Commas are tricky things.
Writers can use commas to make sentences easier to understand, easier to read out loud, or as a way to show their personality.
Sometimes commas have strict rules, while sometimes commas are an option.
English speakers have full arguments over whether or not we should always use an Oxford comma. So it’s understandable if you’re confused.
Here are the three most common ways to use a comma:
Lists and Oxford (or Serial) Commas
I enjoy using an Oxford comma, which is the kind you use in a list of 3 or more items. Sometimes it is also called a serial comma.
My favorite animals are horses, dogs, red pandas, and cows.
That final comma is the Oxford comma. It’s not always necessary but it is helpful. I almost always use it because there definitely are sentences that need this type of comma.
I love my friends, Adele and George Clooney.
Does this mean I’m friends with Adele and George Clooney?! Unfortunately, I’m not friends with Adele or George Clooney. Therefore, a much clearer sentence would be this:
I love my friends, Adele, and George Clooney.
Adding the Oxford comma at the end of this list makes it clear that I love my friends, but I also love Adele and George Clooney. There are writers, however, who will say that the Oxford comma in this type of example means the whole sentence should be re-written to explicitly clarify that I’m not friends with Adele.
Separate Two Independent Clauses With a Comma and a Conjunction
If you have two complete sentences that can stand alone but are related, you can use a comma and a conjunction.
These are the most common conjunctions:
and, for, but, or, so, yet, while
Just remember that you need two independent sentences to use the comma before a conjunction.
Apples are my favorite fruit, but I like oranges after a workout.
I love to travel, yet I prefer to sleep in my own bed.
Use Commas After Introductory Phrases or Words
An introductory word or phrase gives context to a sentence. Using a comma here will increase clarity of the situation or emphasize the timing of events.
The introductory phrase (or word) helps the reader understand why or how the second part of the sentence takes place.
Tired from her run, Kate sat in the kitchen.
Confused by his response, Emma didn’t know what to do.
Suddenly, the lights went out.
Each of these introductory phrases changes how you understand the sentence.
Kate could be sitting in her kitchen for many different reasons. However, now we know that she probably doesn’t have enough energy to go anywhere else until she rests in the kitchen for a little bit.
I’ve covered the most frequent comma usages here. If you’re looking for an even more thorough explanation on commas, here is an article from Grammarly.