The Structure Comma with

Ambiguous Elements


Among its four uses, the structure comma signals the presence of a potentially confusing construction in a sentence.

Use the Comma with Detached Modifiers

Use a comma or comma pair to signal when a modifier and the element being modified are separated from each other by other words. This often happens with modifiers placed at the end of sentences:

The dog watched the squirrel,crouching.

“Crouching” modifies how the dog watched, but it is positioned closer to “the squirrel.” Without the comma, the sentence could be misread to mean that the squirrel was crouching.

The squirrel munched an acorn,oblivious to the danger.

Here again, without the comma, the sentence could be misread to mean that the acorn was oblivious to danger, which, although accurate about acorns, is not the meaning intended in this context.


Be sure you know the difference between a detached modifier and a misplaced modifier:

Expanded Insights

Be sure you know the difference between a detached modifier and a misplaced modifier:

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A detached modifier is both common and correct in English sentences. Misplaced modifiers, however, are incorrect and need revision. The problem with a misplaced modifier is that the element it modifies isn’t obvious. Consider this example:

I’ve somehow misplaced the picture of the dog that Elli framed.

A natural reading of this sentence miscommunicates that Elli framed a dog. The writer needs to revise the structure to communicate the actual idea that Elli framed the picture, not the dog.

I’ve somehow misplaced Elli’s framed picture of the dog.

This version of the sentence is better, but it still invites confusion—while Elli framed the picture, she may not own the picture, as the phrase “Elli’s framed picture of the dog.” suggests. Perhaps the following option, although more indirect, works better for this instance:

I’ve somehow misplaced the picture that Elli framed, the one of the dog.

Even better, separate the idea into two sentences:

I’ve somehow misplaced the picture that Elli framed. It’s that picture of the dog.

Use the Comma with Uncommon Elliptical Constructions

Writers sometimes leave out part of a clause, usually its verb, that can be inferred from its context. Use a comma with such elliptical clauses:

Ji-a went to bed; Sophie,to the party.

In this example, readers must infer that the verb “went” in the first clause is also implied in the second clause in order for the sentence to makes sense. The comma in these instances signals the presence of an implied element that English readers are not used to inferring.

Don’t Use It with Common Elliptical Constructions

Some elliptical constructions are so common that their implied meanings are unambiguous to English readers. In these cases, a comma isn’t necessary:

I like tea more than coffee.

The example above features an implied subject and verb: “I like tea more than I like coffee. But this construction is so common that inserting a comma to signal the implied elements would be far more confusing to readers:

Incorrect: I like tea more than, coffee.

Did you notice that the previous sentence included an entire implied dependent clause? Probably not, because you’re so used to the construction. Here is that full sentence written out: “But this construction is so common that inserting a comma to signal the implied elements would be far more confusing to readers than not inserting a comma to signal the implied elements.

English readers don’t need to read that final dependent clause to understand the contrast in the sentence. This can be the tricky part about using an elliptical construction; it often comes down to the writer’s judgment to decide when to use the comma with an implied element, and went not,.

(Hopefully, you’ve realized that the final comma in the previous sentence signals the implied phrase “to use the comma with an implied element.” Hopefully, you’ve also realized that it’s both awkward and unnecessary.)

Use the Comma with Reduplicated Words

Whenever a word is repeated side-by-side, also called reduplicated, place a structure comma between the two words to ensure readers understand that the repetition is not a typo.

Such reduplication often occurs as a coordinate element, expressing intensity:

It was a bad,bad day.

Writers also use reduplication in dialogue to express heightened emotion or hesitation:

“But,but I love you!”

Sometimes, a noun phrase ends with a helping verb immediately before the predicate’s helping verb:

Explaining what clarity is,is hard to do.

In this example, “explaining what clarity is” is the subject of the sentence. If the reduplicated “is” that results seems awkward, a writer could (perhaps should) revise the sentence: “Clarity is difficult to explain.”

Don’t Use It with a Reduplicated “That”

An exception to this reduplication rule is “that”:

Leonor told Ariel that that was a great meal.

The rule doesn’t apply because the example isn’t really reduplication—the word “that” performs two distinct functions in such constructions. Its first occurrence works as a conjunction; the second, a pronoun. The resulting sentence, however, could (perhaps, again, should) be revised:

Leonor told Ariel, “That was a great meal.”

Leonor complimented Ariel on making such a great meal.

Use the Comma with Potentially Misleading Sentences

Sometimes, a sentence’s construction can cause readers to misread the writer’s meaning. For instance:

The band didn’t perform last night because they were sick.

This sentence could be read two ways: it could mean that the band’s sickness caused them not to perform, or it could meant that the band’s ill health had nothing to do with why they didn’t perform last night. To alleviate this confusion, insert a structure comma that shows where the main thought of the sentence ends:

The band didn’t perform last night,because they were sick.

Employ this comma usage as a last resort. If you can, revise the sentence to eliminate potential miscommunications:

Because they fell sick, the band didn’t perform last night.

Knowledge Check

Click on the option that correctly uses the comma with ambiguous elements:

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