27 Punctuation

Using punctuation is critical to creating clear and correct sentences.


Learning Objectives

After completing this chapter, you will be able to

  • Use commas correctly
    • in lists
    • after introductory words or phrases
    • with coordinate and subordinate conjunctions
    • around parenthetical phrases
    • with modifiers and adjectives
  • Use semi-colons correctly to join sentences
  • Use colons correctly to introduce lists, quotes and examples
  • Use apostrophes correctly to make contractions and possessives



Commas are used to separate grammatical items in a sentence.

Watch this video[1] to understand how to use commas correctly:


Review Comma Use

Use commas to separate items in a series or a list of three or more items.

When you list three or more items in a sentence, use a comma before each item in the list, including one before the word and, but, or or. Items in a list can include nouns, verbs, and even phrases.

Nouns I like apples, oranges, and grapes.
Verbs I swim, run, and do yoga to stay in shape
Verb phrases Janice drove down the street, stopped the car, and opened the trunk.
Adjectives She was smart, well-educated, and experienced.


If a sentence contains a list of only two items, do not use a comma between them.

Use commas with an introductory word or phrase

Sometimes a comma is used near the beginning of a sentence to let the reader know where the introductory word, phrase, or clause ends and the main idea begins.

Introductory word Therefore, the scientists had to end the study early.
Introductory phrase According to meteorologists, smoke from forest fires creates its own weather patterns.


Common introductory words include the following:

Sometimes a comma is used after an introductory dependent phrase before an independent clause begins.

Other times, a comma can be used after an introductory dependent clause before an independent clause begins.

Introductory dependent clauses often begin with these common subordinating conjunctions:

Tip: Do not use a comma if the sentence ends with a dependent clause.

Use commas to surround interrupters and appositives

An interrupting word or phrase interrupts the flow of a sentence. Usually, when an interrupting word or phrase is omitted, the sentence still makes sense and the meaning of the sentence does not change. IN other words, an interrupting word or phrase is not essential to the sentence.

Interrupter word Many Indigenous communities, however, never ceded their land claims.
Appositive phrase My teacher, exhausted and frustrated, ended class early.


Common interrupting words include the words however and for example.

An appositive is a noun or noun phrase that describes another noun or noun phrase already mentioned in the sentence. Use commas before and after an appositive since the sentence still makes sense when the appositive is removed from the sentence and the meaning of the sentence does not change.

Use commas with interrupting non-defining clauses

A non-defining clause adds extra, non-essential information to a sentence, You can think of it as a parenthetical phrase; the phrase could be removed without harming the grammar or meaning of the sentence.

A defining clause contains information that is critical to the meaning of the sentence.

Non-defining clause

(with comma)

I live near Lake Superior, which is one of the largest fresh water lakes in the world.
Defining clause

(without comma)

My teacher is the woman who won the award.


An interrupting phrase that starts with the word which is usually non-essential and requires commas. Remember, you can tell if a phrase is non-essential to the sentence if the meaning of the sentence does not change and still makes sense when the phrase is removed.

You can tell if a phrase is essential to the sentence if the meaning of the sentence is changed or no longer makes sentence when it is removed.

Sometimes comma are required for interrupting phrases that begin with who as well; however, a phrase that begins with who can also be essential. Be sure to check to see if the phrase can be removed from the sentence in order to determine if commas are required or not.


Use commas with conjunctions.

You must use a comma with a coordinating conjunction (FANBOYS) when the conjunction is being used to join two complete sentences.

You use a comma with a subordinating conjunction when the dependent (incomplete) clause is at the beginning of the sentence.

Coordinating conjunction

(with a comma to join two sentences

I missed the final, and I didn’t complete most of the homework.
Coordinating conjunction

(without a comma because second half of the sentence is not complete on its own)

I missed the final and didn’t complete most of the homework.
Subordinating conjunction

(with a comma because the dependent clause is at the beginning)

Because I was sick, I stayed home.
Subordinating conjunction

(without a comma because the dependent clause is at the end)

I stayed home because I was sick.


Commas are used before coordinating conjunctions that join two independent clauses. The most common coordinating conjunctions form the acronym FANBOYS (For, And, Nor, But, Or, Yet, So).

Some sentences contain the words for, and, nor, but, or, yet, so; however, these words do not require a comma before them in the sentence because an independent clause does not come before and after the word.

Use commas with descriptive words.

