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Basic Grammar and Punctuation: Commas

The tutorials below address basic grammar and punctuation errors writers routinely have. Use these guidelines to proofread and correct errors in your papers before submission. For hands-on help, see a tutor in your campus Learning Support Commons.

About Commas

Commas separate parts of a sentence or set off words or phrases from the rest of a sentence.

There are 4 main uses of commas in sentence construction. Using a comma in these 4 cases adds clarity to your writing, but using commas where they're not needed will cause confusion.

Read on to learn how to use commas properly.

Comma Use One -

Using commas in a series tells your reader that you are providing a list. Your reader may be confused otherwise.

For example:

Her house was decorated in shades of green, blue, and purple. (a list of 3 colors)

We elect official representatives: a president, vice-president, secretary and treasurer. (How many were elected? 3 or 4?)

Comma Use Two -

Using commas with coordinating conjunctions tells your reader that you are discussing two related sentences, not just two things.

When combining sentences into a compound sentence, you need a comma before the coordinating conjunction. For example:

I like peanut butter, and I like jelly.

He eats macaroni, but he won't eat cheese.

BUT when combining two nouns or verbs, you don't need a comma. For example:

I like peanut butter and jelly.

He eats macaroni or cheese but not both.

Comma Use Three –

Using commas after introductory words, phrases, and clauses tells your reader what is introduction and what is the main point.

For example:

In the back of the room, two kids whispered and giggled. (Two kids whispered is the main point; in the back just describes where.)

Slipping and sliding, the car inches slowly across the icy roads. (The car inches is the main point; slipping just describes how.)

Note this special kind of introductory element - the dependent clause of a complex sentence

If the subordinating conjunction comes at the beginning of the sentence – a comma comes at the end of the dependent clause.

WrongEven though I would rather go to the beach I went to the library to study.

RightEven though I would rather go to the beach, I went to the library to study.

If the subordinating conjunction comes in the middle or at the end of the sentence – no comma is required.

Wrong – School is not all about studying, since there are lots of clubs and fun activities on campus.

Right – School is not all about studying since there are lots of clubs and fun activities on campus.

Comma Use Four –

Non-essential elements may be important description, but they are not essential to the construction of a sentence. If you can remove the element without creating a question, then it is non-essential.

Essential element - Students who play sports must have a good GPA. (Which students must have a good GPA?)

Non-essential element - The teacher, who plays flute, enjoys music. (Any teacher enjoys music, not just flute players.)

Commas used to set off non-essential elements indicate which parts of the sentence are extra description or an aside comment. 

For example:

Tropicana Fields, currently located in St. Petersburg, may be moved north to Clearwater.

The students, hoping to get the best classes, enrolled before Fall semester.

Each package, however, contained a broken vase. (However is sometimes used to join sentences but can also act as an aside. Note the comma both before and after.)

I subscribe to the St. Petersburg Times, which has great articles on ecological issues. (Non-essential elements can come at the end of a sentence.)

Other uses of commas provide clarity in details:

1) Use commas to separate two or more adjectives:

The girl was very fond of her little, fluffy, black kitties.

2) Use commas in dates, addresses, place name, and long numbers:

1600 Pennsylvania Ave., Washington, D.C., is where the White House is located.

July 4, 1776 is when the Declaration of Independence was signed.

I won 1,000,000 dollars in the Florida Lotto!

3) Use commas to set off a direct quotation from the rest of the sentence:

My mother used to tell me, "What goes around comes around."

"Come live with me and be my love," quoted the romantic young man.