This guide is meant to give you, as a writer, a thorough foundation in comma usage. I won't cover every use, but I will go over a majority of them, all of which are worth knowing.
As far as this tutorial's subject matter is concerned, I feel comfortable explaining about ninety percent of what follows. However, I want this to be as accurate as possible, so I've gone to other sources online to back me up (primarily to fill in the gaps of my knowledge in terminology). I've included the links to these sources immediately below as well as in the author's description. I will refer to them throughout the tutorial by their source number (Source 1, Source 2, etc). If you wish to better your grammar even further, I particularly recommend grammarbook.com (Sources 2 and 3). Note that all the examples I give in this tutorial were not taken from the sources; they are my own.
Food for thought:
Published writers misuse commas and break other grammatical rules all the time. Why? Because they have reasons for doing so (usually to guide a reader into reading a sentence in a particular way). You can add a comma here or take one from there in your prose, even if it's incorrect; but when you do, it has to be for a reason.
One of the most common (and easily fixed) misuses of the comma has to do with compound sentences. But first, what is a compound sentence?
- A compound sentence is a sentence made up of two parts (two independent clauses) that have been connected by coordinating conjunctions (and, but, for, or, nor, yet, so). Basically, these types of sentences:
1) Jenny snatched the hat from my head, and she ran away with it.
2) Nick could go to the movies, or he could stay home.
3) Nathan called it a night, but Martha was just getting started.
- Does this structure look familiar? Good. The examples listed above have commas splitting them up, correct? Notice the words I put in bold? These words (the subjects) are the reason for the commas. Since it restates who is doing the action, you need to put a comma. However, if one were to not restate who is in action, then the comma wouldn't be needed. For example...
1) Jenny snatched the hat from my head and ran away with it. (Notice how I got rid of "she?" This is why there is no comma)
2) Nick could go to the movies or stay home. (This time I got rid of "he could," so no comma).
3) Nathan called it a night, but Martha was just getting started. (This time I couldn't get rid of the comma and the name. Why? Because we need to state that it's Martha who's just getting started instead of Nathan. You can only omit the comma and name if it is a single person or object continuing in action).
This is a well-known one, but I think it's worth bringing up. If you're making a list of three or more actions or objects, you need commas separating the items from each other. For example...
1) Jimmy grabbed the fork, dug it into the cake, and shoved the dessert into his mouth. (Commas after "fork" and "cake").
2) I picked up eggs, milk, flour, and cookies at the store today. (Commas after "eggs," "milk," and "flour")
- As you can see, it's a simple concept. However, there is a debate as to whether there should be a comma before the final item (in this case, the commas immediately following "cake" and "flour") or not. Grammatically speaking, it is acceptable to omit it. However, including it isn't wrong either, and if anything, it aids in reader comprehension (which, between you and me, is a desirable thing).
- But there is one loophole to this rule. If all the actions or objects have the word "and" between them, then you don't need any commas. For example...
3) The dog ran ahead and stopped and lifted its leg.
4) I picked up the chip and held it and looked at it and ate it.
- Doing this can sometimes be an effective choice, but if you're not careful, it can easily sound stupid. The dog example isn't too bad (though using commas and only the one "and" would have been better), but the chip example is plain ridiculous. Just know you can do it if the situation requires.
Here is the one I see most people never catching. It has to do with description. Here's the rule: whenever more than one word (usually adjectives) describes another, you need to separate them with commas. For example:
1) Anna pulled out an old, dirty jacket. (Both "old" and "dirty" describe "jacket," so they need a comma between them).
2) The big, red ball slammed into Eric's face. (Both "big" and "red" describe "ball," so throw in a comma between them).
- Here's where things get a little tricky...
3) The woman flipped her honey blonde hair. (This time I didn't need a comma. This is because "honey" and "blonde" don't both describe "hair." "Honey" actually describes "blonde," so no comma is needed).
4) He slapped on his cherry red cap. (Same as the last one: "cherry" describes "red," not "cap," so no comma).
- If you have trouble deciding whether you need a comma or not, Jane Straus (the author of Sources 2 and 3) says that if you can put "and" between the two words without changing the meaning, then you need a comma.
1) Anna pulled out an old and dirty jacket. (The word "and" fits between the adjectives, so yes, a comma is needed).
2) The woman flipped her honey and blonde hair. (As you can see, "and" doesn't fit at all unless you meant to say she was flipping honey as well as blonde hair. No comma is needed).
Any questions regarding comma usage in dialogue can be found in The How To's of Dialogue: Grammar and Otherwise.
Sentences beginning with Dependent Clauses:
According to Source 3, dependent clauses (the author refers to them as "weak clauses") begin with words like although, since, if, when, because. If a sentence begins with a dependent clause, you need a comma at the end of that clause. You can tell something is a dependent clause if it cannot function as a sentence by itself. Let's identify some...
1) If I were to slap you... (See, not a full sentence. It is, therefore, a dependent clause)
2) Because I dislike crowds... (Once again, this isn't a sentence. It's just the beginning of one).
