21.16: Punctuation
This section covers the major marks of punctuation: commas, apostrophes, semicolons, colons, periods, question marks, exclamation points, dashes, and parentheses. (For using brackets and ellipses, see Quotations .)
Commas
Commas alert readers to brief pauses within sentences.
Commas with Main Clauses
Use a comma before a coordinating conjunction ( for, and, nor, but, or, yet , or so ) joining main clauses:
Businesses in the metropolitan area are growing, and unemployment is down.
Many job seekers use online sites like Indeed.com, but a few still send traditional cover letters and résumés through the mail.
A solution must be determined soon, or the problem will continue.
Commas with Introductory Information
Use a comma after an introductory element at the start of a sentence:
After class is over , we should get lunch and review our notes.
Shuffling his feet nervously , he waited for the train.
However , the circumstances have not changed.
Commas with Nonessential and Essential Information
(See Editing Focus: Commas with Nonessential and Essential Information for a related discussion of commas.)
Nonessential information refers to information that is usually not necessary to the basic meaning of a sentence. Nonessential information is set off by commas. In the following sentence, the word original tells readers which labs no longer meet the needs of the teachers and students. The underlined information adds information but does not change the meaning of the sentence and thus is nonessential to the basic meaning:
The original technical education labs , which were installed 50 years ago, no longer meet the needs of the teachers and students.
Essential information , on the other hand, is necessary to the meaning of the sentence. In following example, the word original is no longer part of the sentence; the underlined words convey necessary information about the labs:
The technical education labs that were installed 50 years ago no longer meet the needs of the teachers and students.
You can test whether information is nonessential by removing the information. If the meaning of the sentence is unchanged, the information is nonessential. If the meaning becomes too general or changes, the information is essential. In the sentence above, only the labs installed 50 years ago, as opposed to other labs, no longer meet the needs of teachers and students. Note, also, the use of which with nonessential information and that with essential information.
Commas Around Nonessential Information
Place commas around information that is not essential to the meaning of a sentence:
The entire technology department , which consists of nine teachers and five staff members, has contributed to a report on the needed updates to the technical education labs.
The technology department chair , who teaches welding, wrote the final report.
Updates to the labs will begin in June , when school is not in session .
No Commas Around Essential Information
Do not place commas around essential information:
According to the technical education teachers, the labs need equipment that students are likely to encounter in the workplace .
Faculty who teach auto mechanics have requested updates to their lab.
The teachers are concerned about the labs because students are not learning the skills they need .
The amount of lab space that needs to be updated is substantial.
The department has consulted the industry expert Stacy James .
Serial (Oxford or Harvard) Commas
For clarity, use a comma between items in a series:
He studied all the notes, emails, memos, and reports related to the data breach.
Be aware, however, that certain style manuals, such as the AP Stylebook , do not use the serial comma, also called the Oxford or Harvard comma.
Commas with Numbers, Dates, Titles with Names, and Addresses
The sign gave the city’s population as 122,887.
Nobel Prize winner Toni Morrison died on August 5, 2019.
Diana Wong, M.D., is a practicing obstetrician.
The mailing address for the Smithsonian Institution is 600 Maryland Avenue SW, Washington, D.C., 20002.
Common Comma Errors
Misplaced commas can make sentences choppy and obscure the intended meaning.
No Comma after a Subject or a Verb
Anyone who was still at the party, left when the band stopped playing.
The party ended, after the band stopped playing.
No Comma after a Conjunction Connecting Parts of a Compound Subject, Verb, or Object
Some musicians in the band, and many of the guests danced until midnight. (compound subject)
The band stopped after two hours, and took a well-deserved break. (compound verb)
Guests enjoyed the music, and the dancing. (compound object)
No Comma after a Series
The band played 80s rock, punk, and new wave, all night long.
No Comma before an Indirect Quotation
Online reviews say, that the band is the best in the area.
Apostrophes
An apostrophe has two functions. It indicates possession, and it forms contractions.
Apostrophes to Show Possession
Use an apostrophe and -s to indicate possession with a singular noun or an indefinite pronoun:
Jack ’ s brother is my sister ’ s coworker.
In their family, everyone ’ s favorite dessert is ice cream.
If the ’s in a singular noun is pronounced, add apostrophe -s :
The business ’ s inconsistent hours caused customers to go elsewhere.
