ACT Sentence Structure: Fragments, Run-Ons & Parallel Structure Mastery Guide
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16 Sentence Structure Rules · Every Fragment Type · All Run-On Fixes · 12 Parallel Structure Patterns · Wrong & Right Examples
Published: May 2026 | Updated: May 2026 | ~15 min read
51-56% CSE weight on ACT English -- sentence structure is a major CSE subcategory | 16 Sentence structure rules covered in this guide | 12 Parallel structure patterns with wrong/right examples | ~8-10 Sentence structure questions per 50-question Enhanced ACT English section |
Fragment Missing subject or verb -- the most common sentence error | Run-On Two independent clauses without proper connection | Comma Splice Run-on joined by comma alone -- extremely common trap | Parallel Items in a list or comparison must use the same grammatical form |
Table of Contents
Introduction: Sentence Structure Is the Architecture of ACT English
A student who masters ACT punctuation (comma rules, semicolons, apostrophes) has addressed approximately half of the Conventions of Standard English (CSE) questions. The other half -- sentence structure -- requires a different kind of competence. Punctuation rules ask: is this mark correctly placed? Sentence structure rules ask a more fundamental question: is this a sentence at all?
Fragments, run-ons, comma splices, and faulty parallelism account for approximately 8-10 questions in every ACT English section. These errors are among the most reliably testable because they involve structural properties of sentences that can be verified objectively. Either an independent clause is present or it is not. Either the items in a list share the same grammatical form or they do not. Like punctuation, sentence structure has definitive right answers -- but unlike punctuation, the rules require understanding sentence anatomy before applying them.
This guide covers all 16 sentence structure rules across six areas: sentence foundations, six fragment types, five run-on types, comma splices specifically, subordinate clauses, and parallel structure with 12 distinct patterns. Each rule includes a wrong example, a right example, the test to identify the error, and the specific ACT fix. This is everything a student needs to make sentence structure a reliable strength on ACT English.
1. What ACT Sentence Structure Tests -- and Why It Matters
Sentence Structure Error | What It Is | How Often Tested | Consequence If Missed |
Fragment | A group of words punctuated as a sentence but missing a subject, a verb, or both -- or containing only a dependent clause | High -- 2-3 questions per section | Students often 'hear' fragments as correct because they follow naturally from the previous sentence in context |
Run-on sentence | Two independent clauses joined without appropriate punctuation or connecting words | High -- 2-3 questions per section | Students often accept run-ons because the ideas are closely related -- but close relationship does not make the structure correct |
Comma splice | A specific type of run-on: two independent clauses joined only by a comma (no coordinating conjunction) | Very High -- appears in almost every ACT administration | Comma splices are the most common sentence structure error in student writing and on the ACT |
Faulty parallel structure | Items in a list or comparison that use different grammatical forms (mixing gerunds with infinitives, nouns with clauses, etc.) | High -- 2-3 questions per section | Students often miss parallelism errors because the individual items seem fine -- the error is in the inconsistency of forms, which requires comparing all items simultaneously |
Misplaced modifier | A modifier (phrase or clause) positioned so it appears to describe the wrong word or no word at all | Moderate -- 1-2 questions per section | Misplaced modifiers often sound acceptable when read quickly; catching them requires identifying what word the modifier actually modifies |
Subject-verb disagreement within complex sentence | Choosing the wrong verb form when subject and verb are separated by an intervening phrase | Moderate -- 1-2 questions per section | Intervening phrases confuse students into agreeing the verb with the nearest noun rather than the actual subject |
Sentence Structure Is Worth Drilling First for Many Students: Unlike some grammar concepts where rules overlap, each sentence structure category has a clean, learnable rule set. A student who understands what makes a complete sentence, identifies independent vs dependent clauses reliably, and applies the 4 run-on fixes automatically can expect to answer 8-10 sentence structure questions correctly per ACT. That improvement alone can add 2-3 ACT English points.
2. Part 1: Sentence Foundations -- What Makes a Complete Sentence
Before identifying fragments and run-ons, every student must have an airtight understanding of what a complete sentence requires. These are the two non-negotiable elements:
REQUIREMENT 1: A SUBJECT | REQUIREMENT 2: A PREDICATE (VERB) |
Who or what the sentence is about Can be a noun, pronoun, or noun phrase Example: 'The scientist' / 'She' / 'Running fast' MUST be explicitly stated (implied subjects = fragments in formal writing) | What the subject does or is Must be a finite verb (not a gerund or infinitive alone) Example: 'discovered' / 'is running' / 'had been tested' 'Running' alone is NOT a finite verb -- 'is running' IS a finite verb |
A complete sentence also requires INDEPENDENCE -- it must express a complete thought and not begin with a subordinating word that makes it dependent on another clause. Subject + verb is necessary but not sufficient if the structure is dependent.
