For some reason or other, I paid serious attention when my middle school teacher taught us about comma rules. I’m not saying I’m a comma expert or anything, but I have been known to give lots of comma corrections while editing. And it’s come to my attention that maybe not everyone knows the comma rules. (Thanks for being honest, Allie.)
So, let’s explore the mighty comma in all its glory and learn how it functions so we have fewer red pen marks from our editors!
Why are there so many comma rules?!
I’m with you, guys. There are a wealth of comma rules that make them so darn confusing. The function of a comma is to add clarity to a sentence. Sometimes, they act as breaths or pauses in a sentence’s flow. (Hot tip: just because you want there to be a pause in a sentence doesn’t mean a comma should go there.)
It can be tricky to remember all the rules—even editors need to look them up sometimes! You are not alone in your confusion, so please don’t feel discouraged. We’re here to help. And no, we’re not going through aaallll the comma rules!
Commas and coordinating conjunctions
Real quick review: coordinating conjunctions are and, or, but, nor, yet, for, and so. When any of these are present in a sentence AND the sentence consists of two independent clauses, you must use a comma.
ex. We learned about commas, but we forgot most of the rules.
The clauses in this sentence are independent, meaning they each contain a subject and a predicate. They can be separated by a period and still be complete sentences. (We learned about commas. We forgot most of the rules.) If you’d like to incorporate these two thoughts into one sentence, you add a comma followed by a coordinating conjunction.
A note: Sometimes, if one or both of the independent clauses are short, a comma isn’t needed. (ex. She was scared and she ran.) But this is a personal preference.
When conjunctions DON’T receive a comma
If the second part of the sentence does not have a subject, you do not need to put a comma before the coordinating conjunction.
ex. We learned about commas but forgot most of the rules.
In this instance, the subject (we) is implied in the second phrase. “Forgot most of the rules” is an incomplete sentence and, therefore, cannot stand on its own. Commas are not necessary for these sentences.
A sentence with a subordinating conjunction does not need a comma. Subordinating conjunctions link a dependent clause to an independent clause. Some of the most common subordinating conjunctions are after, although, as, as if, because, before, how, if, since, than, though, unless, until, when, where, and while.
ex. She likes to drink coffee while she dresses in the morning.
Note that if the dependent clause “while she dresses in the morning” was put at the beginning of the sentence, it WOULD need a comma (see below: introductory clause).
Commas and so
So can be a tricky conjunction. A quick rule of thumb is this:
- If you can put “so that” in the sentence, then so is a subordinating conjunction and DOES NOT need a comma.
- If you can substitute so with “therefore,” then so is a coordinating conjunction and DOES need a comma.
Subordinating: He adjusted the rearview mirror so (that) he could see better.
Coordinating: I published a book, so I’m an author now. or I published a book, therefore I’m an author now.
Commas and introductory phrases, clauses, or words
You have your main clause, which includes the subject and predicate. Sometimes, though, we like to get fancy and introduce an introductory phrase, clause, or word into the equation. Use a comma between an introductory phrase/clause/word and the main clause.
Introductory phrases and introductory clauses are similar. While an introductory clause has its own subject and verb, an introductory phrase does not. In either case, a comma is needed.
Introductory phrase: Every morning, she needs a large cup of coffee.
Introductory clause: While she dresses in the morning, she likes to drink her coffee.
Introductory word: Today, she drank the whole pot of coffee.
Using commas to offset a non-essential phrase
For phrases, clauses, or words that aren’t essential to the meaning of the sentence, offset them with commas. If the non-essential phrase is in the middle of the sentence, place one comma before the phrase and one comma after the phrase.
ex. My brother, Bill, ran a marathon last week.
ex. My library book, which is terribly overdue, is lost somewhere in my house.
In both examples, the phrases offset by the commas are not necessary to the sentence. Each sentence still makes sense if you take out those phrases.
Commas and essential phrases
If the phrase is essential to the sentence’s meaning, do not use a comma to offset it. An example of this would be phrases beginning with That—also known as relative clauses.
ex. It’s important that you not add a comma to this sentence.
The phrase “that you not add a comma to this sentence” is essential. Without it, the meaning of the sentence would change. The reader wouldn’t know what was important.
Comma rules for lists
The Oxford comma
We’re probably all familiar with the use of commas to separate listed items in a sentence. However, there are a couple of ways to format these—with or without the Oxford comma.
With an Oxford comma: She brought chips, dip, and brownies to the picnic.
Without an Oxford comma: She brought chips, dip and brownies to the picnic.
Technically, either option is correct, though the Oxford comma is a point of contention for many people. (Currently, as I write this, Grammarly is yelling at me with its red line in my example without the Oxford comma…) Whether or not you use an Oxford comma, keep things consistent. It’s also worth noting that your editor may or may not correct your commas in lists depending on the style guide they use.
Multiple descriptor comma rules
There are two different comma rules when we use multiple adjectives to describe the same noun. If there are two or more coordinate adjectives in a sentence, each adjective should be separated by a comma. Coordinate adjectives are equal in status, meaning their order can be switched and the sentence will still make sense. Another tip: if you can separate the adjectives with “and,” they are coordinate adjectives and need a comma between them.
ex. The large, hairy dog barked at the mailman. or The hairy, large dog barked at the mailman. or The large and hairy dog barked at the mailman.
Sometimes, a sentence has multiple non-coordinate adjectives. Non-coordinate adjectives are not equal; one adjective is more important than the other and must be ordered in a specific way. Otherwise, the sentence won’t make sense. For sentences with two or more non-coordinate adjectives, a comma is not necessary.
ex. She wore a red wool sweater to the concert.
If you think too hard about this rule, it gets more and more confusing. Use this website for a quick reference on coordinate and non-coordinate adjectives. Or just ask an editor or certified grammar nerd for help!
Comma rules conclusion
Commas clarify. But if used incorrectly, they just add confusion. Like all grammar rules, sometimes comma rules can be broken. But be sure it’s an intentional choice that doesn’t affect the integrity of the sentence.
That’s all she wrote!
About the Writer: Brigid Levi is a freelance writer and editor based in the Philadelphia area. She has three children, a husband-child, and a dog. When she’s not freelancing or working on her own writing, Brigid can be found under all the blankets with coffee, tea, or wine (depending on the time of day) and a sweeping historical fiction novel. She hopes to publish her YA fantasy/adventure novel in the near future! Find out more about Brigid on her website.
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