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Sentence Structure

Identify and correct sentence structure errors including fragments, run-ons, comma splices, misplaced modifiers, and faulty parallelism.

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Sentence Structure

Sentence Types

  1. Simple: One independent clause. "The dog barked."
  2. Compound: Two independent clauses joined by conjunction or semicolon. "The dog barked, and the cat hissed."
  3. Complex: One independent + one dependent clause. "When the dog barked, the cat hissed."
  4. Compound-Complex: Multiple independent + at least one dependent clause.

Fragments (Always Wrong on the SAT)

A fragment is a group of words that looks like a sentence but lacks a subject, a verb, or a complete thought.

  • "Running through the park on a sunny day." (no subject + finite verb)
  • "Because the experiment was successful." (dependent clause alone)

Run-On Sentences (Always Wrong)

A run-on joins two independent clauses without proper punctuation or conjunction.

  • Fused sentence: "I ran she walked"
  • Comma splice: "I ran, she walked"

Fixes for Run-Ons

  1. Period: "I ran. She walked."
  2. Semicolon: "I ran; she walked."
  3. Comma + conjunction: "I ran, and she walked."
  4. Subordination: "While I ran, she walked."

Subordination and Coordination

Coordinating Conjunctions (FANBOYS)

For, And, Nor, But, Or, Yet, So — join equal elements.

Subordinating Conjunctions

Because, although, when, while, if, since, unless, until, after, before — make one clause dependent.

Parallel Structure

Elements in a series or comparison must match grammatically:

  • ✗ "She likes reading, to write, and cooking."
  • ✓ "She likes reading, writing, and cooking."

Also applies to correlative conjunctions:

  • "Both the teacher and the students were present."
  • "Not only did she study, but she also practiced."

SAT Tips

  1. Every sentence needs: subject + finite verb + complete thought
  2. Dependent clauses CANNOT stand alone as sentences
  3. When combining sentences, choose the option that preserves the original meaning
  4. Parallel structure applies to lists, comparisons, and both/and constructions

📚 Practice Problems

1Problem 1easy

❓ Question:

Which is correct?

A) I love reading, my sister prefers sports. B) I love reading; my sister prefers sports. C) I love reading my sister prefers sports.

💡 Show Solution

Solution:

Two complete sentences:

  • "I love reading"
  • "My sister prefers sports"

Check each option:

A) Comma alone (comma splice) ❌ B) Semicolon (correct way to join) ✓ C) No punctuation (run-on) ❌

Other correct options:

  • "I love reading, and my sister prefers sports." (comma + FANBOYS)
  • "I love reading. My sister prefers sports." (two sentences)

Answer: B

SAT Tip: Comma CANNOT join two complete sentences alone!

2Problem 2medium

❓ Question:

Which is correct?

A) Walking to school, the rain started falling. B) Walking to school, I felt the rain start falling. C) Walking to school, it rained. D) The rain, walking to school, started.

💡 Show Solution

Solution:

Opening modifier: "Walking to school"

Rule: Must describe the subject immediately after comma

Check each:

A) The rain walked to school? ❌ B) "I" walked to school ✓ (makes sense!) C) "It" (rain) walked to school? ❌ D) Awkward/unclear ❌

Answer: B

SAT Tip: Opening modifying phrase must clearly describe the subject that follows!

3Problem 3hard

❓ Question:

Which maintains parallel structure?

A) The goals are to increase revenue, reducing costs, and improve efficiency. B) The goals are to increase revenue, to reduce costs, and improving efficiency. C) The goals are to increase revenue, to reduce costs, and to improve efficiency. D) The goals are increasing revenue, to reduce costs, and to improve efficiency.

💡 Show Solution

Solution:

Parallel structure: All items must have same form

Check each:

A) to increase, reducing, improve (THREE DIFFERENT FORMS) ❌ B) to increase, to reduce, improving (NOT ALL SAME) ❌ C) to increase, to reduce, to improve (ALL INFINITIVES) ✓ D) increasing, to reduce, to improve (NOT ALL SAME) ❌

Answer: C

SAT Tip: In a list, all items should match: all infinitives, all -ing forms, all nouns, etc.

4Problem 4easy

❓ Question:

Identify the error: "Running through the park on a sunny afternoon."

💡 Show Solution

Error: This is a sentence fragment — it has no main subject and verb.

"Running through the park on a sunny afternoon" is a participial phrase. It describes an action but doesn't tell us WHO is doing it and doesn't have a complete predicate.

Fix options:

  1. Add a subject and verb: "She was running through the park on a sunny afternoon." ✅
  2. Attach to a complete sentence: "Running through the park on a sunny afternoon, she felt free." ✅

What makes a complete sentence:

  1. A subject (who/what)
  2. A verb (action/state)
  3. A complete thought

Answer: Fragment — needs a subject and a main verb to be complete.

5Problem 5easy

❓ Question:

Identify the error: "Running through the park on a sunny afternoon."

💡 Show Solution

Error: This is a sentence fragment — it has no main subject and verb.

