Punctuation matters if you want to deliver a precise and crisp message. It may seem that there is nothing that hard in using commas; however, comma rules might be really tricky.
We’ve set up a list of comma rules, and examples of embarrassing mistakes that will help you to enhance your writing style and avoid misunderstanding.
Rule #1. You need a comma before coordinating conjunction linking two independent clauses
A group of words that can easily serve as a separate sentence is called an independent clause. When you want to combine two such independent clauses in one sentence using a coordinating conjunction (and, but, or, so, etc.), there should be a comma before this coordinating conjunction.
I went to the mall to score new boots, but I failed to find my size.
Both clauses in this sentence could stand alone as separate sentences. Coordinating conjunction but combines them into one sentence, so we should use a comma.
Rule #2. A comma is used to separate items
When you have a sentence with a list of items, you should separate them with commas.
John was obsessed with parties, girls, and sports cars.
If you have such a queue, you should use a comma to separate it. However, there are slight differences in comma usage in different English styles. Look at the example above, see a comma before “and”? It is called “Oxford comma,” and some styles require its usage or not.
For example, the style guide for newspaper reporters called AP Style does not require its use. However, in American and Canadian English, it is a common thing to use the Oxford comma. So, if you are writing in American English, it is better to stick with it.
Here is what can happen if you fail to follow this rule:
Rule #3. A comma is used to join dependent and independent clauses
If in your sentence there are two clauses, and one depends on another and follows it, you should not separate them with a comma. But in the case when a dependent clause stands at the beginning of a sentence, it is right to put a comma before the clause it depends on.
You should read more if you’re going to become a journalist. (The dependent clause follows the one it depends on, so no comma is needed.)
If you’re going to become a journalist, you should read more. (The dependent clause starts the sentence, so the comma is needed after it).
Rule #4. You should use commas after introductory words
Sometimes you need an introductory word (“however”) or group of words (“on the other hand”) to start your sentence. There might be different reasons for it, including providing more information and preparing the reader to the main part of a sentence. The rule is that a comma should follow such words and group of words.
Finally, I had enough money to buy this car.
Tip: it is common to use adverbs as introductory words, and lots of them end in “ly.” So, if you have a word ending in “ly” at the beginning of your sentence, be sure to put a comma after it.
Rule #5. Use a comma in sentences beginning with “Yes” or “No”
This one is a quite simple rule. If you have “yes” or “no” at the beginning of a sentence, you need a comma after them. Easy.
Yes, I’d like to have some more ice cream.
Rule #6. A comma is used when you need to interrupt a sentence to provide more information
When your sentence is interrupted by a phrase that is not grammatically connected with it, you need to set this phrase off with commas.
This car I told you about, which had this nice built-in audio system, was bought yesterday by some banker.
It is really important to follow this rule.
Rule #7. You should use a comma with direct quotatio
It is a simple rule many people often forget to follow. When you see a direct quotation, be sure to use a comma.
“I’d rather die than accept this job offer,” she told her friend.
Exact punctuation here is a matter of style, similar to the Oxford comma. In the American and Canadian English, it is common to put the comma inside the quotation mark, while the British style accepts placing the comma after it.
Rule #8. Commas separate elements in an address
When you are writing an exact address with building number, road, city, and state, it is correct to separate these elements with commas.
Our new office is located at 350 Lincoln Road, Miami Beach, FL 33139.
Rule #9. Use a comma to separate elements in dates
The same as with addresses, when you have a sentence with weekday, month, day, and year mentioned, comma rules tell that you need to separate them.
Sunday, March 3, 2019, was a day we’ve finally launched our Chrome and Firefox browser extensions.
Tip: you need a comma after the date as well, it will separate it from the rest of the sentence. However, if your date consists only of day and month, you don’t need to use a comma as a separator.
Rule #10. You need to use commas with titles
If you write a person’s name followed by his or her title, you need to put one comma before it, and one after to separate it from the remainder of the sentence.
Kimberly Johnson, a TV host, is now running for a major in her home town.
Rule #11. You need commas in numbers as well
When you have a number longer than four digits, use commas to separate them into groups of three. You should count three digits from the right.
Rule #12. Use commas with negations
If your sentence contains a negation, i.e. “the contradiction or denial of something” as dictionaries explain it, you need to set it off with commas.
I went to Barcelona, not Madrid, for my vacation this year.
Tip: you still need a comma even if the negation occurs at the end of your sentence.
Rule #13. Always use a comma for direct address
When you need to address someone or something in a sentence directly, it is correct to put a comma before it.
You should allow more privacy on Facebook, Mark.
Look at what will happen if you fail to follow this rule:
Rule #14. Use commas to separate coordinate adjectives
If two adjectives independently modify a noun, they are called coordinate adjectives, and you need to separate them with a comma.
If you can put “and” between adjectives or rearrange them, and the sentence will still make sense, then you have coordinate adjectives and need to separate them with a comma.
Travel is a fun, exciting way to spend your time. (You can add “and” or rearrange adjectives with no harm to the sense of a sentence.)
Rule #15. Appositive adjective require commas
In English, there is such a thing as an appositive adjective. It is used to emphasize the description of a noun or pronoun and follows them. You need to use commas to set them off.
Hugo Boss, the type of perfume he preferred, was the one she always loved.
You can meet such constructions in fiction or academic writing. It is undesirable to use appositive adjectives in your writing as they make it wordy and harder to read.