Before directly diving into comma rules, there are some terms that we need to know.
Sentence Structure
Sentence structure refers to how a sentence is formed. A complete sentence consists of words, clauses, phrases, and other elements that provide information or a complete thought.
Clauses
A clause is a group of words that contains a subject and a verb. There are two types of clauses:
Independent Clause
These are clauses that can stand on their own, meaning they provide a complete thought.
Example: She enjoys painting. (This sentence makes sense by itself.)
Dependent Clause
These clauses do not provide complete information on their own and depend on an independent clause for meaning. Dependent clauses often begin with subordinating conjunctions such as after, although, as, because, before, even though, if, since, unless, until, when, where, and while.
Example: Because it was raining. (this thought feels incomplete until paired with an independent clause).
Phrases
Phrases are groups of words that do not have a subject or a verb, and they do not express a complete thought. Phrases provide additional information about the subject of the sentence.
Example: Under the bright moon(a prepositional phrase), the children played. (This phrase adds detail to the sentence but cannot stand on its own.)
Compound Sentences
A compound sentence consists of two independent clauses joined by a conjunction (such as FANBOYS: For, And, Nor, But, Or, Yet, So).
Example: Sarah baked cookies, and her brother helped clean the kitchen.
Comma Splice
A comma splice occurs when two independent clauses are joined by a comma.
Incorrect: She went to the store, she bought apples.
This error can be improved by using a semi-colon or comma + fanboys.
Correct: She went to the store, and she bought apples. (Comma + FANBOYS)
Or: She went to the store; she bought apples. (Semicolon for two independent clauses without conjunction)
Sentence Fragment
A sentence fragment is an incomplete sentence that is missing a subject or a verb or does not express a complete thought.
Incorrect: Running to the store. (Missing a subject)
Correct: She was running to the store.
FANBOYS and Commas
FANBOYS stands for For, And, Nor, But, Or, Yet, So, and these words are used to join two independent clauses with a comma.
Example: The sun was shining, so we decided to go hiking.
How to Use Comma
1. Joining Two Independent Sentences
When you need to connect two independent clauses (complete sentences), you can do so by using a comma followed by one of the FANBOYS: For, And, Nor, But, Or, Yet, So. This rule helps avoid the error known as a comma splice.
Incorrect: The sun is shining, we are going for a walk.
Correct: The sun is shining, so we are going for a walk.
2. Dependent Clause Followed by an Independent Clause
If a dependent clause comes before an independent clause, place a comma after the dependent clause.
Correct: Because it was late, we decided to head home.
3. Unnecessary Information (Non-essential Clauses)
Unnecessary information is information that can be removed without changing the meaning of the sentence. If the information is unnecessary to understand the main point of the sentence, it should be surrounded by commas.
Example: The cat, which had a white tail, was sleeping on the porch. (Removing the clause “which had a white tail” doesn’t change the meaning of the sentence.)
“That” vs “Which” Phrases
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“That” phrases never get commas because they provide the necessary information.
Example: The car that she bought is red. (The phrase “that she bought” is essential to know which car.)
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“Which” phrases always get commas. They provide extra, unnecessary information that can be removed without changing the main meaning.
Example: Her car, which is red, is parked outside. (The phrase “which is red” just adds extra information, but it’s not essential to know which car.)
Exception with Prepositions and “Which”
When a preposition is followed by “which,” the comma depends on whether the information is necessary or not:
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If the information is necessary, no comma.
Example: The picnic table on which the food was resting was tipped over.
(The phrase “on which the food was resting” is necessary to identify the specific picnic table.) -
If the information is unnecessary, use a comma.
Example: The donation box at the Kindergarten Library, in which over 30 books were being stored, mysteriously disappeared. (The phrase “in which over 30 books were being stored” is extra information, and removing it doesn’t change the overall meaning.)
4. Using “Where” Phrases
When using “where” in a sentence, you need to decide if the information is necessary (essential) or not (non-essential). This determines whether you use commas:
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Necessary information: No commas are used because the “where” phrase is essential to the meaning of the sentence.
Example: The city where I was born is very small. (The phrase “where I was born” is necessary to specify which city, so no commas are used.)
