How to Use Commas Correctly: Rules, Examples, and the Mistakes Almost Everyone Makes

Commas are the most frequently used punctuation mark in English writing and the most frequently misused. Understanding how to use commas correctly is one of the highest-impact writing skills you can develop, whether you're a student drafting an essay, an ESL writer working to produce natural-sounding English, or a content creator whose credibility depends on polished prose. This guide covers every major comma rule, shows you how each one works with clear examples, and explains the mistakes that trip up even experienced writers.

Why Commas Matter in English Writing

Commas do more than add pauses to a sentence. They organize information, separate ideas, prevent ambiguity, and signal grammatical relationships between parts of a sentence. A missing comma can change meaning entirely. A misplaced comma can make a sentence confusing or ungrammatical. Consider the classic example:

"Let's eat, Grandma." (An invitation to Grandma to eat with us.)
"Let's eat Grandma." (Something considerably more alarming.)

That single comma is the difference between a family dinner and a horror story. At a less dramatic level, comma errors in professional and academic writing signal carelessness to readers and editors, undermine the credibility of an otherwise strong piece of writing, and, for ESL writers, can obscure ideas that are expressed correctly in every other respect. For a comprehensive overview of all English punctuation, read our ultimate punctuation guide.

The Main Comma Rules: With Examples

Rule 1: Use a Comma Before a Coordinating Conjunction Joining Two Independent Clauses

When two independent clauses (complete sentences) are joined by a coordinating conjunction (for, and, nor, but, or, yet, so — remembered by the acronym FANBOYS), place a comma before the conjunction.

Correct: "She finished the report, and her colleague submitted it."
Correct: "He wanted to apply for the position, but the deadline had passed."
Incorrect: "She finished the report and her colleague submitted it." (Missing comma before "and.")

Note that this rule applies when both sides of the conjunction are independent clauses, meaning each could stand alone as a sentence. If the second part is not an independent clause, no comma is needed: "She finished the report and submitted it."

Rule 2: Use a Comma After an Introductory Element

When a sentence begins with an introductory word, phrase, or clause before the main subject and verb, place a comma after the introductory element.

Correct: "After reviewing the data, the team revised their conclusions."
Correct: "However, the results were not statistically significant."
Correct: "To improve clarity, the editor restructured the opening paragraph."
Incorrect: "After reviewing the data the team revised their conclusions." (Missing comma after introductory phrase.)

Short introductory elements of one or two words (such as "First," "However," or "Indeed,") also require a comma, particularly when the introductory word is a conjunctive adverb or transition word.

Rule 3: Use Commas to Separate Items in a List

When listing three or more items in a series, place a comma after each item except the last. The comma before the final "and" or "or" is called the Oxford comma or serial comma.

With Oxford comma: "The report covered sales, marketing, and operations."
Without Oxford comma: "The report covered sales, marketing and operations."

Whether to use the Oxford comma depends on the style guide you are following. APA, Chicago, and most academic and business style guides recommend it. AP style, used in journalism, does not require it. When in doubt, use it. The Oxford comma prevents ambiguity and is rarely wrong. For more on the rules around related punctuation marks, read our article on apostrophes and hyphens.

Rule 4: Use Commas to Set Off Non-Restrictive Clauses and Phrases

A non-restrictive clause or phrase adds information to a sentence but is not essential to the sentence's meaning. Set it off with commas on both sides. A restrictive clause, by contrast, is essential to the sentence's meaning and should not be set off with commas.

Non-restrictive (use commas): "My editor, who has a PhD in linguistics, reviewed the manuscript." (The clause "who has a PhD in linguistics" adds information but is not essential to identifying who the editor is.)
Restrictive (no commas): "The editor who reviewed the manuscript has a PhD in linguistics." (The clause "who reviewed the manuscript" identifies which editor, so it is essential and should not be set off.)

The distinction between "which" and "that" is closely related to this rule. "That" introduces restrictive clauses (no commas). "Which" introduces non-restrictive clauses (use commas). "The report that was submitted last week contained errors" vs. "The report, which was submitted last week, contained errors."

Rule 5: Use Commas to Set Off Parenthetical and Transitional Expressions

Words and phrases that interrupt the flow of a sentence to add a comment, clarification, or transition should be set off with commas on both sides.

"The study, however, did not control for age."
"This approach, in our view, is the most effective."
"The findings, to put it simply, were inconclusive."

Common parenthetical expressions include: however, therefore, moreover, for example, in fact, of course, on the other hand, in contrast, and as a result. These expressions require a comma both before and after when they appear in the middle of a sentence.

Rule 6: Use a Comma to Separate Coordinate Adjectives

When two or more adjectives each independently modify the same noun and could be joined by "and," they are called coordinate adjectives and should be separated by a comma.

Correct: "She delivered a clear, concise presentation." (Clear and concise both independently describe the presentation.)
Correct: "It was a long, difficult editing process."
No comma needed: "She wore a bright red jacket." (Bright modifies "red jacket" as a unit, not the jacket independently, so no comma.)

A quick test: if you can insert "and" between the adjectives and the sentence still makes sense, they are coordinate and need a comma. "A clear and concise presentation" works, so the comma is correct. "A bright and red jacket" sounds unnatural, so no comma is needed.

