How do dashes and parentheses set off extra information on the ACT, and why must a dash or parenthesis match its partner?
Dashes and parentheses on ACT English: using a pair of dashes or parentheses (or a pair of commas) to set off a nonessential element, the matching-pair rule that you cannot open with a dash and close with a comma, and using a single dash to introduce an explanation or list after a complete clause.
A focused answer to dashes and parentheses on ACT English: setting off nonessential information with a matching pair of dashes, parentheses, or commas, the rule that the opening and closing marks must match, and using a single dash like a colon to introduce an explanation or list after a complete clause.
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What this skill is asking
Dashes and parentheses both set off extra information, and the ACT tests two things about them: that a pair of them (or a pair of commas) brackets a nonessential element, and that the opening and closing marks match. The favorite trap is mismatched marks, opening with a dash and closing with a comma, which is always wrong. A single dash also has a second use, introducing an explanation after a complete clause, much like a colon.
Pairs set off nonessential information
The core idea is the same as the nonessential comma: a removable element gets brackets on both sides, and the brackets must be the same kind.
The reason this matters: when an underlined portion includes only the closing mark, the correct option is the one whose mark matches the opening mark already in the sentence. So read backward to find what opened the element, then close it with the same kind of mark.
The single dash as an introducer
A lone dash near the end of a sentence usually is not a bracketing dash; it is doing the colon's introducing job.
So a dash can appear singly (introducing) or in a pair (bracketing). The way to tell: if the dash sits between two parts and the second part runs to the end of the sentence as an explanation, it is a single introducing dash; if extra information sits between two marks in the middle of the sentence, you need a matching pair.
Choosing the right mark on an underlined portion
When an underlined portion is the closing mark of a set-off element, match it to the opening mark.
Why matching is the whole game
Dash and parenthesis questions are usually decided by one check: does the closing mark match the opening mark? The marks are interchangeable as long as they are used in matching pairs, so the ACT rarely asks you to prefer a dash over a comma on style alone; it asks you to keep the pair consistent. The single-dash introducer is the one extra case, and it follows the colon's complete-clause rule. This topic is really the nonessential-comma rule extended to two more mark types, plus a colon-like use, so it reuses logic you already have.
Try this
Q1. What are the three ways to set off a nonessential element in the middle of a sentence, and what is the matching-pair rule? [Recall]
- Cue. A pair of commas, a pair of dashes, or a pair of parentheses. The matching-pair rule says the opening and closing marks must be the same kind: you cannot open with a dash and close with a comma, or open with a parenthesis and close with a dash.
Q2. A sentence reads "The professor (a Nobel laureate, retired last year." What is wrong, and how do you fix it? [Short explanation]
- Cue. The element "a Nobel laureate" opens with a parenthesis but never closes with one (it closes with a comma instead), so the pair does not match. Fix it by closing with a parenthesis: "The professor (a Nobel laureate) retired last year." The opening and closing marks now match.
Exam-style practice questions
Practice questions written in the style of ACT exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
ACT English (style)1 marksChoose the best option: 'The first car she ever owned, a rusty hatchback - was surprisingly reliable.' (A) NO CHANGE (B) hatchback, was (C) hatchback) was (D) hatchback; wasShow worked answer →
The correct answer is (B), "hatchback, was". The phrase "a rusty hatchback" is a nonessential element set off from the sentence, and it opened with a comma after "owned", so it must close with a comma too. The matching mark for the opening comma is a closing comma.
Why not the others: (A) opens with a comma but closes with a dash, which do not match; (C) closes with a parenthesis with no opening one; (D) a semicolon would need an independent clause after it, but "was surprisingly reliable" is not independent. The pair must match: comma to comma.
ACT English (style)1 marksChoose the best option: 'He finally found what he had been searching for all summer, the perfect campsite.' (A) NO CHANGE (B) for all summer - the perfect campsite (C) for, all summer the perfect campsite (D) for all summer the perfect campsiteShow worked answer →
The correct answer is (B), "for all summer - the perfect campsite". The first part is a complete independent clause, and "the perfect campsite" is an explanation or emphatic addition at the end. A single dash can introduce that explanation, working much like a colon.
Why not the others: (A) uses a comma, which is too weak to set off this emphatic ending cleanly and risks a splice feel; (C) adds a stray comma and drops the needed mark; (D) gives no punctuation before the addition. A single dash after a complete clause correctly introduces the explanatory phrase.
Related dot points
- Commas and unnecessary commas on ACT English: the four jobs commas do (separating items in a series, setting off nonessential elements, following introductory elements, and joining clauses with a coordinating conjunction), and recognizing the unnecessary commas the ACT inserts between a subject and verb or around essential information.
A focused answer to commas on ACT English: the four jobs a comma does (series, nonessential elements, introductory elements, joining clauses with a coordinating conjunction) and the unnecessary commas the test plants, such as a comma between a subject and its verb or around essential information, with a routine for deciding.
- Colons and semicolons on ACT English: the semicolon joins two independent clauses (or separates complex list items), the colon introduces a list, explanation, or example after a complete clause, and the rule that both require a complete independent clause before them, with the contrast to a comma.
A focused answer to colons and semicolons on ACT English: the semicolon links two independent clauses, the colon introduces a list, explanation, or example after a complete clause, both need a full independent clause before them, and how each differs from a comma, with a routine for choosing the right mark.
- Common punctuation traps on ACT English: the deliberate errors the test reuses (a comma splitting a subject and verb, a comma splice, a colon after an incomplete clause, mismatched paired marks, and the strategy of choosing the option with the fewest unjustified marks), and a unifying when-in-doubt-leave-it-out habit.
A focused answer to the recurring punctuation traps on ACT English: the subject-verb comma, the comma splice, the colon after an incomplete clause, mismatched paired marks, and over-punctuation, plus the unifying habit of choosing the option that uses no unjustified mark, with worked diagnosis.
- Run-ons and comma splices on ACT English: recognizing two independent clauses joined with no punctuation (fused) or with only a comma (splice), and applying the four standard fixes (period, semicolon, comma plus a coordinating conjunction, or subordination) to the underlined portion.
A focused answer to run-ons and comma splices on ACT English: how to recognize two independent clauses fused with no punctuation or joined with only a comma, and the four standard fixes (period, semicolon, comma plus a FANBOYS conjunction, or subordination), and how each answer choice maps to one of them.
Sources & how we know this
- Description of the ACT English Test — ACT, Inc. (2025)
- Preparing for the ACT Test — ACT, Inc. (2025)