Structure | Subject? | Verb? | Independent? | Sentence? |
She runs every morning. | YES (She) | YES (runs) | YES | ✅ COMPLETE SENTENCE |
Running every morning. | NO | NO (gerund, not finite verb) | -- | ❌ FRAGMENT (no subject or finite verb) |
Because she runs every morning. | YES (she) | YES (runs) | NO (because makes it dependent) | ❌ FRAGMENT (dependent clause) |
She runs every morning, she feels energised. | TWO subjects | TWO verbs | TWO independent clauses joined by comma alone | ❌ COMMA SPLICE (run-on) |
She runs every morning; she feels energised. | TWO subjects | TWO verbs | YES (semicolon correctly joins them) | ✅ CORRECT |
3. Part 2: Fragments -- The 6 Types and How to Fix Every One
A fragment is a group of words punctuated as a sentence that lacks a subject, a finite verb, or independent clause status. The ACT tests six distinct fragment types. Recognising each type is the key to fixing it correctly.
Concept F1: Missing-Subject Fragment
Definition: A phrase or clause that has a verb but no stated subject. Often follows a complete sentence and describes or continues the action of the previous subject.
❌ Wrong: The scientist worked late into the night. Hoping to complete the experiment. [no subject in second 'sentence']
✅ Right: The scientist worked late into the night, hoping to complete the experiment. [attach the participial phrase to the main clause with a comma]
The Test: Ask: WHO is doing the action? If no answer exists in that group of words -- it is a subject fragment. Fix: attach it to the previous sentence with a comma or rewrite to add a subject.
ACT Fix: Most missing-subject fragments are participial phrases (-ing or -ed phrases). The fix is almost always: join with a comma to the sentence whose subject is implied.
Concept F2: Missing-Verb Fragment (Noun Phrase Fragment)
Definition: A group of words with a noun but no finite verb. Common when a noun phrase with multiple modifiers is mistaken for a complete sentence.
❌ Wrong: The ancient, crumbling tower at the edge of the village. [no verb -- what does the tower DO?]
✅ Right: The ancient, crumbling tower at the edge of the village stood for centuries. [verb 'stood' added]
The Test: Ask: What does the subject DO or what IS it? If no answer exists -- it is a verb fragment. Fix: add a finite verb, or attach to an adjacent sentence that provides a predicate.
ACT Fix: Long, complex noun phrases are easily mistaken for sentences because they 'feel substantial.' Length is not a substitute for a verb. Always verify: is there a finite verb?
Concept F3: Dependent Clause Fragment
Definition: A clause with both subject and verb but beginning with a subordinating conjunction (because, although, since, when, while, if, unless, though, as, after, before, until), making it dependent on a main clause that is absent.
❌ Wrong: Although she had studied for weeks. [subject: she; verb: had studied; but 'although' makes it dependent]
✅ Right: Although she had studied for weeks, she still felt nervous. [main clause added after the dependent clause] OR She had studied for weeks. [subordinating conjunction removed]
The Test: Subordinating conjunctions: because, although, since, when, while, if, unless, though, as, after, before, until, whereas, even though. Any clause beginning with these words is dependent -- it needs a main clause.
ACT Fix: The ACT frequently places dependent clause fragments after a period following a complete sentence. The fix: either remove the period and attach with a comma, or remove the subordinating conjunction to make the clause independent.
Concept F4: Relative Clause Fragment
Definition: A clause beginning with a relative pronoun (which, that, who, whom, whose, where, when) that is punctuated as a standalone sentence instead of being attached to the noun it modifies.
❌ Wrong: The report was finally published. Which had been delayed for three years. ['Which had been delayed' is a relative clause modifying 'report' -- not a sentence]
✅ Right: The report, which had been delayed for three years, was finally published. [relative clause embedded in the main clause]
The Test: Relative pronouns that signal a relative clause: which, that, who, whom, whose, where, when. A clause beginning with these words cannot stand alone. Fix: embed the relative clause into the sentence containing the noun it modifies.
ACT Fix: ACT frequently uses 'which' fragments. The most common error: a sentence followed by a period and 'Which [verb]...' This is always wrong. 'Which' begins a relative clause, not an independent sentence.
Concept F5: Infinitive Phrase Fragment
Definition: A phrase beginning with 'to + verb' (the infinitive form) that is not attached to a main clause. Infinitives are not finite verbs and cannot serve as the predicate of a sentence.
❌ Wrong: To understand the complexity of the issue. [infinitive phrase -- no subject, no finite verb]
✅ Right: To understand the complexity of the issue, readers must review the full report. [infinitive phrase becomes an introductory element with a main clause]
The Test: Infinitive phrases begin with 'to + verb': to run, to understand, to complete. These are NOT finite verbs -- they cannot be the main verb of a sentence. Fix: attach to a main clause as an introductory or concluding phrase.
ACT Fix: Infinitive fragments often appear at the start of a passage or paragraph in the ACT -- they look like topic sentences but have no main clause. The fix always involves adding a main clause subject + finite verb after the infinitive phrase.
Concept F6: Appositive Phrase Fragment
Definition: A noun phrase that renames or describes an adjacent noun but is punctuated as its own sentence instead of being integrated into the sentence containing the noun it renames.
