coming into a sentence as modifiers (i.e., pulling the wagons; scouting the trail) look also for forms ending in -ed or corresponding forms like broken or known (the traveling party advertised in the handbill; the leader chosen by the group). Look for a to- form, alone or part of a phrase (the distances to be covered). To punctuate such modifiers, the basic question  is: How important is the added material to the main point of the sentence? If it's added comment of optional information, use a comma or commas. If it's needed to make the main point, use no punctuation.

Commas:         The Mormons, persecuted for their beliefs, kept moving west. (the main point is that they kept moving west)

No Commas:    Members  challenging the leadership were severely criticized. (the main point is that it was those members who were criticized)

No commas:     The restaurant excluded guests without shoes.
                          (other guests were welcome)
                          We saved containers suitable for recycling.
                          (we discarded the others)
                          The counselor running the camp talked like a drill sergeant.
                          (only that particular one)

Modifiers are nonrestrictive when they merely tell us more about something that we have already identified. Commas set off the added information--not needed to tell us which one or what kind.

Commas:        Her friend  Mayra, replacing the camp counselor, used a new system.
                        (we already have her name)
                        Recycled paper, made from newspapers and books, helps save the forest.
                        (we already know the kind of paper)

    An appositive is a second noun placed next to the first as an added label. Most appositives are not needed to single out one thing among others (it's already been labeled and identified). They are usually added comment and therefore nonrestrictive. However, use no comma when the added detail is needed to tell two things apart:

Commas:     Pizza, the original finger food, became the national dish of the young.

No Comma:  They had trouble telling apart Washington the city and Washington the state.

Important Tip: Use dashes to set off a modifier that already contains one or more commas. The dashes then signal the major breaks:

Dashes: Her sister--a stubborn, hard-driving competitor-- won many prizes.

Comma:    Like many immigrants, their grandmother came as an indentured servant.
                In colonial etiquette books, women were instructed in the art of passivity.

    Set off introductory verbals or verbal phrases regardless of length. Look for -ing forms coming as modifiers before the subject (present participles). Look for -ing forms coming into a sentence as modifiers (i.e., pulling the wagons; scouting the trail) look also for forms ending in -ed or corresponding forms like broken or known (past participles). Look for a to- form, alone or part of a phrase (infinitives):

Comma:      Smiling awkwardly, the new arrivals looked at the camera.
                    Warned of the ice, the ship took a southern route.
                    Known for its shallows, the river challenged even experienced pilots.
                    To read more about early Americans, click on Colonial America.

    Set off verbal phrases that go with the sentence as a whole. Such sentence modifiers (absolute constructions) do not modify any one part of a sentence but go with the whole sentence. They may appear at either the beginning or later at the end of the sentence. Some comment on the sentence as a whole; some provide explanation of background for the main statement:

Comma:    To tell the truth, I never heard the name.
                   The biographer did well, considering the lack of documents.
                   Their guides having failed them, the travelers turned back.

Commas are optional with expressions linking two sentences. Tags like after all, of course, unfortunately, on the other hand, on the whole, as a rule, and certainly help us go on from one sentence to the next. Depending on how much you would make the transitional tag stand out when reading aloud, set it off from the rest of the sentence. The commas are now often omitted in the open punctuation of much writing about current affairs.

Optional:      After all, Chicago was a working class city.
                      New York had, of course, once been a Dutch town.
                      Los Angeles, on the other hand, had been part of Mexico.
                      Newspapers played up the incident, of course.

    Tags that are set off require two commas if they do not come first or last in the sentence:
Commas:     Institutions do not, as a rule, welcome dissent.

    Use commas when transitional tags add explanation or examples to the same sentence. Use a comma before but not after such as  and  especially. Use a comma before and after tags like for example, for instance, namely, and that is. (The second comma is optional except for that is.)

One Comma:   Industry giants fight over programming languages, such as Java.
                         Companies discover new marketing tools, especially web sites.
Two Commas: Internet buying is growing rapidly, for example, shopping for used or rare books.
                         Two areas of Internet sales have been extremely profitable, namely, stock market transactions and pornography.
                          Internet sales promote disintermediation, that is, cutting out the middleman.

Series:     New sports became popular: soccer, jogging, and lacrosse.
                 The fans threw bottles, taunted officers, and rocked cars.
                 Only 18 percent of this country's 56 million families are conventionally "nuclear," with bread-winning fathers,          homemaking mothers, and resident children.  --Jane Howard

    The basic A, B, and C pattern can be stretched to four elements or more:

Series: The stand sold nuts, raisins, apples, and every other kind of organic lunch.
              The repertory of the humpback whales includes groans, chirps, clicks, bugles, and roars.

