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When to Use a Comma?

by Boston College
June 2, 2024
9 min read
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Sometimes, the hardest part of writing isn't the content itself but the grammar rules behind it. In order to craft clear, comprehensive sentences that can be easily understood by your readers, I find it critical to understand an essential component of all written work: the comma. If used correctly, the symbol can help bring out the meaning behind your words, but it can be confusing if not.

They play a crucial role in clarifying meaning, adding structure, and aiding comprehension. In order to reach your full potential, you will need to know how to use commas correctly in order to enhance your writing skills. After reading this article, you will have a better understanding of when to use a comma again.

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Understanding the Basics of Commas

Commas are a type of punctuation that has versatile purposes, helping indicate pauses and separate different elements within a sentence. They ensure that your writing flows smoothly and that your intended meaning is conveyed effectively. Otherwise, your sentences would be unnecessarily long and fail to highlight important concepts effectively.

Furthermore, commas play a critical role in enhancing the readability of your text. The appropriate usage of commas guides your readers through the structure of your sentences, allowing for a more coherent and organized presentation of your ideas.

The Role of Commas in English Grammar

In English grammar, commas are used to separate items in a list, set off introductory words or phrases, and create a distinction between separate independent clauses within a sentence. Commas also clarify relationships between words and phrases to avoid any confusion. They help readers make sense of the message you are trying to portray.

Moreover, commas can also be used to emphasize and create a dramatic effect on particular aspects of your writing. With strategic placement, you can divert attention to specific words or phrases, influencing the tone and rhythm of your sentences.

Given how many functions commas fulfill, it can be easy to use them incorrectly or even have an inaccurate representation of their purpose. Contrary to popular belief, commas are not arbitrary marks to be scattered randomly throughout your writing. They aren't just decorum for your writing. Commas are specific guidelines you need to fulfill clarity and coherence.

It is okay to make mistakes, however. While some rules of comma usage may seem straightforward, others require a deeper understanding of sentence structure and grammar. By honing your comma skills, you can elevate the quality of your writing and engage your readers more effectively.

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Rules for Using Commas

To provide more depth into the different situations in which commas come into play, here are a couple of situations in which commas are used to hopefully provide some greater insight and guidance.

Commas in Lists

One of the primary functions of commas is to separate items in a list. This practice, known as the serial comma or Oxford comma, is particularly crucial in avoiding ambiguity. By using commas to separate each item in a list, you ensure that every element is distinguishable and properly clear.

When you are the author, it is hard to see how the same text can be confusing without the commas, but it can make a world difference.

For example, consider the sentence:

"I want to thank my parents, Serena Williams and Michael Jordan."

Without the Oxford comma after noun phrases such as "Serena Williams," the sentence could be misinterpreted as thanking your parents, who are Serena Williams and Michael Jordan. Therefore, the Oxford comma plays a role in maintaining clarity and precision in your writing.

comma use

Example: "We need to buy eggs, milk, bread, and cheese from the grocery store."

In this sentence, commas are used to separate the items in the list ("eggs," "milk," "bread," and "cheese"), making it clear to the reader that each item is distinct and separate from the others.

Commas with Coordinate Adjectives

When two or more adjectives are used to describe the same noun, they are referred to as coordinate adjectives and require commas to separate them. This helps avoid confusion as it ensures that each adjective is distinctly linked to the noun it modifies.

By inserting commas between the adjectives, you create a rhythm that guides the reader through the description smoothly. For instance, in the phrase "She wore a long, flowing dress," the commas serve to emphasize the individual qualities of the dress, enhancing the reader's visual image.

Example: "She lives in a charming, historic house."

In this sentence, "charming" and "historic" are coordinate adjectives modifying the noun "house." The comma between "charming" and "historic" helps to separate the two adjectives, indicating that they are distinct and equally modify the noun "house."