❌ Wrong: She was awarded a prestigious honour. A recognition of her decades of service. ['A recognition...' is an appositive renaming 'honour' -- not a standalone sentence]
✅ Right: She was awarded a prestigious honour, a recognition of her decades of service. [appositive integrated with comma]
The Test: Appositive phrases rename or explain the preceding noun. They cannot stand alone as sentences. Fix: attach to the noun they rename with a comma (or dash) rather than a period.
ACT Fix: Appositive fragments are common in journalistic writing and often 'sound right' because they add natural explanation. But natural-sounding does not mean structurally correct. Always verify: does this phrase have its own subject and finite verb? If not, it is an appositive fragment.
4. Part 3: Run-On Sentences -- The 5 Types and 4 Fixes
A run-on sentence occurs when two or more independent clauses are joined without appropriate punctuation or connecting words. The ACT tests five distinct run-on configurations and expects students to know all four standard fixes.
The 5 Run-On Types
Run-On Type | What It Is | Example | Fix Required |
Fused sentence | Two independent clauses with no punctuation or conjunction between them | She studied the data she discovered an error. | Separate with period, semicolon, or add comma + FANBOYS |
Comma splice (most common) | Two independent clauses joined by a comma alone (no FANBOYS) | She studied the data, she discovered an error. | Add FANBOYS after comma, replace comma with semicolon, or separate into sentences |
FANBOYS without comma | Two independent clauses joined by FANBOYS (and/but/so) without a preceding comma | She studied the data and she discovered an error. | Add comma before FANBOYS: 'She studied the data, and she discovered an error.' |
Semicolon before FANBOYS | A semicolon used immediately before a FANBOYS conjunction -- wrong combination | She studied the data; and she discovered an error. | Remove the semicolon and replace with a comma: 'She studied the data, and she discovered an error.' |
Conjunctive adverb without semicolon | Two independent clauses joined by a conjunctive adverb (however, therefore, moreover) without a semicolon before it | She studied the data, however she discovered an error. | Semicolon before conjunctive adverb + comma after: 'She studied the data; however, she discovered an error.' |
The 4 Fixes for ANY Run-On
Fix 1: PERIOD -- Separate into Two Complete Sentences
She studied the data. She discovered an error. [always correct; may not always be stylistically preferred]
Fix 2: SEMICOLON -- Join Two Independent Clauses Without a Conjunction
She studied the data; she discovered an error. [semicolon signals close relationship between clauses]
Fix 3: COMMA + FANBOYS -- Join Two Independent Clauses With a Coordinating Conjunction
She studied the data, and she discovered an error. [FANBOYS: For And Nor But Or Yet So -- comma required before them when joining two independent clauses]
Fix 4: SUBORDINATION -- Make One Clause Dependent
When she studied the data, she discovered an error. [subordinating conjunction 'when' makes first clause dependent -- no longer two independent clauses]
Which Fix Does the ACT Prefer? The ACT tests whether all four fixes are correctly understood -- but NO CHANGE (the original) is also a valid answer if the original sentence is already correctly structured. When choosing between fixes in answer choices: eliminate any choice that creates a new error (comma splice, semicolon before FANBOYS). Among the remaining correct options, choose the one that best serves the passage's style -- formal or concise.
5. Part 4: Comma Splices -- The Most Tested Run-On Variant
The comma splice is so frequently tested on ACT English that it deserves its own section. It is simultaneously the most common sentence structure error in student writing and the most common sentence structure question on the ACT.
Comma Splice Scenario | Wrong | Correct Fix | Why This Fix |
Two short, closely related clauses | The rain fell, the streets flooded. | The rain fell, and the streets flooded. OR The rain fell; the streets flooded. | Comma + FANBOYS adds logical connection. Semicolon signals close relationship. |
Second clause provides a result or consequence | She trained daily, she improved rapidly. | She trained daily, so she improved rapidly. OR She trained daily; as a result, she improved rapidly. | FANBOYS 'so' names the cause-effect relationship. Conjunctive adverb 'as a result' after semicolon also correct. |
Second clause provides a contrast | He wanted to leave, she insisted on staying. | He wanted to leave, but she insisted on staying. OR He wanted to leave; however, she insisted on staying. | FANBOYS 'but' names the contrast. 'However' after semicolon also names the contrast. |
Long, complex clauses where a period is cleaner | The committee had reviewed the proposal for weeks, they ultimately voted to reject it. | The committee had reviewed the proposal for weeks. They ultimately voted to reject it. | A period is always a valid fix and is often the clearest choice for long clauses. |
Clause beginning with a conjunctive adverb | The data was incomplete, therefore the results were unreliable. | The data was incomplete; therefore, the results were unreliable. | Semicolon BEFORE conjunctive adverb (therefore, however, moreover, consequently). Comma AFTER the conjunctive adverb. |
⚠️ The Conjunctive Adverb Trap: Words like 'however,' 'therefore,' 'moreover,' 'consequently,' 'furthermore,' 'nevertheless,' 'accordingly,' and 'thus' are NOT coordinating conjunctions (FANBOYS). They cannot join two independent clauses with just a comma before them. The correct pattern is: [independent clause]; [conjunctive adverb], [independent clause]. The comma goes AFTER the conjunctive adverb -- not before it.
