How do you tell a complete sentence from a fragment on the ACT, and how do you fix an underlined portion that leaves a sentence incomplete?
Complete sentences and fragments on ACT English: a clause needs a subject and a finite verb and must express a complete thought, recognizing fragments created by missing verbs, -ing verbs without a helper, and stray subordinators, and fixing an underlined portion to form a complete sentence.
A focused answer to complete sentences and fragments on ACT English: a sentence needs a subject and a finite verb and a complete thought, how fragments arise from missing or -ing verbs and stray subordinators, and how to fix an underlined portion that leaves a sentence incomplete. The foundation of the sentence-structure questions.
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What this skill is asking
The most basic sentence-structure skill on the ACT is telling a complete sentence from a fragment. Many Conventions questions hinge on it: an underlined portion may leave a "sentence" without a real verb, or a stray subordinating word may turn a complete thought into a dependent clause that cannot stand alone. If you can reliably spot what makes a clause complete, you can fix these fast, and they are common.
What makes a clause complete
An independent clause is the unit that can be a sentence by itself. It has a subject and a finite verb and finishes a thought.
The trickiest fragments look like sentences because they have a subject and an -ing word. But "-ing" forms (present participles) are not finite verbs on their own; they need a helping verb ("is walking", "were walking"). So "The committee debating the issue" is a fragment, while "The committee was debating the issue" is a sentence.
The three fragment types the ACT tests
Almost every ACT fragment is one of three kinds, and each has a standard fix.
Fixing a fragment in an underlined portion
When an underlined portion creates a fragment, the right option restores a subject plus a finite verb and a complete thought.
Why this skill anchors the section
Fragments are tested directly, but the skill also underpins the next two topics. To fix run-ons and comma splices, you first have to know what counts as an independent clause, because a run-on is two independent clauses joined wrongly. And to join clauses correctly, you need to tell independent from dependent. So "what makes a sentence complete" is the foundation: get it solid and a large block of Conventions questions becomes routine.
Try this
Q1. What three things does an independent clause need, and which one is missing in "The cyclists racing toward the finish line"? [Recall]
- Cue. It needs a subject, a finite verb, and a complete thought. "The cyclists racing toward the finish line" has a subject ("cyclists") but no finite verb, because "racing" is a participle, so it is a fragment. Fix it with "The cyclists raced toward the finish line."
Q2. Explain why "Since the museum reopened last spring" is a fragment, and give one way to fix it. [Short explanation]
- Cue. It has a subject ("museum") and a finite verb ("reopened"), but the subordinator "Since" makes the clause dependent, so it cannot stand alone. Fix it by removing the subordinator ("The museum reopened last spring.") or by attaching it to an independent clause ("Since the museum reopened last spring, attendance has doubled.").
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 for the underlined portion: 'The hikers reaching the summit just before noon.' (A) NO CHANGE (B) hikers reached the summit (C) hikers, reaching the summit, (D) hikers who reached the summitShow worked answer →
The correct answer is (B), "hikers reached the summit". The original is a fragment: "reaching" is a participle, not a finite verb, so there is no real verb and no complete thought. Changing "reaching" to "reached" gives the subject ("hikers") a finite verb and completes the sentence.
Why not the others: (A) keeps the fragment; (C) adds commas but still has no finite verb ("reaching" is still a participle); (D) turns the verb into a relative clause ("who reached"), which again leaves no main verb for "hikers". Only (B) forms a complete sentence.
ACT English (style)1 marksChoose the best option: 'Because the storm knocked out the power for three days.' (A) NO CHANGE (B) The storm knocked out the power for three days. (C) Since the storm knocked out the power for three days. (D) The storm, knocking out the power for three days.Show worked answer →
The correct answer is (B). The original is a fragment because the subordinator "Because" turns the clause into a dependent one that cannot stand alone. Removing "Because" leaves an independent clause: "The storm knocked out the power for three days."
Why not the others: (A) keeps the fragment; (C) swaps one subordinator for another ("Since"), which is still dependent; (D) replaces the finite verb "knocked" with the participle "knocking", creating a different fragment. Only (B) is a complete sentence.
Related dot points
- 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.
- Joining clauses on ACT English: the three connector types (coordinating conjunctions with a comma, subordinating conjunctions that make a clause dependent, and conjunctive adverbs that need a semicolon), how each is punctuated, and choosing the connector whose logical relationship and punctuation are both correct.
A focused answer to joining clauses on ACT English: coordinating conjunctions (comma before, FANBOYS), subordinating conjunctions (make one clause dependent), and conjunctive adverbs (semicolon before, comma after), how each is punctuated, and how to choose the connector whose logic and punctuation are both right.
- Verb tense and consistency on ACT English: keeping tense consistent with the surrounding sentences unless the meaning requires a change, using context (other verbs, time words) to set the right tense, and avoiding unjustified shifts in an underlined verb.
A focused answer to verb tense and consistency on ACT English: matching an underlined verb to the tense of the surrounding passage, using time words and nearby verbs to set the tense, and telling a wrong shift from a justified change of time, with a routine for choosing the consistent verb.
- Modifier placement on ACT English: the rule that a modifier should sit next to the word it describes, recognizing dangling modifiers (an introductory phrase whose subject is missing) and misplaced modifiers, and fixing an underlined portion so the word right after an introductory modifier is the one it logically describes.
A focused answer to modifier placement on ACT English: the rule that a modifier sits beside what it describes, how dangling modifiers leave an introductory phrase with no logical subject and how misplaced modifiers attach to the wrong word, and how to fix an underlined portion so the modifier lands correctly.
Sources & how we know this
- Description of the ACT English Test — ACT, Inc. (2025)
- Preparing for the ACT Test — ACT, Inc. (2025)