How to Use Commas
The comma is arguably the most important punctuation mark. Comma rules might make your head spin at first, but it becomes more intuitive once you learn the basics. Scroll through all the rules, or use the following links to jump ahead.
Items in a Series and the Serial Comma (Oxford Comma)
Rule: Use commas to separate items in a series of three or more.
Choose your weapon. I have two guns, a hammer, six knives, and a spiked bat.
Note that the comma separating the last item is called a serial or Oxford comma. The Chicago Manual of Style recommends its usage to avoid confusion:
He killed his parents, Joe Exotic and Carol Baskin.
Without the serial comma, it is unclear whether he killed his parents AND Joe AND Carol or if Joe and Carol are his parents.
He killed his dad, Joe Exotic, and Carol Baskin.
This sentence is still ambiguous. Is Joe Exotic his dad? In cases like this, where an item can be mistaken for an appositive, use conjunctions (connector words: and, but, so, for, yet, etc.).
He killed his dad and Joe Exotic and Carol Baskin.
If the items in the list are long or include paired items, you can use both conjunctions and commas to clarify.
You can take a gun and the hammer, or the bat and a knife, or just the two guns and nothing else.
Commas with Independent and Dependent Clauses
Between Two Independent Clauses
Rule: Use a comma and coordinating conjunction (for, and, nor, but, or, yet, so) to separate two independent clauses (complete sentences).
I killed the zombies, and I burned their bodies in the yard.
If the clauses are very short and closely connected, the comma is not necessary.
Save bullets and stab zombies.
Between Independent and Dependent Clauses
Comma usage between independent and dependent clauses depends on which comes first.
Dependent Clauses and Subordinate Conjunctions
A clause has a verb and a subject. The difference between independent and dependent clauses is that independent clauses form complete thoughts and can therefore stand on their own. A dependent clause does not form a complete thought and depends on an independent (main) clause.
Dependent clauses generally start with subordinating conjunctions (or conjunctive phrases), which are words or phrases that show the relationship between dependent and independent clauses; for example,
Relationships in time: since, until, as long as, as soon as, before, after, when, as, while
While you were sleeping, we killed the rest of the zombies.
Comparisons or degree: than, rather, other, otherwise, as, else, as much as, as far as, as well as
They're all dead as far as I can tell.
Condition or assumption: if, though, unless, except, without, once
Once the zombies leave, we can get out of here.
Reason or concession: as, why, because, for, since, though, although, albeit
I can't come with you because I was bitten.
Purpose or result: that, so that, in order to, such that
I killed him so that he wouldn't kill us.
There was an exit where we saw that big sign that said EXIT.
Manner: as if, as though
You run from zombies as if you've never seen one before.
Indirect questions: whether, why, when
She did not know whether they would make it out alive.
Back to commas...
Dependent Clauses at the Beginning
Rule: When a dependent clause comes before an independent (main) clause, it is followed by a comma.
After he killed them, he buried their bodies in the field.
Dependent Clauses at the End
Rule: When a dependent clause comes after the main clause, a comma is usually not needed.
She took a nap after she finished burying the bodies.
If the dependent clause is nonrestrictive (not essential) or used to emphasize contrast, it is preceded by a comma.
She loved cats, although she hated people.
Dependent Clauses in the Middle
This one's a little tricky. Pop quiz:
Which of the following sentences has correct comma usage?
a. He was starting to get antsy, and after Shelly told him about the lack of water, he decided it was time to move.
b. He was starting to get antsy, and, after Shelly told him about the lack of water, he decided it was time to move.
c. He was starting to get antsy and, after Shelly told him about the lack of water, he decided it was time to move.
Let's look at the sentence without the dependent clause.
He was starting to get antsy, and he decided it was time to move.
We already learned that two main clauses are joined by a comma and coordinating conjunction. Now squeeze the dependent clause in there.
HINT: You will later see how additional words/phrases/clauses in the middle of sentences are surrounded by commas.
Answer: Technically, b is correct, but the second comma between the conjunctions (and/after) is not necessary and looks choppy, so answer a is preferred. The additional comma in b, however, may be used for emphasis or clarity.
Rule: When a dependent clause stands between two clauses joined by a coordinating conjunction (for, and, nor, but, or, yet, so), a comma follows the dependent clause, but the conjunctions need not be separated.
