Commas are notoriously difficult to master: there are few hard-and-fast rules, especially with creative writing, and exceptions that require editorial judgement abound. Editors and writers who want clear, simple rules that can be applied across the board will find fiction editing a challenge—and may do unintentional harm to the manuscript.
The primary function of commas is to create clarity by separating some words and grouping others, which means a comma needed for clarity should never be considered optional. The secondary function of commas is to control the forward rhythm of the prose for emotional and artistic effect, and there are many ways to use optional commas to do so.
Misplaced commas, however, can interfere with the natural rhythm of language—and even change your meaning.
"Intruded commas are worse than omitted ones." (Words into Type, 3rd Edition, p. 184)
When Alexander Pope wrote "a little learning is a dangerous thing," he could have been talking about commas, because many of the unnecessary and interruptive commas I see in published novels appear to be the result of a misapplication of the rules.
The rules themselves can appear deceptively simple. But applying them correctly sometimes requires a deeper understanding of syntax and grammar than even many copyeditors possess.
The result of this lack of understanding is commas that "impede rather than facilitate reading."*
*From "Problems with Punctuation" in Line by Line: How to Edit Your Own Writing by Claire Kehrwald Cook. I love how Cook categorizes commas as "helpful" and "harmful" in this chapter rather than "right" and "wrong," since the latter words foster a simplistic and dangerous approach to applying comma rules.
Misapplied comma rule #1
Two independent clauses joined by a coordinating conjunction usually require a comma before the coordinating conjunction—unless the clauses are short and closely related.
This is one of the best known comma rules. And most writers and (hopefully!) all editors know the difference between independent clauses and dependent clauses. But sometimes a dependent clause can be mistaken for an independent clause, leading to harmful commas.
But first, an often overlooked comma rule:
Except with independent clauses, don't add a comma between two equal grammatical units joined by a coordinating conjunction.
Many grammar books don't even list this rule, and most that do give it only a brief mention before moving on. I suspect this is because, as Claire Kehrwald Cook says in Line by Line: How to Edit Your own Writing, "if you understand where to use commas, you can readily infer where not to use them."
After all, if you need to be told to put a comma before the coordinating conjunction that connects two independent clauses (units that have a subject and a verb and could stand alone as complete sentences), you can assume you aren't supposed to add commas other times…right?
But for such a seemingly simple and straightforward rule, failing to give it much thought can lead to misplaced commas.
Fortunately, June Casagrande gives a lot of attention to this rule in the chapter on commas in The Best Punctuation Book, Period, actually listing each individual instance where you shouldn't stick a comma: between compound verbs that share a subject, between compound subjects that share a verb, between two objects that share the same verb, and between any two sentence elements that attach to a single stem.
Pay careful attention to that last one.
Both phrases and clauses can share a stem word or phrase. For example, these two prepositional phrases share the preposition "by," which is elided in the second case.
I did it by hustling and (by) bustling.
But when the two sentence elements attaching to a single stem are dependent clauses sharing a subordinating conjunction, trouble can ensue. Since clauses are often quite a bit longer than phrases, it can be easy to miss when two of them share a stem, resulting in the second dependent clause being mistaken for an independent clause and a comma being incorrectly added.
I was starting to feel as though he was the child, and I was the parent. X
This is a fairly short example, so it's easier to see the error: "I was the parent" shares the stem as though with "he was the child," and thus is not an independent clause. And the comma is not only incorrect, it's harmful, making the sentence more difficult to comprehend.
With longer, more complex sentences, this can get trickier to identify. I myself almost stuck in an unneeded comma in an earlier paragraph.*
...resulting in the second dependent clause being mistaken for an independent clause, and a comma being incorrectly added. X
Those were phrases, not clauses, but because the second phrase was a fair distance from the stem phrase "resulting in," it was almost instinctive to stick in an unneeded comma. I catch myself wanting to add these commas all the time when writing.
And unless you read a lot of books on grammar and punctuation, you've probably never read about this exception to our first misapplied comma rule: two independent clauses that branch off and are modified by the same dependent clause should not be separated by a comma.** It could be considered implicit in the "closely related" exception to the comma rule governing independent clauses, but for those of us try-hards who like to follow the rules whenever possible, it's still helpful to have this exception spelled out.
The two independent clauses in the following example are both things that happen "when the rains come," so separating them hinders both comprehension and flow.
When the rains come, the grass grows and the herds arrive. ✓
When the rains come, the grass grows, and the herds arrive. X
As you can see, knee-jerk commas placement can lead to errors and awkward phrasing, understandable when writing, but less so when editing. So always approach commas with thoughtfulness and care.
*While this comma is not grammatically needed, with long, difficult-to-read clauses and phrases, a comma can be added if needed to aid comprehension. There could also be artistic reasons to create a pause. This is a judgement call, not necessarily a mistake. Clarity and artistry trump rules.
**If you're curious where I found confirmation of this exception to the rule, it's mentioned in both The Handbook of Good English by Edward D. Johnson and The Copyeditor's Handbook by Amy Einsohn and Marilyn Schwartz.
Misapplied comma rule #2
When an adverb or adverbial phrase modifies the whole sentence or the independent clause it precedes (and sometimes follows or interrupts), it (usually) needs to be set off by commas.