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Unnecessary information: Use commas when the “where” phrase just adds extra details that are not needed to understand the main point.
Example: My favorite restaurant, where I always order pizza, is just around the corner. (The phrase “where I always order pizza” is extra information, and you can remove it without changing the basic meaning of the sentence.)
5. Commas with City, State, and Country Names
When writing city and state (or country), use a comma after the city name and after the state or country name.
Example: I moved to Dallas, Texas, last year. (Comma after “Dallas” and “Texas.”)
If you’re using a country instead of a state, the same rule applies.
Example: She visited Paris, France, during the summer. (Comma after “Paris” and “France.”)
6. Commas with Names
Whether you need a comma around a name depends on how specific the person is in the sentence:
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If the name is specific, and we already know who you’re talking about, use commas.
Example: My brother, Jake, is coming home today. (Since you only have one brother, the name “Jake” just adds extra detail, and you use commas.)
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If the name is not specific, and the sentence doesn’t clearly identify the person, don’t use commas.
Example: My friend Sarah is coming over later. (Since “friend” is not specific, you don’t use commas around “Sarah.”)
Comma Rules for Conjunctive Adverbs
Conjunctive adverbs are words that connect ideas between two sentences. Some examples include: However, Therefore, Instead, Moreover, Likewise, Nevertheless, In addition, and As a result
1. When the conjunctive adverb is at the beginning of a sentence
Place a comma after the conjunctive adverb.
Examples:
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However, she decided to stay home.
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Therefore, the meeting was rescheduled.
2. When the conjunctive adverb is in the middle of a sentence
Put a comma before and after the conjunctive adverb.
Examples:
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He was, however, unsure about the answer.
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The team, as a result, won the game.
3. When connecting two independent sentences
Use a semicolon before the conjunctive adverb, followed by a comma.
Formula: Independent sentence + semicolon + conjunctive adverb + comma + Independent sentence.
Examples:
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She wanted to leave early; however, the train was delayed.
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We planned to go hiking; instead, we stayed inside due to the rain.
4. When the conjunctive adverb is at the end of a sentence
In this case, the conjunctive adverb refers back to the previous sentence.
Examples:
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He usually loves spicy food. He wasn’t feeling well today, though.
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Sarah offered to help. We appreciated her efforts nevertheless.
Comma Rules for Prepositional Phrases
Prepositional phrases start with a preposition and end with a noun. They can appear at the beginning, middle, or end of a sentence. Whether or not you need a comma depends on whether the information in the phrase is necessary or not.
Some common prepositions are: in, of, to, for, with, on, at, from, by, about, as, into, like, through, after, over, between, during, before, among, around
1. When the prepositional phrase adds unnecessary information:
If the information isn’t needed to understand the sentence, put a comma around the phrase.
Example: My sister, with her long brown hair, is always noticed in a crowd.
Here, the phrase doesn’t change the meaning of the sentence since we already know which sister we’re talking about.
2. When the prepositional phrase adds necessary information:
If the prepositional phrase is essential to the sentence’s meaning, don’t use a comma.
Example: The keys in the red box belong to the shed.
In this case, the phrase tells us which keys we’re referring to, so no comma is needed.
Comma Rules for Lists
When listing multiple items in a sentence, we use commas. Here are some rules to follow:
1. Listing three or more items
Place a comma between each item when there are three or more items.
Examples:
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Correct: I need to buy apples, oranges, and bananas.
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Incorrect: I need to buy apples, and bananas.
It is easy to be confused while using comma + fanboys when listing two items using commas. Make sure that the sentence after the comma is always an independent sentence.
Example:
Correct: She packed her bag, and she left for the trip.
Incorrect: She packed her bag, and left for the trip.
3. Comma with adjective lists
When listing adjectives that describe a noun, if the adjectives can be switched without changing the meaning, use a comma between them.
Examples:
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Correct: He wore a warm, cozy sweater.
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Correct: She had a bright blue car.
In the first sentence, “warm” and “cozy” can be switched to “cozy, warm sweater,” so a comma is needed.
In the second sentence, “bright” and “blue” describe different things (bright is describing blue, not the car itself). So, no comma is needed because switching them would change the meaning.