Rule 7: Use a Comma to Set Off Direct Address

When addressing someone directly by name or title, set off the name or title with a comma. This is the rule illustrated by the Grandma example at the start of this guide.

"Thank you, Dr. Carter, for your feedback."
"Please review this section, James, before we submit."
"Let's begin, everyone."

Rule 8: Use a Comma to Separate Contrasting Elements

When a sentence contains a contrasting element introduced by "not," "but," or "yet," set it off with a comma.

"It was the methodology, not the findings, that reviewers questioned."
"She revised the introduction, not the conclusion."

Rule 9: Use a Comma in Dates, Addresses, and Numbers

Commas follow specific conventions in dates, addresses, and large numbers:

Dates: "The study was published on March 15, 2023, in the Journal of Applied Research." (Note the comma after the year when the date appears in the middle of a sentence.)
Addresses: "The conference was held in Chicago, Illinois, in October." (Comma after the state when it appears in the middle of a sentence.)
Numbers: Use commas to separate groups of three digits in large numbers: 1,000; 25,000; 1,250,000.

The Most Common Comma Mistakes

Even experienced writers make these errors consistently. Knowing them by name helps you avoid them in your own writing and catch them in review.

The Comma Splice

A comma splice occurs when two independent clauses are joined by a comma alone, without a coordinating conjunction. This is one of the most common grammatical errors in English writing.

Comma splice: "The results were promising, the team decided to proceed."
Corrected with conjunction: "The results were promising, so the team decided to proceed."
Corrected with semicolon: "The results were promising; the team decided to proceed."
Corrected by separating: "The results were promising. The team decided to proceed."

The Missing Oxford Comma

Omitting the Oxford comma can create genuine ambiguity, particularly when the final items in a list could be interpreted as a pair.

Without Oxford comma: "I'd like to thank my editors, Patty Frank and Dr. Carter." (This could mean the editors are Patty Frank and Dr. Carter, or it could mean something else entirely.)
With Oxford comma: "I'd like to thank my editors, Patty Frank, and Dr. Carter." (Now clearly three separate parties.)

The Comma After "And"

Placing a comma immediately after a coordinating conjunction is almost always incorrect.

Incorrect: "She reviewed the draft, and, sent her comments."
Correct: "She reviewed the draft and sent her comments."

The Missing Comma After an Introductory Element

This is one of the most common comma errors among students and ESL writers. When a sentence begins with an introductory phrase or clause, the comma after it is not optional.

Incorrect: "Before submitting the application she proofread it three times."
Correct: "Before submitting the application, she proofread it three times."

Using a Comma to Separate a Subject From Its Verb

Do not place a comma between a subject and its verb, even if the subject is long or complex.

Incorrect: "The study published last year in the Journal of Applied Research, found no significant effect."
Correct: "The study published last year in the Journal of Applied Research found no significant effect."

Comma Rules for ESL Writers

For writers whose first language is not English, comma usage is particularly challenging because comma conventions differ significantly across languages. In some languages, commas are used more sparingly than in English. In others, they appear in places where English does not use them. A few specific points for ESL writers:

In English, do not place a comma before "that" when it introduces a restrictive clause: "The article that I cited was published in 2021" (no comma before "that").
In English, conjunctive adverbs like "however," "therefore," and "moreover" used at the start of a sentence are followed by a comma: "However, the results differed."
In English, do not place a comma between a verb and its object: "She decided, to revise the draft" is incorrect. "She decided to revise the draft" is correct.
Introductory phrases in English almost always require a comma: "In addition to the survey data, interviews were conducted."

FAQs

How do you use commas correctly?

The most important comma rules to master are: use a comma before a coordinating conjunction joining two independent clauses, after an introductory element, to separate items in a list, to set off non-restrictive clauses, to set off parenthetical expressions, and to set off direct address. Avoiding the comma splice, using the Oxford comma, and not placing commas between subjects and verbs cover the most common errors. For a focused list of practical comma tips, read our article on eight comma tips for writers.

What is a comma splice and how do you fix it?

A comma splice is the error of joining two independent clauses with only a comma. To fix it, add a coordinating conjunction after the comma, replace the comma with a semicolon, or separate the clauses into two sentences. Comma splices are one of the most common grammatical errors in student and professional writing and one of the first things editors and instructors look for.

Should you always use the Oxford comma?

In most contexts, yes. The Oxford comma, the comma before the final "and" or "or" in a list, prevents ambiguity and is required by APA, Chicago, and most academic and business style guides. AP style, used in journalism, does not require it. When no specific style guide is required, using the Oxford comma is the safer choice because it rarely creates problems and sometimes prevents genuine misreading.

When should you not use a comma?

Do not use a comma between a subject and its verb, between a verb and its object, before "that" in a restrictive clause, immediately after a coordinating conjunction, between two adjectives where the first modifies the second as a unit (such as "bright red"), or to join two independent clauses without a coordinating conjunction (which creates a comma splice).

What is the difference between a restrictive and a non-restrictive clause?

A restrictive clause is essential to the meaning of the sentence and identifies which person or thing is being discussed. It is not set off with commas. A non-restrictive clause adds information that is helpful but not essential to the sentence's meaning. It is set off with commas on both sides. The words "that" and "which" signal this distinction: "that" introduces restrictive clauses (no commas), while "which" introduces non-restrictive clauses (commas required).

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