Commas don’t have to be confusing.
After all, you know what a comma is: the punctuation used to mark a division in a sentence, like the separation of words, phrases, a clause, or a sequence.
And commas often accompany a conjunction, which is a word that connects phrases, clauses, or sentences (e.g., and, because, but, and however) or any other words or expressions that provide a similar function (e.g., in any case).
The trick is knowing how to properly use commas and conjunctions together.
This cheat sheet will help explain exactly when commas and conjunctions should be used together, and why it matters (without—we hope—putting you into a comma-induced coma).
Know your clauses
The use of a comma has a lot to do with the clauses you’re combining. Two clauses that typically need a comma between them are an independent clause (a clause that could be its own stand-alone sentence) and a dependent clause, which cannot stand alone.
Consider this example:
- We could still see the cat, which was following 10 feet behind us.
The first half, We could still see the cat, is an independent clause, because it can stand alone as its own sentence. The second half, which was following 10 feet behind us, is a dependent clause, because it cannot be its own sentence. It is dependent upon the clause in the beginning of the sentence to make sense.
Know your conjunctions
In addition to the conjunctions mentioned way above, there are also coordinating conjunctions. These are the words that can connect two independent clauses.
There are seven total: for, and, nor, but, or, yet, and so. These always require a comma.
An easy way to remember all seven is by using the acronym FANBOYS.
What is a relative pronoun?
A relative pronoun is a word that is used to refer back to a previously mentioned noun. Relative pronouns are often used to join sentences. Which, that, whose, whoever, whomever, who, and whom are the most commonly used ones.
Here is an example:
- The writer who wrote this article has a cold.
In this sentence, who is the relative pronoun that refers back to the noun the writer.
(Hang in there. We’re getting back to commas soon.)
What is a dependent adverbial clause?
A dependent adverbial clause, or subordinate adverbial clause, is a clause that also acts as, or modifies, an adverb. It cannot stand alone as its own sentence, so dependent adverbial clauses must be used as part of a larger sentence structure that contains an independent clause.
Look at this sentence:
- The mouse returned when we turned off the lights.
When we turned off the lights is the dependent adverbial clause, and the mouse returned is an independent clause.
After all that, how do you know when two clauses need a comma to separate them, and when you can do without?
Check out our comma cheat sheet
Did you use a coordinating conjunction like and, but, and or to link two independent clauses? If so, add a comma like we did in this example:
- We didn’t get to it, but tomorrow is a new day.
Did you use a relative pronoun like who, whom, which, what (or one of their compounds -ever or -soever) with a clause that is essential for identification? If so, leave out the commas, as we did in this example:
- The boy who is playing the clarinet is very talented. (Which boy is it? Here, the instrument is an essential piece of information.)
- Pro tip: if you are not sure if your clause is essential, see if deleting it changes the meaning of your sentence.
- For example: Anton, who plays both the clarinet and piano, is very talented. Since we have specific information about the boy (Anton), the clause is no longer essential. It takes a comma.
Did you use a relative pronoun like that, that was not essential for identification? If so, then no comma:
- The skirt that I bought yesterday is already ripped.
Did you use an dependent adverbial clause before an independent clause? If so, add a comma as in this example:
- When I cook, my kids sit at my feet. (My kids sit at my feet is the independent clause, when I cook is the dependent adverbial clause.)
Did you use a dependent adverbial clause after an independent clause? If so, then you do not need to add a comma.
- The cow eats grass when we look away. (The cow eats grass is the independent clause, when we look away is the dependent adverbial clause.)
Fun fact: the conjunctions even though, whereas, though, and although do take a comma when they are part of a dependent adverbial clause that follows an independent clause.
- She really wanted to take out the trash, even though it wasn’t full.
Good news, you CAN start sentences with conjunctions!
And, if you are using a conjunction at the beginning of a sentence (like we just did), you should only put a comma after it if it is going to be the first in a series of commas. That means that if the only comma your sentence is going to have is the one you put in after the initial conjunction, you should remove it.
For example, you would not need to use a comma after your opening conjunction in the sentence below, because the comma after the word and would be the only one in the sentence:
- And that was the end of the matter.
However, you would need to use one after the opening conjunction in the sentence below, because the sentence calls for a series of commas:
- So, she told the truth anyway, even though she knew it would end her career.
Comma and non-conjunctions: so and too
How do you use commas when it comes to words like so and too (or any other non-conjunctions that are joining clauses mid-sentence)?
When it comes to using the word so, the rule of thumb is that if it begins your independent clause, there should be a comma. However, if it is at the beginning of a dependent clause, you can skip the comma.
Still unsure if you should use a comma? Try switching out the word so with either therefore or so that. If therefore works, then the comma is needed.
- My sister was tired all day, so she went to bed early requires a comma because it is similar to saying My sister was tired all day, therefore she went to bed early.
If so that can be used without changing the meaning, then you will want to skip the comma.
- I went to the beach so I could get a better view of the sunset works just the same as saying I went to the beach so that I could get a better view of the sunset.
Since either way works, you do not need a comma.
As for the word too, it all depends on the emphasis you are looking for. A comma only needs to appear before the word too if you are using it to mark a shift of thought in the middle of a sentence like in the example: I, too, like cats. But it’s not needed at the end of the sentence: I like cats too.
Some of these rules are easier to remember than others, but with practice—and this guide—you’ll soon be debating comma placement like the best of them. Just be wary of those “Oxford or not” debates. They’re not for the faint at heart!