6. Part 5: Subordinate Clauses and Misplaced Modifiers
Subordinate clauses and modifying phrases must be correctly positioned -- adjacent to the word or clause they modify. The ACT tests two sentence structure errors related to modification: dangling modifiers and misplaced modifiers.
Concept MS1: Dangling Modifier
Definition: An introductory modifying phrase whose implied subject does not match the grammatical subject of the main clause. The modifier 'dangles' because it has nothing to correctly modify.
❌ Wrong: Arriving late to the meeting, the presentation had already started. ['Arriving late' modifies 'the presentation' -- but a presentation cannot arrive late]
✅ Right: Arriving late to the meeting, she found the presentation had already started. [now 'arriving late' correctly modifies 'she' -- the actual person who arrived late]
The Test: The test: read the introductory phrase. Ask: WHO is doing this action? Then check: is that person the grammatical subject of the main clause? If not -- dangling modifier.
ACT Fix: The fix for a dangling modifier is always to change the subject of the main clause to the person or thing doing the action in the modifier. Never fix by rewriting the modifier itself unless the question's answer choices offer that option.
Concept MS2: Misplaced Modifier
Definition: A modifying phrase or clause positioned too far from the word it modifies, creating ambiguity or absurdity about what is being modified.
❌ Wrong: She almost drove her children to school every day. ['almost' modifies 'drove' -- implying she almost drove but didn't; the intended meaning is 'almost every day']
✅ Right: She drove her children to school almost every day. ['almost' now modifies 'every day' -- the intended meaning]
The Test: Modifiers should be placed immediately adjacent to the word or phrase they modify. If a modifier's position creates an unintended or absurd meaning -- it is misplaced.
ACT Fix: Single-word adverbs (only, almost, nearly, just, even) are the most frequently misplaced modifiers on ACT English. Verify: does the placement of this word create any unintended reading? If so, move it adjacent to what it truly modifies.
7. Part 6: Parallel Structure -- All 12 Patterns
Parallel structure requires that grammatically equal ideas be expressed in grammatically equal forms. When a sentence lists or compares items, all items must be in the same grammatical category. The ACT tests 12 distinct parallel structure scenarios. Each is illustrated below with a wrong and right example.
SECTION A: Lists and Series
When three or more items are listed in a series, all items must be in the same grammatical form.
❌ Not parallel: She enjoys swimming, to run, and cooking.
✅ Parallel: She enjoys swimming, running, and cooking.
Pattern: Gerund + Gerund + Gerund. All three list items must share the same form (here: gerunds = -ing verbs used as nouns).
❌ Not parallel: The plan requires efficiency, that workers cooperate, and dedication.
✅ Parallel: The plan requires efficiency, cooperation, and dedication.
Pattern: Noun + Noun + Noun. Embedding a clause ('that workers cooperate') among nouns breaks parallelism. Convert the clause to a matching noun form.
❌ Not parallel: He is talented, hard-working, and has determination.
✅ Parallel: He is talented, hard-working, and determined.
Pattern: Adjective + Adjective + Adjective. 'Has determination' is a verb phrase -- it cannot be parallel with adjectives. Convert to 'determined.'
SECTION B: Correlative Conjunctions
Correlative conjunctions always come in pairs and require parallel structure in both halves: both...and, either...or, neither...nor, not only...but also, as...as, more...than, the same...as.
❌ Not parallel: She is both talented and has experience.
✅ Parallel: She is both talented and experienced.
Pattern: Both [adjective] and [adjective]. Both sides of 'both...and' must match the same grammatical form. 'Has experience' is a verb phrase; 'experienced' is the matching adjective.
❌ Not parallel: Either we complete the project by Friday or to ask for an extension.
✅ Parallel: Either we complete the project by Friday or we ask for an extension.
Pattern: Either [subject+verb clause] or [subject+verb clause]. Both halves of either...or must mirror the same clause structure.
❌ Not parallel: Not only did she finish first, but also the highest score was hers.
✅ Parallel: Not only did she finish first, but also she earned the highest score.
Pattern: Not only [subject+verb] but also [subject+verb]. The clause structure must mirror on both sides: inversion ('did she finish') vs standard ('she earned').
SECTION C: Comparisons
When two things are compared, both sides of the comparison must be in the same grammatical form and must compare equivalent things (not a thing to an action, or a noun to a clause).
❌ Not parallel: The cost of this plan is higher than the alternative plan.
✅ Parallel: The cost of this plan is higher than the cost of the alternative plan. OR This plan costs more than the alternative plan.
Pattern: Compare [cost] to [cost], not [cost] to [plan]. Illogical comparisons on the ACT compare a noun to an incompatible noun -- fix by making both sides compare the same type of element.
❌ Not parallel: Running is more effective for weight loss than to diet.
✅ Parallel: Running is more effective for weight loss than dieting.
