ACT English · Sentence Structure
Parallel Structure on the ACT: Every Rule, Named and Explained
Questions about sentence structure occupy about 20-25% of the ACT’s English section. Thus, knowing proper syntactical parallel is essential. Students who lose points here often don’t understand the rules of parallelism as well as they might think–or they misidentify more complex structures as not in parallel when they actually are.
So pay attention to the grammatical function of words and phrases in the sentence, not surface-level parts of speech. The good news is that specific “anchors” are conspicuous, which means you don’t need to have a deep command of the entire syntax of the passage: a fixed grammatical point will direct you to the proper construction. If you know how to find the anchor, then you can move through these questions more swiftly.
Rules covered in this guide
| Rule | Named Method | Frequency |
|---|---|---|
| Parallel lists — nouns, verbs, adjectives, and phrases | The List-Lock Method | Very High |
| Correlative conjunctions (both…and, not only…but also, either…or) | The Mirror Rule | Medium |
| Finding the anchor when the non-underlined portion is distant | The Anchor Hunt | High |
| Function over form — when surface mismatch is not an error | The Function Test | Medium |
| The infinitive/gerund swap trap | The Swap-and-Check | Medium |
Rule 1
Parallel Lists — Nouns, Verbs, Adjectives, and Phrases
Very High FrequencyWhen a sentence lists two or more items joined by a coordinating conjunction — most commonly “and,” “or,” or “but” — every item in the list must be the same grammatical form. A list of nouns stays nouns. A list of verb phrases stays verb phrases. A list of adjectives stays adjectives. Mixing grammatical forms inside a list is a parallel structure error.
The ACT almost always underlines only one item in the list — typically the last one — and the non-underlined items are your anchor. Your job is to identify the grammatical form of the non-underlined items and match the underlined item to that form.
Named Method
The List-Lock Method
When you see a list connected by “and,” “or,” or “but,” lock in the grammatical form of the first non-underlined item. That item is your anchor — it defines what form every other item in the list must take. Then read the underlined item and ask: does it match the anchor’s form? If not, eliminate it and look for the answer choice that does match.
Example: “The program requires applicants to demonstrate leadership, community involvement, and they must show financial need.” The first two items are noun phrases — “leadership” and “community involvement.” Lock those in. The underlined item “they must show financial need” is a clause — a completely different grammatical structure. The correct fix must be a noun or noun phrase: “financial need.” Apply the List-Lock: find the form, match the form, done.
✓ Correct — all list items match
The director praised the cast for their energy, their precision, and their commitment to the material.
✗ Incorrect — final item breaks the pattern
The director praised the cast for their energy, their precision, and how committed they were to the material.
ACT-style practice question
The new urban planning initiative emphasizes building affordable housing, expanding public transit networks, and green spaces should be created throughout the city.
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Rule 2
Correlative Conjunctions (Both…And, Not Only…But Also, Either…Or)
Medium FrequencyCorrelative conjunctions come in pairs — one part before the first element, one part before the second. The grammatical structure that immediately follows the first conjunction must be mirrored exactly by the grammatical structure that immediately follows the second conjunction. Whatever form comes after the first half of the pair, the same form must come immediately after the second half.
The ACT tests this by placing the second half of the correlative pair in the underlined portion, making the mismatch invisible unless you check what grammatical structure follows the first conjunction and confirm it is mirrored after the second.
| Conjunction Pair | Correct Pattern | Common Error |
|---|---|---|
| both…and | both [noun/verb/adj] and [same form] | both [noun] and [clause] |
| not only…but also | not only [verb phrase] but also [verb phrase] | not only [verb phrase] but also [noun] |
| either…or | either [noun] or [noun] | either [noun] or [infinitive phrase] |
| neither…nor | neither [adj] nor [adj] | neither [adj] nor [clause] |
| whether…or | whether [infinitive] or [infinitive] | whether [infinitive] or [gerund] |
Named Method
The Mirror Rule
Find the first half of the correlative pair. Identify the exact grammatical structure immediately following it — the word or phrase right after that first conjunction. Then move to the second half of the pair and ask: does the same grammatical structure appear immediately after it? If not, the structure is broken. The fix is always to make what follows the second conjunction mirror what follows the first — not the other way around, since the first half is usually not underlined.
Example: “The study found that participants were not only more productive but also an improvement in their sleep was noted.” After “not only”: an adjective — “more productive.” After “but also”: a clause — “an improvement in their sleep was noted.” Not mirrored. Correct fix: “but also sleeping better” or “but also better rested” — an adjective or adjective phrase that mirrors the structure after “not only.”
✓ Correct — mirrored structure after each conjunction
The renovation was intended not only to modernize the facade but also to improve the building’s energy efficiency.
✗ Incorrect — structures after each conjunction don’t match
The renovation was intended not only to modernize the facade but also improved energy efficiency was a goal.
ACT-style practice question
The scholarship committee evaluates applicants based on both their academic achievement and also the applicant demonstrating leadership in the community.
