Commas, Dashes or Brackets: Choosing How Loudly to Interrupt

You want to drop an aside into a sentence. English gives you three ways, and they are not interchangeable — they differ in how much attention they draw.

• The report, which nobody read, was thorough.
• The report — which nobody read — was thorough.
• The report (which nobody read) was thorough.

Same words, three different sentences.

Commas: the default

The quietest option. The aside sits in the flow of the sentence at the same volume as everything around it, and the reader barely registers the interruption.

Use commas when the aside genuinely belongs — when it is additional information the reader should absorb rather than notice.

The limitation: commas are already doing several other jobs in most sentences. If the sentence contains commas for lists or clauses, adding a comma-bracketed aside makes it hard to tell which comma is doing what. That is the moment to reach for something else.

Dashes: the loud option

Em dashes push the aside forward. They create a genuine break, and whatever sits between them gets emphasis it would not otherwise have.

Use them when the interruption is the point:

• The committee — all seven of whom had voted for it — now claimed to have opposed it.

That aside is the most interesting thing in the sentence. Commas would have buried it.

Dashes also rescue sentences whose asides already contain commas, since they are visually distinct from everything else going on.

The limitation: they are emphatic, so frequency destroys them. Three pairs on a page and the prose starts to sound breathless.

Brackets: the quiet aside

Parentheses do the opposite of dashes. They demote. Whatever sits inside them is marked as secondary — useful, but skippable.

• The survey (conducted in March) found no change.

The reader can skip the bracket and lose nothing essential. That is exactly what brackets promise, and the promise is worth keeping: putting something important inside them buries it.

They suit references, dates, clarifications, and definitions — anything the reader might want but does not need.

The test that decides it

Ask how much attention the aside deserves.

• It belongs in the sentence → commas.
• It should stop the reader → dashes.
• It could be skipped → brackets.

Most writers pick one and use it for everything, which means they have given up a real tool. Deliberately varying them is one of the cheapest ways to make prose sound controlled.

Two mechanical rules

Both marks or neither. An aside opened with a dash closes with a dash; opened with a comma, closes with a comma. Mixing them is a common and jarring error: The report — which nobody read, was thorough.

The sentence must survive removal. Delete the aside and its marks. What remains should be a complete, correct sentence. If it is not, the aside was not an aside — it was part of the sentence, and the punctuation is wrong.

Checked against Merriam-Webster, the Chicago Manual of Style and the AP Stylebook. Spotted an error? Tell us — see our editorial policy.