Sentence Fragments & Run-Ons
Learn to identify sentence fragments and run-ons, test for complete sentences with subject-verb-finished thought, and correct them using proper punctuation or added words.
What you'll do in this lesson
A voice-first session with the Crimsora tutor on Sentence Fragments & Run-Ons, then targeted practice and FRQs — with the tutor adapting to where you get stuck.
What this lesson covers
Every sentence you write needs to do one thing: express a complete thought. When a sentence is missing a subject or verb, or when two complete sentences are stuck together without proper punctuation, your reader gets confused. In this lesson, you'll learn the subject-verb-finished-thought test that writers use to check whether they've actually written a sentence—and how to fix it when they haven't.
What Makes a Complete Sentence
A complete sentence has three parts working together: a subject (who or what is doing something), a verb (the action or state of being), and a finished thought (the sentence expresses a complete idea, not a fragment or dependent clause left hanging). The subject tells you who or what. The verb tells you what action they take or what state they are in. The finished thought means you don't wonder "and then what?" when you read it.
For example, "The dog barked" is a complete sentence: the dog (subject) barked (verb), and the thought is finished—you understand the whole idea. "Because the dog was scared" has a subject and verb, but it doesn't feel finished. You want to know what happened. That's a dependent clause, not a complete sentence on its own.
The subject-verb-finished-thought test is your tool. Ask yourself: Does this sentence have a subject? Does it have a verb? Does it express a finished thought, or do I feel like something is missing? If you answer yes to all three, it's a sentence. If you answer no to any one, it's a fragment.
For example, "The dog barked" is a complete sentence: the dog (subject) barked (verb), and the thought is finished—you understand the whole idea. "Because the dog was scared" has a subject and verb, but it doesn't feel finished. You want to know what happened. That's a dependent clause, not a complete sentence on its own.
The subject-verb-finished-thought test is your tool. Ask yourself: Does this sentence have a subject? Does it have a verb? Does it express a finished thought, or do I feel like something is missing? If you answer yes to all three, it's a sentence. If you answer no to any one, it's a fragment.
Identifying Sentence Fragments
A sentence fragment is a group of words that is missing one or more of the three parts of a complete sentence. Fragments are incomplete and leave your reader confused.
Missing subject: "Ran down the street quickly." Who ran? You don't know. This is a fragment.
Missing verb: "The dog in the yard." The dog what? Barked? Played? Slept? Without a verb, the thought isn't finished. This is a fragment.
Missing finished thought (dependent clause): "Although it was raining." This has a subject (it) and a verb (was raining), but it doesn't express a complete thought. You wonder what happened because of the rain. Fragments that depend on another clause are very common, and students often write them by mistake.
To fix a fragment, you have two main strategies: add the missing part, or attach it to a nearby complete sentence. "Ran down the street quickly" becomes "The dog ran down the street quickly" (add subject). "Although it was raining, we played outside" (attach the dependent clause to a complete sentence).
Missing subject: "Ran down the street quickly." Who ran? You don't know. This is a fragment.
Missing verb: "The dog in the yard." The dog what? Barked? Played? Slept? Without a verb, the thought isn't finished. This is a fragment.
Missing finished thought (dependent clause): "Although it was raining." This has a subject (it) and a verb (was raining), but it doesn't express a complete thought. You wonder what happened because of the rain. Fragments that depend on another clause are very common, and students often write them by mistake.
To fix a fragment, you have two main strategies: add the missing part, or attach it to a nearby complete sentence. "Ran down the street quickly" becomes "The dog ran down the street quickly" (add subject). "Although it was raining, we played outside" (attach the dependent clause to a complete sentence).
Identifying Run-Ons and Comma Splices
A run-on sentence happens when two complete sentences are joined without any punctuation at all. The words just keep going, and your reader loses track of where one thought ends and another begins.
Run-on: "The storm arrived suddenly the power went out and everyone gathered in the living room."
A comma splice is a special type of run-on: two complete sentences joined by only a comma. A comma alone is not strong enough to connect two complete sentences.
Comma splice: "The storm arrived suddenly, the power went out."
Both are wrong because each sentence is complete. The rule is: a comma can separate items in a list, or it can help show extra information in the middle of a sentence, but it cannot be the only thing holding two complete sentences together.
