SAT® · Reading and Writing: Boundaries — Within Sentences
Paired Commas Around an Interrupter
An interrupter dropped into the middle of a sentence needs a comma before it and a comma after it, because the two marks work as one matched set, not two separate pauses.
An interrupter is a phrase that adds extra information about something already named, without being needed to identify it. Because it sits inside the sentence rather than at the end, it needs a boundary on both sides. Think of the two commas as a single tool with two ends: open the bracket, say the extra thing, close the bracket. If you only hear a pause on one side when you read aloud, that is not proof the sentence only needs one comma — plenty of real interrupters get written with just a stray comma before or after, and that is always wrong when the phrase is genuinely optional information in the middle.
The reliable check is deletion. Cover or cross out everything between the two commas, including the commas themselves, and read what remains. If the leftover sentence is complete and makes sense on its own, the pair was placed correctly. 'Marie Curie, the only person to win Nobel Prizes in two sciences, died in 1934' collapses cleanly to 'Marie Curie died in 1934.' If deleting the bracketed material leaves a broken sentence, or leaves out a comma that should be there, something is missing — as in 'The cellist, who had toured for decades retired in June,' where the phrase 'who had toured for decades' opens with a comma but never closes, stranding 'retired in June' without its own boundary.
This sits alongside the other inside-sentence marks — dashes and parentheses can also bracket an interrupter, and like commas they must appear in matching pairs. The habit to build is the same across all three: find where the extra information starts and stops, then check that both edges carry the same kind of mark.
Key terms
- Interrupter
- A phrase inserted mid-sentence that adds extra, non-essential information about the word next to it.
- Appositive
- A noun phrase that renames or adds detail to a nearby noun, such as 'the only person to win Nobels in two sciences.'
- Deletion test
- Removing the bracketed phrase and its marks to check that the remaining sentence still stands on its own.
- Paired punctuation
- Marks that must appear in matching sets, such as two commas, two dashes, or two parentheses, around one interrupter.
Watch it explained
- How it worksHow does deleting everything between the paired commas prove whether they were placed correctly?
- Worked exampleWalk me through placing both commas in 'Marie Curie the only person to win Nobels in two sciences died in 1934'.
- Worked exampleWalk me through why 'The cellist, who had toured for decades retired in June' is short one mark.
- Common mistakeWhy doesn't one comma suffice when the interrupter is sitting in the middle of the sentence?
Check yourself
End of topic.