TACHS: Sentence boundaries: catch comma splices and fragments
Tell a complete sentence from a fragment, spot two sentences joined by only a comma, and check that semicolons have a complete thought on both sides.
How can I tell whether a line is a correct sentence, a fragment or a comma splice?
Short answer
A sentence needs a subject, a verb and a complete thought. Two complete thoughts need a period, a semicolon, or a comma plus a joining word, and a dependent clause must attach to a main clause.
Know first: Subjects and verbs, Joining words such as *and, but, so*
Step 1 of 5
Every sentence needs one complete thought
A complete thought has a subject and a verb and can stand alone: The bell rang. Two errors break that rule.
A fragment is a piece of a sentence punctuated as if it were whole. When the bell rang. has a subject and a verb, but when leaves the thought unfinished. Hoping for a snow day. has no subject or main verb at all.
A comma splice joins two complete thoughts with only a comma: The bell rang, we packed up.
| Error | Example | Fix |
|---|---|---|
| Comma splice | The bell rang, we packed up. | The bell rang, so we packed up. Or use a period or a semicolon. |
| Fragment | When the bell rang. | Attach it: When the bell rang, we packed up. |
| Semicolon after a dependent clause | When the bell rang; we packed up. | Use a comma. A semicolon needs a complete thought on both sides. |
Step 2 of 5
Test the punctuation in each line
Worked example: A ferry ride
Which line contains an error in standard written English? Choose No error if all three lines are correct.
Line 1: The ferry left the dock at noon, the gulls followed it out of the harbor.
Line 2: My brother stood at the rail with his camera.
Line 3: When the wind picked up, the passengers moved inside.
- ALine 1
- BLine 2
- CLine 3
- DNo error
- 1
Line 1
The ferry left the dock at noon is complete. The gulls followed it out of the harbor is complete too. A comma alone cannot join them, so this is a comma splice.
- 2
Line 2
One subject, one verb, one complete thought. Correct.
- 3
Line 3
When the wind picked up is dependent, but a main clause follows the comma. Correct.
- 4
See why the other choices are there
Line 3 starts with when, which makes it look like a fragment until you read past the comma. No error tempts anyone who reads Line 1 as one long, smooth sentence.
Answer
Line 1. Fix it with a period, a semicolon, or , and the gulls followed.
Wrong: Although the soup was hot; Dev ate it quickly.
Right: Although the soup was hot, Dev ate it quickly.
Although the soup was hot cannot stand alone, so a semicolon cannot follow it. A comma attaches the dependent clause to the main one.
Step 3 of 5
Judge each line by its words, not its length
Check yourself · Question 1
Which line contains an error in standard written English? Choose No error if all three lines are correct.
Line 1: The puppy slept on the porch all afternoon.
Line 2: Until the mail carrier came up the steps.
Line 3: Then it barked at every passing car.
Answer: B
Until the mail carrier came up the steps leaves the thought unfinished. It needs a main clause, as in The puppy slept until the mail carrier came up the steps.
Check yourself · Question 2
Which line contains an error in standard written English? Choose No error if all three lines are correct.
Line 1: The museum was crowded; however, we found a quiet bench.
Line 2: Mom bought tickets for the planetarium show.
Line 3: Since the show started at two, we ate lunch first.
Answer: D
Line 1 uses a semicolon between two complete thoughts with a comma after however. Lines 2 and 3 are complete sentences.
Trap answer: Line 1
A correct sentence that looks risky
- Why it looks right
- However is often part of a comma splice, so its appearance sets off an alarm.
- Why it's wrong
- Cover each side of the semicolon: The museum was crowded and we found a quiet bench are both complete. That is exactly when a semicolon belongs.
- The right answer
- No error. Every line has a correct boundary.
Common mistake
Treating every long line as a run-on.
- Why it's tempting
- Long sentences feel crowded, so it seems one of them must be broken.
- Do this instead
- Length is not the test. A long sentence with a correct joining word is fine, and a short one can be a fragment. Cover each side and check.
Step 4 of 5
What to remember
Remember
- Two complete thoughts need a period, a semicolon, or a comma plus and, but, or, so or yet.
- A line that starts with because, although, when or until needs a main clause to finish it.
- A semicolon needs a complete thought on both sides.
Step 5 of 5
Practice on a real question
Use what you just learned on this question, then check the explanation.
Try another one
In your own words
In the practice question, what were the two complete thoughts in the line with the error, and what was holding them together?