4 Punctuation
Learn how common U.S. English punctuation marks clarify sentence structure, show possession and exact words, and signal a sentence’s purpose.
How punctuation guides readers
Punctuation shows how ideas in a sentence fit together and helps readers understand what a writer means. The conventions here follow common U.S. English usage.
organize sentence parts
separate parts of a sentence, but they should not be inserted simply wherever a speaker might pause.
Use in these situations:
Items in a series: We packed sandwiches, fruit, and water. The comma before and is the serial comma; use it consistently unless a required style guide says otherwise.
After an introductory clause or phrase: When the rain stopped, we went outside. Before sunrise, the hikers began their climb.
Between independent clauses joined by a coordinating conjunction: The road was icy, so we drove slowly. The coordinating conjunctions are and, but, for, nor, or, so, and yet.
Around nonessential information that can be removed without changing the sentence’s essential meaning: My aunt, who lives nearby, grows tomatoes. Do not set off information needed to identify a noun: The aunt who lives nearby grows tomatoes.
Between coordinate adjectives that describe a noun equally and can be joined by and: It was a cold, windy day.
To introduce or interrupt direct speech: Maya said, “We are ready.” “We are,” Maya said, “ready.”
A occurs when a comma alone joins two complete sentences. Write The bell rang, and the students left or The bell rang; the students left—not The bell rang, the students left. Also, do not put a comma between a subject and its verb: The students in the front row are ready.
show possession and omission
show possession or omitted letters in contractions. For possession, use these forms:
Singular possessive: Add ’s: the teacher’s desk; James’s notebook.
Plural possessive ending in s: Add an apostrophe after the s: the teachers’ lounge; the dogs’ toys.
Irregular plural possessive: Add ’s: the children’s books.
In a contraction, place the apostrophe where letters are omitted: can’t means cannot, and we’re means we are. Do not use an apostrophe to make an ordinary plural: write three books, not three book’s.
Distinguish commonly confused forms: it’s means it is or it has, while its means “belonging to it.” You’re means you are, while your shows possession. Who’s means who is, while whose asks or tells whose item it is.
enclose exact words
Use around a person’s exact spoken or written words. A comma can introduce a quotation after a dialogue tag: Lena said, “I found the key.” A quotation that is a complete sentence usually begins with a capital letter; a quoted phrase within your own sentence usually does not: He called the plan “a useful first step.”
In standard U.S. usage, and periods generally go inside closing : “We should leave,” Ana said. and go outside: The sign read “Keep out”; we turned back.
Place a question mark or exclamation point inside the when it belongs to the quoted words, and outside when it belongs to the sentence around the quotation: He asked, “Are you ready?” Did she say, “We are ready”? The same placement principle applies to end punctuation when a quotation falls at the end of a sentence.
and connect ideas
A colon points forward to an explanation, example, quotation, or list. Usually, the words before a colon should form a complete sentence.
List: Bring three items: a pencil, a notebook, and a folder.
Explanation: We canceled the picnic: the forecast called for thunderstorms.
Quotation: The note offered one instruction: “Stay on the path.”
Do not place a colon directly after a verb or preposition that leads into a list. Write Bring a pencil, a notebook, and a folder, not Bring: a pencil, a notebook, and a folder.
A semicolon links closely related independent clauses—groups of words that could each stand as a sentence—without a coordinating conjunction: The sky darkened; rain began to fall. Use a semicolon before a transitional word such as however or therefore when it joins two independent clauses, and follow the transition with a comma: We had planned to walk; however, the trail was closed.
A semicolon can also separate items in a series when those items already contain : The guests came from Albany, New York; Dover, Delaware; and Salem, Oregon. Do not use a semicolon to join a fragment to a complete sentence. If either side cannot stand alone, a different mark is usually needed.
match sentence purpose
Choose an end mark that matches the sentence’s purpose:
Period: Ends a statement or a mild command: The library closes at six. Please return the book.
Question mark: Ends a direct question: When does the library close? An indirect question takes a period: She asked when the library closes.
Exclamation point: Signals strong feeling or forceful emphasis: Watch out! Use it sparingly in formal writing.
A sentence normally needs one end mark. When a quotation comes at the end of a sentence, place the end punctuation according to whether it belongs to the quoted words or to the sentence as a whole, following the quotation-mark conventions.
Apply the conventions together
The examples bring several punctuation choices together: We need paper, scissors, and glue. It’s my brother’s turn; the other players’ turns come next. “That’s enough,” said Mia. I have one goal: finish the draft; then I can revise it. “Where is the draft?” Mia asked. She found it!
Use to organize sentence parts and series, but not to join complete sentences by themselves or separate a subject from its verb. Use for possession and contractions, not ordinary plurals. Put around exact words and place nearby punctuation according to standard U.S. conventions. Use a colon to introduce material that follows a complete thought, and a semicolon to connect closely related complete clauses or clarify a complex list. End statements, direct questions, and emphatic sentences with periods, question marks, and exclamation points, respectively.