"Running through the park on a sunny afternoon" is a participial phrase. It describes an action but doesn't tell us WHO is doing it and doesn't have a complete predicate.

Fix options:

  1. Add a subject and verb: "She was running through the park on a sunny afternoon." ✅
  2. Attach to a complete sentence: "Running through the park on a sunny afternoon, she felt free." ✅

What makes a complete sentence:

  1. A subject (who/what)
  2. A verb (action/state)
  3. A complete thought

Answer: Fragment — needs a subject and a main verb to be complete.

6Problem 6medium

❓ Question:

Combine these sentences effectively: "The experiment yielded surprising results. The scientists decided to repeat it. They wanted to confirm their findings."

💡 Show Solution

Option 1 — Subordination: "Because the experiment yielded surprising results, the scientists decided to repeat it to confirm their findings." ✅ (Uses "because" to show cause-effect; "to confirm" combines sentences 2 and 3)

Option 2 — Relative clause: "The experiment, which yielded surprising results, prompted the scientists to repeat it to confirm their findings." ✅

Option 3 — Participial phrase: "Surprised by the results, the scientists decided to repeat the experiment to confirm their findings." ✅

Avoid:

  • "The experiment yielded surprising results, and the scientists decided to repeat it, and they wanted to confirm their findings." ❌ (Too many "ands" — choppy)

SAT Principle: The most concise, clear combination is usually the best answer. Avoid unnecessary words and repetition.

Answer: "Because the experiment yielded surprising results, the scientists decided to repeat it to confirm their findings."

7Problem 7medium

❓ Question:

Combine these sentences effectively: "The experiment yielded surprising results. The scientists decided to repeat it. They wanted to confirm their findings."

💡 Show Solution

Option 1 — Subordination: "Because the experiment yielded surprising results, the scientists decided to repeat it to confirm their findings." ✅ (Uses "because" to show cause-effect; "to confirm" combines sentences 2 and 3)

Option 2 — Relative clause: "The experiment, which yielded surprising results, prompted the scientists to repeat it to confirm their findings." ✅

Option 3 — Participial phrase: "Surprised by the results, the scientists decided to repeat the experiment to confirm their findings." ✅

Avoid:

  • "The experiment yielded surprising results, and the scientists decided to repeat it, and they wanted to confirm their findings." ❌ (Too many "ands" — choppy)

SAT Principle: The most concise, clear combination is usually the best answer. Avoid unnecessary words and repetition.

Answer: "Because the experiment yielded surprising results, the scientists decided to repeat it to confirm their findings."

8Problem 8medium

❓ Question:

Fix the run-on sentence: "The storm knocked out power to the entire neighborhood residents had to use candles and flashlights for three days."

💡 Show Solution

This is a run-on sentence — two independent clauses with no punctuation or conjunction between them.

Fix 1 — Period: "The storm knocked out power to the entire neighborhood. Residents had to use candles and flashlights for three days."

Fix 2 — Semicolon: "The storm knocked out power to the entire neighborhood; residents had to use candles and flashlights for three days."

Fix 3 — Comma + conjunction: "The storm knocked out power to the entire neighborhood, so residents had to use candles and flashlights for three days."

Fix 4 — Subordination: "After the storm knocked out power to the entire neighborhood, residents had to use candles and flashlights for three days."

Best for SAT: Fix 4 (subordination) is often the best answer because it shows the relationship between the clauses (cause → effect).

Answer: Any of these fixes would work; subordination shows the clearest logical connection.

9Problem 9medium

❓ Question:

Fix the run-on sentence: "The storm knocked out power to the entire neighborhood residents had to use candles and flashlights for three days."

💡 Show Solution

This is a run-on sentence — two independent clauses with no punctuation or conjunction between them.

Fix 1 — Period: "The storm knocked out power to the entire neighborhood. Residents had to use candles and flashlights for three days."

Fix 2 — Semicolon: "The storm knocked out power to the entire neighborhood; residents had to use candles and flashlights for three days."

Fix 3 — Comma + conjunction: "The storm knocked out power to the entire neighborhood, so residents had to use candles and flashlights for three days."

Fix 4 — Subordination: "After the storm knocked out power to the entire neighborhood, residents had to use candles and flashlights for three days."

Best for SAT: Fix 4 (subordination) is often the best answer because it shows the relationship between the clauses (cause → effect).

Answer: Any of these fixes would work; subordination shows the clearest logical connection.

10Problem 10hard

❓ Question:

Fix the parallel structure error: "The scholarship program aims to identify talented students, providing financial support, and to connect them with mentors."

💡 Show Solution

Error: The list items are not in parallel form:

  • "to identify talented students" (infinitive)
  • "providing financial support" (gerund — NOT parallel!)
  • "to connect them with mentors" (infinitive)

Fix — Use consistent infinitives: "The scholarship program aims to identify talented students, to provide financial support, and to connect them with mentors." ✅

Or — Use consistent gerunds: "The scholarship program aims at identifying talented students, providing financial support, and connecting them with mentors." ✅

Or — Simplify with one "to": "The scholarship program aims to identify talented students, provide financial support, and connect them with mentors." ✅

Rule: Items in a list must be in the same grammatical form (all infinitives, all gerunds, all nouns, etc.).