Los Angeles ’ s airport, LAX, is one of the busiest in the United States.
If the ’s is not pronounced in a singular noun, some writers choose to add an apostrophe alone; however, MLA, APA, and Chicago use the apostrophe and s in these cases:
David Myers ’ book, The Pursuit of Happiness , was published in 1992.
David Myers ’ s book, The Pursuit of Happiness , was published in 1992.
When the noun is plural and ends in -s , place the apostrophe after the final -s :
American households ’ incomes have grown since the 1970s because more women have entered the workforce.
These families ’ expenses have risen too.
When the noun is plural and does not end in -s , add an apostrophe and -s :
Social media ’ s effect on contemporary life cannot be underestimated.
During the pandemic, parents’ stress grew as they helped with their children ’ s schooling.
Apostrophes to Form Contractions
Contractions are common in speech and in informal writing. Use an apostrophe in contractions:
When I say I can ’ t , I mean I won ’ t .
It ’ s the best option under the circumstances.
“ You ’ re the best friend anyone can have,” Mikayla said.
They ’ re driving to their favorite hangout spot.
Common Apostrophe Errors
Apostrophes are not used to form plural nouns, singular verbs, or personal or relative pronouns.
Not in Plural Nouns
How many hotel rooms [not room’s ] should be reserved for the wedding?
The Lewises and the Riveras [not Lewis’s and Rivera’s or Lewis’ and Riveras’ ] have confirmed their reservations.
Not with Verbs Ending in -s
Nikki runs [not run’s ] every day.
Jamal walks [not walk’s ] to work.
Not with Possessive Personal Pronouns or Relative Pronouns
The book is yours [not your’s ].
The dog was barking and wagging its [not it’s ] tail.
Whose [not who’s ] apartment is this?
Other Punctuation
Semicolons
The semicolon joins main clauses (a clause that contains a subject and a predicate and can stand alone as a sentence). A semicolon is also used to separate items in a series that contain commas.
-
Use a semicolon to join main clauses that are closely related in meaning and that are not joined by a coordinating conjunction (
for
,
and
,
nor
,
but
,
or
,
yet
, or
so
).
Originally built in 1928, the school had been remodeled multiple times ; the result was an architectural mashup. -
Use a semicolon to join main clauses that are connected by a transitional word or phrase such as
for example
,
however
,
therefore
,
indeed
,
or after all
:
The governor has proposed increased funding to K-12 public schools ; however , the legislature must approve the budget. -
Use a semicolon between items in a series that contain internal commas:
The candidates for the award are Michael, who won the essay competition ; Sasha, the top debater; and Giselle, who directed several student productions.
Colons
A colon introduces lists, summaries, and quotations. A colon also separates titles from subtitles.
- A colon can introduce a list: Successful athletes have the following qualities : physical ability, mental toughness, commitment, and optimism .
-
A colon can also introduce a summary or an explanation, which may or may not be a main clause (a clause that contains a subject and a predicate and can stand alone as a sentence):
The team had one goal left before the end of the season: to win the state championship. -
Book titles often include a subtitle. A colon separates the subtitle from the title:
Forcing the Spring: Inside the Fight for Marriage Equality
End Punctuation
A sentence ends with a period, a question mark, or an exclamation point.
-
A
period
ends declarative (statement) and imperative (command) sentences:
The administration canceled classes .
Do not attempt to drive to school this morning . -
A
question mark
ends a direct question and indicates uncertainty in dates:
Where is Times Square ?
She asked, “What time is it ? ” -
An
exclamation point
ends an emphatic or emotional sentence:
“What a mess ! ” she blurted out.
“Stop ! That hurts ! ” he shouted.
Dashes and Parentheses
Dashes and parentheses enclose nonessential information in a sentence.
-
Use a
dash
or dashes to set off nonessential information, to indicate a contrast or a pause, or to mark a change of direction.
We did not notice the rain at first — it began so softly — but soon we were soaked.
Nothing is as exciting as seeing a snowy owl in a winter farm field — except maybe seeing two snowy owls. -
Use
parentheses
to enclose nonessential information such as explanations, asides, examples, and dates.
He graduated with high honors ( magna cum laude ) and found a job immediately.
The city of Madison ( home of the University of Wisconsin ) is the state capital of Wisconsin.