ACT English: Conventions of Standard English: Sentence Structure and Formation

Overview: Sentence Structure and Formation

Sentence structure questions on the ACT English test ask you to identify and fix errors in how clauses and phrases are connected. These questions make up a significant chunk of the Conventions of Standard English category, so understanding them well can directly boost your score.

This guide covers the four main error types you'll encounter: run-on sentences, comma splices, misplaced modifiers, and faulty parallelism.

Types of Questions

Run-On Sentences

A run-on sentence happens when two or more independent clauses (complete thoughts that could stand alone as sentences) are joined without proper punctuation or a connecting word.

Example 1:

Run-on: "My cat loves chasing lasers she can do it all day." Corrected: "My cat loves chasing lasers; she can do it all day."

Example 2:

Run-on: "After finishing his homework he played video games his friends joined him later." Corrected: "After finishing his homework, he played video games. His friends joined him later."

There are four standard ways to fix a run-on:

1. Add a period and make two separate sentences
2. Add a semicolon between the independent clauses
3. Add a comma + coordinating conjunction (for, and, nor, but, or, yet, so)
4. Make one clause dependent by adding a subordinating word (because, although, when, etc.)

On the ACT, look for spots where two complete thoughts collide with nothing between them. Read the sentence aloud in your head, and you'll often hear where one idea ends and another begins.

Misplaced Modifiers

A modifier is a word, phrase, or clause that describes something else in the sentence. When it's placed too far from the word it's supposed to modify, the meaning gets confusing or unintentionally funny.

The key rule: a modifying phrase at the beginning of a sentence must describe the subject that immediately follows the comma.

Example 1:

Misplaced: "Running fast, the wind couldn't catch up with me." (This says the wind was running fast.) Corrected: "Running fast, I couldn't be caught by the wind."

Example 2:

Misplaced: "Having finished the race, the medal was awarded to John." (This says the medal finished the race.) Corrected: "Having finished the race, John was awarded the medal."

When you spot an introductory phrase followed by a comma, check: does the subject right after the comma logically perform that action? If not, you need an answer choice that puts the correct subject in that position.

Comma Splices

A comma splice occurs when two independent clauses are connected with only a comma. A comma by itself isn't strong enough to join two complete thoughts.

Example 1:

Comma splice: "We drove to the beach, we enjoyed the sunny weather." Corrected: "We drove to the beach and enjoyed the sunny weather."

Example 2:

Comma splice: "She loves ice cream, she eats it every day." Corrected: "She loves ice cream, and she eats it every day."

Fixing a comma splice uses the same tools as fixing a run-on:

1. Replace the comma with a period to create two sentences
2. Replace the comma with a semicolon
3. Add a coordinating conjunction after the comma (comma + and, but, so, etc.)
4. Make one clause dependent (e.g., "Because she loves ice cream, she eats it every day.")

The difference between a run-on and a comma splice is small: a run-on has no punctuation between the clauses, while a comma splice has a comma that isn't doing enough. The fixes are the same.

Parallelism

Parallelism means that items in a list or series all follow the same grammatical form. If two items are gerunds (-ing words), the third one should be too.

Example 1:

Faulty: "He loves running, to swim, and reads a lot." Corrected: "He loves running, swimming, and reading."

Example 2:

Faulty: "She enjoys dancing, painting, and to sing." Corrected: "She enjoys dancing, painting, and singing."

When you see a list or series in an ACT question, check that every item matches in form. This applies to verb forms, noun phrases, and even clause structures. If two out of three items are gerunds, the odd one out is your error.

Tips for Success

Know your grammar rules. The error types above cover most sentence structure questions on the ACT. Make sure you can also recognize independent vs. dependent clauses, since that distinction drives most of these corrections.

Practice with real ACT passages. The more you work through actual test questions, the faster you'll recognize these patterns. Start by identifying the error type before looking at the answer choices.

Don't rush past short questions. Sentence structure errors can be subtle, especially comma splices that "sound" fine when you read quickly. Train yourself to pause at every comma between two clauses and ask: are both sides independent? If so, a comma alone won't cut it.

Practice Questions

Practice Question 1

Walking quickly, the distance seemed shorter.

A. Walking quickly, I found the distance seemed shorter. B. I found the distance seemed shorter, walking quickly. C. Walking quickly was the distance seemed shorter. D. The distance seemed shorter, walking quickly.

Correct Answer: A. The original sentence has a misplaced modifier. "Walking quickly" is an introductory phrase, so the subject right after the comma needs to be the person doing the walking. In the original, "the distance" follows the comma, which makes it sound like the distance was walking. Option A fixes this by placing "I" as the subject, making it clear who was walking quickly.

Practice Question 2

He enjoys reading, to write, and playing soccer.

A. He enjoys reading, writing, and playing soccer. B. He enjoys to read, to write, and playing soccer. C. He enjoys read, write, and play soccer. D. No change.

Correct Answer: A. This is a parallelism error. The three activities in the list need to match in grammatical form. "Reading" and "playing" are gerunds, but "to write" is an infinitive. Option A fixes this by making all three items gerunds: "reading, writing, and playing."

Practice Question 3

My brother loves playing football he's on the field every day.

A. My brother, who loves playing football, he's on the field every day. B. My brother loves playing football. He's on the field every day. C. Football, my brother loves playing, he's on the field every day. D. No change.

Correct Answer: B. This is a run-on sentence. Two independent clauses ("My brother loves playing football" and "he's on the field every day") are joined with no punctuation at all. Option B fixes it by separating them into two complete sentences with a period. Option A creates a different problem by leaving "he's" stranded after the clause, and Option C rearranges the words into a confusing structure.

Practice Question 4

We drove to the beach, we enjoyed the sunny weather.

A. We drove to the beach we enjoyed the sunny weather. B. We drove to the beach and enjoyed the sunny weather. C. Since we enjoyed the sunny weather, so we drove to the beach. D. No change.

Correct Answer: B. This is a comma splice: two independent clauses joined by only a comma. Option A makes it worse by removing the comma entirely (creating a run-on). Option C uses "since" and "so" together, which is redundant and grammatically incorrect. Option B properly joins the clauses with the coordinating conjunction "and," creating one smooth sentence.