Answer: "...to identify talented students, provide financial support, and connect them with mentors."

11Problem 11hard

❓ Question:

Fix the parallel structure error: "The scholarship program aims to identify talented students, providing financial support, and to connect them with mentors."

💡 Show Solution

Error: The list items are not in parallel form:

  • "to identify talented students" (infinitive)
  • "providing financial support" (gerund — NOT parallel!)
  • "to connect them with mentors" (infinitive)

Fix — Use consistent infinitives: "The scholarship program aims to identify talented students, to provide financial support, and to connect them with mentors." ✅

Or — Use consistent gerunds: "The scholarship program aims at identifying talented students, providing financial support, and connecting them with mentors." ✅

Or — Simplify with one "to": "The scholarship program aims to identify talented students, provide financial support, and connect them with mentors." ✅

Rule: Items in a list must be in the same grammatical form (all infinitives, all gerunds, all nouns, etc.).

Answer: "...to identify talented students, provide financial support, and connect them with mentors."

12Problem 12expert

❓ Question:

Which revision most effectively combines these sentences? "Marie Curie was a pioneering scientist. She was born in Poland. She moved to France. She conducted groundbreaking research on radioactivity. She won two Nobel Prizes." (A) "Marie Curie was a pioneering scientist who was born in Poland and moved to France and conducted groundbreaking research on radioactivity and won two Nobel Prizes." (B) "Born in Poland, Marie Curie moved to France, where she conducted groundbreaking research on radioactivity, ultimately winning two Nobel Prizes." (C) "Marie Curie, a pioneering scientist, she was born in Poland, moved to France, conducted groundbreaking research, and won two Nobel Prizes."

💡 Show Solution

Evaluate each option:

(A) Chains everything with "and" — repetitive and hard to follow. ❌

(B) Uses varied sentence structure:

  • "Born in Poland" — participial phrase (concise)
  • "moved to France" — main clause
  • "where she conducted..." — relative clause (shows location)
  • "ultimately winning" — participial phrase (shows culmination) ✅ This is the best answer — concise, clear, and well-structured.

(C) "a pioneering scientist, she was born" — this creates a grammar error. After the appositive "a pioneering scientist," the sentence shouldn't add "she." ❌

Why (B) is best:

  1. Most concise — eliminates "she was" repetition
  2. Shows logical flow — birth → move → research → results
  3. Uses varied construction — participial phrase, main clause, relative clause
  4. The word "ultimately" connects the achievement to the journey

Answer: (B) — it combines the information most effectively with varied syntax and logical progression.

13Problem 13expert

❓ Question:

Which revision most effectively combines these sentences? "Marie Curie was a pioneering scientist. She was born in Poland. She moved to France. She conducted groundbreaking research on radioactivity. She won two Nobel Prizes." (A) "Marie Curie was a pioneering scientist who was born in Poland and moved to France and conducted groundbreaking research on radioactivity and won two Nobel Prizes." (B) "Born in Poland, Marie Curie moved to France, where she conducted groundbreaking research on radioactivity, ultimately winning two Nobel Prizes." (C) "Marie Curie, a pioneering scientist, she was born in Poland, moved to France, conducted groundbreaking research, and won two Nobel Prizes."

💡 Show Solution

Evaluate each option:

(A) Chains everything with "and" — repetitive and hard to follow. ❌

(B) Uses varied sentence structure:

  • "Born in Poland" — participial phrase (concise)
  • "moved to France" — main clause
  • "where she conducted..." — relative clause (shows location)
  • "ultimately winning" — participial phrase (shows culmination) ✅ This is the best answer — concise, clear, and well-structured.

(C) "a pioneering scientist, she was born" — this creates a grammar error. After the appositive "a pioneering scientist," the sentence shouldn't add "she." ❌

Why (B) is best:

  1. Most concise — eliminates "she was" repetition
  2. Shows logical flow — birth → move → research → results
  3. Uses varied construction — participial phrase, main clause, relative clause
  4. The word "ultimately" connects the achievement to the journey

Answer: (B) — it combines the information most effectively with varied syntax and logical progression.

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❓ Frequently Asked Questions

What is Sentence Structure?▾
Identify and correct sentence structure errors including fragments, run-ons, comma splices, misplaced modifiers, and faulty parallelism.
How can I study Sentence Structure effectively?▾
Start by reading the study notes and working through the examples on this page. Then use the flashcards to test your recall. Practice with the 13 problems provided, checking solutions as you go. Regular review and active practice are key to retention.
Is this Sentence Structure study guide free?▾
Yes — all study notes, flashcards, and practice problems for Sentence Structure on Study Mondo are free to access. No account is needed.
What course covers Sentence Structure?▾
Sentence Structure is part of the SAT Prep course on Study Mondo, specifically in the Standard English Conventions section. You can explore the full course for more related topics and practice resources.
Are there practice problems for Sentence Structure?▾
Yes, this page includes 13 practice problems with detailed solutions. Each problem includes a step-by-step explanation to help you understand the approach.