Where writers and editors seem to go astray with this rule is recognizing when an adverb or adverbial phrase is a sentence adverb (also known as a conjunctive adverb or transition word) and when it's a regular adverb in the opening or closing position of a sentence.
Adverbs like "however" and "of course" have more than one meaning, and some meanings/uses call for commas and some don't. Most people see the distinction with "however"—I don't believe I've ever seen a comma misused in a published book when "however" means "in whatever way" as opposed to "on the other hand"—but I frequently see misplaced commas with "of course" when it means "certainly" or "as might be expected" as opposed to "on the other hand." I see this often enough I fear it's publishing professionals rather than writers who are introducing this error.
I get into the grammar nitty gritty in this post—"Is 'of course' always followed by a comma? Of course not!"—but honestly, there's a much easier way with sentence adverbs: listen for a pause, then trust your ears.*
However you plan to get it done, just make sure it happens by Friday. (No comma. Also note lack of pause.)
It needs to happen by Friday. However, how that happens is immaterial. (Comma needed for clarity of meaning, which is "on the other hand" here.)
Of course I'll be there for your party! (No comma. No pause.)
I'm planning to be at the party. Of course, who knows what will come up between now and then. (Comma required for clarity of meaning, which is "on the other hand.")
Automatically sticking a comma after "of course" or "so" or "however"—or any introductory element—could drastically change the meaning of the sentence (more in this article). And even if the reader gets the meaning from the context (as they often will), the comma interferes with the natural rhythm of language and can cause the reader to momentarily stumble.
As an extension of this comma rule, adverbs at the end of sentences sometimes get set apart with interruptive commas as well. While it's not incorrect to use a comma before "too" and "either," it's becoming less and less common to do so in informal writing. And writers and editors who stick commas before adverbs in this position routinely—without listening to the rhythm of the prose—end up with awkwardly halting sentences like these:
1. I would like a cookie, instead.
2. I don't want to go, either.
3. "Wow," he said, enthusiastically. (To be fair, copyeditors rarely add this comma, and it can occasionally be used for emphasis.)
And a misplaced comma could change the meaning with end-of-sentence adverbs as well. I saw something similar to the following example sentence in a published book recently:
I communicated that to Josephine, clearly.
Setting off "clearly" makes it sound like a sentence adverb, like the speaker is saying that the fact that she communicated the thing in question to Josephine should be obvious. But based on the context, the speaker was actually trying to say that the thing in question was communicated to Josephine in a clear manner.
Editors who have learned to trust their instincts rather than automatically follow what they believe to be a rule avoid doing harm. If following the "rule" results in an unnatural rhythm or a meaning not in keeping with the context, it may be that you're misunderstanding or misapplying the rule.
*I'm not advocating the "stick a comma wherever you hear a pause" school of punctuation; however, it is my opinion that skillful use of punctuation requires both an understanding of grammar rules and a sensitivity to nuance and rhythm.
Misapplied comma rule #3
Precede participles and participial phrases with a comma unless they directly follow the noun they modify.
This rule doesn't cause problems that often, but occasionally issues arise with identifying participles and participial phrases. Participles function as adjectives, modifying a particular noun. But not every -ing word that looks like a present participle is modifying a noun—sometimes it's part of the verb, sometimes it's a gerund acting as a noun, and sometimes it's an adverb—and misidentifying the grammatical function of these words/phrases can lead to unnecessary, and occasionally harmful, commas.
Usually when I see one of these unneeded commas, it's caused by a prepositional phrase in the middle of the predicate (verb phrase).
1. John was on the bench waiting for his ride.
2. John was on the bench, waiting for his ride.
Is the sentence "John was waiting for his ride" with an adverbial prepositional phrase inserted in the middle of the verb "was waiting" (#1)? Or Is it "John was on the bench," with "waiting for his ride" added as additional information about John (#2)?
It could be either, depending on the emphasis desired by the author. But adding a comma automatically because of strict adherence to a rule that may not apply runs the risk of altering the sentence unnecessarily. And with more complex sentences that require several commas, being free to leave out this one can aid the overall flow.
Here's another example adapted from something I read recently in a published book:
Sally doesn't have to wander around, freezing anymore.
In this sentence, "freezing" is an adverb modifying the phrasal verb "wander around." The writer or editor mistook it for a participle modifying the noun "Sally" and added an interruptive comma. Compare with the following, where "freezing" is a participle:
Sally wandered around the town, freezing her buns off.
One way to test this is to move what you think might be a participial phrase to immediately after the subject of the sentence (or the noun you think the phrase is modifying—sometimes it's not the subject). If the sentence no longer makes sense, it's probably not a participle.
Sally, freezing anymore, doesn't have to wander around. X
Sally, freezing her buns off, wandered around the town. ✓
This test wouldn't work for the first example where John's waiting for a ride, but it's still useful for determining when a comma would be intrusive and harmful.
Mastering commas requires not only extensive knowledge of the rules but also sensitivity to nuance. Being overly rule-bound can lead to poor comma usage, but so can a loosey-goosey attitude. Punctuation needs to serve the writer's intent, especially in fiction. So remember, clarity and artistry trump rules, and when in doubt, it's usually better to leave it out.