Digital SAT · Boundaries
How to Solve Setting Off Extra Information on the Digital SAT
A phrase adds extra, nonessential information to a sentence, and you punctuate its edges. The core rule is symmetry: whatever mark opens the aside must close it, so two commas, two dashes, or two parentheses, never one of each. If the phrase is essential to the meaning, it takes no punctuation at all. The choices test whether you can tell a removable aside from information the sentence needs, and match the marks on both sides.
- per test
- 4 per test per test
- typical difficulty
- Medium to hard typical difficulty
- practice questions
- 173 practice questions
Frequency reflects how often this question type appears on a full-length Digital SAT. The difficulty mix reflects every question of this type across our bank.
What the question bank shows
An aside opens and closes with the same mark: two commas, two dashes, or two parentheses.
If the sentence survives deletion, the phrase is nonessential and takes paired punctuation.
The in-house bank carries plenty of these, so practice spans easy to hard forms.
How to recognize setting off extra information questions
- A descriptive phrase sits in the middle of the sentence.
- The choices mix single and paired commas, dashes, and parentheses.
- Removing the phrase still leaves a complete, sensible sentence.
- The prompt tests punctuation, not word choice.
Why students miss these
The step-by-step method
- 1
Find the aside
Locate the phrase that adds detail, and see if the sentence works without it.
- 2
Decide essential or extra
If deleting it changes or breaks the meaning, it is essential and takes no marks.
- 3
Match both ends
For a true aside, use the same mark on each side: two commas, two dashes, or two parentheses.
- 4
Reject the mismatch
Eliminate any choice that opens with one mark and closes with another.
Worked examples
Easy example
Jane Goodall began studying wild chimpanzees in the forests of Tanzania in 1960, when she was just twenty-six years old. Her research, a decades-long study of primate ______ transformed the way scientists around the world understand animal behavior.
A: Incorrect. Without a closing comma the appositive merges with 'transformed,' and the opening comma has no partner.
B: Incorrect. A semicolon would mark a clause boundary, but a noun phrase is being set off, not an independent clause.
C: Incorrect. A colon introduces an explanation or list and cannot close a comma-opened supplement.
D: Correct. 'A decades-long study of primate society' renames 'research' and opens with a comma, so it needs a matching comma to close.
Explanation
The appositive 'a decades-long study of primate society' opens with a comma, so it must close with a comma.
Easy example
The common octopus is famous for its ability to vanish against the seafloor. This shy ______ a master of disguise among ocean animals, can change both the color and the texture of its skin in less than a second.
A: Incorrect. A semicolon joins two independent clauses, but 'a master of disguise among ocean animals' is a renaming phrase, not a clause.
B: Incorrect. A colon introduces a list or explanation and cannot pair with the closing comma already in the sentence.
C: Incorrect. With no punctuation, the comma later in the sentence is left without its matching opening comma.
D: Correct. The appositive 'a master of disguise among ocean animals' is nonessential and is closed by a comma, so a comma must also open it.
Explanation
The renaming phrase is closed by a comma in the sentence, so it must open with a matching comma.
Easy example
The Great Barrier Reef lies just off the northeastern coast of Australia. This immense ______ a system of nearly three thousand individual reefs, is so large that it can easily be seen from space.
A: Incorrect. Without an opening comma, the nonessential phrase is not set off, leaving the closing comma after "reefs" unmatched.
B: Incorrect. A semicolon must separate two independent clauses, but "a system of nearly three thousand individual reefs" is a phrase, not a clause.
C: Incorrect. A colon must follow a complete independent clause, but "This immense structure" is not yet a complete sentence.
D: Correct. A comma opens the nonessential phrase "a system of nearly three thousand individual reefs," which is closed by the comma after "reefs," forming a matched pair.
Explanation
The phrase "a system of nearly three thousand individual reefs" is nonessential and is already closed by a comma after "reefs," so it must be opened with a matching comma.
The common traps
| Pattern | What it does | The tell |
|---|---|---|
| Mismatched marks | Opened the aside with one mark and closed it with another. | The opening and closing punctuation must be the same kind. |
| Punctuated the essential | Set off a phrase the sentence actually needs. | Delete the phrase; if the meaning breaks, use no marks. |
| Only one mark | Fenced one side of a mid-sentence aside but not the other. | A mid-sentence aside needs a mark on both ends. |
Try it: two real questions
The axolotl is a type of salamander found in the wild only in a few shallow lakes near Mexico City. Unlike most amphibians, which lose their juvenile features as they mature, it keeps its feathery external ______ the frilly organs that allow it to breathe underwater--for its entire life, never developing the lungs that other salamanders eventually grow.
Which choice completes the text so that it conforms to the conventions of Standard English?
The axolotl is a type of salamander found only in a few lakes near Mexico City. This unusual ______ able to regrow entire lost limbs, has become a favorite subject for scientists who study regeneration.
Which choice completes the text so that it conforms to the conventions of Standard English?
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Related reading
Common questions
How do you punctuate extra information on the SAT?
Decide whether the phrase is nonessential by deleting it. If the sentence still works, set it off with a matching pair of marks, two commas, two dashes, or two parentheses, on both sides.
Can you mix a comma and a dash around a phrase?
No. The marks that open and close an aside must match. A comma on one side and a dash on the other is always wrong, even though it can look acceptable.
When does a phrase take no punctuation?
When it is essential, meaning the sentence needs it to identify or complete the idea. Essential phrases are not fenced off, so no commas, dashes, or parentheses go around them.
How do I tell essential from nonessential?
Remove the phrase and read what is left. If the sentence stays complete and keeps its meaning, the phrase is extra and gets paired marks; if not, it is essential and gets none.
Practice setting off extra information the way it is tested
Start with the free 16-question diagnostic, then drill this type with step-by-step reasoning on every question.
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