Sometimes a list of descriptive words known as adjectives may appear before a noun in a sentence. You may or may not need to include a comma between a list of two or more adjectives in a sentence.

Coordinate adjectives describe the noun equally. You can put the adjectives in any order, and you could put the word “and” between them.

Cumulative adjectives build on each other and they cannot be reordered. If your have cumulative adjectives, you do not place commas between them; similarly, putting the word and between them does not work.

Coordinate adjectives

(use a comma)

Maria carried the wet, muddy puppy into the house.

You can reorder the adjectives: It was a muddy, wet puppy.

You can put “and” between the adjectives: It was muddy and wet.

Cumulative adjectives

(don’t use a comma)

I know those four red-headed girls.

You can’t reorder the adjectives or put “and” between them.

There are two questions you must ask in order to determine if a comma is necessary between two or more adjectives:

  1. Does the sentence make sense if you place the word “and” between the adjectives?
  2. Does the sentence make sense if you reverse the order of the adjectives?


If the answer is YES to both of these questions, then a comma IS needed.



If the answer is NO to either of these questions, then a comma IS NOT needed.

Use commas to separate elements in addresses and dates.

Dates My mom was born on July 1, 1950, in Thunder Bay.

Jeremy said he wrote his test on Friday, September 11, 2005.

Addresses I sent the letter to 1450 Nakina Dr., Thunder Bay, ON P7C 4W1.

Make sure you forward the mail to 1234 Parkway Ave., Toronto, ON M4B 1B4, starting tomorrow. 


Separate date and address elements with commas.


Do not use commas in any of the following situations:


Commas in addresses:


Do not use a comma in these situations:


Watch this video[2] to practice comma use:



Colons (:) are used to introduce some addition information following a complete sentence. The information provided after a colon can be used to introduce different types of information.

1. Introduce a list


2. Introduce a term


3. Introduce a clause


4. Introduce a phrase


Tip: Do not use a colon if an independent clause does not appear before the list, word, phrase, or another independent clause.


Semi-colons (;) can be used to connect two related independent clauses to make a complex sentence. A semicolon is a mark to signal a partial separation of things. Unlike a period, which signals a “stop”, a semicolon says “yield” or flow into the next thought.

Semicolons have two uses:

1. To replace a period between two closely related sentences.


2. To separate items in a list when commas are already used.

Tip: Do not use a semicolon between two sentences that are not closely related. Use a period instead.

Watch this video[3] to understand how to use these punctuation marks:



Apostrophes are used for two reasons:

  1. to create a contraction (it is = it’s)
  2. to create a possessive (owned by Deborah = Deborah’s)



 A contraction is a word that is formed by combining two words. In a contraction, an apostrophe indicates where one or more letters have been left out when the two words are combined. Contractions are commonly used in informal writing but not in formal writing.

Common Contractions

Apostrophes can also be used to shorten words (of the clock = o’clock), to shorten numbers (1993 = ’93), or dialect (runnin’).


Apostrophes are used with a noun or indefinite pronoun to show who or what belongs to something or someone.


To determine where the apostrophe goes in a word that shows possession, you must first determine if the noun or indefinite pronoun is singular or plural.

Determining whether or not to place an apostrophe before or after an s to show possession in a sentence is a three-step process:


Apostrophes to Show Joint or Separate Ownership

 Apostrophes can be used to show joint ownership or individual ownership.


Apostrophes in Hyphenated Compound Words

To show possession when using hyphenated compound words, add an apostrophe and an s at the end of the last hyphenated word regardless of whether or not the nouns are singular or plural.


Watch these videos to review what you’ve learned about apostrophes[4] [5].


Additional Resources

Complete the LinkedIn Learning course called Advanced Grammar with Judy Steiner-Williams. There’s a great section on punctuation.

  1. Shannon, D. (2021, March 28). Commas 1 [Video]. YouTube. https://youtu.be/wLjyfbqRyiU.
  2. Shannon, D. (2021, March 28). Commas 2 (video). YouTube. https://youtu.be/EfHxlvMRXuE
  3. Shannon, D. (2021, March 28). Commas and semicolons [Video]. YouTube. https://youtu.be/N9wWrBIBbnk.
  4. Shannon, D. (2021, March 28). Apostrophes 1 [Video]. YouTube. https://youtu.be/0FuzpY1sN1w.
  5. Shannon, D. (2021, March 28). Apostrophe2 [Video]. YouTube. https://youtu.be/Xbu9ZWfgwYw.


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