And why sometimes, it’s not even an error.
Web Bonus: More Examples
Note that the examples above all use a noun or pronoun followed by a participle, making them particularly sentence-like and confusing. In all of the following examples (except for the first three), the participle directly follows the comma. The same principle applies to both though: the words after the comma could not stand on their own as a sentence. They make a phrase, not a clause, and it’s fine to join an independent clause and a phrase with a comma.
He watched the sun as it continued to sink behind the trees, his eyes struggling to stay open as the darkness gathered around him. (Timubktu, Paul Auster)
Dobser hung in his bonds, facing the wall, his ears plugged by Pevara’s weaves. (A Memory of Light, Robert Jordan & Brandon Sanderson)
It stood open a crack by intention, the sturdy lock on the outside left hanging as if someone had forgotten to close it. (A Memory of Light, Robert Jordan & Brandon Sanderson)
Pevara reacted immediately, throwing weaves at the two men while forming a thread of spirit. (A Memory of Light, Robert Jordan & Brandon Sanderson)
Half a dozen swallows darted back and forth in the middle distance, skimming the field as they combed the air for mosquitos. (Timubktu, Paul Auster)
The book she had been reading was under her pillow, pressing its cover against her ear as if to lure her back into its printed pages. (Inkheart, Cornelia Funke)
I slowly crept from the bushes to the back door, checking the handle to see if it was unlocked. (Apocalypsis, Elle Casey)
I started backing up, getting ready to run. (Rosemary and Rue: An October Daye Novel, Seanan McGuire)
The light fixed to the front of the train clicks on and off as the train hurtles past the school, squealing on iron rails. (Divergent, Veronica Roth)
Appositives Often Follow a Clause and a Comma
Confusing participial phrases with clauses is one reason you might be creating commas splices. Another reason could be appositives. You’re also probably used to seeing appositives after commas.
An appositive is a noun or noun phrase that’s placed next to another noun or noun phrase to help identify it. (2)
Here are two examples:
It always took him a few moments to find his way out of that other world, the labyrinth of printed letters. (Inkheart, Cornelia Funke) [“The labyrinth of printed letters” is a noun phrase that tells you more about that other world.]
My curiosity is a mistake, a betrayal of Abnegation values. (Divergent, Veronica Roth) [“A betrayal of Abnegation values” is a noun phrase that tells you what the mistake was.]
Again, the important distinction is that the appositives after the comma couldn’t stand alone as sentences by themselves. They’re weak enough to be joined to the main clause by a comma.
Remember this rule: If you have a main clause—something that can stand alone as a sentence—and you put a comma after it, what comes after that comma should not be able to also stand alone as its own sentence. If it can, you’ve created a comma splice.
Next: The Exceptions Are Enough to Drive You Crazy