What a complete sentence needs
A complete sentence, or independent clause, has a subject and a verb and makes sense on its own: The bell rang. A dependent clause has a subject and a verb but starts with a word like because, when, although or if, so it cannot stand alone: when the bell rang.
| Problem | Wrong | Right | Why |
|---|---|---|---|
| Fused sentence | The game was canceled it rained all day. | The game was canceled because it rained all day. | Two sentences ran together with nothing between them. |
| Comma splice | The power went out, we lit candles. | The power went out, so we lit candles. | A comma alone cannot join two sentences. |
| Fragment: dependent clause | We stayed home. Because the road was closed. | We stayed home because the road was closed. | Because the road was closed cannot stand alone. |
| Fragment: no main verb | We stayed inside. Waiting for the storm to pass. | We stayed inside, waiting for the storm to pass. | Waiting is not a main verb. Join it to the sentence before. |
| Fragment: no subject | Mia studied for hours. And then went to bed. | Mia studied for hours and then went to bed. | And then went to bed has no subject of its own. |
Four ways to fix a run-on
- Period: The power went out. We lit candles.
- Semicolon: The power went out; we lit candles.
- Comma plus and, but, or, so, yet, for, nor: The power went out, so we lit candles.
- Make one part dependent: When the power went out, we lit candles.
Worked examples
Example 1: find the two sentences
Problem My phone died I couldn't call for a ride.
- Find each subject and verb: phone died, I couldn't call. Two complete sentences.
- They are joined by nothing, so this is a fused sentence.
- The second is a result of the first, so so shows the link.
Answer My phone died, so I couldn't call for a ride.
Example 2: attach a fragment
Problem After the concert ended. We waited an hour for the bus.
- After the concert ended starts with After, so it is dependent and cannot stand alone.
- Join it to the next sentence. Since it comes first, add a comma after it.
Answer After the concert ended, we waited an hour for the bus.
Common mistakes and fixes
| Mistake | Fix |
|---|---|
| Using however with a comma to join sentences | Use a semicolon: It rained; however, we played. |
| Starting a sentence with Because and stopping too soon | Finish the thought: Because it rained, we stayed in. |
| Splitting off an example with For example or Such as | Such as apples and pears. is a fragment. Join it to the sentence before. |
| Thinking every short sentence is a fragment | Stop. is complete: the subject you is understood. |
Practice
Five sentence boundary questions
Which is a comma splice?
- When the power went out, we lit candles.
- The power went out, so we lit candles.
- The power went out, we lit candles.
- The power went out; we lit candles.
Show answer
Answer: The power went out, we lit candles.
Two complete sentences are joined by a comma alone. The others join them correctly with so, a dependent clause, or a semicolon.
Which is a sentence fragment?
- The road was closed.
- We stayed home because the road was closed.
- Because the road was closed.
- The road was closed, so we stayed home.
Show answer
Answer: Because the road was closed.
Because makes the clause dependent, so it cannot stand alone. The other three are complete sentences.
What is the best fix for this run-on? The game was canceled it rained all day.
- The game was canceled, it rained all day.
- The game, was canceled it rained all day.
- The game was canceled it, rained all day.
- The game was canceled because it rained all day.
Show answer
Answer: The game was canceled because it rained all day.
Because turns the second part into a dependent clause and shows the cause. A comma alone makes a comma splice, and the other two put commas in the wrong places.
Which correctly fixes the fragment? We stayed inside. Waiting for the storm to pass.
- We stayed inside; waiting for the storm to pass.
- We stayed inside, waiting for the storm to pass.
- We stayed inside. Waited for the storm to pass.
- We stayed inside, and waiting for the storm to pass.
Show answer
Answer: We stayed inside, waiting for the storm to pass.
Joining the phrase to the sentence with a comma makes one complete sentence. A semicolon needs a full sentence after it, Waited for the storm to pass has no subject, and and waiting has no verb to match stayed.
Which of these is a complete sentence?
- The tall man in the blue coat.
- After the movie ended.
- Running down the hall.
- Stop.
Show answer
Answer: Stop.
Stop. is a command, and commands have an understood subject, you. The others are missing a main verb or a main clause.
Frequently asked questions
Is a run-on the same as a long sentence?
No. A run-on is two or more complete sentences joined without correct punctuation. A long sentence can be perfectly correct if its parts are joined properly, and a very short one, like I ran she walked, can be a run-on.
Are fragments ever okay?
Writers sometimes use a fragment on purpose for effect, like Not again. in a story or ad. Purdue OWL notes that in academic and other formal writing you should avoid them. In school essays and on tests, write complete sentences.
What is the fastest way to check my essay for these errors?
Read it backward, one sentence at a time, from the last sentence to the first. Out of context, a fragment sounds unfinished, and a run-on sounds like two thoughts. Then check every comma that sits between two complete sentences.
Sources
- Purdue OWL, Sentence Fragments, accessed October 1, 2026
- Purdue OWL, Identifying Independent and Dependent Clauses, accessed October 1, 2026
- Purdue OWL, Run-ons, Comma Splices, and Fused Sentences (exercise answers), accessed October 1, 2026