Commas with Nonrestrictive Elements
Rule: Use commas to separate nonrestrictive (nonessential) elements from the main clause; for example,
She went to bed early, exhausted from a long day of killing zombies. (nonrestrictive: comma)
She went to bed early, but, stressed about how many people died that day, she couldn't fall asleep. (nonrestrictive: commas)*
She always went to bed exhausted from killing zombies. (restrictive: no comma)
*(Note that the comma after but in the second example is not necessary and is often omitted unless needed for emphasis or clarity.)
Benjamin, with his machete, went to hunt zombies. (nonrestrictive: commas)
Benjamin went to hunt zombies with his machete. (restrictive: no comma)
Parenthetical Elements (always nonrestrictive)
His accidental death was, to say the least, disappointing.
We will need to burn his body, of course.
If a stronger break is needed, or if there are commas within the parenthetical element, use dashes or parentheses instead.
He packed extra weapons (a big knife, a crowbar, and two hand grenades) and went hunting alone.
Examples of other nonrestrictive elements are mentioned below.
Commas with Appositives
My cousin, Lavinia Fisher, was a serial killer.
In the above example, Lavinia Fisher is an appositive. An appositive is a word, phrase, or clause that is placed in apposition (side-by-side) with a noun that it serves to rename or identify.
Rule: Set off appositives with commas only if they are nonrestrictive (not necessary in identifying who or what you are talking about).
My cousin, Lavinia Fisher, was a serial killer. (nonrestrictive: I have only one cousin.)
My cousin Lavinia Fisher was a serial killer. (restrictive: I have more than one cousin, so the appositive is necessary to identify which one.)
Commas with Relative Clauses
Relative clauses provide information about whomever or whatever it is you're talking about. These clauses start with that/which/who/whom/whose. Comma usage depends on whether the clause is restrictive or nonrestrictive. Restrictive relative clauses specify/define the noun.
Rule: Use commas to separate relative clauses from the rest of the sentence only if they are nonrestrictive.
The zombies, which were growing in number by the second, were coming from the east. (nonrestrictive)
The man we met yesterday, whose name I can't remember, is now one of them. (nonrestrictive)
I saw the zombie that killed my friend. (restrictive: no comma)
That vs. Which
In American English, that (or who/whom/whose) is typically used with restrictive clauses (no comma), and which (or who/whom/whose) is used with nonrestrictive clauses (with comma). See examples above.
In British English, which is often substituted for that.
Commas with "Such as" and "Including"
Commas usage with such as and including depends on whether the information they introduce is restrictive (essential to the meaning of the main clause).
Rule: Use commas to set off nonrestrictive information following such as or including.
Loud activities, such as singing or skipping, should be avoided. (nonrestrictive: commas)
Everyone, including the baby, was eaten by zombies. (nonrestrictive: commas)
Activities such as singing or skipping should be avoided. (restrictive: no commas)
Commas with "For example"
Rule: For example, that is, namely, and other similar expressions should be followed by a comma and preceded by an em dash or semi-colon. Alternatively, the entire phrase can be enclosed in parentheses or em dashes.
When fighting zombies, you should protect vulnerable body parts; for example, arms and legs.
Vulnerable body parts (for example, arms and legs) should be covered when fighting zombies.
When using abbreviations i.e. (“that is”) and e.g. (“for example”), enclose the phrase in parentheses.
The smell of zombies (i.e., rotting flesh) sticks to your clothes for weeks.
Commas with Introductory Elements
Rule: Separate introductory words/phrases/clauses with a comma; for example,
Dripping with blood, she took a deep breath in and smiled.
Rejuvenated by her evening bloodbath, she danced all night long.
Before eating, the family members played games.
A comma should not be used if the phrase is introducing an inverted sentence (when the verb is before the subject).
Before the children stood a dog with three heads.
After Jacob returned from his killing spree, he took a long nap.
Introductory Words (e.g., yes, no, OK, well)
Yes, you may use the washroom.
No, you may not remove your blindfold.
OK, you can remove your blindfold but not your handcuffs.
Well then, what are you waiting for?
A comma usually follows an exclamatory oh or ah unless it is followed by an exclamation mark (or a dash) or forms part of a phrase (e.g., “oh boy,” “ah yes,” "oh yeah?").
Ah, what a lovely day for an exorcism!
The comma is sometimes eliminated in informal prose or dialogue.
Oh yes I will!
Note: if the introductory phrase/clause is short (no more than four words), the comma is optional.
Before dinner they danced around the fire.
