This part was requested by _ChatBug_.

What is a comma?

While a period ends a sentence, a comma indicates a smaller break. Some writers think of a comma as a soft pause—a punctuation mark that separates words, clauses, or ideas within a sentence.

Contrary to popular belief, commas don't just signify pauses in a sentence. Of all the punctuation marks in English, the comma is perhaps the most abused and misused. And it's no wonder. There are tons of rules about comma usage, and often the factors that determine whether you should use one are quite subtle. Unfortunately, I won't be able to cover all the rules here, but I will highlight what I deem are the most misused ways and the most important rules to remember.

Do note that I have previously mentioned in this section some ways to use commas (i.e, comma splices, the oxford comma, etc.), so this part will not touch upon those rules, but they are still important to know and understand.

Comma After Introductory Phrase

A comma normally follows participial phrases that introduce a sentence:

Correct: Grabbing her umbrella, Kate raced out of the house. Confused by her sister's sudden change in mood, Jill stayed quiet.

When an adverbial phrase begins a sentence, it's often followed by a comma but it doesn't have to be, especially if it's short. As a rule of thumb, if the phrase is longer than about four words, use the comma. You can also use a comma with a shorter phrase when you want to emphasize it or add a pause for literary effect.

Correct: After the show, Cleo will be signing autographs. Behind the building there is enough space to park two limousines. Without knowing why, I crossed the room and looked out the window. In 1816 life was very different. Suddenly, an angry black cat sprang from the shadows.

But, if there is a chance of misreading the sentence, use the comma:

Incorrect: Before eating the family said grace.

Correct: Before eating, the family said grace.

Commas with Interrupters or Parenthetical Elements

Interrupters are little thoughts that pop up in the middle of a sentence to show emotion, tone, or emphasis. A parenthetical element is a phrase that adds extra information to the sentence but could be removed without changing the meaning of the sentence. Both interrupters and parenthetical elements should be set off with commas.

Incorrect: The weather I was happy to see was beginning to clear.

Correct: The weather, I was happy to see, was beginning to clear.

Incorrect: Geoff's cooking skills if you can call them skills left something to be desired.

Correct: Geoff's cooking skills, if you can call them skills, left something to be desired.

Incorrect: It was sadly the last day of camp.

Correct: It was, sadly, the last day of camp.

Incorrect: Mary unlike Anne is very organized.

Correct: Mary, unlike Anne, is very organized.

Comma with a Question Tag

A question tag is a short phrase or even a single word that is added to the end of a statement to turn it into a question. Writers often use question tags to encourage readers to agree with them. A question tag should be preceded by a comma.

Correct: These willow trees are beautiful, aren't they? You didn't actually write a 600-page vampire romance novel, did you? I know, right?

Comma with Direct Address

When addressing another person by name, set off the name with commas.

Correct: Mom, I can't find my shoes! Cleo, there's someone on the phone for you. Hello, Chester.

Comma with an Appositive

An appositive is a word or phrase that refers to the same thing as another noun in the same sentence. Often, the appositive provides additional information about the noun or helps to distinguish it in some way. If you could remove the appositive without changing the meaning of the sentence, it is said to be nonessential and should be set off with commas. If the appositive is necessary, it's said to be essential and it should not be set off with commas.

Nonessential appositives:

Correct: My mother, Angela, is a wonderful cook. The painter, one of the city's most promising young artists, began showing his work in galleries before he was sixteen. Chocolate, my favorite treat, always makes me feel better after a bad day.

Essential appositives:

Correct: Edgar Allan Poe's poem The Raven is a classic. Alec Baldwin's brother Stephen is the most underrated Baldwin. The detective Sherlock Holmes is one of literature's greatest sleuths.

Comma After Introductory Adverbs

Correct: Finally, I went running.

Correct: Unsurprisingly, I saw a duck when I went running.

Many adverbs end in "ly" and answer the question "how?" How did someone do something? How did something happen? Adverbs that don't end in "ly," such as "when" or "while," usually introduce a dependent clause, which rule number two in this post already covered.

Also insert a comma when "however" starts a sentence, too. Phrases like "on the other hand" and "furthermore" also fall into this category.

Starting a sentence with "however," however, is discouraged by many careful writers. A better method would be to use "however" within a sentence after the phrase you want to negate, as in the previous sentence.

Comma Before Parenthesis

Parentheses are used to give additional information to the reader—information that would disrupt the flow of the sentence if written as a nonrestrictive clause. Commas may be placed after the closing parenthesis but not before either the opening or the closing parenthesis. If the sentence would not require any commas if the parenthetical statement were removed, the sentence should not have any commas when the parentheses are added.

Correct: After opening the new cookie tin, Chester had a hard time replacing the lid. After opening the new cookie tin (and eating several of the cookies), Chester had a hard time replacing the lid.

Incorrect: After opening the new cookie tin, (and eating several of the cookies), Chester had a hard time replacing the lid. After opening the new cookie tin (and eating several of the cookies,) Chester had a hard time replacing the lid.

Comma with As Well As

The phrase "as well as" usually doesn't require commas unless it's part of a nonrestrictive clause.

Correct: Please proofread for grammatical mistakes as well as spelling.

Correct: Spelling mistakes, as well as grammatical errors, are distracting to readers.

Comma with Such As

The phrase "such as" requires commas if it introduces a nonrestrictive clause.

Correct: Coniferous trees, such as pine and spruce, do not drop their needles in the winter.

If "such as" introduces a restrictive clause, omit the commas.

Correct: Trees such as pine and spruce do not drop their needles in the winter.

Comma Before Too

Using a comma before "too" is optional.

Correct: I like bananas too. I too like bananas.

A comma simply adds emphasis.

Correct: I like bananas, too. I, too, like bananas.

The Internet is a great resource if you feel the need to look up all the rules. I also suggest you check out the sources listed for this part in the References part.

If you learned something new, please give this part a vote!