Did you know that no other form of punctuation is more important to understand than the comma?

Recently I saw this printed on a t-shirt, and it’s a great example of how a comma can change the meaning of a sentence (and maybe give you a chuckle besides).

The comma tells the reader to pause. In this case, grandma is being directly addressed in the sentence. Commas separate a noun of direct address from the rest of the sentence.

The comma has two primary functions: it sets off nonessential expressions that interrupt the flow of thought from subject to verb, and it separates elements within a sentence to clarify their relationship to one another.

Although there are many grammar rules for commas, here are four general ways to use commas:

1) Between Items in a Series – When listing three or more items in a sentence, place a comma between each item of the list. You have the option to choose whether to include the final comma. If your list is complex, omitting the comma may confuse the reader about where the second-to-last item leaves off and the last begins. In that case, include the comma in order to avoid confusion.

2) Between Two Sentences – When you put two sentences together with a conjunction (such as and, but, or, or nor), you must also include a comma. It must be a complete sentence on both sides of the conjunction.

Example: I heard that the price of gasoline would increase, but I did not realize that the price would skyrocket.

Note: Do not add a comma if you are putting two phrases together separated by a conjunction.

Example: I heard that the price of gasoline would increase but didn’t realize it would skyrocket.

3) To Attach Words to the Front or Back of Your Sentence – Most of the sentences that we compose consist of a short core sentence with details added to the core sentence. When you add information to the front or back of your sentence, you will want to alert the reader by adding a comma in order to help your reader understand your message.

Example: Certainly, John will be at the meeting.

Example: Although he missed the last meeting, John’s attendance record has been perfect.

4) To Set Off Interruptions or a Nonessential Component – Commas are used to set off a word, phrase, or clause that interrupts the main thought of a sentence. In order to tell whether you need commas, you must decide whether the added words are essential to the meaning of the sentence or whether they simply provide extra detail to the sentence.

In order to tell a reader that a group of words is a nonessential component, you place commas in front and in back of the group of words. Test by deciding if omitting the group of words changes the meaning of the sentence.

Example: Mr. Smith, who is the company president, will attend the meeting.

In this example, the information about Smith being the company president has no bearing on the main idea of the sentence: that he will be at the meeting. Since that information is extra, let the reader know by placing commas on either side of that phrase.

An essential clause is a dependent clause that cannot be omitted without changing the meaning of the main clause. Essential clauses are not set off by commas.

Example: Applicants who speak Spanish will be considered for the job.

This sentence contains information that is essential to the meaning of the sentence: “who speak Spanish.” If commas were placed around those words, the main idea is simply “applicants will be considered for the job.”

Although there are more rules about commas, I hope these few basics will help add some clarity for your writing purposes.