3) Although John likes apples...
4) As Nick ate the hot dog...
- Now that we've identified the dependent clauses, let's finish the sentences by joining them with the independent clauses (the part of the sentence that can stand alone as its own sentence). I have put the dependent clauses we are familiar with in bold.
5) If I were to slap you, would you hold it against me? (Once again, the comma is at the end of the dependent clause, which is "if I were to slap you").
- Note that dependent clauses beginning with "if" are easy to catch, as they're all scenario questions. "If I did this," "if the water was green," etc.
6) Because I dislike crowds, I avoid big cities.
7) Although John likes apples, he doesn't like apple cider.
8) As Nick ate the hot dog, he wished it was a bratwurst.
- Not too bad once you get the hang of it. If you play close attention, you'll also notice that there tend to be natural pauses where these commas appear. Don't use these pauses as the primary identifiers, but be aware of them.
has reminded me of a fact worth clarifying. If the independent clause comes first, then no comma is needed to separate the two elements. Here are some examples with the dependent clauses still in bold.
1) Would you hold it against me if I were to slap you?
2) I avoid big cities because I dislike crowds.
- See? So just for clarification, it is only when the dependent clause comes first that you need a comma.
If there is a phrase in your sentence that isn't vital to the sentence's meaning, you want to surround it with commas. Source 4 refers to these phrases as parenthetical phrases. They signal a digression of sorts, and they can sometimes be easy to identify because they often use words like "which" or "who." Each example will show you the sentence with the parenthetical phrase and then without it.
1) With the Phrase: The roller coaster, which was old and rickety, was our next destination.
Without the Phrase: The roller coaster... was our next destination. (See how the sentence functions fine without the parenthetical phrase? Commas are necessary to separate it).
2) With the Phrase: Johnny, who hated rides, refused to go on the roller coaster.
Without the Phrase: Johnny... refused to go on the roller coaster. (Although the parenthetical phrase illuminates why Johnny won't go on the roller coaster, it still doesn't serve a vital purpose in the sentence's interpretation. Put in the commas)
- However, not all parenthetical phrases start with "who" or "which". For example...
3) With the Phrase: The Ferris Wheel, that old and rickety ride, was our next destination.
Without the Phrase: The Ferris Wheel... was our next destination. (Still no problem taking the parenthetical phrase out, so commas remain necessay)
4) With the Phrase: Johnny, the guy with the weak stomach, refused to go on the roller coaster.
Without the Phrase:
refused to go on the roller coaster. (Once again, the parenthetical phrase isn't necessary, so use commas)
- However, sometimes this excess information can become vital to the sentence's interpretation. In such cases (often involving person identification), commas cannot be used.
5) With the Phrase: The guy who had a weak stomach refused to go on the roller coaster. (Once again, note that there are no commas)
Without the Phrase: The guy... refused to go on the roller coaster. (The sentence may seem to make sense, but who is this "guy"? "The guy" is just too vague; we have no clue which guy they are talking about. That's why "who had a weak stomach" becomes vital to the sentence. It identifies who is refusing to get on the roller coaster. Therefore, if the parenthetical phrase becomes necessary to identify an object or person, then you can't put commas around it.)
6) With the Phrase: It was Kate's husband, John, who was playing cards.
Without the Phrase: It was Kate's husband... who was playing cards. (Note that "John" is unnecessary, so we put commas around it. John is unnecessary because Kate can only have one husband. Whether his name is there or not, we still know who it is playing cards)
7) With the Phrase: Kate's daughter Cara was glaring at her twin.
Without the Phrase: Kate's daughter... was glaring at her twin. (You'll notice that there are no commas surrounding "Cara". This is because without "Cara," we have no clue which of Kate's twins is glaring at the other. Her name, therefore, becomes vital, and commas cannot be used).
If the word or phrase forces a pause/digression (similar to those caused by the parenthetical phrases) in the middle of a sentence, then commas should surround it.
1) I would say, therefore, that you are guilty!
2) I enjoy playing Duck Hunt. I would not, however, go hunting.
3) I suppose, all things considered, you did an okay job.
4) I, of course, would never do that!
A comma splice is a grammatical no-no. It's basically when you use a comma when you should instead be using an ending punctuation mark (period, question mark, exclamation point) or a semicolon. To reference Source 2, it's when two independent clauses are connected solely by a comma. Here are some examples of comma splices and their simple solutions.
1) Comma Splice: I decided to try lutefisk, it was not agreeable. (Incorrect)
Correct Form: I decided to try lutefisk; it was not agreeable. (Corrected: a semicolon)
I decided to try lutefisk. It was not agreeable. (Corrected: a period)
I decided to try lutefisk, but it was not agreeable. (Corrected: a conjunction to make it a compound sentence)
2) Comma Splice: Johnathan received anthrax in the mail, he died. (Incorrect)
Correct Form: Johnathan received anthrax in the mail; he died. (Corrected: a semicolon)
Johnathan received anthrax in the mail! He died. (Corrected: an exclamation point)
Johnathan received anthrax in the mail, and he died. (Corrected: a conjunction to make it a compound sentence)
If you're comparing two contrasting ideas, then it becomes necessary to put a comma between them for distinction.