Pattern: Gerund than Gerund. Both sides of 'more...than' must be in the same form. 'Running' is a gerund; 'to diet' is an infinitive. Use 'dieting' to match.
SECTION D: Infinitive Structures
When infinitives are listed or compared, maintain the same infinitive structure throughout.
❌ Not parallel: Her goals are to learn, growing, and achieve success.
✅ Parallel: Her goals are to learn, to grow, and to achieve success. OR Her goals are learning, growing, and achieving success.
Pattern: Infinitive + Infinitive + Infinitive, OR Gerund + Gerund + Gerund. Never mix infinitives and gerunds in the same series.
❌ Not parallel: The committee decided to review the proposal, to request additional data, and that they would postpone the vote.
✅ Parallel: The committee decided to review the proposal, to request additional data, and to postpone the vote.
Pattern: Infinitive + Infinitive + Infinitive. The embedded clause ('that they would postpone') breaks the parallel series of infinitives. Replace with matching infinitive.
SECTION E: Clause Structures
When clauses are listed or compared, all clauses must be in the same structural form.
❌ Not parallel: The report concluded that costs were rising, that efficiency had declined, and productivity would fall.
✅ Parallel: The report concluded that costs were rising, that efficiency had declined, and that productivity would fall.
Pattern: That [clause] + That [clause] + That [clause]. When 'that' introduces a series of noun clauses, it must appear before EACH clause in the series -- not just the first two.
❌ Not parallel: What matters is not where you start but your destination is what counts.
✅ Parallel: What matters is not where you start but where you end up.
Pattern: Not [clause] but [clause]. Both halves of 'not...but' must be parallel noun clauses beginning with 'where' (or equivalent structure).
SECTION F: Mixed Structures -- The Hardest Patterns
The ACT sometimes combines multiple parallelism violations in a single sentence, or embeds a parallelism error within a longer structure where the broken element is not obvious.
❌ Not parallel: The programme was designed to identify talented students, providing them with resources, and for ensuring their success.
✅ Parallel: The programme was designed to identify talented students, to provide them with resources, and to ensure their success.
Pattern: Infinitive + Infinitive + Infinitive. Three actions after 'designed to': all must be infinitives. Gerund 'providing' and prepositional phrase 'for ensuring' are both wrong forms -- convert all to 'to + verb.'
✅ The Parallel Structure Test: When you see a list or comparison, identify the FIRST item's grammatical form. That form is the template for all other items. Cover each other item individually and ask: is this in the SAME grammatical form as the first? If any item fails -- parallelism error. The first item always sets the pattern because it is grammatically committed before the others appear.
8. Part 7: Subject-Verb Agreement Within Complex Sentences
When intervening phrases separate a subject from its verb, ACT English tests whether the student can identify the TRUE subject and match the verb to it -- not to the nearest noun.
Sentence Structure | True Subject | Nearest Noun (Trap) | Correct Verb | Wrong Verb |
The list of requirements [verb] been updated. | list (singular) | requirements (plural) | has been | have been |
The team of researchers [verb] published the findings. | team (singular) | researchers (plural) | has published | have published |
Each of the students [verb] required to submit a form. | each (singular) | students (plural) | is | are |
The data collected from all 50 sites [verb] been analysed. | data (singular -- treated as collective) | sites (plural) | has | have |
Neither the manager nor the employees [verb] aware of the change. | employees (plural -- 'nor' rule: verb agrees with closer subject) | manager (singular) | were | was |
The 'Neither/Nor' and 'Either/Or' Rule When two subjects are connected by either...or or neither...nor, the verb agrees with the CLOSER (second) subject. 'Neither the student nor the teachers were...' -- agree with 'teachers' (closer). 'Neither the teachers nor the student was...' -- agree with 'student' (closer). This specific rule is tested on both ACT and SAT.
9. The 4-Step Sentence Structure Decision Process
Apply this 4-step process to every ACT English sentence structure question:
Identify the Boundaries of Each Clause
Read the full sentence (and adjacent sentences if needed). Identify each independent clause: find its subject and finite verb. Draw an imaginary boundary between each independent clause. Count the clauses: one clause = check for fragment completeness. Two+ clauses = check how they are joined.
Check for Independent Clause Status
For each clause identified: does it have a subject AND a finite verb AND can it stand alone? If yes = independent clause. If it begins with a subordinating conjunction (because, although, when, since...) or a relative pronoun (which, who, that...) = dependent clause. Dependent clause alone = fragment. Dependent clause joined to independent clause correctly = fine.
Check the Connection Between Clauses
If two independent clauses are present: is the connection between them correct? Period = always fine. Semicolon = fine if no FANBOYS follows. Comma + FANBOYS = fine. Conjunctive adverb = needs semicolon before it. Comma alone = comma splice. Nothing = fused sentence.
Check for Parallel Structure and Modifier Placement
If the sentence contains a list or comparison: are all items in the same grammatical form? If the sentence contains an introductory phrase: does its implied subject match the main clause's grammatical subject? If an adverb is present: is it placed adjacent to what it modifies?