Rule 3
Finding the Anchor When the Non-Underlined Portion Is Distant
High FrequencyOn many ACT parallel structure questions, the anchor — the non-underlined element that sets the required grammatical form — is not in the same sentence as the underlined portion. It may appear one or two sentences earlier in the passage, buried inside a longer clause. Students who only read the underlined sentence have no way of identifying what form they are supposed to match.
The rule itself is unchanged: match the grammatical form of the anchor. What changes is the reading strategy — you must actively hunt for the anchor beyond the underlined sentence before you can evaluate any answer choice.
Named Method
The Anchor Hunt
When you encounter a potential parallelism question, do not immediately read the answer choices. Instead, look for the conjunction that signals a list or parallel structure — “and,” “or,” “but,” or a correlative pair. Then trace backward from that conjunction to find every non-underlined item in the list. Those items are your anchors. Once you have identified the anchor’s grammatical form, apply the List-Lock or Mirror Rule to the answer choices.
If the list seems to span multiple sentences or the anchors are hard to find, look for a series marker in the surrounding passage — a phrase like “first,” “second,” “in addition,” or “finally” that signals the list is continuing from an earlier sentence. The non-underlined item connected to that series marker is your anchor, regardless of how far away it sits from the underlined portion.
✓ Correct — underlined item matches the distant anchor
The foundation funds programs that train teachers, supply schools with materials, and connect students with mentors. [All verb phrases — list is parallel across the full passage sentence.]
✗ Incorrect — underlined item breaks form established far away
The foundation funds programs that train teachers, supply schools with materials, and the connection of students with mentors. [Verb phrase → verb phrase → noun phrase: broken.]
ACT-style practice question
The research team had three primary objectives: to document changes in the local bird population, to measure variations in soil composition, and an analysis of water quality at five sites along the river was also conducted.
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Rule 4
Function Over Form — When Surface Mismatch Is Not an Error
Medium FrequencyNot every sentence that looks non-parallel is actually a parallel structure error. Two items that appear different on the surface can both be functioning as the same grammatical role — and when they do, the sentence is correct. The ACT tests this by presenting sentences that look like parallel structure violations but are not, specifically to catch students who over-apply the rule.
The real test of parallelism is grammatical function, not surface form. A gerund phrase (“swimming laps”) and a noun phrase (“lap swimming”) both function as nouns and can appear in the same list without a parallelism error, as long as both are performing the same grammatical role. The error only exists when two items that are supposed to play the same role are playing different roles.
Named Method
The Function Test
For each item in a list or correlative pair, ask: what grammatical role is this item playing in the sentence — subject, object, modifier, or predicate? If all items are playing the same role, the structure is parallel, even if the surface words look different. Only flag an error when two items are playing different roles.
Example: “She enjoyed the silence, the solitude, and reading by the fire.” This looks non-parallel: two nouns and a gerund phrase. But apply the Function Test: all three items function as direct objects of “enjoyed.” Subject-object-object-object — same role throughout. This sentence is not a parallel structure error. The ACT will include this kind of sentence in an answer choice to test whether you over-flag correct answers.
✓ Correct — different surface forms, same function
The committee valued transparency, accountability, and acting with integrity in all of its decisions. [All three function as direct objects — parallel.]
✗ Incorrect — genuinely different grammatical roles
The committee valued transparency, accountability, and the staff were expected to act with integrity. [Noun, noun, clause — the clause plays a different grammatical role entirely, as it is a fully independent clause.]
ACT-style practice question
The expedition members were selected for their endurance, their navigational expertise, and because they were able to remain calm under pressure.
Rule 5
The Infinitive/Gerund Swap Trap
Medium FrequencyInfinitives (“to run,” “to build,” “to demonstrate”) and gerunds (“running,” “building,” “demonstrating”) are both verb forms that can function as nouns. Because they are interchangeable in many grammatical contexts — and because both can be parallel to each other within a list — the ACT uses them to construct a specific trap: offering a gerund as a “fix” for what appears to be a parallel structure error when the actual error is something else entirely, or when the anchor requires an infinitive specifically.
The trap works in both directions: students sometimes accept a gerund because it looks like it fixes parallelism when it actually breaks it, and sometimes reject an infinitive thinking it’s non-parallel when it is correct. The decision rule is always the same: check the anchor first and match its exact verb form.
Named Method
The Swap-and-Check
When you see an answer choice that swaps an infinitive for a gerund (or vice versa), perform this two-step check before accepting it. Step 1: Find the anchor. Is the anchor an infinitive or a gerund? Step 2: Does the answer choice match the anchor’s exact verb form? If the anchor is an infinitive, the correct answer must also be an infinitive — not a gerund, even if both mean the same thing.
The reason this trap is so effective: infinitives and gerunds often feel interchangeable in spoken English. “I like to swim” and “I like swimming” mean the same thing. But in a parallel list where the established form is “to swim,” the correct parallel item is “to run” — not “running.” The meaning may be identical; the form is not. On the ACT, form is what the question is testing.
✓ Correct — anchor is infinitive; answer matches
The internship program teaches students to set priorities, to manage deadlines, and to communicate professionally in a workplace environment.