1) You say tomato, I say tomahto!
2) Mac likes pie, not cake.
Sentences beginning with words like Yes, Well, Therefore, However:
Often enough, if you begin a sentence with one of these words, you'll need a comma immediately after that word. For example:
1) Yes, I do enjoy long walks on the beach.
2) No, I wanted Diet Coke. ("No" rarely fits this rule, but it does when it's the answer to a yes-or-no question)
3) Well, I suppose we could go to the pier.
4) Therefore, you shall die!
5) However, I have been known to drink recreationally.
- I'll next show you an exception to this rule. You'll be able to identify these exceptions since a comma after the opening word would violently contort the sentence in both fluidity and meaning.
6) However you look at it, we're in a pickle. (See? no comma after "however". You may notice that I put a comma after "it," but that's only because "However you look at it" is a dependent clause, which, as we established earlier, merits its own comma.)
- Now let's see what this sentence would look like with a misplaced comma after "However"...
7) However, you look at it, we're in a pickle.
- See? Try saying that while pausing for the commas. Doesn't sound normal, and it doesn't make much sense, does it? Just be wary while following the rule; don't assume there will be a comma just because a sentence begins with these words. Instead, let it be a strong signal for you to test the waters.
According to Source 5, an absolute phrase is a phrase made up of a noun and its modifiers. Commas are necessary to separate them from the rest of the sentence. In the following examples, I will put the absolute phrases in bold. Note that in these phrases, almost all the verbs they contain will be conjugated to end in "ing".
1) Bert glared at him, nostrils flaring. (Comma after "him")
Nostrils flaring, Bert glared at him. (Comma after "flaring")
2) Jim smiled nervously, his brow sweating, his heart racing.
His brow sweating, his heart racing, Jim smiled nervously. (This time there are two absolute phrases side by side, "his brow sweating" and "his heart racing". Note that the commas separate the absolute phrases from the text as well as each other)
3) The baby played in the garden, his hands probing the soil, his fingers seeking out worms, until his mother took him inside. (This time I placed the two absolute phrases in the middle of the sentence, resulting in a total of three commas for complete separation).
Absolute Phrases without the Subject:
For the following explanation, know that every verb has a subject. A subject is the noun that is put into action by the verb. For example, in the phrase "John ate an apple," the subject is "John" since he is the one eating the apple. That being said...
If you ever think something is an absolute phrase but the subject of the verb is outside of the phrase, still put commas around it. Note that this verb will still end in "ing". Here are some examples so you get an idea of what I'm talking about.
1) Margaret made her way towards the store exit, pushing through the crowd. (Who is pushing? Margaret is, so Margaret is the subject. Even though "Margaret" is outside of the phrase in bold, we still need that comma after "exit" to separate the phrase).
2) Looking around to make sure Mom was gone, Sally made a mad dash for the cookie plate. (Comma after "gone")
3) Billy raised his hand, not understanding, and asked a question. (Note that there are commas on both sides of the phrase since it interrupts the middle of the sentence).
"Having" done something:
Separate such phrases from text with commas. Remember that it's not the word "having" that guarantees commas; it's having done something. For example...
1) Having finished my meal, I rose and left.
2) I threw in the towel, having lost all hope.
3) John had no choice, having been challenged, but to accept.
Single words that answer how one feels:
If you have a single word describing a character's emotions in your text that fits this model...
"He/she was [insert emotion]"
... but it's not tied to any verbs like "was," you need to use commas to separate it.
1) Nicole stared at the lottery ticket, shocked. (Notice how "shocked" has no verbs tied to it? Do you also feel how disconnected it is from the subject, "Nicole"? The fact it's dangling by itself like this is what makes it require comma separation).
Shocked, Nicole stared at the lottery ticket. (Like always, moving it to the other end of the sentence doesn't change the need for a comma).
Model: "She was [shocked]"
2) Billy slammed the door shut, furious.
Furious, Billy slammed the door shut.
Model: "He was [furious]"
3) Matt stared at his date, dumbstruck.
Dumbstruck, Matt stared at his date.
Model: "He was [dumbstruck]"
4) Jenna blinked, confused, and gave him a questioning look. (As you can see, this can occur in the middle of the sentence as well. Put a comma on each side of the word).
Model: "She was [confused]"
Directly addressing someone:
When directly addressing someone, separate their name or title with commas.
1) I bestow upon you, Arthur, the Excalibur!
2) William, keep it down!
3) It's about time you be heading home, son.
4) Please, sir, may I have another!
Separating statements from Questions:
According to Source 2, if you have a statement and a question paired together, a comma needs to separate the two elements. Here are some examples. The statement will be normal text, the question in bold.
1) You'll be there for the big game, won't you?
2) You enjoyed the movie, right?
- Also note that even though half the sentence is a statement, you still end it with a question mark.