10. ACT-Specific Sentence Structure Traps at the 33+ Score Level
High-Difficulty Trap | Why Students Miss It | Score Level | Detection Strategy |
Embedded dependent clause fragment | A dependent clause is long and detailed enough that it sounds complete. 'Although researchers from three major institutions had spent years investigating the phenomenon and had published several peer-reviewed papers.' The length disguises the missing main clause. | 33+ trap | Identify the first word: 'although' = subordinating conjunction = dependent clause. No matter how long or detailed, it is a fragment without a main clause. |
Conjunctive adverb mistaken for FANBOYS | Students see 'however,' 'therefore,' or 'moreover' and treat them like 'but,' 'so,' or 'and.' Using a comma before 'however' (like a comma before 'but') creates a comma splice. | 30+ trap | Memorise: however/therefore/moreover/consequently/furthermore = conjunctive adverbs = NEED semicolon before them. FANBOYS only = For And Nor But Or Yet So. |
Parallel structure violation buried in a long list | 'The project required careful planning, extensive research, collaboration from multiple teams, and that all results would be verified independently.' The 'that' clause breaks parallelism with the three preceding nouns. | 32+ trap | Identify the first item's form. Check every subsequent item against that form. The violation is often in the last item of a 4+ item list -- the longest distance from the established pattern. |
Dangling modifier with a passive main clause | 'Having completed the analysis, the results were published.' The analysis was completed by researchers -- but 'the results' is the grammatical subject. Results do not complete analyses. | 33+ trap | Any introductory -ing phrase must have a main clause whose grammatical subject is the one doing the -ing action. Passive constructions almost always produce dangling modifiers. |
Neither...nor subject-verb agreement with compound structure | 'Neither the director nor the board members was informed.' Students see 'board members' (plural) closest to the verb and choose 'was' incorrectly, or see 'director' (singular) as the first subject and choose 'was' for the wrong reason. | 31+ trap | Verb agrees with the CLOSER subject. 'Board members' is closer. Plural = 'were.' The answer: 'Neither the director nor the board members were informed.' |
11. Quick Reference: 16 Rules at a Glance
# | Rule | Category | One-Line Summary | Tested Frequency |
1 | Complete sentence requires subject + finite verb | Foundation | No subject OR no finite verb = fragment | Very High |
2 | Independent clause can stand alone | Foundation | A clause with subordinating conjunction at start cannot stand alone | Very High |
3 | Missing-subject fragment | Fragments | Participial phrase without main clause is a fragment | High |
4 | Missing-verb fragment | Fragments | Noun phrase alone is a fragment -- no finite verb present | High |
5 | Dependent clause fragment | Fragments | Because/although/when/since clauses cannot stand alone | Very High |
6 | Relative clause fragment | Fragments | Which/who/that clauses cannot stand alone as sentences | High |
7 | Infinitive phrase fragment | Fragments | To + verb phrases are not finite verbs -- cannot be predicates | Moderate |
8 | Appositive phrase fragment | Fragments | Renaming phrases cannot stand alone -- attach to the noun | Moderate |
9 | Comma splice | Run-ons | Two independent clauses + comma alone = always wrong | Very High |
10 | Fused sentence | Run-ons | Two independent clauses with no connection = always wrong | High |
11 | Four run-on fixes | Run-ons | Period / Semicolon / Comma+FANBOYS / Subordination | Very High |
12 | Conjunctive adverb rule | Run-ons | However/therefore need semicolon before, comma after | High |
13 | List parallelism | Parallel | All list items must match the form of the first item | Very High |
14 | Correlative conjunction parallelism | Parallel | Both...and / either...or / neither...nor require matching forms | High |
15 | Comparison parallelism | Parallel | Compare equivalent grammatical structures and equivalent things | High |
16 | Dangling/misplaced modifier | Modifiers | Introductory phrase subject must match main clause subject | Moderate |
12. Sentence Structure Practice Strategy
Week | Focus | Daily Practice | Milestone |
Week 1 | Sentence foundations + all 6 fragment types | For each fragment type: read 10 examples, identify the type in under 5 seconds, write the correction. Practise identifying independent vs dependent clauses by reading 20 sentences and labelling each clause. | Fragment types identified in under 5 seconds; dependent clause recognition automatic |
Week 2 | Run-ons, comma splices, and the 4 fixes | 15 run-on questions from official ACT materials; for each: identify the type, write all 4 possible fixes, determine which appears in the answer choices | All 4 run-on fixes automatic; comma splice identified instantly; conjunctive adverb rule applied correctly |
Week 3 | Parallel structure -- all 12 patterns | 20 parallel structure questions; for each: identify the first item's form, check every subsequent item, identify the violation type from the 12 patterns | All 12 parallel patterns recognisable; first-item template check automatic |
Week 4 | Modifiers + subject-verb agreement in complex sentences | 10 dangling modifier questions; 10 subject-verb agreement questions with intervening phrases; practise identifying the true subject in complex noun phrases | Dangling modifier detection automatic; true subject identified regardless of intervening phrase length |
Week 5 | Full integration + timed practice sections | Two full 50-question ACT English sections timed. After each: categorise every sentence structure error by type. Identify which of the 16 rules appears in each wrong answer. | All 16 rules applied correctly; sentence structure questions averaging under 40 seconds each |
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13. Frequently Asked Questions (12 FAQs)
Based on Enhanced ACT English CSE specifications and common student questions about sentence structure.
