English Punctuation Rules

Punctuation means standard marks and signs in writing and printing to separate words into sentences, clauses, and phrases in order to clarify meaning. A properly punctuated sentence will help the reader understand the organization of the writer’s ideas.

The ACT English test includes questions that address both the rules and usage of punctuation. You should be able to identify and correct errors involving the following punctuation marks:

  1. Commas
  2. Apostrophes
  3. Colons and Semicolons
  4. Parentheses and Dashes
  5. Periods, Question Marks, and Exclamation Points

1. Commas

A comma is used to indicate a separation of ideas or elements within a sentence.

1.1 Use a comma with a coordinating conjunction to separate independent clauses within a sentence.

A coordinating conjunction connects words, phrases, or clauses that are of equal importance in the sentence. For example,

  • Jenny sings in the choir, and she plays the guitar in a rock band.
  • Amanda enjoys her job, but she is looking forward to her vacation.
  • His mother doesn’t eat meat, nor does she eat dairy products.
  • Jordan will be playing football this year, for he made the team.
  • Frank earned a promotion, so we decided to celebrate.
  • I just completed my workout, yet I’m not tired.

1.2 Use a comma to separate elements that introduce and modify a sentence.

For example,

  • Yesterday, I painted the entire garage.
  • Before deciding on a major at college, Rana discussed her options with her parents.

1.3 Use commas before and after a parenthetical expression.

A parenthetical expression is a phrase that is inserted into the writer’s train of thought. Parenthetical expressions are most often set off with commas. For example,

  • Stephanie’s decision, in my opinion, was not in her best interest. The new park, of course, is a popular tourist destination. 

1.4 Use commas before and after an appositive.

An appositive is a noun or phrase that renames the noun that precedes it. For example,

  • My brother, a well-respected scientist, made an important discovery.
  • Mr. Smith, the fifth-grade math teacher, was a favorite among the students.

1.5 Use a comma to set off an interjection.

For example,

  • Well, it’s about time that you got here!
  • Say, did you pass your history test?

1.6 Use commas to separate coordinate adjectives.

If two adjectives modify a noun in the same way, they are called coordinate adjectives. Coordinate adjectives can also be joined with and (without a comma). For example,

  • We walked the long, dusty road to the abandoned farm. OR We walked the long and dusty road to the abandoned farm.
  • My cousin received a dedicated, signed copy of her favorite book. OR My cousin received a dedicated and signed copy of her favorite book.

1.7 Use commas to set off a nonrestrictive phrase or clause.

A nonrestrictive phrase or clause is one that can be omitted from the sentence without changing the meaning of the sentence. Nonrestrictive clauses are useful because they serve to further describe the nouns that they follow. For example,

  • My sister’s dog, forever annoying, barks at me whenever I visit.
  • Katie celebrated her birthday, which was in June, with a party and a chocolate cake.

1.8 Use a comma to separate items in a list or series.

For example,

  • Jill decided to purchase a leash, a collar, and a water dish for her dog.
  • Skippy packed his suitcase, put on his jacket, and left the house.
  • Please bring the following items to camp: pillow, blanket, toothbrush, and other personal hygiene products.

1.9 Use commas in dates, addresses, place names, numbers, and quotations.

Commas generally separate a quotation from its source. For example,

  • Mary is leaving for Jamaica on January 7, 2004.
  • The Library of Congress is located at 101 Independence Avenue, Washington, D.C.
  • Annual tuition is currently $42,500.
  • ‘"My sister is a nurse," Becky said proudly.

Do not use a comma:

- to separate a subject from a verb.

The police officer walked down to the corner.
NOT - The police officer, walked down to the corner.

- to separate an adjective from the word it modifies.

The pretty girl sat in front of me on the bus.
NOT - The pretty, girl sat in front of me on the bus.

- before a coordinate conjunction and a phrase (NOT an independent clause with its own subject and a verb).

Jeff likes to relax on his couch and listen to music.
NOT - Jeff likes to relax on his couch, and listen to music.

- to separate two independent clauses; this is known as a comma splice.

I plan to attend a liberal arts college. My parents want me to get a well-rounded education.
NOT - I plan to attend a liberal arts college, my parents want me to get a well-rounded education.

2. Apostrophes

An apostrophe is used to form possessives of nouns, to show the omission of letters in contractions, and to form plurals of letters and numbers with 's'.

2.1 Add an apostrophe and an 's' to form the possessive of singular nouns, plural nouns, or indefinite pronouns that do not end in 's'.

For example,

  • My friend’s house is at the end of the street.
  • The Women’s Society meets every Thursday at the high school.
  • Someone’s bicycle is leaning against the building.

