Online Writing Lab

Roane State Community College

Guide to Comma Use

Learning when to and when not to use commas is a difficult and sometimes overwhelming task for many writers, but it is absolutely essential because commas are signals that tell readers which words need to be separated from each other or which words are not essential to the basic grammar of a sentence. This is just a quick reference guide for the most common uses and misuses of the comma.

Here are a few of the most common places to use commas:

We bought eggs, milk, and bread.

Laughing, he stood up.

Laughing at the stupidity of it, he stood up.

With the laughter getting louder, we realized he had stood up.

The cat, which had just eaten the mouse, curled up to go to sleep.

The cat was sleepy after eating the mouse, which wasn’t surprising. [Remember that nonessential doesn’t mean unimportant, just that it’s not part of the main clause or that it is not necessary to identify the subject.]

The cat was tired, so it curled up and went to sleep.

Here are a few of the most common mistakes writers make when using commas:

The cat was tired, it curled up and went to sleep. [This creates a comma splice error, a type of run on sentence.]

The cat was tired, because it had just eaten the mouse.

I like pastas although, I also like many meat dishes.

I like pastas but, I also like many meat dishes.


Comma Do’s and Don’t’s

Understanding when and when not to use commas can be really confusing; however, using commas correctly in our writing helps to take our writing to a more advanced level. It certainly doesn’t “make” the essay, but correct comma use definitely puts the finishing touches on and written work.

This list of comma do’s and don’t’s will help you to learn when you should use commas and when you should leave them out. Don’t give up; practice makes perfect! Review this information along with the information on commas in your Keys for Writers text (Section 47), and you’ll be a comma pro in no time!

Comma DO’s

DO -

Note: When a transitional expression joins two independent clauses, a semicolon should be used instead of a comma.
Mr. Wilson was unable to cope from his tireless touring; for example, he was on the verge of a breakdown when the tour finally ended.

Technology, so they say, is indeed the wave of the future. (parenthetical expression)

As an actor, Russell Brand is a comedian, not a dramatist. (contrasting element)

The snake slithered through the tall grass, the sunlight shining now and then on its skin. (absolute phrase).

Comma DON’T’s


Comma Splices

One major sentence error that writers often struggle with is the comma splice error. This error is a type of run on sentence because it contains two main ideas or sentences joined incorrectly with only a comma. A comma is used to create pause in a sentence and to separate the main idea from nonessential elements of the sentence. It is not a strong enough piece of punctuation to join two sentences together.

Consider this comma splice:

Joe likes eggs, Melissa likes cereal.

Here we have two sentences or complete ideas that are joined only by a comma, but remember, the comma is not a strong enough punctuation mark to join two complete sentences.  Here are some corrected versions:

Joe likes eggs, but Melissa likes cereal. (coordinating conjunction added)

A comma can only be used to join two sentences together when it is helped out by a coordinating conjunction like for, and, nor, but, or, yet, so.

Joe likes eggs; Melissa likes cereal. (semicolon used instead of a comma)

We can replace the comma with the semicolon because the semicolon is a much stronger punctuation mark. It is strong enough by itself to join two sentences together. One caution about the semicolon, though: It should only be used to join sentences that have closely related ideas, and using it too frequently can create choppiness in our   writing. Also, the words on each side of the semicolon should create a full sentence (independent clause). If not, the semicolon probably hasn’t been used correctly.

Joe likes eggs; however, Melissa likes cereal.  (semicolon with conjunctive adverb)

We can use a conjunctive adverb after the semicolon if we want to more clearly show a relationship between the sentences. Conjunctive adverbs are words like however, nevertheless, consequently, as a result, therefore. Remember that a comma needs to follow the conjunctive adverb, and a semicolon should come before it as in the example above.

Although Joe likes eggs, Melissa likes cereal. (subordinating conjunction at the beginning of sentence, so a comma is acceptable punctuation)

We can use a subordinating conjunction (dependent word) like because, although, as, until, unless, when to join two sentences together. Notice that in the above example we have the dependent word although at the beginning of the sentence. Because of this, the clause “Although Joe likes eggs” becomes a dependent clause, meaning that it cannot stand alone as a complete sentence. What we end up with, then, is one dependent clause and one independent clause (complete sentence). A comma is strong enough to join a dependent and independent clause together, so this comma use is acceptable and does not create a comma splice error.

If we wanted, we could also invert the order of these clauses to come up with this:

Melissa likes cereal although Joe likes eggs.

In this case, the dependent word is in the middle of the sentence, so no comma is needed (remember that commas are usually not needed in front of dependent words).

Sometimes we need to use a relative pronoun like which or that to correct a comma splice. Here is an example:

Joe likes eggs, these are his favorite breakfast food. (comma splice)

Joe likes eggs, which are his favorite breakfast food. (correct)

For more help with correcting comma splice errors, you can review Section 39 of the Keys for Writers text.