What sentence structure questions appear on the ACT English test?
The ACT English section tests sentence structure as part of the Conventions of Standard English (CSE) category, which accounts for 51-56% of the 50-question Enhanced ACT English section. Sentence structure questions test: sentence fragments (groups of words punctuated as sentences that lack a subject, finite verb, or independent clause status), run-on sentences and comma splices (two independent clauses joined without appropriate punctuation or connecting words), parallel structure (ensuring grammatically equal ideas are expressed in grammatically equal forms), and modifier placement (introductory phrases must correctly relate to the main clause's grammatical subject). Together, these sentence structure sub-categories account for approximately 8-10 questions per ACT English section.
What is a sentence fragment and how do I identify it on the ACT?
A sentence fragment is a group of words punctuated as a sentence that is missing a required element. There are three ways a fragment can fail: (1) No subject -- a phrase or clause with a verb but no stated subject, often a participial phrase like 'Having completed the report.' (2) No finite verb -- a noun phrase with no predicate, like 'The ancient tower at the edge of the village.' (3) Not independent -- a clause that has both subject and verb but begins with a subordinating conjunction (because, although, since, when) or a relative pronoun (which, who, that) that makes it dependent on a main clause that is absent. Identification strategy: ask three questions. Does it have a subject? Does it have a finite verb? Can it stand alone without depending on another clause? If any answer is no -- it is a fragment.
What is a comma splice and how do I fix it on the ACT?
A comma splice is the error of joining two independent clauses with only a comma -- no coordinating conjunction. Example: 'She studied all night, she passed the exam.' Both clauses are complete sentences, but a comma alone cannot join them. There are four correct fixes: (1) Replace the comma with a period: 'She studied all night. She passed the exam.' (2) Replace the comma with a semicolon: 'She studied all night; she passed the exam.' (3) Add a FANBOYS conjunction after the comma: 'She studied all night, so she passed the exam.' (4) Use a subordinating conjunction to make one clause dependent: 'Because she studied all night, she passed the exam.' The comma splice is the most frequently tested run-on error on both the ACT and SAT.
What is parallel structure on the ACT?
Parallel structure requires that items in a list or comparison be expressed in the same grammatical form. When you list three or more items, or compare two things using correlative conjunctions (both...and, either...or, not only...but also), all parts must match grammatically. Example: 'She enjoys swimming, running, and to bike' violates parallelism -- two gerunds and one infinitive. Correct: 'She enjoys swimming, running, and biking.' The test: identify the grammatical form of the FIRST item in the list or the first half of the comparison. That form is the template. Every subsequent item must match it.
What is the difference between a run-on sentence and a comma splice?
A comma splice is a specific type of run-on sentence. A run-on sentence is the broad category: any sentence in which two independent clauses are joined without appropriate punctuation or connecting words. A comma splice is the specific sub-type in which the two independent clauses are joined by a comma alone (without a coordinating conjunction). A fused sentence is the sub-type in which the clauses are joined with no punctuation at all. All comma splices are run-on sentences, but not all run-on sentences are comma splices -- a sentence with no punctuation between two independent clauses is a run-on but not a comma splice.
How do I know when to use a semicolon vs a comma on the ACT?
Use a semicolon to join two complete, independent clauses without a coordinating conjunction: 'She studied; she passed.' Never use a semicolon before a FANBOYS conjunction (for, and, nor, but, or, yet, so) -- a semicolon before FANBOYS is always wrong. Never use a semicolon between a dependent and independent clause -- 'Although she studied; she was nervous' is wrong. Use a comma before FANBOYS when joining two independent clauses: 'She studied, so she passed.' Use a comma after an introductory dependent clause or phrase: 'Although she was tired, she continued.' The core test: is there a complete independent clause on BOTH sides of the semicolon? If yes, semicolon is valid. If either side is not a complete independent clause, the semicolon is wrong.
What is a dangling modifier and how does it appear on the ACT?
A dangling modifier is an introductory participial phrase or infinitive phrase whose implied subject does not match the grammatical subject of the main clause. Example: 'Exhausted after the marathon, the couch seemed inviting.' The phrase 'Exhausted after the marathon' implies that a person is exhausted -- but 'the couch' is the grammatical subject of the main clause. Couches cannot be exhausted from marathons. Correct: 'Exhausted after the marathon, she found the couch inviting.' The fix: change the main clause's grammatical subject to the person or thing performing the action in the introductory phrase. The most common ACT dangling modifier involves a passive main clause -- passive constructions typically have non-human grammatical subjects, which almost always dangle introductory phrases describing human actions.
How are correlative conjunctions tested on the ACT?
