Some people say that commas often act as breaks in the flow of sentences to "breathe." However, they're intended to subdivide trains of thought and logical connections. Most use commas to clearly express a statement and use them without paying attention to grammatical rules if they contribute to clarity. So there are just "lucky" people out there who have some kind of "gut feeling" for proper comma usage. For those of you who are still stumbling through the grammar jungle (and don't worry - the majority of both native speakers and language learners struggle with grammar rules), we'll go through all these ten rules for you!
But before we head over to the comma usage here, we should explain the two terms "Independent Clause" and "Dependent Clause," since these two terms will come up quite often in this article, and it would be beneficial for you to know the exact meaning.
An independent clause is a sentence that contains a subject (f.e. "I," "my brother," "Steve," "the football team") and a verb ("play," "say," "read," etc.), and therefore can stand on its own as it completes a thought.
I just had dinner.
The dog was barking.
My sister is sleeping.
A dependent clause, however, as the name suggests, depends on another clause to make sense, even though it still contains a subject and verb. Those clauses either begin with subordinating conjunctions, relative pronouns, or name specific people, things, places, and ideas (--> "noun clauses").
When we arrived at school
If we leave early
Since 8 o'clock
Whom I met at work
Where I went to school
That was made in Germany
Whatever you choose
Whether she wanted or not
How he made it
Intuitively we want to know what happens next. This is why a dependent clause can't stand on its own and needs another sentence or clause to be comprehensible. We can either combine a dependent clause with an independent one or only use independent clauses and add them together for more complex sentences.
So, since we've got a bit of background info now, let's head over to the actual comma rules:
When you have two (or more) independent clauses, you combine them with (coordinating) conjunctions such as for, and, nor, but, or, so, and yet. It's essential, however, not to forget the comma before the conjunction.
For more than ten years, he's been working in that company.
For her own sake, she decided to stop smoking.
I was late for school today, and I'd forgotten to do my homework.
Her father was a dentist, and her mother worked as a journalist.
No one knew what to do, nor did they try to find a solution.
He wasn't allowed to own a pet as a child, nor play with the neighbor's dog back then.
My cat tried to steal food from my plate, but there was no food left.
I would've called you yesterday, but my phone's battery had died.
I'd suggest you stay quiet, or you can leave this class immediately.
You can buy your own textbook, or you can rent one from the university's library.
I've decided to clean up my apartment today, so I don't have to do it tomorrow.
We'd never been to that place before, so we were afraid not to arrive there on time.
He was a complete bully, yet he was convinced to have plenty of real friends.
I rarely did my homework in high school, yet I became one of the top ten best students.
But there's one crucial thing to note: if those two independent clauses are relatively short and combined with and or but, you can but don't have to skip the comma:
I prepared dinner and she set the table.
I prepared dinner, and she set the table.
She fell asleep but he kept talking.
She fell asleep, but he kept talking.
Complex sentences that consist of an independent and dependent clause are punctuated in the following two ways:
1) If the dependent clause comes at the beginning of the sentence, place a comma after it. (i.e., before the independent clause)
While the rain fell, the baby slept.
2) If the dependent clause comes at the end of the sentence, there's no comma.
The baby slept while the rain fell.
A comma is also used after introductory subordinate clauses, phrases, and words. This can be seen well by "taking a break" at this point while reading.
If you have a question, don't hesitate to ask.
When you want to leave, call me to pick you up.
To stay in shape for competition, athletes must exercise every day.
On my way to work, I like to listen to audiobooks.
As a matter of fact, we were paying attention.
Hoping to pass the exam, he studied day and night.
Therefore, I strongly recommend taking my advice.
Alternatively, you could borrow one of Beth's dresses.
You set a comma when inserting a word/phrase or a subordinate clause. An insertion means that something is inserted in the middle of the sentence.
Sarah, with whom I've worked for four years now, unexpectedly quit her job today.
Harold, who never believed in ghosts, swears he saw one yesterday evening in the hotel he's currently staying.
We, as a matter of course, have to check your alibi.
Our new colleague at work is, to put it mildly, quite keen to loudly express his opinion.
I have, however, found it extremely difficult to deal with.
He knows, perhaps, half the answers to today's exam.
There is also a comma for appositions. An apposition is an explanatory noun or an explanatory note that is placed next to a reference word (noun or pronoun). The comma rule only applies to appositions that contain more than one word.
Queen Victoria, one of England's greatest monarchs, ruled for sixty-three years.
My teacher, Ms. Smith, is from Wisconsin.
James, the boy with the blue sweater over there, is my best friend.
You use a comma when three or more words, phrases, or main sentences follow one another - or when two or more coordinating adjectives follow one another. (Coordinating adjectives are adjectives that "work together" to describe a noun)
Don't forget to buy some flour, olive oil, toothpaste, and toilet paper!
I bought this dress in 4 different colors: black, royal blue, rosé, and white.
I've packed a bathing suit, sunscreen, a towel, etc.
The table was adorned with golden plates and cutlery, beautiful bouquets of dried flowers, and skillfully folded napkins.
You could tell by the expression on her face that she wasn't in a good mood, hadn't slept for days, and had not yet had her coffee.
She came home from work, had a quick shower, fell into her bed, and sunk into a deep sleep.
That's what I'd do if I won the lottery: I'd quit my job, buy a new car, look for a lovely house to live in, and treat myself to a chocolate cupcake.
She was a kind, warm, friendly woman.
The happy, fluffy dog wagged his tail.
Steve was a headstrong, lively child.
The Oxford (or serial) comma is the final comma in a list of things. There isn't a strict rule of thumb for using this comma, but it helps to make the sentence easier to understand:
Emma's favorite pizza toppings are tuna, artichokes, and pineapple and ham.
Here, the comma indicates that the pineapple and ham flavor is one of Emma's favorite toppings, not pineapple or ham. The list includes three pizza toppings, not four.
Commas are also used in combination with "yes," "no," and "please."
Could you help me, please?
No, I don't know the answer.
Yes, I'd appreciate another cup of coffee.
Please, believe me!
Don't forget to use commas when directly addressing someone - either in person or in written form (letter, email, etc.)
You also use commas after a farewell in letters and emails.
Dear Emma, I hope you're well.
Mrs. Roberts, it was nice meeting you.
Thank you, Paul, for all your help!
Best regards, Will Kingsley.
Excuse me, could you tell me the way to the next bus stop?
Kelly, can you help me with my homework?
You also use a comma together with a question tag.
The weather is lovely today, isn't it?
Hand me the screwdriver, will you?
He's such a handsome young man, don't you think?
When you choose to include a direct quotation, you must not forget to use a comma!
Descartes said, "I think, therefore, I am."
And that's when he shouted, "You're a wizard, Leroy!"
"I'm not hungry," I told my mom.
If you plan on indicating a pause at the end of a sentence, the comma is the way to go.
He was merely ignorant, not stupid.
I didn't mean to hurt him, only making a point.
She wasn't in a bad mood, just hungry.
Whether you're writing a novel and describing a scene or directly quoting someone - if you stumble upon interjecting sentences, always use a comma!
Wait, I didn't mean to scare you!
Oh no, I spilled milk all over my new dress!
Yes, I'd like another cup of tea, thank you.
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