2.2 Add an apostrophe to form the possessive of plural nouns ending in 's'.

For example,

  • The horses’ stalls were filled with straw.
  • I did not enjoy the two brothers’ rendition of my favorite song.

2.3 Add an apostrophe to the last noun to indicate joint possession.

  • Frank and Ruth’s anniversary is in September.

2.4 Add an apostrophe to all nouns to indicate individual possession.

  • Brian’s, Jason’s, and Michael’s computers were all stolen.

2.5 Add an apostrophe to indicate contractions.

  • It’s raining outside again.
  • We’re running against each other in the election.
  • If you’re going to the movie with me, we should leave now.
  • My cousin should’ve taken the bus.
  • Didn’t Kevin know that classes had begun?

2.6 Add an apostrophe to form the plural of letters and numbers.

  • Did you dot your i’s and cross your t’s?
  • There are a total of four 7’s in my phone number.

2.7 Do not use an apostrophe with a possessive pronoun.

The car with the flat tire is ours.
NOT - The car with the flat tire is our’s.

Yours is the dog that barks all night.
NOT - Your’s is the dog that barks all night.

3. Colons and Semicolons

A colon is used before a list or after an independent clause that is followed by information that directly modifies or adds to the clause. An independent clause can stand alone as a complete sentence.

A semicolon is used to join closely related independent clauses when a coordinate conjunction is not used, with conjunctive adverbs to join main clauses, to separate items in a series that contains commas, and to separate coordinate clauses when they are joined by transitional words or phrases.

3.1 Use a colon before a list.

For example,

  • We are required to bring the following items to camp: a sleeping bag, a pillow, an alarm clock, clothes, and personal-care items.

3.2 Use a colon after an independent clause that is followed by information that directly modifies or adds to the clause.

For example,

  • Jennifer encountered a problem that she had not anticipated: a broken Internet link.
  • My sister suggested a great location: the park down the street from our house.

3.3 Colons may also precede direct quotations and should be used in business salutations and titles.

For example,

  • Captain John Paul Jones said: “I have not yet begun to fight.”
  • Blaze: A Story of Courage

3.4 Use a semicolon to join closely related independent clauses when a coordinate conjunction is not used.

For example,

  • Jane starts a new job today; she is very excited.
  • I don’t understand the directions; my teacher must explain them to me.

3.5 Use a semicolon with conjunctive adverbs to join independent clauses.

For example,

  • Skippy is interested in taking the class; however, it does not fit in his schedule.
  • My brother seems short compared to his friends; nevertheless, he is the tallest person in our family.

3.6 Use a semicolon to separate items that contain commas and are arranged in series.

For example,

  • The art museum contained some beautiful, classically designed furniture; bronze, plaster, and marble statues; and colorful, abstract modern art pieces. My first meal at college consisted of cold, dry toast; runny, undercooked eggs; and very strong, acidic coffee.

3.7 Use a semicolon to separate coordinate clauses when they are joined by transitional words or phrases.

When a sentence contains more than one clause, each of which is considered equally as important as the other, the clauses are called “coordinate clauses.”  They are typically joined by a coordinating conjunction, such as and, but, or, so. When a coordinating conjunction is not used, a semicolon should be.

  • My sister and I enjoyed the play; afterward, we stopped for an ice cream cone. OR My sister and I enjoyed the play, and afterward, we stopped for an ice cream cone.
  • Betty often misplaces her keys; perhaps she should get a key locator. OR Betty often misplaces her keys, so perhaps she should get a key locator.

4. Parentheses and Dashes

Parentheses are used to enclose supplemental information that is not essential to the meaning of the sentence. Dashes are used to place special emphasis on a certain word or phrase within a sentence.

4.1 Use parentheses to enclose explanatory or secondary supporting details.

For example,

  • In addition to serving as Class Treasurer (during her junior year), she was also a National Merit Scholar.
  • Alan visited the Football Hall of Fame (on a guided tour) during his summer vacation.

4.2 Use dashes in place of parentheses to place special emphasis on certain words or phrases.

For example,

  • Dr. Evans - a noted scientist and educator - spoke at our commencement ceremony.
  • The Homecoming float - cobbled together with wire and nails - teetered dangerously down the street.

5. Periods, Question Marks, and Exclamation Points

Periods, question marks, and exclamation points are considered 'end punctuation' and should be used at the end of a sentence.

5.1 Use a period to end most sentences.

For example,

  • Scott enrolled in classes at the university.

5.2 Use a question mark to end a direct question.

For example,

  • Do you think it will rain today?

5.3 Use an exclamation point to end an emphatic statement.

For example,

  • Please don’t leave your vehicle unattended!