To test whether you have a run-on or comma splice, break the sentence in two. Can each part stand alone as a complete sentence? If yes, and they're joined by a comma only (or no punctuation), you have a problem. Fix it by using a period, a semicolon, or a conjunction with a comma (and, but, or, yet, so, because).
Run-on: "The storm arrived suddenly the power went out and everyone gathered in the living room."
A comma splice is a special type of run-on: two complete sentences joined by only a comma. A comma alone is not strong enough to connect two complete sentences.
Comma splice: "The storm arrived suddenly, the power went out."
Both are wrong because each sentence is complete. The rule is: a comma can separate items in a list, or it can help show extra information in the middle of a sentence, but it cannot be the only thing holding two complete sentences together.
To test whether you have a run-on or comma splice, break the sentence in two. Can each part stand alone as a complete sentence? If yes, and they're joined by a comma only (or no punctuation), you have a problem. Fix it by using a period, a semicolon, or a conjunction with a comma (and, but, or, yet, so, because).
How to Fix Fragments and Run-Ons
Fixing a fragment means making it complete. If it's missing a subject, add one. If it's missing a verb, add one. If it's a dependent clause, attach it to the sentence before or after it using a comma.
Fragments to fix:
"Waited all day for the phone call." Add subject: "Sarah waited all day for the phone call."
"Because the museum was closed." Attach it: "We changed our plans because the museum was closed."
Fixing run-ons and comma splices means separating the two complete sentences or joining them properly. You have four methods:
Method 1: Period. "The storm arrived suddenly. The power went out." (Two simple sentences.)
Method 2: Semicolon. "The storm arrived suddenly; the power went out." (The semicolon shows the sentences are related.)
Method 3: Comma + Conjunction. "The storm arrived suddenly, and the power went out." (The conjunction shows the relationship.)
Method 4: Make one part dependent. "When the storm arrived suddenly, the power went out." (Turn one sentence into a dependent clause and attach it.)
Your choice depends on the ideas and how closely they relate. All four are correct; the difference is about clarity and style.
Fragments to fix:
"Waited all day for the phone call." Add subject: "Sarah waited all day for the phone call."
"Because the museum was closed." Attach it: "We changed our plans because the museum was closed."
Fixing run-ons and comma splices means separating the two complete sentences or joining them properly. You have four methods:
Method 1: Period. "The storm arrived suddenly. The power went out." (Two simple sentences.)
Method 2: Semicolon. "The storm arrived suddenly; the power went out." (The semicolon shows the sentences are related.)
Method 3: Comma + Conjunction. "The storm arrived suddenly, and the power went out." (The conjunction shows the relationship.)
Method 4: Make one part dependent. "When the storm arrived suddenly, the power went out." (Turn one sentence into a dependent clause and attach it.)
Your choice depends on the ideas and how closely they relate. All four are correct; the difference is about clarity and style.
Key terms
- Sentence fragment.
- A group of words that is missing a subject, a verb, or a finished thought, so it cannot stand alone as a complete sentence.
- Subject.
- The noun or pronoun that tells who or what is doing the action or being described in the sentence.
- Verb.
- The word that shows the action or state of being in the sentence.
- Finished thought.
- An idea that is complete and doesn't leave the reader wondering what happens next; the sentence expresses a whole concept.
- Run-on sentence.
- Two complete sentences joined together with no punctuation between them, making the sentence hard to read.
- Comma splice.
- Two complete sentences incorrectly joined by only a comma, without a conjunction or stronger punctuation.
- Dependent clause.
- A group of words with a subject and verb that does not express a complete thought and cannot stand alone as a sentence.
- Conjunction.
- A word such as and, but, or, yet, so, or because that joins words, phrases, or clauses together.
Worked example
Read the following draft: "The team practiced hard every day. Because they wanted to win the championship. They also studied film on Sundays to improve their plays." Identify any fragments or run-ons, and rewrite the paragraph correctly.
First, I'll test each sentence for subject, verb, and finished thought.
Sentence 1: "The team practiced hard every day." Subject (the team), verb (practiced), finished thought (yes—we know a complete action). This is a complete sentence.
Sentence 2: "Because they wanted to win the championship." Subject (they), verb (wanted), but does it express a finished thought? No. The word "because" signals that this is a dependent clause. It makes the reader ask "because what?" So this is a fragment.
Sentence 3: "They also studied film on Sundays to improve their plays." Subject (they), verb (studied), finished thought (yes). This is a complete sentence.
