Using Commas and Punctuation

You should use commas in the following situations:

Before coordinating conjunctions

In compound sentences that are made up of two long dependent clauses, the clauses are joined by words such as and, but, or, and so.

You could say that cars have hurt the planet, but they’ve also helped people connect with others. 

Many young adults can not afford to live on their own, so they live with their parents instead.

Note that a comma is not required if the two dependent clauses are very short.

I wanted to go to the beach but Jenna wanted to go to the mall. 

Do not use a comma to combine two complete sentences. This is a common mistake I see. The correct way is to use a period to separate them or use a coordinating conjunction to join them.

✘ She did her best, she failed the exam.

🗸 She did her best, but she failed the exam.

Separate multiple adjectives describing the same noun

We use commas to separate a series of adjectives which modify the same noun.

The tall, blond woman is my teacher.

Note: if the adjective is modifying another adjective, there’s no comma:

Today I’m wearing dark blue pants.

Separate multiple items on a list

I need to buy bread, jam, honey, fruit, and salt.

The car smashed into the wall, flipped onto its roof, slid along the road, and finally stopped against a tree.

I met Marissa at her house, we drove to the beach, and then went out for ice cream.

After introductory phrases, adverbs, or clauses

We always place commas after the following types of introductory adverbs or phrases.

After introductory adverbs:

Perhaps surprisingly, research has shown that game-based learning and educational video games can actually help children who struggle to pay attention or focus.

After transitional words:

Therefore, the government should encourage businesses to move to rural areas.

You may wish to add a transition word to unite two independent clauses. The two clauses must either be separated by a period (.), a semicolon (;) or a coordinating conjunction:

Jeremy kept talking in class; therefore, he got in trouble.

Jeremy kept talking in class and therefore he got into trouble.

She went to the store. However, she didn’t find what she wanted to buy.

After prepositional phrases:

In the past, it took much more time for people to travel outside the country.  

After participial phrases:

Having taken on massive debt to complete their education, many young Americans may feel hesitant about buying their own home.

After infinitive phrases:

To get better jobs, young people and their families need to invest in quality education. 

After dependent clauses:

if the phrase begins with the dependent clause (the one following if):

If governments don’t act now to slow global warming, it will have dire consequences for future generations.

After words such as “say” and before a quotation:

Dan Davies, Education Manager, said, “Research has shown that lawyers are typically less resilient than the general population.”

Around parenthetical phrases or clauses

We need commas before and after parenthetical phrases and clauses. A parenthetical phrase or clause inserts within a sentence, interrupting the phrase. Usually, it can be removed without changing the basic meaning of the original sentence.

The canopy, the upper level of the trees in the rainforest, holds a plethora of climbing mammals of moderately large size, which may include monkeys, cats, and porcupines.