✗ Incorrect — gerund swapped in for infinitive anchor
The internship program teaches students to set priorities, to manage deadlines, and communicating professionally in a workplace environment.
ACT-style practice question
The fitness program was designed to improve cardiovascular endurance, to increase muscular strength, and achieving greater overall flexibility.
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Quick-Reference Summary: All 5 ACT Parallel Structure Rules
| Rule | Named Method | The Core Question to Ask | Frequency |
|---|---|---|---|
| Parallel lists — nouns, verbs, adjectives, phrases | The List-Lock Method | What is the form of the non-underlined anchor items — and does the underlined item match it? | Very High |
| Correlative conjunctions (both…and, not only…but also, etc.) | The Mirror Rule | Does the structure after the second conjunction mirror the structure after the first? | Medium |
| Finding the anchor when the non-underlined portion is distant | The Anchor Hunt | Where is the conjunction that signals a list — and what are ALL the non-underlined items in it? | High |
| Function over form — when surface mismatch is not an error | The Function Test | Are all list items playing the same grammatical role — or do they just look different on the surface? | Medium |
| The infinitive/gerund swap trap | The Swap-and-Check | Is the anchor an infinitive or a gerund — and does the answer choice match that exact verb form? | Medium |
How to Approach Parallel Structure Questions on Test Day
Tip 1 — Find the Conjunction Before You Read the Sentence
On any sentence structure question involving a list or comparison, find the conjunction first — “and,” “or,” “but,” or a correlative pair — before you read the underlined portion carefully. The conjunction is what tells you that a parallel structure is in play and where the list items are. Once you know where the list is, identifying the anchor items and checking the underlined item is a mechanical process. Students who read the whole sentence before looking for the conjunction waste time and often miss the structure of the question entirely.
Tip 2 — The Anchor Is Always Non-Underlined — and the ACT Can Hide It
The ACT deliberately places the anchor items far from the underlined portion — sometimes a full sentence away, sometimes buried in a long introductory clause. Students who read only the underlined sentence and the answer choices will have no idea what form they are supposed to match. Before evaluating any answer choice on a parallel structure question, read backward from the conjunction and find every non-underlined item in the list. Those are your anchors. The answer choices cannot be evaluated until you know what you’re matching to.
Tip 3 — Gerunds and Infinitives Are Not Interchangeable When the Anchor Is Set
In everyday English, “I love to swim” and “I love swimming” mean the same thing — and most people treat them as equivalent. On the ACT, they are not equivalent when parallel structure is being tested. If the non-underlined anchor items are infinitives (“to build,” “to design,” “to plan”), the correct parallel item is also an infinitive — never a gerund. If the anchors are gerunds (“building,” “designing,” “planning”), the correct item is also a gerund. The meaning may be identical. The form is not. Run the Swap-and-Check on any answer choice that trades one verb form for the other.
Tip 4 — Parallel Structure and Wordiness Are Not the Same Question
Some students confuse parallel structure errors with wordiness errors because both can produce answer choices that sound unnecessarily long or awkward. The distinction matters because the fix is different. A parallel structure error requires matching a specific grammatical form — you cannot simply choose the shortest answer and call it correct. On the other hand, when two answer choices are equally parallel, the shorter, more direct one is almost always correct. The sequence: fix parallelism first, then prefer concision among the choices that survive the parallel structure check.
Common Questions About ACT Parallel Structure
Use the Anchor Hunt: trace the conjunction backward. When you see “and,” “or,” or a correlative pair near the underlined portion, do not stop at the previous comma. Read the full preceding sentence and identify every item that belongs to the same list. The non-underlined items — however far away they appear — are your anchors.
A practical shorthand: look for series markers in the surrounding passage. Words and phrases like “first,” “second,” “in addition,” “also,” and “finally” signal that a list is continuing across sentences. Find the first item connected to those markers and identify its grammatical form. That form is what you must match in the underlined portion, even if the two items are separated by multiple lines of text.
If you genuinely cannot find the anchor within two or three sentences, look for the verb that governs the entire list — the main verb the list items attach to. What form does that verb require? Objects of “to demonstrate” are typically nouns or infinitives; objects of “including” are typically nouns or gerunds. The governing verb narrows your choices even before you find the specific anchor items.
These are two different error types, and the ACT tests both — sometimes in the same question. The distinction comes down to what kind of problem the wrong answer has.
A parallel structure error means the underlined item is in a different grammatical form from the anchor items it’s supposed to match — a clause where a phrase is required, or a gerund where an infinitive is required. The fix is a form change, not a length change. A wordiness error means the underlined item is grammatically correct and parallel, but uses more words than necessary to express the same idea — typically through redundancy, passive voice where active would work, or unnecessary nominalization (using a noun like “demonstration” when a verb like “demonstrate” would do).
In practice, an answer choice can have both errors simultaneously — it can be non-parallel AND wordy. When that happens, fixing parallelism first usually produces the cleaner, more concise answer automatically. If two choices are equally parallel, choose the shorter, more direct one. But never choose a short answer over a longer one solely because it is shorter — if the shorter answer breaks the parallel structure, it is wrong regardless of its concision.