Commas in Compound Sentences

In compound sentences, which consist of two independent clauses joined by a coordinating conjunction, a comma is used before the coordinating conjunction. This comma, known as a coordinating conjunction comma, acts as a visual cue for readers, signaling a pause between the two clauses. It lets readers know that these are separate sentences that are in support of the same notion.

This pause helps to clarify the relationship between the clauses and aids in the overall comprehension of the sentence structure. For example, in the sentence "The sun was shining brightly, and the birds were singing joyfully," the comma before "and" indicates a natural break between the actions described, allowing the reader to digest the information more easily.

Example: "I went for a walk in the park, and I saw a beautiful sunset."

In this sentence, the comma is used before the coordinating conjunction "and" to separate two independent clauses ("I went for a walk in the park" and "I saw a beautiful sunset") that are joined to form a compound sentence.

Commas in Mental Action

Commas can be used with a verb expressing mental action in certain contexts, particularly when these verbs introduce indirect speech or clauses. When reporting what someone else has said, commas can be used after verbs that express mental actions, such as "think," "believe," "say," "assume," etc., before introducing the reported speech.

Example: She said, "I'll be there at 5 o'clock."

Avoiding Comma Splices and Run-On Sentences

As stated before, using a comma incorrectly can not only ruin the professionalism of your paper but also make it confusing and frustrating to read. The biggest errors are typically found with comma splices and run-on sentences, which hinder the clarity of your writing.

It is inevitable to make mistakes and fall into the pitfalls of comma splices and run-on sentences, but you have to be able to identify them to fix those mistakes rather quickly. Correcting these mistakes quickly can help elevate the quality of your prose to new heights.

writing with commas

Identifying Comma Splices

A comma splice refers to the incorrect use of a comma to join two independent clauses without a coordinating conjunction or appropriate punctuation. While the written clauses should have a more concrete pause in between them, they are joined by just a comma.

These errors can lead to confusion and disrupt the flow of your writing. To rectify this, you can either replace the comma with a semicolon or separate the clauses into two distinct sentences by putting a period in between them.

Delving deeper into the realm of comma splices, it's essential to grasp the nuances of sentence structure and cohesion. By honing your skills in recognizing these errors, you empower yourself to craft compelling and polished compositions that captivate your audience.

Correcting Run-On Sentences

Run-on sentences also occur when two or more relative clauses beginning a sentence are joined without appropriate punctuation or conjunctions. These sentences are often lengthy and convoluted, making it difficult for readers to know which ideas go where. The great thing about commas is that you can actually use them here, either with or without coordinating conjunctions, to break them into shorter, more digestible information.

Unraveling the complexities of run-on sentences unveils a world of opportunities for enhancing the clarity and impact of your writing. By embracing the principles of effective sentence structure, you embark on a journey toward creating prose that resonates with depth and precision.

Example: "I wanted to go to the concert, but I couldn't get tickets."

In this sentence, "I wanted to go to the concert" and "I couldn't get tickets" are both independent clauses joined by the coordinating conjunction "but." The comma before "but" helps to separate the two independent clauses, clarifying the structure of the sentence and improving readability.

Using Commas for Clarity

Commas with Introductory Elements

When a sentence begins with an introductory word, absolute phrase, or clause, it is crucial to use a comma to separate it from the main clause. This creates a separation between the two while simultaneously helping your reader understand how this relates to previous sentences. This simple punctuation mark not only helps in organizing the sentence but also aids in setting the tone for the rest of the text.

Moreover, correct usage of commas with these initial introductory elements, works to eradicate any ambiguity of what it is intending to accomplish. This practice is especially important in academic writing, where clarity and coherence are essential for effective communication.

Example: "Before starting his new job, John took some time off to travel."

In this sentence, "Before starting his new job" is the introductory element. The comma after this phrase helps to separate it from the main clause ("John took some time off to travel"), indicating to the reader that the introductory element is complete before moving on to the main part of the sentence.