Correlative conjunctions are paired connectors: both...and, either...or, neither...nor, not only...but also, as...as, more...than, the same...as. The ACT tests that BOTH halves of a correlative conjunction are in the same grammatical form. 'She is both talented and has experience' violates the rule -- 'talented' is an adjective, 'has experience' is a verb phrase. Correct: 'She is both talented and experienced.' The strategy: when you see a correlative conjunction, immediately identify the grammatical form of the first half. Whatever form that is (adjective, verb, infinitive, noun, clause) -- the second half must be the identical form.
What is subject-verb agreement in complex sentences?
Subject-verb agreement requires the verb to match the TRUE subject in number -- singular subject = singular verb, plural subject = plural verb. In complex sentences, the true subject is often separated from the verb by an intervening phrase, making students incorrectly agree the verb with the nearest noun rather than the actual subject. Example: 'The list of requirements has been updated.' True subject: 'list' (singular), not 'requirements' (plural). Verb: 'has been' (singular). Key principle: prepositional phrases (of requirements, in the room, with the researchers) do not change the subject. Cross out the intervening phrase and match the verb to the true subject.
What is the FANBOYS rule on the ACT?
FANBOYS is a mnemonic for the seven coordinating conjunctions: For, And, Nor, But, Or, Yet, So. These are the ONLY conjunctions that can join two independent clauses when preceded by a comma. Rule: [independent clause], [FANBOYS] [independent clause]. Without a comma before FANBOYS (when joining independent clauses), it creates a run-on. With a semicolon before FANBOYS, it is wrong -- semicolons and FANBOYS cannot combine. Words like 'however,' 'therefore,' 'moreover,' 'consequently' are NOT FANBOYS and cannot follow a comma to join independent clauses -- they require a semicolon before them and a comma after them.
How do I practise sentence structure for the ACT?
The most effective practice sequence: (1) Learn the 16 rules in this guide completely -- understand each with its wrong and right examples. (2) Apply the 4-step decision process to 20 official ACT English questions from past exams. (3) For every sentence structure question you answer incorrectly, identify which rule was tested and why your answer was wrong. (4) Drill the specific rule that caused the error with 10 additional examples from the same category. (5) Take full timed ACT English sections (50 questions, 35 minutes for Enhanced ACT) and apply the 4-step process to every question -- do not rely on 'ear.' The most important preparation principle: sentence structure rules on the ACT are objective and definitive. 'Sounds right' is not a reliable method -- rules are.
Does the Enhanced ACT (2025+) test sentence structure differently?
The Enhanced ACT (April 2025 online, September 2025 paper) maintains the same sentence structure rules but delivers them with an explicit question stem for every question. This means sentence structure questions are now clearly labelled before you read the passage context: 'Which choice avoids creating a sentence fragment?' or 'Which choice correctly joins the two sentences?' This explicit stem is your signal of which category you are in and which of the 16 rules to apply. The rules themselves are identical to previous ACT administrations -- only the presentation format has changed. Students who know the 16 rules can use the explicit stem to trigger the correct rule faster, improving timing on the Enhanced ACT relative to the previous format.
14. EduShaale -- Expert ACT English Coaching
EduShaale builds ACT English sentence structure mastery through rule-based instruction, wrong/right example drilling, and the 4-step decision process that makes sentence structure reliable rather than instinct-based.
All 16 Rules to Automaticity: We teach all 16 sentence structure rules in sequence, building from sentence foundations through the most complex parallel structure patterns. Each rule is learned with its wrong example, right example, and specific ACT test signal.
Fragment Identification Reflex: We train fragment detection as a 5-second reflex: identify the first word (subordinating conjunction? = potential fragment), find the subject, find the finite verb, verify independence. This check takes 5 seconds and catches every fragment type.
Comma Splice Drilling: The comma splice is the most common sentence structure error on ACT English. We drill all four correct fixes until students can identify the comma splice and apply the appropriate fix in under 15 seconds.
Parallel Structure First-Item Template Method: We teach the first-item template check -- identify the first item's grammatical form, check every subsequent item against it -- as a reflex that catches all 12 parallelism pattern violations including the hardest embedded-clause patterns.
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EduShaale's principle: Every ACT sentence structure question has a definitively correct answer based on one of the 16 rules in this guide. Students who know all 16 rules and apply the 4-step decision process answer sentence structure questions in under 40 seconds with high accuracy. This is not a talent -- it is a learnable system.
15. References & Resources
Official ACT Resources
ACT Sentence Structure and Grammar Guides
PrepScholar -- ACT English: Complete Grammar and Rhetoric Guide
PrepScholar -- Run-On Sentences and Comma Splices on ACT English
PrepScholar -- Parallel Structure on the ACT: Complete Guide
Test Innovators -- Enhanced ACT English Section Overview (2026)
Academic Approach -- All About the New Enhanced ACT: English Section
EduShaale ACT English Resources
(c) 2026 EduShaale | edushaale.com | info@edushaale.com | +91 9019525923
ACT is a registered trademark of ACT, Inc. All format information based on ACT's Enhanced ACT specifications. Accurate as of May 2026 -- verify at act.org. This guide is for educational purposes only.
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