Writers should generally not use a comma to connect two independent clauses, and editors of fiction and nonfiction should be alert to this misuse of the comma. The following examples violate this principle and demonstrate what is known as the “comma splice”:
Canceling your vacation is a horrible idea, don’t do it.
The students were in an uproar, some of them walked out of class.
Winter coats should be warm, they don’t need to contain down fill.
I feel like going for a walk, I’ll take the dog out.
You can fix a comma splice in a number of ways: a new sentence can be formed; a different mark of punctuation, like a semicolon or a dash, can be substituted for the comma; or a conjunction can be used between the clauses:
Canceling your vacation is a horrible idea. Don’t do it.
The students were in an uproar; some of them walked out of class.
Winter coats should be warm, but they don’t need to contain down fill.
I feel like going for a walk, so I’ll take the dog out.
Note, however, that commas are acceptable in idiomatic constructions when the second part of the sentence completes the sense of the first and in a series of three or more items:
It’s not just the customers who are exasperated, it’s the employees too.
The greater the risk, the greater the reward.
We came, we saw, we conquered.
Dinner was over, the guests had departed, and all that remained was a giant pile of dirty dishes.
Comma splices are also acceptable in fiction. In dialogue and first-person narration, for example, a character might be excited or upset and thus speak in a rush. The minimal pause conveyed by a comma can clarify sentence structure while conveying the character’s state of mind. Or the author’s style might use splices frequently for some other effect.
In editing fiction a copyeditor is often justified in making emendations for basic points of grammar, and the emendations required to avoid a comma splice are minimal, so a writer may not find them intrusive. Even a writer who uses comma splices as a device may occasionally do so unintentionally in exposition. If an author of fiction consistently breaks a rule, however, an editor would be wise to consider the author’s purpose before making changes. Editors of fiction should also be mindful of how they emend for a comma splice. Do not, for example, introduce a semicolon if the author does not use them elsewhere.