        Groups of words in a series may already contain commas. To prevent misreading, use semicolons to show the major breaks:

Semicolons: Successive waves of African American music have swept over our popular culture: the blues, from the South; reggae, from Jamaica: and rap, from the urban centers.

Tip: In informal or journalistic writing, the last comma in a series is often left out. However, many teachers and editors still require the last comma. Use it to be safe:

Last Comma: Computer programs can now check student papers for spelling errors, awkward sentences, and sexist phrases.

    Dates, addresses, page references, and measurements often come in several parts. Mark them off by a comma (New York, New York). The last item is followed by a comma if the sentence continues. Separate date and year only if the month comes first (October 3, 1999 but 3 October 1999).

Dates:          The date was Tuesday, September 29, 1998.
                      On March 12, 1992, several water pumps stopped working at the nuclear plant.

Address:        Forward mail to 127 Trumball Street, Hurdville, Alabama, starting the first of the month.

Reference:     The quotation is from Chapter 5, page 43, line 7, of the second volume.
Remember especially the comma that separates city and state:

City/State:     The accident occurred at a nuclear power plant near Harrisburg, Pennsylvania.
                        At the Lordstown, Ohio, and South Gate, California, plants, laser equipped robots measure car bodies to make sure they meet exact specifications.

        Use commas to separate the parts of measurements employing more than one unit of measurement. Here the last item is usually not separated from the rest of the sentence:

Measure:    It is rare for a halfback to be only five foot, nine inches tall.
                  Five pounds, three ounces is an unusual weight for this fish.

        Coordinate adjectives work together to tell us which one or what kind. They are interchangeable adjectives. Use a comma between them when you can reverse their order: a brutal, bruising sport (or a bruising, brutal sport); slanted, sensational reporting (sensational, slanted reporting would be the same thing). Use the comma only when an and could take the place of the comma. Both labels are equal parts of the sane picture: a long, highly critical report (it was both long and highly critical).

Comma:     The snoopy, brash new magazine pilloried the most annoying, appalling people in New York and the nation.
                    The crowd expected a hypocritical, cliche-ridden speech. (they expected it to be both, not necessarily in that order)

    Remember that not every pair of adjectives follows this pattern. Do not use the comma when you cannot change the order of two adjectives:

No Comma:  The smooth new manager calmed the angry male customer. ("new smooth manager" and "male angry customer" wouldn't work)

Repetition:     Innovate, innovate! This is the law of the Silicon Valley.

Restatement: We were there in the nine days before Christmas, the Navidad.

Use a comma in sentences that line up several examples or implications of the same idea in parallel form:
Parallel:     Undergraduate education must prepare the student not to walk away from choices, not to leave them to the experts.                                       --Adele Simmons

Use the comma also in sentence that line up opposing ideas in parallel form:
Parallel:     The purpose of a college is education, not training.
                    Students should learn to ask the right questions, not just to give the right answers.

Comment:     The loan was denied, it seems.
                       She opened the door for them, a serious mistake.
                       The trophy, her first, stood on the mantelpiece.

        You will need these interrupting commas especially when you transcribe dialogue. Use them for the tags that start a comment or that address the listener.
Tag Opening:        No, she is not here.
Tag Question:       She is your friend, isn't she?
Direct Address:    Your friends, Marilyn, are worried about you.
    Use the interrupting commas when you hear a slight break in a sentence because of a change from usual word order:
Normal Order:      For her parent's generation, work was a religion.
Unusual Order:     Work, for her parent's generation, was a religion.

Exercise:  Reading to Writing Connection

If you would like to see this site with the first Folio edition of Shakespeare's play, then click on the following picture, and it will connect you. 

 The quality of mercy is not strain'd
  It droppeth as the gentle rain from heaven
  Upon the place beneath: it is twice blest;
  It blesseth him that gives and him that takes:
  'Tis mightiest in the mightiest: it becomes 190
  The throned monarch better than his crown;
  His sceptre shows the force of temporal power,
  The attribute to awe and majesty
  Wherein doth sit the dread and fear of kings;
  But mercy is above this sceptred sway; 195
  It is enthroned in the hearts of kings
  It is an attribute to God himself;
  And earthly power doth then show likest God's
  When mercy seasons justice. Therefore Jew
  Though justice be thy plea consider this
  That in the course of justice none of us
  Should see salvation: we do pray for mercy;
  And that same prayer doth teach us all to render
  The deeds of mercy. I have spoke thus much
  To mitigate the justice of thy plea; 205
  Which if thou follow this strict court of Venice
  Must needs give sentence 'gainst the merchant there

Click here to see the difference with the commas returned to the section.

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To go to the Comma Splice page, click here.

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I would like to acknowledge The Access Handbook by Dolores La Guardia, copyright 2000 by Allyn & Bacon, from which I obtained all of this information about comma splices.

Page prepared by Patricia George.