Comma Usage

Last Updated on by Michael Brockbank

Commas are usually one of the most difficult of punctuation marks to master.  There are so many rules and variations to these separators that knowing all of them by heart could take some time.  For those you have been flagged by editors due to comma usage, this page may be a good one to book mark for future reference.

I. Commas to: Use Before a Coordinating Conjunction to Connect Independent Clauses
If you are connecting an independent clause with a coordinating conjunction, you need to place a comma before the conjunction.
Conjunctions: and, but, or, for, nor, so, yet

Independent clauses reflect the information of the content before the conjunction.
{source}<blockquote>The computer is running really hot<font color=”red”>,</font> but the cooling fans are working.</blockquote>{/source}
In the example above, “The computer is running really hot” and “the cooling fans are working” can be independent sentences from each other.  Adding the “but” in between them keeps the reading fluid and allows for an understanding of the first clause.

An exception to adding a comma before the coordinating conjunction would be if each clause is short.
{source}<blockquote>She ate the orange and it was juicy.</blockquote>{/source}

II. Commas to: Use After Most Introductory Words, Clauses, and Phrases
By using a comma to signify the ending of an idea, the clause then takes precedence for the sentence.
{source}<blockquote>If you drink a lot of coffee<font color=”red”>,</font> you’ll stay awake all night.</blockquote>{/source}
In this example, we see the idea of drinking coffee, but the clause is “you’ll stay awake all night“.  You can also omit the comma all together if you were to re-write the sentence by switching the idea and the clause’s positions.
{source}<blockquote>You’ll stay wake all night if you drink a lot of coffee</blockquote>{/source}
Using a comma to seperate the idea from the clause can also prevent from misreading the sentence and developing an entirely different view of it.
{source}<blockquote>When activated the software plays a musical note.<br>When activated<font color=”red”>,</font> the software plays a musical note.</blockquote>{/source}
In the first sentence, the sentence can easily be misread.  The part of “activated the software” can signify that this is an incomplete sentence as we don’t have information about what activated the software.  However, adding the comma after “activated” signifies the end of the idea and the main subject is about to be added.

III. Commas to: Use to Set Off Nonrestrictive Phrases and Clauses
Nonrestrictive phrases and clauses are extra bits of information that wouldn’t change the meaning of a sentence if they didn’t exist.  A comma is placed to signify that it’s extra information and the sentence can do without it.
{source}<blockquote>I’ll eat the salad<font color=”red”>,</font> even though I’d rather have the pork.</blockquote>{/source}
Restrictive sentences are those that limits or restricts the meaning of the clause.  These do not need commas.
{source}<blockquote>I’ll eat the salad instead of the pork.</blockquote>{/source}

IV. Commas to: Use Around Appositive Phrases
Appositive phrases rename or gives additional information about a prior noun or pronoun.  These phrases are not necessary, but they could offer additional information to the reader regarding the noun.
{source}<blockquote>He loves his golf club<font color=”red”>, a Calliway Diablo.</font><br>
His car<font color=”red”>, a shiny red Corvette,</font> moves very fast.<br>
Bob’s favorite movie<font color=”red”>, Men in Black,</font> stars Will Smith.</blockquote>{/source}
In the above examples, the appositive phrases are in red.  As you can see, the sentences would still make sense if the appositive phrases were omitted.

V. Commas to: Use Around Nonrestrictive Participle and Prepositional Phrases
Participle and prepositional phrases add extra descriptive information about the noun.  However, they are not necessarily needed in order for the sentence to make sense.
{source}<blockquote>My dinner<b>,</b> <font color=”red”>consisting of chicken and garlic potatoes,</font> was a delicious meal.<br>
The orange car<b>,</b> <font color=”red”>in which black smoke was spewing from,</font> was in dire need of repairs.</blockquote>{/source}

VI. Commas to: Use Around the Extra Information in Nonrestrictive Relative Clauses.
If you add nonessential information in a relative clause using the words who, whom, or which use a commas to initiate the information.
{source}<blockquote>My daughter<font color=”red”>, who was wearing bright pink,</font> was noticeable in that crowd of people.<br>
In recent articles<font color=”red”>, which are listed in a magazine,</font> the author used more animals as the subject material.</blockquote>{/source}|
Not all uses of who, whom, and which require commas to set them off in a sentence.
{source}<blockquote>People who eat a lot of vegetables seem to be healthier.</blockquote>{/source}
The relative clause above restricts “people” to a specific subgroup.  As not all people seem healthy, the ones who eat vegetables do.

VII. Commas to: Use to Set off a Transitional Expression
A transitional expression or a conjunctive adverb connect together ideas in your writing.
{source}<blockquote>Most of the stars in the sky<b>,</b> <font color=”red”>however</font><b>,</b> are billions of miles away.</blockquote>{/source}
Words such as however, therefor, nevertheless, above all, of course, otherwise and in fact are those you’d want to offset with commas.
{source}<blockquote>This birthday was a complete success.  <font color=”red”>In fact</font><b>,</b> he got everything he wanted.</blockquote>{/source}

NOTE: Some clients, including the editors at, prefer the usage of a semi-colon prior to the transition expression listed in mid sentence.
{source}<blockquote>Most of the stars in the sky<b>;</b> <font color=”red”>however</font><b>,</b> are billions of miles away.</blockquote>{/source}

VIII. Commas to: Use to Separate Three or More Items in a Series or List
When you include several items in your sentence, you want the reader to realize it is a list.  It is common place to pause when reading off a list to someone.
{source}<blockquote>In my laptop bag is a laptop<font color=”red”>,</font> a charger<font color=”red”>,</font> a notebook<font color=”red”>,</font> and a pen.</blockquote>{/source}

IX. Commas to: Use to Separate Coordinate Evaluative Adjectives
Coordinate adjectives are those that can be revered and using the word and without changing the meaning.
{source}<blockquote>She plays games that are exciting<font color=”red”>,</font> noisy<font color=”red”>,</font> and addicting.<br>
Exciting<font color=”red”>,</font> noisy<font color=”red”>, and addicting</font> games are in high demand.</blockquote>{/source}
A comma is not necessary at the end of a series and the noun that is being modified as in the second example above.

No comma is necessary to separate adjective that provide information regarding size, age, shape, national origin, color, religion, or material.
{source}<blockquote>Entering the <font color=”red”>small square building</font> brought back memories of his drinking days.</blockquote>{/source}

X. Commas to: Use to Separate Direct Quotations from the Verb that Introduces It.
Regardless of the quotation comes before or after the verb, a comma is required.
{source}<blockquote>When asked what he want to be when grown up, the little boy replied<font color=”red”>,</font> “A fireman.”<br>
“I want to be a fireman<font color=”red”>,</font>” the boy announced confidently.</blockquote>{/source}


Michael Brockbank
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