However, there are instances when the comma is needed for clarity.
Before eating the family members played games. (A comma could be useful here.)
Commas with Coordinate Adjectives
When a noun is being modified by more than one adjective, comma usage depends on if the adjectives are coordinate or cumulative.
Cumulative Adjectives build on each other to further modify the noun; for example, the little old lady.
Coordinate Adjectives modify the noun separately. It doesn't matter what order they are in.
Rule: Separate coordinate adjectives with commas.
To test if adjectives are coordinate, try inserting and between them or switching their order. If the sentence still sounds right, they are coordinate and need a comma.
She's a smart, funny lady.
She's a smart and funny lady.
She's funny and smart lady.
She's a little old lady.
She's a little and old lady. (Sounds weird.)
She's an old and little lady. (Sounds weird.)
Commas with Dates
For the month-day-year style, comma usage depends on what information is given.
Both the day of the week and the year are set off with commas.
Monday, October 31
October 31, 2021
Monday, October 31, 2021
If only the month and year are given, no comma is needed.
No comma is needed for a named holiday + year.
For the day-month-year system (standard British) no comma is needed to set off the year.
Commas with Correlative Conjunctions
Correlative conjunctions are conjunctions that work in pairs. For example,
either . . . or
neither . . . nor
both . . . and
whether . . . or
not only . . . but also
Rule: Correlative conjunctions are not usually separated with commas.
You can take either the gun or the knife.
Whether you take the gun or the knife is up to you.
She took both the gun and the knife.
She's not only angry but also spoiled.
Exceptions: Correlative conjunction pairs are sometimes separated with commas if the commas serve another grammatical function; for example, to set off a nonrestrictive element.
Neither the gun, which had only one bullet, nor the knife was enough for her.
OR if the pair joins two independent clauses.
She not only likes guns, but she also likes knives.
Commas with "However," "Therefore," and "Indeed"
However, therefore, thus, hence, indeed, accordingly, and besides are common examples of conjunctive adverbs. Conjunctive adverbs connect and show relationships between two complete thoughts.
Rule: When conjunctive adverbs are used to join two independent clauses, they should be preceded by a semicolon and followed by a comma.
The zombies were fun to kill; however, the smell of rotting flesh was overbearing.
Rule: Unlike conjunctions, these adverbs can be moved around in a sentence and can therefore introduce, interrupt, or conclude a sentence. Separate these adverbs with commas.
She loved to kill zombies. She didn't, however, because she could no longer stand the smell.
Exception: If the break is weak, or if the adverb is essential to the meaning of the clause, skip the comma.
Your mom called and wants you home right after school. You will therefore not have time to hunt zombies today.
Not listening to her mom was a mistake indeed.
Can You Start a Sentence with "However"?
The short answer is yes. As stated above, conjunctive adverbs can be used to introduce, interrupt, and conclude sentences.
You can kill me if you want. However, I'm the only one who knows how to get out of here.
That said, not everyone agrees with this usage. The Chicago Manual of Style (CMOS) is okay with it but considers however to more ponderous and less impactful than the word but.
You can kill me if you want. But I'm the only one who knows how to get out of here.
According to CMOS, "however is more effectively used within a sentence to emphasize the word or phrase that precedes it."
You can kill me if you want. You will, however, regret it.
It's really up to you and your style preference. Maybe your character is more likely to use however at the beginning of a sentence than in the middle. Or maybe they would say but instead. If you really don't want to risk it, you can always follow the rules above and precede with a semi-colon.
You can kill me if you want; however, I'm the only one who knows how to get out of here.
Note that when using however to mean "in whatever way," or "no matter how," do not follow with a comma.
However tired you feel now, it's only gonna get worse the longer we go without food and water.
Commas with "Too" and "Either"
When using too and either to mean "also," you don't need a comma unless misreading is likely. Too in the middle of a sentence is usually set off with commas.
He turned into a zombie; his girlfriend did too.
His family didn't know what to do; I didn't either.
They, too, didn't want to kill in order to live.
Commas with Direct Address
Use a comma to set off words or names used in direct address.
Jack, are you still alive?
Go to Hell, Jack!
Good evening, boils and ghouls!
This, my friends, is gonna be one hell of a ride!
Commas in Place of Words
A comma is sometimes used in place of words.
Last week we killed eight zombies; this week, eighteen.
If the context is clear, the comma may be omitted.
He scared her and she him.