Section 15.10 Parentheticals: Commas, Dashes, and Parentheses Compared
A parenthetical is any word, phrase, or clause inserted into a sentence to provide supplementary information that could be removed without changing the grammatical completeness of the sentence. English offers three ways to set off parenthetical material, and the choice among them is primarily one of emphasis:
The Emphasis Spectrum.
From most to least emphasis:
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Dashes — highest emphasis. The parenthetical calls attention to itself. Use for dramatic asides, surprising information, or material the reader should not miss.
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Commas — neutral emphasis. The parenthetical integrates smoothly into the sentence. Use for nonrestrictive modifiers and routine asides.
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Parentheses — lowest emphasis. The parenthetical is whispered. Use for technical details, citations, abbreviations, or truly peripheral information.
The Same Information, Three Ways.
Compare how the same parenthetical reads with each mark:
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The results—which surprised everyone—were published last week. (dashes: "pay attention to this")
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The results, which surprised everyone, were published last week. (commas: smooth, integrated)
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The results (which surprised everyone) were published last week. (parentheses: "you can skip this if you want")
All three are grammatically correct. The choice depends on the writer’s rhetorical intent.
When Each Works Best.
| Mark | Best for | Example |
|---|---|---|
| Dashes | Dramatic asides, surprising lists, emphasis | Three students—all freshmen—passed. |
| Commas | Nonrestrictive modifiers, routine elaboration | My sister, who lives in Boston, called. |
| Parentheses | Citations, definitions, technical details | The GDP (gross domestic product) fell. |
Key Points.
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All three marks must come in pairs when they enclose material mid-sentence. Do not open a dash or parenthesis without closing it.
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Do not mix marks:
The results—which surprised everyone, were published. -
Overusing dashes diminishes their impact. Reserve them for moments that deserve emphasis.
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In academic writing, commas are the default for nonrestrictive modifiers. Use dashes and parentheses as deliberate alternatives when the emphasis level matters.
