Fixing commas seems to take up a lot of my time as an editor; the manuscripts I’m working on often become littered with comments like “cut comma” and “insert comma here.”
Most writers use commas correctly when making lists, separating direct quotes, and inserting them in dates and addresses, but there are other uses that can cause confusion. So, here is a quick reference guide to my top five uses for commas and the common mistakes associated with them.
1. Use commas after an introductory word, phrase, or clause that is not the subject of the sentence.
“After weeks of waiting, I finally saw Captain Marvel in the theatre.”
“Until he learned he was a wizard, Harry Potter’s life was bleak.”
The mistake: Inserting commas after a word group that functions as the subject when it looks like an introductory phrase.
“Hoarding gold in her den
, is one of a dragon’s most important goals.”
2. Use commas in front of a coordinating conjunction (such as and or but) that joins two independent clauses.
“I sent my daughter to the store for eggs, but she came back with a book of spells instead.”
“Aang is an airbender, and Katara is a waterbender.”
The mistake: Omitting the comma. The important thing to remember here is that the coordinating conjunction joins two independent clauses, which means they can stand alone as their own complete sentences (e.g. “Aang is an airbender. Katara is a waterbender.”).
3. Use commas between coordinate adjectives.
Coordinate adjectives come before a noun or pronoun. They can be joined by and or their order can be changed without messing up the sentence.
“This funny, brave, persistent woman is named Ginny Weasley.”
The adjectives here could easily be joined by and: “This funny and brave and persistent woman is named Ginny Weasley.”
The mistake: Using commas when the adjectives are cumulative, which means they modify the ones that follow it.
For example, “Ginny Weasley, world-famous Quidditch player, is the sports editor for the Daily Prophet.” This is correct because world-famous modifies both Quidditch and player. You also can’t add and between them or change their order.
4. Use commas to set off nonessential additions to a sentence.
Nonessential, or nonrestrictive, words, phrases, and clauses add information to a sentence, but they are not required for its basic meaning to be understood. They provide information like who, whom, whose, which, that, where, when, how many, what kind, or which one.
“Mary Shelley’s best-known novel, Frankenstein, was first published in 1818.”
If you removed the content between the commas, the sentence would still make sense: “Mary Shelley’s best-known novel was first published in 1818.”
The mistake: Confusing nonrestrictive and restrictive clauses. Restrictive words, phrases, or clauses are essential to a sentence because they identify exactly who or what the writer is talking about. These do not receive commas.
For example, “Mary Shelley’s novel Frankenstein was first published in 1818″ does not include commas, because Mary Shelley has written multiple novels; readers wouldn’t know which novel the sentence is referring to without the title.
5. Use commas with transitional expressions, parenthetical expressions, contrasting comments, and absolute phrases.
Transitional expressions are words like however and therefore and phrases like for example and on the other hand.
“Bilbo Baggins had a grand adventure. However, it took a lot of persuasion for him to leave the Shire.”
Parenthetical expressions are like whispered asides. The information they provide is insignificant and could easily be left out.
“This experiment could take a couple of weeks, more or less.”
Contrasting comments begin with words like unlike or in contrast to.
“Unlike Severus Snape, I have a sense of humour.”
Absolute phrases are usually a noun followed by a participle and are used to modify the whole sentence.
“Smaug flew through the sky, the sunlight glinting off his wings.” (Sunlight = noun. Glinting = participle.)
Bonus: The Oxford comma, also known as the serial comma, comes before the last item in a list. I like Oxford commas because they add clarity, but not all publications use them. Defer to house style for this one.