How to use a comma: A punctuation mark with a past, purpose, and plenty of rules

Ah, the comma. It’s that little punctuation mark we often sprinkle throughout our sentences, yet its misuse can lead to confusion or even entirely change the meaning of a statement.

In this article, we’ll dive into the origins of the comma, understand its primary functions, and learn the rules associated with its use.

A brief history of the comma

The word “comma” finds its roots in the Greek word kómma, which means “a piece cut off,” aptly describing its role in “cutting off” parts of sentences.

In ancient Greece, commas were used to indicate a short pause in speech. Later, in the 16th century as printing and literacy rates increased, the comma began to evolve into its current form, and the rules surrounding it became increasingly standardized.

The Role and Rules of the Comma

Speaking of those rules: Here's a brief rundown of several of the most common American English comma rules, including examples of how to apply each. (Note that there is some rule variation among style guides, but this list represents majority opinion.)

Listing

One of the most common usages of the comma is to separate items in a list.

Example: I like reading, writing, and editing.

The infamous Oxford comma—the comma before “and” in a list—has been the subject of much debate. Some style guides recommend using it, while others do not. We suggest always using it for clarity.

Joining independent clauses

When two independent clauses—clauses that can stand alone as sentences—are joined by a coordinating conjunction like "and," "but," or "so," a comma precedes the conjunction. You can remember coordinating conjunctions with the acronym FANBOYS (for, and, nor, but, or, yet, so). The comma goes before the FANBOYS.

Example: She wanted to visit the museum, but she didn’t have enough time.

Setting off introductory elements

When a sentence starts with an introductory word or phrase, it’s often followed by a comma. 

Example: Within a year of the start of the California Gold Rush, the non-native population in California shot from 20,000 to more than 100,000.

While commas are optional for short introductions, we recommend including them for clarity and consistency.

Setting off non-restrictive elements

Non-restrictive elements provide additional information but aren't essential to the main point of the sentence. These elements should be set off with commas.

Example: The Eiffel Tower, located in Paris, is a popular tourist destination.

Addressing someone

When addressing someone directly, their name or title should be separated from the rest of the sentence by commas.

Example: How are you, Matt?

Writing dates

Commas are used to separate various components of dates, including the day of the week from the month, the numerical date from the year, and the year from whatever follows. 

Example: I'll always remember Friday, July 7, 2017, because it's my son's birthday.

Setting off titles

Commas are used to separate titles from names.

Example: James Bond, the spy, has become an iconic character.

Contrasting

To emphasize contrasting parts of a sentence, use commas.

Example: He wanted to play, not study.

Setting off participle phrases

Commas come before phrases that begin with a word ending in "-ing" or "-ed" when the phrase comes at the end of the sentence and is not essential to the sentence's meaning.

Example: She yelled at me, making me cry.

Writing place names

Commas separate the name of a city from the name of a state, province, or country. We also suggest using a comma after the name of the state, province, or country to ensure clarity.

Example: Kansas City, Missouri, is where the Kansas City Chiefs play football.

Attributing quotes

Commas come after quotations, before the names of the people who said them. The comma appears inside the quotation marks.

Example: "It's cold," she said.

Introducing quotes

Commas come before complete one-sentence quotations when the introductions to the quotations are incomplete sentences.

Example: He later asked, "Do you want dessert?"

Setting off dependent clauses

Commas follow dependent clauses—or incomplete sentences—when they come directly before independent clauses—or complete sentences.

Example: After he spent an hour at the gym, he purchased a smoothie.

Joining adjectives

Commas join two or more adjectives that would still make sense if they were written in a different order and joined by the word "and."

Example: It was a dark, stormy night.

Separating conjunctive adverbs

Commas separate conjunctive adverbs, such as however, thus, and furthermore, from the rest of a sentence. A comma generally follows the conjunctive adverb, but if the adverb connects ideas within one sentence, a comma precedes it as well.

Example: Furthermore, you should keep reading.

Avoiding common comma mistakes

Sometimes it's easier to understand how to not use a comma. So if that's how your brain works, this list of common comma mistakes is for you:

Comma splice 

A comma splice occurs when two independent clauses—or complete sentences—are joined by just a comma without a coordinating conjunction.

Incorrect: I love reading, I read every day.

Correct: I love reading, and I read every day.

Overuse 

It's important not to use commas excessively. Be sure you only use them when necessary to clarify meaning.

Restrictive vs. non-restrictive 

Only use commas for non-restrictive—or unnecessary—elements. Do not use them for restrictive—or necessary—elements. For example, “Dogs, who are friendly, make great pets” implies all dogs are friendly. But, “Dogs who are friendly make great pets” refers to specific friendly dogs.

The comma in the digital age

The digital age, particularly the rise of social media and texting, has seen a more relaxed approach to the comma. In some spaces, commas are frequently omitted to save space or time. However, for clear and professional communication, especially in formal writing, the rules of comma usage should be respected and will increase your credibility and authority.

Play fun brian games to practice comma rules

The comma, though small, plays a pivotal role in ensuring clarity and nuance in written communication. Its rules might seem overwhelming at first, but with practice, they become second nature.

A great way to practice these comma rules is in the Elevate brain training app, available on iOS and Android. With more than 40 brain games designed to improve your grammar, vocabulary, and so much more, you can solidify your understanding of comma rules and practice using them, all without feeling like you're studying. 

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So what are you waiting for? Go ahead and try Elevate for free today, and never second-guess your comma usage again.