Commas with Nonessential Elements

Nonrestrictive clauses, such as additional information or explanations within a sentence, should be set off by commas. This grammatical structure allows for a smooth flow of ideas within the sentence, preventing unnecessary interruptions that may hinder the reader's comprehension.

Furthermore, the strategic use of commas with nonessential elements adds depth to your writing by providing supplementary details without disrupting the main narrative. It showcases your ability to incorporate supporting information seamlessly, enhancing the overall quality of your composition.

using a comma

Punctuation with Commas

While commas on their own are essential, writing is an art that requires being able to weave different words and punctuations together. There are certain rules and regulations as to how commas are supposed to be intertwined with other common punctuation marks.

Commas with Quotation Marks

Surprisingly, if you are ever quoting anything in your written work, commas definitely come into play. In American English, commas and periods always appear inside the closing quotation marks; however, in British English, the punctuation marks are placed outside unless they are part of the original quotation.

Additionally, when a quotation is interrupted by a parenthetical element that requires a comma, the comma comes before the closing quotation mark, maintaining proper punctuation rules.

Example (American): She said, "I'll meet you at the restaurant at 6 p.m.," and then added, "Don't forget to bring the gift."

Example (British): She said, "I'll meet you at the restaurant at 6 p.m.", and then added, "Don't forget to bring the gift".

Commas with Parentheses

Whenever you are using parentheses to add a slight remark, information, or explanation, commas act as bookends to separate the parenthetical elements from the rest of the sentence.

Moreover, when a complete sentence is enclosed in parentheses, the period at the end of that sentence still goes inside the closing parenthesis, demonstrating the hierarchical relationship between punctuation marks.

Mastering the correct usage of commas is a valuable skill that will significantly enhance your writing. By understanding the rules and applying them effectively, you can communicate your ideas clearly, ensure reader comprehension, and create engaging and impactful written work.

Example: Sometimes (most times), I ride my bike to school.


Frequently Asked Questions About Commas

Do I need a comma after 'but' in a sentence?

Whether you need a comma after 'but' in a sentence depends on the context and structure of the sentence. In general, if 'but' is joining two independent clauses (complete thoughts that can stand alone as separate sentences), then you typically use a comma before 'but.' This helps to separate the two independent clauses and improve readability.

Does every sentence need a comma?

Not every sentence requires a comma. Whether a comma is needed depends on the sentence's structure and the elements it contains. Simple, short sentences may not necessitate commas if there are no distinct clauses or phrases requiring separation.

Similarly, commands or imperatives often do not demand commas unless clarity or emphasis is needed. In direct speech or quotations, commas are used as needed based on the quoted material's structure, but they aren't necessary in every sentence.

Can a comma replace a period?

While a comma and a period both indicate pauses in a sentence, they serve different purposes and cannot always be used interchangeably. A period typically marks the end of a sentence, indicating a complete thought or idea. On the other hand, a comma is used to separate elements within a sentence, such as clauses, phrases, or items in a list.

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Boston College
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About Fiza

Fiza is a dedicated writer and researcher with expertise in internships, scholarships, career opportunities, and financial aid. Her skills enable her to craft engaging and insightful content that guides students through the complex processes of applying for financial aid and pursuing career opportunities.

She graduated from Boston College, majoring in Applied Psychology and Human Development and Computer Science.


Fiza has experience in writing blog posts, SEO content, and creative storytelling. On her personal blog, she shares engaging narratives through personal anecdotes. Her international experiences have given her a global perspective, enabling her to connect with a diverse audience. Fiza is committed to making a meaningful impact through her writing, always considering the perspectives and experiences of others.

Since joining the team in 2022, Fiza has channeled her passion for guiding students through pivotal stages of their academic journeys. She understands the challenges associated with college life and is dedicated to helping students adjust to their degree programs and manage their finances. Motivated by her own experiences, Fiza is passionate about empowering students by providing guidance and support that she wished she had during her undergraduate years.

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