Now I'll fix the fragment. Since "Because they wanted to win the championship" depends on the nearby sentence, I can attach it to sentence 1 using a comma: "The team practiced hard every day because they wanted to win the championship." Now the dependent clause has a main clause to complete its meaning.
Corrected paragraph: "The team practiced hard every day because they wanted to win the championship. They also studied film on Sundays to improve their plays."
All three sentences now have subjects, verbs, and finished thoughts. The paragraph is complete and clear.
Sentence 1: "The team practiced hard every day." Subject (the team), verb (practiced), finished thought (yes—we know a complete action). This is a complete sentence.
Sentence 2: "Because they wanted to win the championship." Subject (they), verb (wanted), but does it express a finished thought? No. The word "because" signals that this is a dependent clause. It makes the reader ask "because what?" So this is a fragment.
Sentence 3: "They also studied film on Sundays to improve their plays." Subject (they), verb (studied), finished thought (yes). This is a complete sentence.
Now I'll fix the fragment. Since "Because they wanted to win the championship" depends on the nearby sentence, I can attach it to sentence 1 using a comma: "The team practiced hard every day because they wanted to win the championship." Now the dependent clause has a main clause to complete its meaning.
Corrected paragraph: "The team practiced hard every day because they wanted to win the championship. They also studied film on Sundays to improve their plays."
All three sentences now have subjects, verbs, and finished thoughts. The paragraph is complete and clear.
Practice questions
Which of the following is a sentence fragment?
- The coach gave the team new uniforms before the game.
- Running as fast as they could down the field.
- The players huddled together to discuss strategy.
- Everyone cheered when the ball went in the net.
Answer: Running as fast as they could down the field.
"Running as fast as they could down the field" is missing a subject. You know the action (running), but you don't know who is running. It cannot stand alone. The other three sentences all have a subject, a verb, and a finished thought.
Combine these two complete sentences into one sentence using a comma and a conjunction: "Maya finished her homework early. She decided to read a book instead of watching television."
Answer: Maya finished her homework early, so she decided to read a book instead of watching television.
Both sentences are complete, so they cannot be joined by a comma alone. Using a comma and the conjunction "so" (or "and") correctly shows the relationship between the two ideas: the fact that Maya finished early caused her to choose reading. Other correct answers include "and," "but," or using a semicolon instead. The word "so" works best here because it shows cause and effect.
True or False: A comma splice is a run-on sentence.
Answer: True
A comma splice is a type of run-on sentence. Both are problems where two complete sentences are incorrectly joined. A comma splice uses a comma (and only a comma), while a run-on might have no punctuation at all. But both are mistakes that break the rule: two complete sentences need a period, semicolon, or a comma with a conjunction to be separated correctly.
FAQ
- How do I know if something is a dependent clause and not a complete sentence?
- Look for words like because, although, since, while, unless, if, and when at the start. These words signal that the clause depends on another sentence to make complete sense. "Although the game was close" has a subject and verb, but it leaves you hanging—you want to know what happened. Test: Does the sentence feel finished when you read it aloud? If it feels like there's more to come, it's likely dependent, not complete.
- Why is a comma not strong enough to join two complete sentences?
- A comma's job is to separate items in a list or to set off extra information inside a sentence. It is too weak to hold two independent ideas together. Two complete sentences need either a period (to separate them completely), a semicolon (to show they're closely related), or a comma plus a conjunction like "and" or "but." Using a comma alone is called a splice, and it confuses readers about where one thought ends and another begins.
- Should I always use a period to fix a run-on, or are there other ways?
- You have four correct options: a period, a semicolon, a comma with a conjunction, or rewriting to make one part dependent. The choice depends on how the ideas relate. If the sentences are closely tied in meaning, a semicolon or comma-plus-conjunction shows that relationship. If they're separate thoughts, a period is fine. All are grammatically correct; the difference is about clarity and style in your writing.
- How can I avoid writing fragments when I use dependent clauses?
- Attach dependent clauses to a nearby complete sentence using a comma. Write "Because the weather was bad, we stayed inside" instead of writing "Because the weather was bad." as its own sentence. The dependent clause belongs with the main clause, not alone. Think of it as a partnership: the dependent clause and the main clause must travel together to make the thought complete.
Learn this with a teacher, not a page
The Crimsora tutor teaches Sentence Fragments & Run-Ons live — explaining on a whiteboard, asking you questions, and adapting to where you get stuck.