Grammar for college writing
Sentence Boundaries: Fragments and Run-ons
Use this page when you are not sure where one sentence should end and the next should begin.
What a complete sentence needs
A complete sentence has three parts: a subject, a verb, and a complete idea. It can stand alone and make sense.
- I work full time. Subject (I), verb (work), complete idea.
Two kinds of problems happen at the edges of sentences:
- A fragment is a piece of a sentence written as if it were complete. Because I work full time.
- A run-on is two complete sentences joined with no correct connection. I work full time I take two classes. When only a comma joins them, it is called a comma splice: I work full time, I take two classes.
Both problems make readers stop and read again, because they cannot tell where one idea ends and the next begins.
- Independent clause:
- a subject and verb with a complete idea. It can be a sentence by itself.
- Dependent clause:
- a subject and verb that start with a word such as because, when, or although. It cannot stand alone.
- Fragment:
- an incomplete sentence.
- Run-on and comma splice:
- two sentences joined incorrectly.
Finding and fixing fragments
To test a sentence, read it alone, out of the paragraph. Could you say it to someone as a complete statement? If it leaves them waiting for more, it is a fragment.
Three common fragments
- A dependent clause alone. It starts with a word such as because, although, when, if, or since. Because I work full time.
- An example alone. It starts with for example, such as, or like, but it has no verb. For example, my biology class.
- A missing subject or verb. Is important to plan ahead. (no subject) The students in my group. (no verb)
Two ways to fix a fragment
| Fragment | Fix 1: join it to the sentence next to it | Fix 2: add what is missing |
|---|---|---|
| I study at night. Because I work full time. | I study at night because I work full time. | I work full time. |
| Some classes are hard. For example, my biology class. | Some classes are hard, such as my biology class. | For example, my biology class is hard. |
| Is important to plan ahead. | Not needed | It is important to plan ahead. |
Fixing run-ons and comma splices
When two complete sentences meet, connect them in one of four ways.
| Way | Example |
|---|---|
| 1. A period | I work full time. I take two classes. |
| 2. A comma + and, but, so, or, yet | I work full time, but I take two classes. |
| 3. A semicolon (;) | I work full time; I take two classes. |
| 4. A word such as because, although, while | Although I work full time, I take two classes. |
Choose the way that shows the relationship. But and although show contrast. So shows a result. A period is always correct and is often the clearest choice.
Example: sentence boundaries in a paragraph
This paragraph comes from a student’s essay. Each number matches a note below it.
Online classes are a good choice for many working adults.1 They let students study at any time, so a night shift is not a problem.2 However, online classes need strong time management.3 When I took my first online class, I fell behind in the second week.4 Now I plan every week on Sunday; this habit keeps me on schedule.5
- One independent clause. Subject (online classes), verb (are), and a complete idea.
- Comma + so. Two complete sentences, joined correctly. So shows a result.
- However starts a new sentence. However cannot join two sentences with only a comma. See the box below.
- A dependent clause, attached. When I took my first online class cannot stand alone, so it is joined to a complete sentence with a comma.
- A semicolon. The two sentences are closely related, so the writer uses a semicolon. A period would also be correct.
Two common problems
1. However, therefore, and for example between two sentences
These words connect ideas, but they cannot join two sentences with only a comma. Use a period or a semicolon before them.
| Not this | Write this |
|---|---|
| The class is online, however, it has live meetings. | The class is online. However, it has live meetings. |
| I missed the deadline, therefore, I lost points. | I missed the deadline; therefore, I lost points. |
2. A comma between two long sentences
When a sentence feels long, a writer may add a comma to give the reader a pause. A comma cannot hold two complete sentences together by itself. Read each half alone. If both halves are complete, use one of the four ways.
- Comma splice: “My manager changed my schedule, I had to drop my morning class.”
- Fixed: My manager changed my schedule, so I had to drop my morning class.
Patterns you will use often
The punctuation in each pattern is already correct. Fill in each blank with a complete idea.
- To show a reason because .Because , .
- To show a contrast, but .Although , .. However, .
- To show a result, so .; therefore, .
- To give an exampleFor example, is .
When because comes first, put a comma after the first part: Because I work at night, I study in the morning. When it comes in the middle, you usually do not need a comma: I study in the morning because I work at night.
Practice
Is each one a complete sentence, a fragment, or a comma splice?
- Although the reading was long.
- The reading was long, it had many new words.
- The reading was long, but it was interesting.
- For example, the second chapter.
- Studying with a partner helps me remember new words.
Then fix this paragraph: “I chose nursing. Because I like helping people. My first class was difficult, I studied every night. However, I passed.”
Show suggested answers
- Fragment. It starts with although, so it needs a second part: Although the reading was long, I finished it.
- Comma splice. Both halves are complete. Use a period, a semicolon, or a comma + and.
- Complete sentence. A comma + but joins the two sentences correctly.
- Fragment. It has no verb. Add one: For example, the second chapter was very long.
- Complete sentence. The subject is studying with a partner, and the verb is helps.
One possible answer: I chose nursing because I like helping people. My first class was difficult, so I studied every night. However, I passed. The because fragment joins the sentence before it. The comma splice gets so, which shows a result. The last sentence was already correct: However starts a new sentence. Other answers are possible.
Next step
Try this with your own writing
- Read your draft from the last sentence to the first. Out of order, each sentence must stand on its own.
- For each sentence, ask: does it have a subject, a verb, and a complete idea?
- Look at every comma. If the words on both sides are complete sentences, use one of the four ways.
- Look for however and therefore. Is there a period or a semicolon before them?
More practice
The Purdue Online Writing Lab (OWL) is a writing site from Purdue University. Many college classes use it.